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This study was performed to understand the anatomical substrates for Kölliker-Fuse nucleus (KFN) modulation of respiratory-related tongue movement. After application of cholera toxin B subunit (CTb) to the medial branch of the hypoglossal nerve (HGn) and injection of biotinylated dextran amine (BDA) into the KFN ipsilaterally, an overlapping distribution of BDA-labeled axon terminals and CTb-labeled neurons was found in the ventral compartment of the hypoglossal nucleus (HGN) ipsilateral to the application and injection sites. At the electron microscopic level, the BDA-labeled terminals made asymmetrical synaptic contacts predominantly with dendrites of the HGN neurons, some of which were labeled with CTb. Using retrograde tracing combined with in situ hybridization, we demonstrated that almost all the KFN neurons sending their axons to the HGN were positive for vesicular glutamate transporter (VGLUT) 2 mRNA but not glutamic acid decarboxylase 67 mRNA. Using a combination of anterograde and retrograde tracing techniques and immunohistochemistry for VGLUT2, we further demonstrated that the KFN axon terminals with VGLUT2 immunoreactivity established close contact with the HGN motoneurons whose axons constitute the medial branch of the HGn. The present results suggest that glutamatergic KFN fibers may exert excitatory influence upon the HGN motoneurons sending their axons to the medial branch of the HGn for the control of protruder tongue muscles contraction to maintain airway patency during respiration., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Two specific groups of neurons in the dorsolateral pons are activated by dietary sodium deprivation. These two groups are the pre-locus coeruleus (pre-LC) and the inner subdivision of the external lateral parabrachial nucleus (PBel-inner). In each site, after rats are fed an extremely low-sodium diet for over a week, neurons increase their expression of an activity-induced transcription factor, c-Fos. Here, we confirm this observation and extend it by demonstrating that these two groups of neurons express a common marker gene, the constitutively-expressed transcription factor Forkhead box protein 2 (FoxP2). That is, virtually all of the c-Fos activated neurons in both regions also express FoxP2. The expression of FoxP2 by both these groups of neurons suggests that they are developmentally-related subsets derived from the same basic population. Given that FoxP2, unlike c-Fos, is expressed independent of sodium deprivation, this marker may be useful in future studies of the pre-LC and PBel-inner. The molecular definition of these neurons, which project to circuits in the forebrain that influence visceral, appetitive, and hedonic functions, may allow direct experimental exploration of the functional role of these circuits using genetic tools., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Using intrachoroidal injection of the transneuronal retrograde tracer pseudorabies virus (PRV) in rats, we previously localized preganglionic neurons in the superior salivatory nucleus (SSN) that regulate choroidal blood flow (ChBF) via projections to the pterygopalatine ganglion (PPG). In the present study, we used higher-order transneuronal retrograde labeling following intrachoroidal PRV injection to identify central neuronal cell groups involved in parasympathetic regulation of ChBF via input to the SSN. These prominently included the hypothalamic paraventricular nucleus (PVN) and the nucleus of the solitary tract (NTS), both of which are responsive to systemic BP and are involved in systemic sympathetic vasoconstriction. Conventional pathway tracing methods were then used to determine if the PVN and/or NTS project directly to the choroidal subdivision of the SSN. Following retrograde tracer injection into SSN (biotinylated dextran amine 3K or Fluorogold), labeled perikarya were found in PVN and NTS. Injection of the anterograde tracer, biotinylated dextran amine 10K (BDA10K), into PVN or NTS resulted in densely packed BDA10K+terminals in prechoroidal SSN (as defined by its enrichment in nitric oxide synthase-containing perikarya). Double-label studies showed these inputs ended directly on prechoroidal nitric oxide synthase-containing neurons of SSN. Our study thus establishes that PVN and NTS project directly to the part of SSN involved in parasympathetic vasodilatory control of the choroid via the PPG. These results suggest that control of ChBF may be linked to systemic blood pressure and central control of the systemic vasculature., (Published by Elsevier B.V.)

