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Purpose: To test whether visual experience and/or eye movements drive the postnatal development of palisade endings in extraocular muscles., Methods: In three newborn cats, the right eye was covered until 30 days from postnatal (P) day 7 (before opening their eyes), and in three cats both eyes were covered until 45 days, also from P7. To block eye movements, another seven cats received a retrobulbar injection of botulinum neurotoxin A (BoNT-A) into the left orbit at birth and survived for 45 days (three cats) and 95 days (four cats). The distal third of the rectus muscles containing the palisade endings was used for whole-mount preparation and triple-fluorescence labeling with anti-neurofilament along with (1) anti-synaptophysin and phalloidin or (2) anti-growth associated protein 43 (GAP43) and phalloidin. Immunolabeled specimens were analyzed in the confocal laser scanning microscope., Results: After unilateral and bilateral dark rearing, palisade endings were qualitatively and quantitatively equal to those from age-matched controls. After BoNT-A induced eye immobilization for 45 or 95 days, palisade endings were absent in the superior rectus and lateral rectus muscles and only present in the inferior rectus and medial rectus muscle. These BoNT-A-treated palisade endings were rudimentary and reduced in number, and the expression of the neuronal developmental protein GAP43 was significantly reduced., Conclusions: This study demonstrates that eye immobilization, but not visual deprivation, affects palisade ending development. Palisade endings develop in the first month of life, and the present findings indicate that, during this time window, palisade endings are prone to oculomotor perturbations.

Mechanical and metabolic signals associated with skeletal muscle contraction stimulate the sensory endings of thin fiber muscle afferents and produce reflex increases in sympathetic nerve activity and blood pressure during exercise (i.e., the exercise pressor reflex; EPR). The EPR is exaggerated in patients and animals with heart failure with reduced ejection fraction (HF-rEF) and its activation contributes to reduced exercise capacity within this patient population. Accumulating evidence suggests that the exaggerated EPR in HF-rEF is partially attributable to a sensitization of mechanically activated channels produced by thromboxane A 2 receptors (TxA 2 -Rs) on those sensory endings; however, this has not been investigated. Accordingly, the purpose of this investigation was to determine the role played by TxA 2 -Rs on the sensory endings of thin fiber muscle afferents in the exaggerated EPR in rats with HF-rEF induced by coronary artery ligation. In decerebrate, unanesthetized rats, we found that injection of the TxA 2 -R antagonist daltroban (80 μg) into the arterial supply of the hindlimb reduced the pressor response to 30 s of electrically induced 1 Hz dynamic hindlimb muscle contraction in HF-rEF (n = 8, peak ∆MAP pre: 22 ± 3; post: 14 ± 2 mmHg; p = 0.01) but not sham (n = 10, peak ∆MAP pre: 13 ± 3; post: 11 ± 2 mmHg; p = 0.68) rats. In a separate group of HF-rEF rats (n = 4), we found that the systemic (intravenous) injection of daltroban had no effect on the EPR (peak ΔMAP pre: 26 ± 7; post: 25 ± 7 mmHg; p = 0.50). Our data suggest that TxA 2 -Rs on thin fiber muscle afferents contribute to the exaggerated EPR evoked in response to dynamic muscle contraction in HF-rEF., (© 2021 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

Purpose: The purpose of this work was to test whether palisade endings express structural and molecular features of exocytotic machinery, and are associated with acetylcholine receptors, and enzymes for neurotransmitter breakdown., Methods: Extraocular rectus muscles from six cats were studied. Whole-mount preparations of extraocular muscles (EOMs) were immunolabeled with markers for exocytotic proteins, including synaptosomal-associated protein of 25 kDa (SNAP25), syntaxin, synaptobrevin, synaptotagmin, and complexin. Acetylcholine receptors (AChRs) were visualized with α-bungarotoxin and with an antibody against AChRs, and acetylcholinesterase (AChE) was tagged with anti-AChE. Molecular features of multicolor labeled palisade endings were analyzed in the confocal scanning microscope, and their ultrastructural features were revealed in the transmission electron microscope., Results: All palisade endings expressed the exocytotic proteins SNAP25, syntaxin, synaptobrevin, synaptotagmin, and complexin. At the ultrastructural level, vesicles docked at the plasma membrane of terminal varicosities of palisade endings. No AChRs were associated with palisade endings as demonstrated by the absence of α-bungarotoxin and anti-AChR binding. AChE, the degradative enzyme for acetylcholine exhibited low, if any, activity in palisade endings. Axonal tracking showed that axons with multiple en grappe motor terminals were in continuity with palisade endings., Conclusions: This study demonstrates that palisade endings exhibit structural and molecular characteristics of exocytotic machinery, suggesting neurotransmitter release. However, AChRs were not associated with palisade endings, so there is no binding site for acetylcholine, and, due to low/absent AChE activity, insufficient neurotransmitter removal. Thus, the present findings indicate that palisade endings belong to an effector system that is very different from that found in other skeletal muscles.

A new morphological type of somatosensory organ is described. It is found in the glabrous skin of the dog nose (rhinarium or planum nasale) and situated in dermis papillae. The otherwise thick epidermis forms a thin window above the organ. There are only a few layers of keratinocytes in the window and the corneocytes are much thinner than elsewhere. The organ consists of highly branching cells that wrap naked nerve endings emanating from myelinated nerve fibers originating in the outer dermal nerve plexus. The structure entirely fills the top of the dermal papilla. The intercellular spaces of the organ and its surroundings are occupied by an extended areolar basal lamina., (© 2020 The Authors. Journal of Morphology published by Wiley Periodicals, Inc.)

The median nerve is a mixed sensory and motor nerve. It is classically described as the nerve of pronation, of thumb, index finger, middle finger and wrist flexion, of thumb antepulsion and opposition, as well as the nerve of sensation for the palmar aspect of the first three fingers. It takes its name from its middle position at the end of the brachial plexus and the forearm. During its course from its origin at the brachial plexus to its terminal branches, it runs through various narrow passages where it could be compressed, such as the carpal tunnel or the pronator teres. The objective of this review is to summarize the current knowledge on the median nerve's anatomy: anatomical variations (branches, median-ulnar communicating branches), fascicular microanatomy, vascularization, anatomy of compression sites, embryology, ultrasonographic anatomy. The links between its anatomy and clinical, surgical or diagnostic applications are emphasized throughout this review., (Copyright © 2019. Published by Elsevier Masson SAS.)

Recent years have brought an enhanced understanding of keratinocyte contribution to cutaneous nociception. While intra-epidermal nerve endings were classically considered as the exclusive transducers of cutaneous noxious stimuli, it has now been demonstrated that epidermal keratinocytes can initiate nociceptive responses, like Merkel cells do for the innocuous mechanotransduction. In the light of recent in vivo findings, this article outlines this paradigm shift that points to a not yet considered population of sensory epidermal cells., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Dopamine (DA) neuron projections to the striatum are functionally heterogeneous with diverse behavioral roles. We focus here on DA neuron projections to the nucleus accumbens (NAc) medial Shell, their distinct anatomical and functional connections, and discuss their role in motivated behavior. We first review rodent studies showing that a subpopulation of DA neurons in the medial ventral tegmental area (VTA) project to the NAc medial Shell. Using a combinatorial strategy, we show that the majority of DA neurons projecting to the NAc Shell express vesicular glutamate transporter 2 (VGLUT2) making them capable of glutamate co-transmission (DA-GLU neurons). In the NAc dorsal medial Shell, all of the DA neuron terminals arise from DA-GLU neurons, while in the lateral NAc Shell, DA neuron terminals arise from both DA-GLU neurons and DA-only neurons, without VGLUT2. DA-GLU neurons make excitatory connections to the three major cells types, spiny projection neurons, fast-spiking interneuron and cholinergic interneurons (ChIs). The strongest DA-GLU neuron excitatory connections are to ChIs. Photostimulation of DA-GLU neuron terminals in the slice drives ChIs to burst fire. Finally, we review studies that address specially the behavioral function of this subpopulation of DA neurons in extinction learning and latent inhibition. Taking into account findings from anatomical and functional connectome studies, we propose that DA-GLU neuron connections to ChIs in the medial Shell play a crucial role in switching behavioral responses under circumstances of altered cue-reinforcer contingencies., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Glia are abundant components of animal nervous systems. Recognized 170 years ago, concerted attempts to understand these cells began only recently. From these investigations glia, once considered passive filler material in the brain, have emerged as active players in neuron development and activity. Glia are essential for nervous system function, and their disruption leads to disease. The nematode Caenorhabditis elegans possesses glial types similar to vertebrate glia, based on molecular, morphological, and functional criteria, and has become a powerful model in which to study glia and their neuronal interactions. Facile genetic and transgenic methods in this animal allow the discovery of genes required for glial functions, and effects of glia at single synapses can be monitored by tracking neuron shape, physiology, or animal behavior. Here, we review recent progress in understanding glia-neuron interactions in C. elegans . We highlight similarities with glia in other animals, and suggest conserved emerging principles of glial function.

Electroencephalogram monitoring during propofol (PRO) anesthesia typically features low-frequency oscillations, which may be involved with thalamic reticular nucleus (TRN) modulation. TRN receives noradrenergic inputs from the locus coeruleus (LC). We hypothesized that specific noradrenergic connections in the TRN may contribute to the emergence from PRO anesthesia. Intranuclei norepinephrine (NE) injections ( n = 10) and designer receptors exclusively activated by designer drugs (DREADDs) ( n = 10) were used to investigate the role of noradrenergic inputs from the LC to the TRN during PRO anesthesia. Whole-cell recording in acute brain slice preparations was used to identify the type of adrenoceptor that regulates noradrenergic innervation in the TRN. An intracerebral injection of NE into the TRN delays arousal in mice recovering from PRO anesthesia (means ± sd; 486.6 ± 57.32 s for the NE injection group vs. 422.4 ± 48.19 s for the control group; P = 0.0143) and increases the cortical-δ (0.1-4 Hz, 25.4 ± 2.9 for the NE injection group vs. 21.0 ± 1.7 for the control group; P = 0.0094) oscillation. An intra-TRN injection of NE also decreased the EC 50 of PRO-induced unconsciousness (57.05 ± 1.78 mg/kg for the NE injection group vs. 72.44 ± 3.23 mg/kg for the control group; P = 0.0096). Moreover, the activation of LC-noradrenergic nerve terminals in the TRN using DREADDs increased the recovery time [466.1 ± 44.57 s for the clozapine N-oxide (CNO) injection group vs. 426.1 ± 38.75 s for the control group; P = 0.0033], decreased the EC 50 of PRO-induced unconsciousness (64.77 ± 3.40 mg/kg for the CNO injection group vs. 74.00 ± 2.08 mg/kg for the control group; P = 0.0081), and increased the cortical-δ oscillation during PRO anesthesia (23.29 ± 2.58 for the CNO injection group vs. 19.56 ± 1.9 for the control group; P = 0.0213). In addition, whole-cell recording revealed that NE augmented the inhibitory postsynaptic currents in the TRN neurons via the α1-adrenoceptor. Our data indicated that enhanced NE signaling at the noradrenergic terminals of the LC-TRN projection delays arousal from general anesthesia, which is likely mediated by the α1-adrenoceptor activation. Our findings open a door for further understanding of the functions of various LC targets in both anesthesia and arousal.-Zhang, Y., Fu, B., Liu, C., Yu, S., Luo, T., Zhang, L., Zhou, W., Yu, T. Activation of noradrenergic terminals in the reticular thalamus delays arousal from propofol anesthesia in mice.

The waveform of presynaptic action potentials (APs) regulates the magnitude of Ca 2+ currents (I Ca ) and neurotransmitter release. However, how APs control the timing of synaptic transmission remains unclear. Using the calyx of Held synapse, we find that Na + and K + channels affect the timing by changing the AP waveform. Specifically, the onset of I Ca depends on the repolarization but not depolarization rate of APs, being near the end of repolarization phase for narrow APs and advancing to the early repolarization phase for wide APs. Increasing AP amplitude has little effect on the activation but delays the peak time of I Ca . Raising extracellular Ca 2+ concentration increases the amplitude of I Ca yet does not alter their onset timing. Developmental shortening of APs ensures I Ca as a tail current and faithful synaptic delay, which is particularly important at the physiological temperature (35 °C) as I Ca evoked by broad pseudo-APs can occur in the depolarization phase. The early onset of I Ca is more prominent at 35 °C than at 22 °C, likely resulting from a temperature-dependent shift in the activation threshold and accelerated gating kinetics of Ca 2+ channels. These results suggest that the timing of Ca 2+ influx depends on the AP waveform dictated by voltage-gated channels and temperature.

Purpose: There is a substantial body of evidence indicating that corneal sensory innervation is affected by pathology in a range of diseases. However, there are no published studies that have directly assessed whether the nerve fiber density of the different subpopulations of corneal sensory neurons are differentially affected. The present study explored the possibility that the intraepithelial nerve fiber density of corneal polymodal nociceptors and cold thermoreceptors are differentially affected in mice fed with a high-fat high cholesterol (HFHC; 21% fat, 2% cholesterol) diet and in those that also have diabetes., Methods: The mice were fed the HFHC diet for the duration of the experiment (up to 40 weeks). Mice in the diabetes group had hyperglycaemia induced with streptozotocin after 15 weeks on the HFHC diet. Age-matched control animals were fed a standard diet. All corneal nerve fibers were labeled with a pan neuronal antibody (antiprotein gene product 9.5), and polymodal nociceptors and cold thermoreceptors were labeled with antibodies directed against transient receptor potential cation channel, subfamily V, member 1 and transient receptor potential cation channel subfamily M member 8, respectively., Results: The mice fed a HFHC diet and those that in addition have hyperglycemia have similar reductions in corneal nerve fiber density consistent with small fiber neuropathy. Importantly, both treatments more markedly affected the intraepithelial axons of cold thermoreceptors than those of polymodal nociceptors., Conclusions: The results provide evidence that distinct subpopulations of corneal sensory neurons can be differentially affected by pathology.

The auditory system of echolocating bats shows remarkable specialization likely related to analyzing echoes of sonar pulses. However, significant interspecies differences have been observed in the organization of auditory pathways among echolocating bats, and the homology of auditory nuclei with those of non-echolocating species has not been established. Here, in order to establish the homology and specialization of auditory pathways in echolocating bats, the expression of markers for glutamatergic, GABAergic, and glycinergic phenotypes in the subcortical auditory nuclei of Japanese house bat (Pipistrellus abramus) was evaluated. In the superior olivary complex, we identified the medial superior olive and superior paraolivary nuclei as expressing glutamatergic and GABAergic phenotypes, respectively, suggesting these nuclei are homologous with those of rodents. In the nuclei of the lateral lemniscus (NLL), the dorsal nucleus was found to be purely GABAergic, the intermediate nucleus was a mixture of glutamatergic and inhibitory neurons, the compact part of the ventral nucleus was purely glycinergic, and the multipolar part of the ventral nucleus expressed both GABA and glycine. In the inferior colliculus (IC), the central nucleus was found to be further subdivided into dorsal and ventral parts according to differences in the density of terminals and the morphology of large GABAergic neurons, suggesting specialization to sonar pulse structure. Medial geniculate virtually lacked GABAergic neurons, suggesting that the organization of the tectothalamic pathway is similar with that of rodents. Taken together, our findings revealed that specialization primarily occurs with regard to nuclei size and organization of the NLL and IC., (© 2018 Wiley Periodicals, Inc.)

Morphological and functional alterations of peripheral somatosensory neurons during the aging process lead to a decline of somatosensory perception. Here, we analyze the changes occurring with aging in trigeminal ganglion (TG), TRPM8-expressing cold thermoreceptor neurons innervating the mouse cornea, which participate in the regulation of basal tearing and blinking and have been implicated in the pathogenesis of dry eye disease (DED). TG cell bodies and axonal branches were examined in a mouse line (TRPM8 BAC -EYFP) expressing a fluorescent reporter. In 3 months old animals, about 50% of TG cold thermoreceptor neurons were intensely fluorescent, likely providing strongly fluorescent axons and complex corneal nerve terminals with ongoing activity at 34°C and low-threshold, robust responses to cooling. The remaining TRPM8 + corneal axons were weakly fluorescent with nonbeaded axons, sparsely ramified nerve terminals, and exhibited a low-firing rate at 34°C, responding moderately to cooling pulses as do weakly fluorescent TG neurons. In aged (24 months) mice, the number of weakly fluorescent TG neurons was strikingly high while the morphology of TRPM8 + corneal axons changed drastically; 89% were weakly fluorescent, unbranched, and often ending in the basal epithelium. Functionally, 72.5% of aged cold terminals responded as those of young animals, but 27.5% exhibited very low-background activity and abnormal responsiveness to cooling pulses. These morpho-functional changes develop in parallel with an enhancement of tear's basal flow and osmolarity, suggesting that the aberrant sensory inflow to the brain from impaired peripheral cold thermoreceptors contributes to age-induced abnormal tearing and to the high incidence of DED in elderly people., (© 2018 Wiley Periodicals, Inc.)