We performed this study to understand the anatomical substrates of parabrachial nucleus (PBN) modulation of orexin (ORX)-containing neurons in the hypothalamus. After biotinylated dextranamine (BDA) injection into the lateral PBN and immunostaining of ORX-containing neurons in the rat, the prominent overlap of the distribution field of the BDA-labeled fibers and that of the ORX-immunoreactive (ir) neurons was found in the lateralmost part of the dorsomedial nucleus and adjacent dorsal perifornical area (this overlapping field was referred to as "suprafornical area" in the present study), and the labeled axon terminals made asymmetrical synaptic contacts with somata and dendrites of the ORX-ir neurons. We further revealed that almost all the "suprafornical area"-projecting lateral PBN neurons were positive for vesicular glutamate transporter 2 mRNA and very few of them were positive for glutamic acid decarboxylase 67 mRNA. The present data suggest that ORX-containing neurons in the "suprafornical area" may be under the excitatory influence of the glutamatergic lateral PBN neurons probably for the regulation of arousal and waking., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The interposed nuclei (IN) of the cerebellum play a crucial role in the classically conditioned eyeblink circuit. It has previously been shown in well-trained animals that injecting the IN with GABA(A) antagonists produces short-latency conditioned responses (SLRs). The mechanism underlying SLR generation is not clear. According to one concept, SLRs originate in cerebellar nuclei in response to direct inputs from collaterals of mossy fibers. An alternate explanation is that SLRs are produced by extra-cerebellar circuits that are excited by increased tonic activity in cerebellar nuclei or by the combined action of inputs to cerebellar nuclei from mossy fiber collaterals and incompletely blocked Purkinje cells. In the present study, we examined whether cerebellar afferent axons in the middle cerebellar peduncle (MCP) participate in SLR expression. We hypothesized that if SLRs are evoked by the sensory mossy fiber input to the IN and cerebellar cortex, then blocking the MCP should abolish these responses. Well-trained animals, which had been implanted with dual injection cannulae in the left IN and the left MCP, were injected with gabazine (GZ) into the IN to produce SLRs followed by an injection of the sodium channel blocker tetrodotoxin (TTX) into the MCP. TTX infusions in the MCP suppressed both CRs and SLRs. These findings suggest that the expression of SLRs depends on both direct and cerebellar cortex-mediated sensory information from the mossy fiber system.

Pharmacological manipulations of gamma-aminobutyric acid (GABA) neurotransmission in the nucleus pontis oralis (PnO) of the rat brainstem produce alterations in sleep/wake behavior. Local applications of GABA(A) receptor antagonists and agonists increase REM sleep and wake, respectively. These findings support a role for GABAergic mechanisms of the PnO in the control of arousal state. We have been investigating sources of GABA innervation of the PnO that may interact with local GABA(A) receptors in the control of state. Utilizing a retrograde tracer, cholera toxin-B subunit (CTb), injected into the PnO and dual-label immunohistochemistry with an antibody against glutamic acid decarboxalase-67 (GAD67), we report on a previously unidentified GABAergic neuronal population projecting to the contralateral PnO appearing as a column of cells, with long-axis in the sagittal plane, extending through the midbrain and pons. We refer to these neurons as the mesopontine GABAergic column (MPGC). The contiguous, columnar, anatomical distribution suggests operation as a functional neural system, which may influence expression of REM sleep, wake and other behaviors subserved by the PnO.

Distribution and time course of the occurrence of "dark" neurons were compared with the EEG activity and behavior of rats during 4-aminopyridine (4-AP) induced epileptic seizures. A crystal of the K(+) channel blocker 4-AP (0.5 mg/kg) was placed onto the exposed parieto-occipital cortex of Halothane-anesthetized rats for 40 min. Thereafter, the anesthesia was discontinued and the behavioral signs of the epileptic seizure activity were observed. The presence of "dark" neurons was demonstrated by the sensitive silver method of Gallyas in rats sacrificed at 0, 3 and 6 h after the end of the 4-AP crystal application. The EEG activity was recorded in the rats with longer survival times. The EEG analysis revealed the generalization of the epileptic seizures. We found that the formation of "dark" neurons in the hippocampus and the pontine reticular formation paralleled the generalization of the seizures.