Acute pain represents a crucial alarm signal to protect us from injury. Whereas the nociceptive neurons that convey pain signals were described more than a century ago, the molecular sensors that detect noxious thermal or mechanical insults have yet to be fully identified. Here we show that acute noxious heat sensing in mice depends on a triad of transient receptor potential (TRP) ion channels: TRPM3, TRPV1, and TRPA1. We found that robust somatosensory heat responsiveness at the cellular and behavioural levels is observed only if at least one of these TRP channels is functional. However, combined genetic or pharmacological elimination of all three channels largely and selectively prevents heat responses in both isolated sensory neurons and rapidly firing C and Aδ sensory nerve fibres that innervate the skin. Strikingly, Trpv1 -/- Trpm3 -/- Trpa1 -/- triple knockout (TKO) mice lack the acute withdrawal response to noxious heat that is necessary to avoid burn injury, while showing normal nociceptive responses to cold or mechanical stimuli and a preserved preference for moderate temperatures. These findings indicate that the initiation of the acute heat-evoked pain response in sensory nerve endings relies on three functionally redundant TRP channels, representing a fault-tolerant mechanism to avoid burn injury.

It is generally believed that the unencapsulated sensory nerve terminals of modality specific C- and Aδ-neurons lack structural specialization. Here we determined the morphology of functionally defined polymodal receptors and cold thermoreceptors in the guinea pig corneal epithelium. Polymodal receptors and cold thermoreceptors were identified by extracellular recording at the surface of the corneal epithelium. After marking the recording sites, corneas were processed to reveal immunoreactivity for the transient receptor potential channels TRPV1 (transient receptor potential cation channel, subfamily V, member 1) or TPRM8 (transient receptor potential cation channel subfamily M member 8). Polymodal receptor nerve terminals (n = 6) were TRPV1-immunoreactive and derived from an axon that ascended from the sub-basal plexus to the squamous cell layer where it branched into fibers that ran parallel to the corneal surface and terminated with small bulbar endings (ramifying endings). Cold thermoreceptor nerve terminals were TRPM8-immunoreactive (n = 6) and originated from an axon that branched as it ascended through the wing cell and squamous cell layers and terminated with large bulbar endings (complex endings). These findings indicate that modality specific corneal sensory neurons with unencapsulated nerve endings have distinct nerve terminal morphologies that are likely to relate to their function.

Purpose: To analyze in a frontal-eyed mammal (cat) the postnatal development of palisade endings in extraocular muscles (EOMs) and to compare the spatiotemporal and quantitative patterns of palisade endings among individual rectus muscles., Methods: Cats of different ages ranging from birth to adult stage were studied. EOM whole-mount preparations were fluorescently labeled using six combinations of triple staining and analyzed in the confocal laser scanning microscope., Results: Palisade endings developed postnatally and passed in each rectus muscle through the same, three developmental steps but in a heterochronic sequence and to a different final density per muscle. Specifically, palisade ending development was first completed in the medial rectus and later in the inferior, lateral, and superior rectus. The highest density of palisade endings was observed in the medial rectus and the lowest in the lateral rectus whereas values for the inferior and superior rectus were in between. Palisade endings expressed high levels of growth associated protein 43 during development and were supplied by axons that established motor terminals., Conclusions: Cats open their eyes 7 to 10 days after birth and later develop a complex three-dimensional visuomotor climbing and jumping behavior depending on accurate binocular vision and fine tuning of the ocular movements. Our findings indicate that palisade ending development correlates with important landmarks in visuomotor behavior and provide support for our previous notion that palisade endings play an important role for convergence eye movements in frontal-eyed species.

Key Points: The intracellular concentration of free calcium ions ([Ca 2+ ] i ) in a nerve terminal controls both transmitter release and synaptic plasticity. The rapid triggering of transmitter release depends on the local micro- or nanodomain of highly elevated [Ca 2+ ] i in the vicinity of open voltage-gated Ca 2+ channels, whereas short-term synaptic plasticity is often controlled by global changes in residual [Ca 2+ ] i , averaged over the whole nerve terminal volume. Here we describe dynamic changes of such global [Ca 2+ ] i in the calyx of Held - a giant mammalian glutamatergic nerve terminal, which is particularly suited for biophysical studies. We provide quantitative data on Ca 2+ inflow, Ca 2+ buffering and Ca 2+ clearance. These data allow us to predict changes in [Ca 2+ ] i in the nerve terminal in response to a wide range of stimulus protocols at high temporal resolution and provide a basis for the modelling of short-term plasticity of glutamatergic synapses., Abstract: Many aspects of short-term synaptic plasticity (STP) are controlled by relatively slow changes in the presynaptic intracellular concentration of free calcium ions ([Ca 2+ ] i ) that occur in the time range of a few milliseconds to several seconds. In nerve terminals, [Ca 2+ ] i equilibrates diffusionally during such slow changes, such that the globally measured, residual [Ca 2+ ] i that persists after the collapse of local domains is often the appropriate parameter governing STP. Here, we study activity-dependent dynamic changes in global [Ca 2+ ] i at the rat calyx of Held nerve terminal in acute brainstem slices using patch-clamp and microfluorimetry. We use low concentrations of a low-affinity Ca 2+ indicator dye (100 μm Fura-6F) in order not to overwhelm endogenous Ca 2+ buffers. We first study voltage-clamped terminals, dialysed with pipette solutions containing minimal amounts of Ca 2+ buffers, to determine Ca 2+ binding properties of endogenous fixed buffers as well as the mechanisms of Ca 2+ clearance. Subsequently, we use pipette solutions including 500 μm EGTA to determine the Ca 2+ binding kinetics of this chelator. We provide a formalism and parameters that allow us to predict [Ca 2+ ] i changes in calyx nerve terminals in response to a wide range of stimulus protocols. Unexpectedly, the Ca 2+ affinity of EGTA under the conditions of our measurements was substantially lower (K D  = 543 ± 51 nm) than measured in vitro, mainly as a consequence of a higher than previously assumed dissociation rate constant (2.38 ± 0.20 s -1 ), which we need to postulate in order to model the measured presynaptic [Ca 2+ ] i transients., (© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.)

Knowledge of the molecular mechanisms underlying signaling of mechanical stimuli by muscle spindles remains incomplete. In particular, the ionic conductances that sustain tonic firing during static muscle stretch are unknown. We hypothesized that tonic firing by spindle afferents depends on sodium persistent inward current (INaP) and tested for the necessary presence of the appropriate voltage-gated sodium (NaV) channels in primary sensory endings. The NaV 1.6 isoform was selected for both its capacity to produce INaP and for its presence in other mechanosensors that fire tonically. The present study shows that NaV 1.6 immunoreactivity (IR) is concentrated in heminodes, presumably where tonic firing is generated, and we were surprised to find NaV 1.6 IR strongly expressed also in the sensory terminals, where mechanotransduction occurs. This spatial pattern of NaV 1.6 IR distribution was consistent for three mammalian species (rat, cat, and mouse), as was tonic firing by primary spindle afferents. These findings meet some of the conditions needed to establish participation of INaP in tonic firing by primary sensory endings. The study was extended to two additional NaV isoforms, selected for their sensitivity to TTX, excluding TTX-resistant NaV channels, which alone are insufficient to support firing by primary spindle endings. Positive immunoreactivity was found for NaV 1.1 , predominantly in sensory terminals together with NaV 1.6 and for NaV 1.7 , mainly in preterminal axons. Differential distribution in primary sensory endings suggests specialized roles for these three NaV isoforms in the process of mechanosensory signaling by muscle spindles. NEW & NOTEWORTHY The molecular mechanisms underlying mechanosensory signaling responsible for proprioceptive functions are not completely elucidated. This study provides the first evidence that voltage-gated sodium channels (NaVs) are expressed in the spindle primary sensory ending, where NaVs are found at every site involved in transduction or encoding of muscle stretch. We propose that NaVs contribute to multiple steps in sensory signaling by muscle spindles as it does in other types of slowly adapting sensory neurons., (Copyright © 2017 the American Physiological Society.)

The inner thoracic cavity is lined by the parietal pleura, and the lung lobes are covered by the visceral pleura. The parietal and visceral plurae form the pleural cavity that has negative pressure within to enable normal respiration. The lung tissues are bilaterally innervated by vagal and spinal nerves, including sensory and motor components. This complicated innervation pattern has made it difficult to discern the vagal vs. spinal processes in the pulmonary visceral pleura. With and without vagotomy, we identified vagal nerve fibres and endings distributed extensively in the visceral pleura ('P'-type nerve endings) and triangular ligaments ('L'-type nerve endings) by injecting wheat germ agglutinin-horseradish peroxidase as a tracer into the nucleus of solitary tract or nodose ganglion of male Sprague-Dawley rats. We found the hilar and non-hilar vagal pulmonary pleural innervation pathways. In the hilar pathway, vagal sub-branches enter the hilum and follow the pleural sheet to give off the terminal arborizations. In the non-hilar pathway, vagal sub-branches run caudally along the oesophagus and either directly enter the ventral-middle-mediastinal left lobe or follow the triangular ligaments to enter the left and inferior lobe. Both vagi innervate: (i) the superior, middle and accessory lobes on the ventral surfaces that face the heart; (ii) the dorsal-rostral superior lobe; (iii) the dorsal-caudal left lobe; and (iv) the left triangular ligament. Innervated only by the left vagus is: (i) the ventral-rostral and dorsal-rostral left lobe via the hilar pathway; (ii) the ventral-middle-mediastinal left lobe and the dorsal accessory lobe that face the left lobe via the non-hilar pathway; and (iii) the ventral-rostral inferior lobe that faces the heart. Innervated only by the right vagus, via the non-hilar pathway, is: (i) the inferior (ventral and dorsal) and left (ventral only) lobe in the area near the triangular ligament; (ii) the dorsal-middle-mediastinal left lobe; and (iii) the right triangular ligament. Other regions innervated with unknown vagal pathways include: (i) the middle lobe that faces the superior and inferior lobe; (ii) the rostral-mediastinal inferior lobe that faces the middle lobe; and (iii) the ventral accessory lobe that faces the diaphragm. Our study demonstrated that most areas that face the dorsal thoracic cavity have no vagal innervation, whereas the interlobar and heart-facing areas are bilaterally or unilaterally innervated with a left-rostral vs. right-caudal lateralized innervation pattern. This innervation pattern may account for the fact that the respiratory regulation in rats has a lateralized right-side dominant pattern., (© 2016 Anatomical Society.)

Purpose: To define the firing properties of sensory nerve terminals innervating the adult mouse cornea in response to external stimuli of differing modality., Methods: Extracellular electrical activity of single corneal sensory nerve terminals was recorded in excised eyes of C57BL/6J mice. Eyes were placed in a recording chamber and were continuously superfused with warm saline solution. Nerve terminal impulse (NTI) activity was recorded by means of a glass pipette (tip ∼ 50 μm), applied on the corneal surface. Nerve terminal impulse discharges were stored in a computer for offline analysis., Results: Three functionally distinct populations of nerve terminals were identified in the mouse cornea. Pure mechanonociceptor terminals (9.5%) responded phasically and only to mechanical stimuli. Polymodal nociceptor terminals (41.1%) were tonically activated by heat and hyperosmolal solutions (850 mOsm·kg-1), mechanical force, and/or TRPV1 and TRPA1 agonists (capsaicin and allyl isothiocyanate [AITC], respectively). Cold-sensitive terminals (49.4%) responded to cooling. Approximately two-thirds of them fired continuously at 34°C and responded vigorously to small temperature reductions, being classified as high-background activity, low-threshold (HB-LT) cold thermoreceptor terminals. The remaining one-third exhibited very low ongoing activity at 34°C and responded weakly to intense cooling, being named low-background activity, high-threshold (LB-HT) cold thermoreceptor terminals., Conclusions: The mouse cornea is innervated by trigeminal ganglion (TG) neurons that respond to the same stimulus modalities as corneal receptors of other mammalian species. Mechano- and polymodal endings underlie detection of mechanical and chemical noxious stimuli while HB-LT and LB-HT cold thermoreceptors appear to be responsible for basal and irritation-evoked tearing and blinking, respectively.

Previous studies had shown that the HIV-1 capsidic glycoprotein gp120 (strain IIIB) modulates presynaptic release-regulating NMDA receptors on noradrenergic and glutamatergic terminals. This study aims to assess whether the chemokine CXC4 receptors (CXCR4s) has a role in the gp120-mediated effects. The effect of CXCL12, the endogenous ligand at CXCR4, on the NMDA-mediated releasing activity was therefore investigated. Rat hippocampal synaptosomes were preloaded with [ 3 H]noradrenaline ([ 3 H]NA) or [ 3 H]D-aspartate ([ 3 H]D-Asp) and acutely exposed to CXCL12, to NMDA or to both agonists. CXCL12, inactive on its own, facilitated the NMDA-evoked tritium release. The NMDA antagonist MK-801 abolished the NMDA/CXCL12-evoked tritium release of both radiolabelled tracers, while the CXCR4 antagonist AMD 3100 halved it, suggesting that rat hippocampal nerve endings possess presynaptic release-regulating CXCR4 receptors colocalized with NMDA receptors. Accordingly, Western blot analysis confirmed the presence of CXCR4 proteins in synaptosomal plasmamembranes. In both synaptosomal preparations, CXCL12-induced facilitation of NMDA-mediated release was dependent upon PLC-mediated src-induced events leading to mobilization of Ca 2+ from intraterminal IP 3 -sensitive stores Finally, the gp120-induced facilitation of NMDA-mediated release of [ 3 H]NA and [ 3 H]D-Asp was prevented by AMD 3100. We propose that CXCR4s are functionally coupled to NMDA receptors in rat hippocampal noradrenergic and glutamatergic terminals and account for the gp120-induced modulation of the NMDA-mediated central effects. The NMDA/CXCR4 cross-talk could have a role in the neuropsychiatric symptoms often observed in HIV-1 positive patients.

Spinal afferent neurons play a major role in detection and transduction of painful stimuli from internal (visceral) organs. Recent technical advances have made it possible to visualize the endings of spinal afferent axons in visceral organs. Although it is well known that the sensory nerve cell bodies of spinal afferents reside within dorsal root ganglia (DRG), identifying their endings in internal organs has been especially challenging because of a lack of techniques to distinguish them from endings of other extrinsic and intrinsic neurons (sympathetic, parasympathetic, and enteric). We recently developed a surgical approach in live mice that allows selective labeling of spinal afferent axons and their endings, revealing a diverse array of different types of varicose and nonvaricose terminals in visceral organs, particularly the large intestine. In total, 13 different morphological types of endings were distinguished in the mouse distal large intestine, originating from lumbosacral DRG. Interestingly, the stomach, esophagus, bladder, and uterus had less diversity in their types of spinal afferent endings. Taken together, spinal afferent endings (at least in the large intestine) appear to display greater morphological diversity than vagal afferent endings that have previously been extensively studied. We discuss some of the new insights that these findings provide., (Copyright © 2016 the American Physiological Society.)

Sensory receptors are distributed throughout the oral cavity, pharynx, and larynx. Laryngeal sensitivity is crucial for maintaining safe swallowing, thus avoiding silent aspiration. Morphologic description of different receptor types present in larynx vary because of the study of many different species, from mouse to humans. The most commonly sensory structures described in laryngeal mucosa are free nerve endings, taste buds, muscle spindles, glomerular and corpuscular receptors. This study aimed at describing the morphology and the distribution of nerve endings in premature newborn glottic region. Transversal serial frozen sections of the whole vocal folds of three newborns were analyzed using an immuno-histochemical process with a pan-neuronal marker anti-protein gene product 9.5 (PGP 9.5). Imaging was done using a confocal laser microscope. Nerve fiber density in vocal cord was calculated using panoramic images in software Morphometric Analysis System v1.0. Some sensory structures, i.e. glomerular endings and intraepithelial free nerve endings were found in the vocal cord mucosa. Muscle spindles, complex nerve endings (Meissner-like, spherical, rectangular and growing) spiral-wharves nerve structures were identified in larynx intrinsic muscles. Nervous total mean density in vocal cord was similar in the three newborns, although they had different gestational age. The mean nerve fiber density was higher in the posterior region than anterior region of vocal cord. The present results demonstrate the occurrence of different morphotypes of sensory corpuscles and nerve endings premature newborn glottic region and provide information on their sensory systems., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

This MiniReview focuses on the role played by nitric oxide (NO) and hydrogen sulfide (H 2 S) in physiology of the upper and lower urinary tract. NO and H 2 S, together with carbon monoxide, belong to the group of gaseous autocrine/paracrine messengers or gasotransmitters, which are employed for intra- and intercellular communication in almost all organ systems. Because they are lipid-soluble gases, gaseous transmitters are not constrained by cellular membranes, so that their storage in vesicles for later release is not possible. Gasotransmitter signals are terminated by falling concentrations upon reduction in production that are caused by reacting with cellular components (essentially reactive oxygen species and NO), binding to cellular components or diffusing away. NO and, more recently, H 2 S have been identified as key mediators in neurotransmission of the urinary tract, involved in the regulation of ureteral smooth muscle activity and urinary flow ureteral resistance, as well as by playing a crucial role in the smooth muscle relaxation of bladder outlet region. Urinary bladder function is also dependent on integration of inhibitory mediators, such as NO, released from the urothelium. In the bladder base and distal ureter, the co-localization of neuronal NO synthase with substance P and calcitonin gene-related peptide in sensory nerves as well as the existence of a high nicotinamide adenine dinucleotide phosphate-diaphorase activity in dorsal root ganglion neurons also suggests the involvement of NO as a sensory neurotransmitter., (© 2016 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).)