The primary parasympathetic center of the submandibular and sublingual salivary glands is the superior salivatory (SS) nucleus, neurons of which receive excitatory (glutamatergic) and inhibitory (GABAergic and glycinergic) synaptic transmissions in rats. In the present study, to examine postnatal neural development, we focused on inhibitory transmission to the SS neurons in neonatal rats from postnatal day 2 (P2) to P14. Conventional and gramicidin-perforated whole-cell patch-clamp techniques were applied to the neurons in brainstem slices. The decay time constants of GABAergic and glycinergic postsynaptic currents (PSCs) consisted of fast (tau(fast)) and slow (tau(slow)) components. Both tau(fast) and tau(slow) of PSC components tended to become faster with development. The equilibrium potential of Cl(-) (E(Cl-)) was estimated from the reversal potentials of total PSCs (GABAergic plus glycinergic). The E(Cl-) in the P8-P14 group was significantly more negative than E(Cl-) in the P2-P7 group. Exogenous GABA application at the resting potentials produced depolarization in 83% of SS neurons at P2-P7 and accompanied the action potential in some neurons. In contrast, at P8-P14, GABA evoked hyperpolarization in 78% of SS neurons; therefore, SS neurons did not acquire mature inhibitory systems until P14. The development of SS neurons is discussed as compared with the development of peripheral salivary gland tissue and brainstem neurons that participate in oral motor and sensory functions.

Rostral ventral medulla (RVM) contains significant numbers of local GABAergic neurons which may subserve respiratory chemosensory and baroreceptor reflexes. Nicotinic mechanisms stimulate release of GABA in certain brainstem neurons. Whether the GABAergic neurons at RVM express nicotinic cholinergic receptors (nAChRs) is not known. We used glutamic acid decarboxylase 67-kDa isoform (GAD67) and parvalbumin (PV) as anatomical markers to identify the GABAergic neurons of the RVM and caudal pons and performed double labeling to evaluate the expression of alpha-7 and alpha-4 nAChRs by GAD67 and PV-imnunoreactive (ir) cells at these sites. GAD67-ir cells were found at the ventrolateral pontomedullary border in areas adjacent to the A5 noradrenergic cell group and overlapping the facial nucleus lateral subnuclei and para-facial zones. Of 205 GAD67-ir cells labeled at these sites, 74% exhibited immunoreactivity for alpha-7 nAChRs. Alpha-4 immunoreactivity was also present in 35% of GAD67-ir cells at these sites. The PV-ir cells of RVM and caudal pons were found medial to the facial nucleus and lateral to the pyramid in a column distinct from the GAD67-ir cells. Virtually all the PV-ir cells demonstrated immunoreactivity for alpha-4 nAChR (95%) and alpha-7 (93%) subunits of nAChRs. Differential expression of GAD67 and PV by neurons at the pontomedullary border implies that PV may not be a valid marker for GABAergic neurons. The expression of alpha-4 and alpha-7 nAChRs by GAD67-ir cells suggests nicotinic cholinergic modulation of GABAergic signaling at these ventrolateral pontomedullary sites.

We previously have shown that forebrain inputs increase responses of amiloride-sensitive NaCl-best neurons to the conditioned stimulus (CS) in the rat parabrachial nucleus (PBN) after the establishment of conditioned taste aversion (CTA) to NaCl. In the present study, we examined the effects of aversively-conditioned NaCl taste stimulation on Fos-like immunoreactivity (FLI) in the PBN using awake intact and decerebrate rats. In Experiment 1, the CTA-trained and sham-conditioned control rats were intraorally infused with 0.1 M NaCl or 0.1 M NaCl mixed with 10(-4) M amiloride, a sodium-channel blocker. Significantly more NaCl-stimulated FLI was observed in the central medial (cms) and external lateral subnuclei (els) of PBN in the CTA-trained group than in the control group. In both groups, amiloride markedly reduced NaCl-stimulated FLI in the cms but not in the els. In Experiment 2, we found that after decerebration, there was no significant difference in FLI between the CTA-trained and sham-conditioned groups. These results suggest that (1) amirolide-sensitive taste information of NaCl projects mainly to the cms; (2) sensory information of aversive taste stimuli is likely to be represented in the els; and (3) forebrain inputs are required for elevated FLI in the PBN after CTA.

The present study examined the neural projection from the inferior colliculus to the pontine nuclei in guinea pig. This projection has been reported in other animals, and our goal was to establish the projection in guinea pig, a commonly used auditory model. Ultimately, we wanted to determine if the pontine nuclei could be a component of the descending auditory system from the inferior colliculus to the cochlear nucleus. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was injected into one inferior colliculus of 10 animals and the pontine nuclei examined under a light microscope to detect PHA-L-labeled fibers. PHA-L-labeled fibers were observed in the ipsilateral pontine nuclei in 70% of the animals. While the majority of labeled fibers were smooth in appearance, a few fibers with en passant type varicosities (indicating synapses) were observed in the dorsolateral area of the pontine nuclei, adjacent to the lateral lemniscus. These findings do not support a robust projection from the inferior colliculus to the pontine nuclei in guinea pig. This is in opposition to findings in bat in which the projection may play a major role in modulating responses to sound.