Key Points: In the present study, we document the role of compact myelin in regulating the structural and functional properties of ion channels at the nerve terminals, using electrophysiology, dynamic Na(+) imaging and immunohistochemistry. The subcellular segregation of Na(+) channel expression and intracellular Na(+) dynamics at the heminode and terminal was lost in the dysmyelinated axon from Long-Evans shaker rats, which lack compact myelin. In Long-Evans shaker rats, loss of the Nav β4 subunit specifically at the heminode reduced resurgent and persistent Na(+) currents, whereas K(+) channel expression and currents were increased. The results of the present study suggest that there is a specific role for compact myelin in dictating protein expression and function at the axon heminode and in regulating excitability of the nerve terminal., Abstract: Axon myelination increases the conduction velocity and precision of action potential propagation. Although the negative effects of demyelination are generally attributed to conduction failure, accumulating evidence suggests that myelination also regulates the structural properties and molecular composition of the axonal membrane. In the present study, we investigated how myelination affects ion channel expression and function, particularly at the last axon heminode before the nerve terminal, which regulates the presynaptic excitability of the nerve terminal. We compared the structure and physiology of normal axons and those of the Long-Evans shaker (LES) rat, which lacks compact myelin. The normal segregation of Na(+) channel expression and dynamics at the heminode and terminal was lost in the LES rat. Specifically, NaV -α subunits were dispersed and NaV β4 subunit was absent, whereas the density of K(+) channels was increased at the heminode. Correspondingly, resurgent and persistent Na(+) currents were reduced and K(+) current was increased. Taken together, these data suggest a specific role for compact myelin in the orchestration of ion channel expression and function at the axon heminode and in regulating excitability of the nerve terminal., (© 2016 The Authors. The Journal of Physiology © 2016 The Physiological Society.)

Lacosamide is an anti-epileptic drug that is also used for the treatment of painful diabetic neuropathy acting through voltage-gated sodium channels. The aim of this work was to evaluate the effects of acute application of lacosamide on the electrical activity of corneal cold nerve terminals in lacrimo-deficient guinea pigs. Four weeks after unilateral surgical removal of the main lachrimal gland in guinea pigs, corneas were excised and superfused in vitro at 34°C for extracellular electrophysiological recording of nerve terminal impulse activity of cold thermosensitive nerve terminals. The characteristics of the spontaneous and the stimulus-evoked (cooling ramps from 34°C to 15°C) activity before and in presence of lacosamide 100µM and lidocaine 100µM were compared. Cold nerve terminals (n=34) recorded from dry eye corneas showed significantly enhanced spontaneous activity (8.0±1.1 vs. 5.2±0.7imp/s; P<0.05) and cold response (21.2±1.7 vs. 16.8±1.3imp/s; P<0.05) as well as reduced cold threshold (1.5±0.1 vs. 2.8±0.2 Δ°C; P<0.05) to cooling ramps compared to terminals (n=58) from control animals. Both lacosamide and lidocaine decreased spontaneous activity and peak response to cooling ramps significantly (P<0.05). Temperature threshold was increased by the addition of lidocaine (P<0.05) but not lacosamide (P>0.05) to the irrigation fluid. In summary, the application of lacosamide results in a significant decrease of the augmented spontaneous activity and responsiveness to cold of corneal sensory nerves from tear-deficient animals. Based on these promising results we speculate that lacosamide might be used to reduce the hyperexcitability of corneal cold receptors caused by prolonged ocular surface dryness due to hyposecretory or evaporative dry eye disease., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The evolution of sensory systems has let mammals develop complicated tactile end organs to enable sophisticated sensory tasks, including social interaction, environmental exploration, and tactile discrimination. The Merkel disc, a main type of tactile end organ consisting of Merkel cells (MCs) and Aβ-afferent endings, are highly abundant in fingertips, touch domes, and whisker hair follicles of mammals. The Merkel disc has high tactile acuity for an object's physical features, such as texture, shape, and edges. Mechanisms underlying the tactile function of Merkel discs are obscured as to how MCs transmit tactile signals to Aβ-afferent endings leading to tactile sensations. Using mouse whisker hair follicles, we show herein that tactile stimuli are transduced by MCs into excitatory signals that trigger vesicular serotonin release from MCs. We identify that both ionotropic and metabotropic 5-hydroxytryptamine (5-HT) receptors are expressed on whisker Aβ-afferent endings and that their activation by serotonin released from MCs initiates Aβ-afferent impulses. Moreover, we demonstrate that these ionotropic and metabotropic 5-HT receptors have a synergistic effect that is critical to both electrophysiological and behavioral tactile responses. These findings elucidate that the Merkel disc is a unique serotonergic synapse located in the epidermis and plays a key role in tactile transmission. The epidermal serotonergic synapse may have important clinical implications in sensory dysfunctions, such as the loss of tactile sensitivity and tactile allodynia seen in patients who have diabetes, inflammatory diseases, and undergo chemotherapy. It may also have implications in the exaggerated tactile sensations induced by recreational drugs that act on serotoninergic synapses., Competing Interests: The authors declare no conflict of interest.

α-Synuclein (α-syn) missense and multiplication mutations have been suggested to cause neurodegenerative diseases, including Parkinson's disease (PD) and dementia with Lewy bodies. Before causing the progressive neuronal loss, α-syn mutations impair exocytosis, which may contribute to eventual neurodegeneration. To understand how α-syn mutations impair exocytosis, we developed a mouse model that selectively expressed PD-related human α-syn A53T (h-α-synA53T) mutation at the calyx of Held terminals, where release mechanisms can be dissected with a patch-clamping technique. With capacitance measurement of endocytosis, we reported that h-α-synA53T, either expressed transgenically or dialyzed in the short term in calyces, inhibited two of the most common forms of endocytosis, the slow and rapid vesicle endocytosis at mammalian central synapses. The expression of h-α-synA53Tin calyces also inhibited vesicle replenishment to the readily releasable pool. These findings may help to understand how α-syn mutations impair neurotransmission before neurodegeneration., Significance Statement: α-Synuclein (α-syn) missense or multiplication mutations may cause neurodegenerative diseases, such as Parkinson's disease and dementia with Lewy bodies. The initial impact of α-syn mutations before neuronal loss is impairment of exocytosis, which may contribute to eventual neurodegeneration. The mechanism underlying impairment of exocytosis is poorly understood. Here we report that an α-syn mutant, the human α-syn A53T, inhibited two of the most commonly observed forms of endocytosis, slow and rapid endocytosis, at a mammalian central synapse. We also found that α-syn A53T inhibited vesicle replenishment to the readily releasable pool. These results may contribute to accounting for the widely observed early synaptic impairment caused by α-syn mutations in the progression toward neurodegeneration., (Copyright © 2016 the authors 0270-6474/16/364408-07$15.00/0.)

Inhibitory synapses comprise only ∼20% of the total synapses in the mammalian brain but play essential roles in controlling neuronal activity. In fact, perturbing inhibitory synapses is associated with complex brain disorders, such as schizophrenia and epilepsy. Although many types of inhibitory synapses exist, these disorders have been strongly linked to defects in inhibitory synapses formed by Parvalbumin-expressing interneurons. Here, we discovered a novel role for an unconventional collagen-collagen XIX-in the formation of Parvalbumin(+) inhibitory synapses. Loss of this collagen results not only in decreased inhibitory synapse number, but also in the acquisition of schizophrenia-related behaviors. Mechanistically, these studies reveal that a proteolytically released fragment of this collagen, termed a matricryptin, promotes the assembly of inhibitory nerve terminals through integrin receptors. Collectively, these studies not only identify roles for collagen-derived matricryptins in cortical circuit formation, but they also reveal a novel paracrine mechanism that regulates the assembly of these synapses., (© 2016 Su et al.)

Purpose: To test whether palisade endings are a general feature of mammalian extraocular muscles (EOMs)., Methods: Thirteen species, some frontal-eyed (human, monkey, cat, and ferret), and others lateral-eyed (pig, sheep, calf, horse, rabbit, rat, mouse, gerbil, and guinea pig) were analyzed. Palisade endings were labeled by using different combinations of immunofluorescence techniques. Three-dimensional reconstructions of immunolabeled palisade endings were done., Results: In all frontal-eyed species, palisade endings were a consistent feature in the rectus EOMs. Their total number was high and they exhibited an EOM-specific distribution. In particular, the number of palisade endings in the medial recti was significantly higher than in the other rectus muscles. In the lateral-eyed animals, palisade endings were infrequent and, when present, their total number was rather low. They were only found in ungulates (sheep, calf, pig, and horse) and in rabbit. In rodents (rat, guinea pig, mouse, and gerbil) palisade endings were found infrequently (e.g., rat) or were completely absent. Palisade endings in frontal-eyed species and in some lateral-eyed species (pig, sheep, calf, and horse) had a uniform morphology. They generally lacked α-bungarotoxin staining, with a few exceptions in primates. Palisade endings in other lateral-eyed species (rabbit and rat) exhibited a simplified morphology and bound α-bungarotoxin., Conclusions: Palisade endings are not a universal feature of mammalian EOMs. So, if they are proprioceptors, not all species require them. Because in frontal-eyed species, the medial rectus muscle has the highest number of palisade endings, they likely play a special role in convergence.

Previous studies have shown that the effects of manual acupuncture (MA) are contributed by collagen fibers and mast cells in local acupoints, at which acupuncture stimulation causes various afferent fiber groups to be excited. However what happens in local nerve fibers and mast cells after MA remains unclear. The aim of this study was to examine the response of cutaneous nerve fibers and mast cells to MA stimulation in acupoint Hegu (LI4). The contralateral LI4 of the same rat was used as a non-stimulated control. Immnohistochemistry analysis were carried out to observe the expression of histamine (HA), serotonin (5-HT) and nociceptive neuropeptides, calcitonin gene-related peptide (CGRP) and substance P (SP), in the LI4 area. Mast cells were labeled with anti-mast cell tryptase antibody and simultaneously with HA or 5-HT primary antibodies to observe their co-expression. Our results showed that SP and CGRP were expressed more highly on the cutaneous nerve fibers of LI4 after MA stimulation than that of the control. Mast cells aggregated in close proximity to the blood vessels in intra-epidermis and dermis and some of them with degranulation in the lower dermis and subcutaneous tissue of LI4. Both mast cells and their granules appeared with HA (+) and 5-HT (+) expression at stimulated L14 sites, while a few intact mast cells with a little expression of 5-HT and HA were distributed in areas of non-stimulated L14. The results indicated that local cutaneous nerve terminals and mast cells responded to MA with higher expression of SP and CGRP in nerve fibers, as well as with aggregation and degranulation of mast cells with HA and 5-HT granules at acupoint LI4. These neuroactive substances may convey signals to certain pathways that contribute to the effects of acupuncture., (Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.)

This article summarises progress to date over an exciting and very enjoyable first 15 years of collaboration with Bob Banks. Our collaboration began when I contacted him with (to me) an unexpected observation that a dye used to mark recycling synaptic vesicle membrane at efferent terminals also labelled muscle spindle afferent terminals. This observation led to the re-discovery of a system of small clear vesicles present in all vertebrate primary mechanosensory nerve terminals. These synaptic-like vesicles (SLVs) have been, and continue to be, the major focus of our work. This article describes our characterisation of the properties and functional significance of these SLVs, combining our complementary skills: Bob's technical expertise and encyclopaedic knowledge of mechanosensation with my experience of synaptic vesicles and the development of the styryl pyridinium dyes, of which the most widely used is FM1-43. On the way we have found that SLVs seem to be part of a constitutive glutamate secretory system necessary to maintain the stretch-sensitivity of spindle endings. The glutamate activates a highly unusual glutamate receptor linked to phospholipase D activation, which we have termed the PLD-mGluR. It has a totally distinct pharmacology first described in the hippocampus nearly 20 years ago but, like the SLVs that were first described over 50 years ago, has since been little researched. Yet, our evidence and literature searches suggest this glutamate/SLV/PLD-mGluR system is a ubiquitous feature of mechanosensory endings and, at least for spindles, is essential for maintaining mechanosensory function. This article summarises how this system integrates with the classical model of mechanosensitive channels in spindles and other mechanosensory nerve terminals, including hair follicle afferents and baroreceptors controlling blood pressure. Finally, in this time when there is an imperative to show translational relevance, I describe how this fascinating system might actually be a useful therapeutic drug target for clinical conditions such as hypertension and muscle spasticity. This has been a fascinating 15-year journey in collaboration with Bob who, as well as having an astute scientific mind, is also a great enthusiast, motivator and friend. I hope this exciting and enjoyable journey will continue well into the future., (© 2015 The Author. Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.)

Central nerve terminals contain a small number of synaptic vesicles (SVs) that must sustain the fidelity of neurotransmission across a wide range of stimulation intensities. For this to be achieved, nerve terminals integrate a number of complementary endocytosis modes whose activation spans the breadth of these neuronal stimulation patterns. Two such modes are ultrafast endocytosis and activity-dependent bulk endocytosis, which are triggered by stimuli at either end of the physiological range. Both endocytosis modes generate endosomes directly from the nerve terminal plasma membrane, before the subsequent production of SVs from these structures. This review will discuss the current knowledge relating to the molecular mechanisms involved in the generation of SVs from nerve terminal endosomes, how this relates to other mechanisms of SV production and the functional role of such SVs., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Injection of the melanocortin-3/4 receptor agonist melanotan-II (MTII) into the nucleus of the solitary tract (NTS) produces rapid and sustained reduction of food intake. Melanocortin-4 receptors (MC4Rs) are expressed by vagal afferent endings in the NTS, but it is not known whether these endings participate in MTII-induced reduction of food intake. In experiments described here, we evaluated the contribution of central vagal afferent endings in MTII-induced reduction of food intake. Examination of rat hindbrain sections revealed that neuronal processes expressing immunoreactivity for the endogenous MC4R agonist α-melanoctyte-stimulating hormone course parallel and wrap around anterogradely labeled vagal afferent endings in the NTS and thus are aptly positioned to activate vagal afferent MC4Rs. Furthermore, MTII and endogenous MC4R agonists increased protein kinase A (PKA)-catalyzed phosphorylation of synapsin I in vagal afferent endings, an effect known to increase synaptic strength by enhancing neurotransmitter release in other neural systems. Hindbrain injection of a PKA inhibitor, KT5720, significantly attenuated MTII-induced reduction of food intake and the increase in synapsin I phosphorylation. Finally, unilateral nodose ganglion removal, resulting in degeneration of vagal afferent endings in the ipsilateral NTS, abolished MTII-induced synapsin I phosphorylation ipsilateral to nodose ganglion removal. Moreover, reduction of food intake following MTII injection into the NTS ipsilateral to nodose ganglion removal was significantly attenuated, whereas the response to MTII was not diminished when injected into the contralateral NTS. Altogether, our results suggest that reduction of food intake following hindbrain MC4R activation is mediated by central vagal afferent endings., (Copyright © 2014 the authors 0270-6474/14/3312636-10$15.00/0.)

Ca(2+)-dependent transmitter release occurs in a fast and in a slow phase, but the differential roles of Ca(2+) buffers and Ca(2+) sensors in shaping release kinetics are still controversial. Replacing extracellular Ca(2+) by Sr(2+) causes decreased fast release but enhanced slow release at many synapses. Here, we established presynaptic Sr(2+) uncaging and made quantitative Sr(2+)- and Ca(2+)-imaging experiments at the mouse calyx of Held synapse, to reveal the interplay between Ca(2+) sensors and Ca(2+) buffers in the control of fast and slow release. We show that Sr(2+) activates the fast, Synaptotagmin-2 (Syt2) sensor for vesicle fusion with sixfold lower affinity but unchanged high cooperativity. Surprisingly, Sr(2+) also activates the slow sensor that remains in Syt2 knock-out synapses with a lower efficiency, and Sr(2+) was less efficient than Ca(2+) in the limit of low concentrations in wild-type synapses. Quantitative imaging experiments show that the buffering capacity of the nerve terminal is markedly lower for Sr(2+) than for Ca(2+) (~5-fold). This, together with an enhanced Sr(2+) permeation through presynaptic Ca(2+) channels (~2-fold), admits a drastically higher spatially averaged Sr(2+) transient compared with Ca(2+). Together, despite the lower affinity of Sr(2+) at the fast and slow sensors, the massively higher amplitudes of spatially averaged Sr(2+) transients explain the enhanced late release. This also allows us to conclude that Ca(2+) buffering normally controls late release and prevents the activation of the fast release sensor by residual Ca(2+)., (Copyright © 2014 the authors 0270-6474/14/3412622-14$15.00/0.)

The distribution, location, and spatial arrangement of mechanoreceptors are important for neural signal conciseness and accuracy in proprioceptive information required to maintain functional joint stability. The glenohumeral joint capsule and labrum are mechanoreceptor-containing tissues for which the distribution of mechanoreceptors has not been determined despite the importance of these tissues in stabilizing the shoulder. More recently, it has been shown that damage to articular mechanoreceptors can result in proprioceptive deficits that may lead to recurrent instability. Awareness of mechanoreceptor distribution in the glenohumeral joint capsule and labrum may allow preservation of the mechanoreceptors during surgical treatment for shoulder instability, and in turn retain the joint's proprioceptive integrity. For this reason, we sought to develop a neuroanatomical map of the mechanoreceptors within the capsule and labrum. We postulated that the mechanoreceptors in these tissues are distributed in a unique pattern, with mechanoreceptor-scarce regions that may be more appropriate for surgical dissection. We determined the neuroanatomical distribution of mechanoreceptors and their associated fascicles in the capsule and labrum from eight human cadaver shoulder pairs using our improved gold chloride staining technique and light microscopy. A distribution pattern was consistently observed in the capsule and labrum from which we derived a neuroanatomical map. Both tissues demonstrated mechanoreceptor-dense and -scarce regions that may be considered during surgical treatment for instability. Capsular fascicles were located in the subsynovial layer, whereas labral fascicles were concentrated in the peri-core zone. The capsular fascicles presented as a lattice network and with a plexiform appearance. Fascicles within the labrum resembled a cable structure with the fascicles running in parallel. Our findings contribute to the neuroanatomical knowledge of the two glenohumeral joint stabilizers, namely, capsule and labrum, primarily involved in the onset of shoulder instability and recurrent instability. Neuroanatomical knowledge of articular mechanoreceptors is important for (i) developing a topographical map that reflects correspondence between the joint and surrounding musculature, (ii) understanding proprioceptive deficits that are only partially restored post surgical and post rehabilitative treatment, and (iii) gaining further knowledge about articular mechanoreceptors., (© 2014 Anatomical Society.)

Dry eye disease (DED) is a multifactorial disorder affecting the composition and volume of tears. DED causes ocular surface dryness, cooling, and hyperosmolality, leading ultimately to corneal epithelium damage and reduced visual performance. Ocular discomfort is the main clinical symptom in DED. However, the peripheral neural source of such unpleasant sensations is still unclear. We analyzed in excised, superfused mouse eyes, the effect of NaCl-induced hyperosmolality (325-1005 mOsm·kg(-1)) on corneal cold thermoreceptor and polymodal nociceptor nerve terminal impulse (NTI) activity. Osmolality elevations at basal corneal temperature (33.6°C) linearly increased the ongoing NTI frequency of cold thermoreceptors, at a mean rate of 0.34 imp·s(-1)/10 mOsm. This frequency increase became significant with osmolality values greater than 340 mOsm. Comparison of cold thermoreceptor activity increase induced by a dynamic temperature reduction of 1.8°C under iso- and hyperosmolal (360-mOsm) conditions provided evidence that more than 50% of the increased firing response was attributable to hyperosmolality. Comparatively, activation of corneal polymodal nociceptor endings by hyperosmolal solutions started with values of 600 mOsm and greater. Sensitization of polymodal nociceptors by continuous perfusion with an "inflammatory soup" (bradykinin, histamine, prostaglandin E2 [PGE2], serotonin, and adenosine triphosphate [ATP]) did not enhance their activation by hyperosmolal solutions. High osmolality also altered the firing pattern and shape of cold and polymodal NTIs, possibly reflecting disturbances in local membrane currents. Results strongly suggest that tear osmolality elevations in the range observed in DED predominantly excite cold thermoreceptors, supporting the hypothesis that dryness sensations experienced by these patients are due, at least in part, to an augmented activity of corneal cold thermoreceptors., (Copyright © 2014 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Airway sensory nerve excitability is a key determinant of respiratory disease-associated reflexes and sensations such as cough and dyspnea. Inflammatory signaling modulates mitochondrial function and produces reactive oxygen species (ROS). Peripheral terminals of sensory nerves are densely packed with mitochondria; thus, we hypothesized that mitochondrial modulation would alter neuronal excitability. We recorded action potential firing from the terminals of individual bronchopulmonary C-fibers using a mouse ex vivo lung-vagal ganglia preparation. C-fibers were characterized as nociceptors or non-nociceptors based upon conduction velocity and response to transient receptor potential (TRP) channel agonists. Antimycin A (mitochondrial complex III Qi site inhibitor) had no effect on the excitability of non-nociceptors. However, antimycin A increased excitability in nociceptive C-fibers, decreasing the mechanical threshold by 50% and increasing the action potential firing elicited by a P2X2/3 agonist to 270% of control. Antimycin A-induced nociceptor hyperexcitability was independent of TRP ankyrin 1 or TRP vanilloid 1 channels. Blocking mitochondrial ATP production with oligomycin or myxothiazol had no effect on excitability. Antimycin A-induced hyperexcitability was dependent on mitochondrial ROS and was blocked by intracellular antioxidants. ROS are known to activate protein kinase C (PKC). Antimycin A-induced hyperexcitability was inhibited by the PKC inhibitor bisindolylmaleimide (BIM) I, but not by its inactive analog BIM V. In dissociated vagal neurons, antimycin A caused ROS-dependent PKC translocation to the membrane. Finally, H2O2 also induced PKC-dependent nociceptive C-fiber hyperexcitability and PKC translocation. In conclusion, ROS evoked by mitochondrial dysfunction caused nociceptor hyperexcitability via the translocation and activation of PKC.

Lgr5/6 proteins are stem cell markers in various tissues. However, what determines their restricted expression pattern in these tissues remains unknown. We found that in skin, Lgr6 is not only expressed in the central isthmus, directly above the hair follicle bulge cells as reported previously, but also in the interfollicular epidermis. Lgr6 expression in skin is highly correlated with the innervation sites of cutaneous nerves. In the hair follicle, Lgr6 closely localizes with the surrounding nerve endings and their corresponding Schwann cells throughout the entire hair cycle. Furthermore, ablation of cutaneous nerves leads to degeneration of Schwann cells and diminished expression of Lgr6. Our results demonstrate that the nerve endings/Schwann cells control Lgr6 expression in skin, implying that they play a role in regulation of skin epithelial cells., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

At the nerve terminal, neurotransmitter release is triggered by Ca(2+) influx through voltage-gated Ca(2+) channels (VGCCs). During postnatal development, VGCC subtypes in the nerve terminal switch at many synapses. In immature rodent cerebella, N-type and P/Q-type VGCCs mediate GABAergic neurotransmission from Purkinje cells (PCs) to deep nuclear cells, but as animals mature, neurotransmission becomes entirely P/Q-type dependent. We reproduced this developmental switch in rat cerebellar slice culture to address the underlying mechanism. Chronic block of cerebellar neuronal activity with tetrodotoxin (TTX) in slice culture, or in vivo, reversed the switch, leaving neurotransmission predominantly N-type channel-dependent. Brain-derived neurotrophic factor or neurotrophin-4 rescued this TTX effect, whereas pharmacological blockade of neurotrophin receptors mimicked the TTX effect. In PC somata, unlike in presynaptic terminals, TTX had no effect on the proportion of Ca(2+) channel subtype currents. We conclude that neuronal activity activates the neurotrophin-TrkB signaling pathway, thereby causing the N-to-P/Q channel switch in presynaptic terminals.

Peptidergic neurones play a pivotal role in the neuromodulation of widespread areas in the nervous system. Generally, it has been accepted that the peptide release from these neurones is regulated by their firing activities. The terminal nerve (TN)-gonadotrophin releasing hormone (GnRH) neurones, which are one of the well-studied peptidergic neurones in vertebrate brains, are characterised by their spontaneous regular pacemaker activities, and GnRH has been suggested to modulate the sensory responsiveness of animals. Although many peptidergic neurones are known to exhibit burst firing activities when they release the peptides, TN-GnRH neurones show spontaneous burst firing activities only infrequently. Thus, it remains to be elucidated whether the TN-GnRH neurones show burst activities and, if so, how the mode switching between the regular pacemaking and bursting modes is regulated in these neurones. In this study, we found that only a single pulse electrical stimulation of the neuropil surrounding the TN-GnRH neurones reproducibly induces transient burst activities in TN-GnRH neurones. Our combined physiological and morphological data suggest that this phenomenon occurs following slow inhibitory postsynaptic potentials mediated by cholinergic terminals surrounding the TN-GnRH neurones. We also found that the activation of muscarinic acetylcholine receptors induces persistent opening of potassium channels, resulting in a long-lasting hyperpolarisation. This long hyperpolarisation induces sustained rebound depolarisation that has been suggested to be generated by a combination of persistent voltage-gated Na(+) channels and low-voltage-activated Ca(2+) channels. These new findings suggest a novel type of cholinergic regulation of burst activities in peptidergic neurones, which should contribute to the release of neuropeptides.

If a patient asks 'why does my shoulder hurt?' the conversation will quickly turn to scientific theory and sometimes unsubstantiated conjecture. Frequently, the clinician becomes aware of the limits of the scientific basis of their explanation, demonstrating the incompleteness of our understanding of the nature of shoulder pain. This review takes a systematic approach to help answer fundamental questions relating to shoulder pain, with a view to providing insights into future research and novel methods for treating shoulder pain. We shall explore the roles of (1) the peripheral receptors, (2) peripheral pain processing or 'nociception', (3) the spinal cord, (4) the brain, (5) the location of receptors in the shoulder and (6) the neural anatomy of the shoulder. We also consider how these factors might contribute to the variability in the clinical presentation, the diagnosis and the treatment of shoulder pain. In this way we aim to provide an overview of the component parts of the peripheral pain detection system and central pain processing mechanisms in shoulder pain that interact to produce clinical pain.

Due, in part, to the unique structure of the tooth, dental pain is initiated via distinct mechanisms. Here we review recent advances in our understanding of inflammatory tooth pain and discuss 3 hypotheses proposed to explain dentinal hypersensitivity: The first hypothesis, supported by functional expression of temperature-sensitive transient receptor potential channels, emphasizes the direct transduction of noxious temperatures by dental primary afferent neurons. The second hypothesis, known as hydrodynamic theory, attributes dental pain to fluid movement within dentinal tubules, and we discuss several candidate cellular mechanical transducers for the detection of fluid movement. The third hypothesis focuses on the potential sensory function of odontoblasts in the detection of thermal or mechanical stimuli, and we discuss the accumulating evidence that supports their excitability. We also briefly update on a novel strategy for local nociceptive anesthesia via nociceptive transducer molecules in dental primary afferents with the potential to specifically silence pain fibers during dental treatment. Further understanding of the molecular mechanisms of dental pain would greatly enhance the development of therapeutics that target dental pain.

Peripheral neural mechanisms underlying the sensations of irritation, discomfort, and itch accompanying the eye allergic response have not been hitherto analyzed. We explored this question recording the changes in the electrical activity of corneoconjunctival sensory nerve fibers of the guinea pig after an ocular allergic challenge. Sensitization was produced by i.p. ovalbumin followed by repeated application in the eye of 10% ovalbumin on days 14 to 18. Blinking and tearing rate were measured. Spontaneous and stimulus-evoked (mechanical, thermal, chemical) impulse activity was recorded from mechanonociceptor, polymodal nociceptor and cold corneoscleral sensory afferent fibers. After a single (day 14) or repeated daily exposures to the allergen during the following 3 to 4days, tearing and blinking rate increased significantly. Also, sensitization was observed in mechanonociceptors (transient reduction of mechanical threshold only on day 14) and in polymodal nociceptors (sustained enhancement of the impulse response to acidic stimulation). In contrast, cold thermoreceptors showed a significant decrease in basal ongoing activity and in the response to cooling. Treatment with the TRPV1 and TRPA1 blockers capsazepine and HC-030031 reversed the augmented blinking. Only capsazepine attenuated tearing rate increase and sensitization of the polymodal nociceptors response to CO2. Capsazepine also prevented the decrease in cold thermoreceptor activity caused by the allergic challenge. We conclude that changes in nerve impulse activity accompanying the ocular allergic response, primarily mediated by activation of nociceptor's TRPV1 and to a lesser degree by activation of TRPA1 channels, explain the eye discomfort sensations accompanying allergic episodes., (Copyright © 2013 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Schwann cells are primarily discussed in the context of their ability to form myelin. However there are many subtypes of these neural crest derived cells including satellite cells of the dorsal root ganglia and autonomic ganglia, the perisynaptic Schwann cells of the neuromuscular junction and the non-myelin forming Schwann cells which ensheathe the unmyelinated fibres of the peripheral nervous system which are about 80% of peripheral nerves. This review discusses the many functions of these Schwann cell subsets including their seminal role in axonal ensheathment, perineuronal organisation, maintenance of normal neural function, synapse formation, response to damage and repair and an increasingly recognised active role in pain syndromes., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Background: The decline in voluntary muscle contraction during low-frequency nerve stimulation is used clinically to assess the type and degree of neuromuscular block. The mechanism underlying this depression is unknown., Methods: Simultaneous electrophysiological measurements of neurotransmitter release and prejunctional Ca currents were made at mouse neuromuscular junctions to evaluate the hypothesis that decreases in nerve terminal Ca currents are responsible for low-frequency depression., Results: Under conditions generally used to measure Ca currents at the neuromuscular junction, increasing the frequency of nerve stimulation briefly from 0.017 to 0.1-1 Hz caused a simultaneous reduction in the release of the neurotransmitter acetylcholine to 52.2 ± 4.4% of control and the Ca current peak to 75.4 ± 2.0% of control (P < 0.001, n = 5 experiments for both measurements, mean ± SEM for all data). In conditions used for train-of-four monitoring (4 stimuli, 2 Hz), neurotransmitter release declined to 42.0 ± 1.0% of control and the Ca current peak declined to 75.8 ± 3.3% of control between the first and fourth stimulus (P < 0.001, n = 7 experiments for both measurements). Depression in acetylcholine release during train-of-four protocols also occurred in the absence of neuromuscular-blocking drugs., Discussion: The results demonstrate that neuromuscular depression during train-of-four monitoring is due to a decline in nerve terminal Ca currents, hence reducing the release of acetylcholine. As similar processes may come into play at higher stimulation frequencies, agents that antagonize the decline in Ca currents could be used to treat conditions in which neuromuscular depression can be debilitating.

Our aim in the present study was to determine whether a glutamatergic modulatory system involving synaptic-like vesicles (SLVs) is present in the lanceolate ending of the mouse and rat hair follicle and, if so, to assess its similarity to that of the rat muscle spindle annulospiral ending we have described previously. Both types of endings are formed by the peripheral sensory terminals of primary mechanosensory dorsal root ganglion cells, so the presence of such a system in the lanceolate ending would provide support for our hypothesis that it is a general property of fundamental importance to the regulation of the responsiveness of the broad class of primary mechanosensory endings. We show not only that an SLV-based system is present in lanceolate endings, but also that there are clear parallels between its operation in the two types of mechanosensory endings. In particular, we demonstrate that, as in the muscle spindle: (i) FM1-43 labels the sensory terminals of the lanceolate ending, rather than the closely associated accessory (glial) cells; (ii) the dye enters and leaves the terminals primarily by SLV recycling; (iii) the dye does not block the electrical response to mechanical stimulation, in contrast to its effect on the hair cell and dorsal root ganglion cells in culture; (iv) SLV recycling is Ca(2+) sensitive; and (v) the sensory terminals are enriched in glutamate. Thus, in the lanceolate sensory ending SLV recycling is itself regulated, at least in part, by glutamate acting through a phospholipase D-coupled metabotropic glutamate receptor.

This paper is motivated by a recent experimental research by Levitan and colleagues (Wong MY, Zhou C, Shakiryanova D, Lloyd TE, Deitcher DL, Levitan ES. Neuropeptide delivery to synapses by long-range vesicle circulation and sporadic capture. Cell 2012; 148(5): 1029-1038), which discovered and explained the circulation of dense core vesicles (DCVs) between the neuron soma and nerve terminals. We developed a compartmental mechanistic model to simulate this circulation. The model includes five compartments, the axonal compartment and four en passant boutons, which are small axonal varicosities that are present in many axon terminals. By postulating expressions for DCV fluxes between the compartments and for the rates of DCV capture in the boutons and utilizing conservation of DCVs, ODEs modeling concentrations in each of the compartments were developed. The equations were then solved numerically. The obtained results provide insight into how DCV circulation develops, what the circulation is at steady state, and how it may be affected by defects in retrograde transport., (Copyright © 2013 John Wiley & Sons, Ltd.)