Head direction (HD) cells located in several regions of the brain, including the postsubiculum, retrosplenial cortex, lateral dorsal thalamic nucleus, anterior dorsal thalamic nucleus, and lateral mammillary nucleus, provide a signal of the rat's momentary directional heading. Experimental evidence suggests that vestibular inputs are critical for the maintenance these cells' directional sensitivity. However, it is still unclear how vestibular information is conveyed to the HD cell-related circuitry. In a recent study, the supragenual nucleus (SG) was suggested as a putative relay of vestibular inputs to this circuitry. In the present study, using anterograde and retrograde tract-tracing methods, we first investigated whether the SG is in a position to convey vestibular inputs. Next, we examined the projections of the SG with the Phaseolus vulgaris leucoagglutinin method. Our results indicate that the SG receives direct inputs from the medial vestibular nucleus and projects to elements of the HD cell-related circuitry, providing a massive input to the contralateral dorsal tegmental nucleus and a moderately dense projection to the shell region of the lateral mammillary nucleus. Overall, the present findings serve to clarify how vestibular inputs reach the HD cell-related circuit and point out the SG as an important interface to this end.

The caudal pontine reticular formation nucleus (cPRF) is implicated in seizure propagation to the spinal cord in several forms of generalized convulsive seizures, including audiogenic seizures (AGS). Focal microinjection studies implicate cPRF as a requisite neuronal network site subserving generalized AGS in the moderate severity substrain of genetically epilepsy-prone rats (GEPR-3s). AGS in GEPR-3s culminate in generalized clonus, but daily repetition of AGS (AGS kindling) results in an additional seizure behavior, facial and forelimb (F and F) clonus, not seen prior to kindling. This study examined cPRF neuronal firing changes and seizure behaviors during AGS in GEPR-3s. We examined extracellular cPRF neuronal responses to acoustic stimuli (12 kHz) and observed neuronal firing during AGS. cPRF neurons exhibited onset responses to acoustic stimuli before and after AGS kindling. After AGS kindling, increased neuronal firing occurred, and response latencies were prolonged. Tonic neuronal firing occurred during generalized clonus, which changed to burst firing after AGS kindling. Burst firing also occurred during F and F clonus. Increased neuronal firing and the change from tonic to burst firing suggest that AGS kindling involves increased cPRF excitability. These data support an important role for cPRF neurons in generation of generalized clonus in unkindled GEPR-3s, which is increased by AGS kindling. The increased cPRF response latency might reflect a greater role of rostral components of the AGS neuronal network in transmission of acoustic responses to cPRF. This study also suggests that cPRF neurons may be involved in F and F clonus, which was unexpected since F and F clonus is thought to originate primarily in forebrain structures.

Urotensin II (UII) is a vasomodulatory peptide that was not predicted to elicit CNS activity. However, because we have recently shown that the urotensin II receptor (UII-R) is selectively expressed in rat mesopontine cholinergic (MPCh) neurons, we hypothesize that UII may have a central function. The present study demonstrates that the UII system is able to modulate MPCh neuron activity. Brain slice experiments demonstrate that UII excites MPCh neurons of the mouse laterodorsal tegmentum (LDTg) by activating a slow inward current. Furthermore, microinfusion of UII into the ventral tegmental area produces a sustained increase in dopamine efflux in the nucleus accumbens, as measured by in vivo chronoamperometry. In agreement with UII activation of MPCh neurons, intracerebroventricular injections of UII significantly modulate ambulatory movements in both rats and mice but do not significantly affect startle habituation or prepulse inhibition. The present study establishes that UII is a neuromodulator that may be exploited to target disorders involving MPCh dysfunction.

Our previous studies have demonstrated that stimulation of cardiac sympathetic afferents activates neurons in the parabrachial nucleus (PBN), a region known to play a role in central integration of cardiovascular autonomic reflexes. However, phenotypes of these activated neurons have not been well identified. Glutamate, an important excitatory neurotransmitter in the brain, is involved in PBN-mediated cardiovascular responses. Recent identification of vesicular glutamate transporter 3 (VGLUT3) has provided a novel and unique marker to locate distinctive perikarya of neurons that use glutamate as a neurotransmitter. The action of glutamate in the brain is influenced by nitric oxide. Thus, using triple immunofluorescent labeling, the present study examined expression of c-Fos, an immediate early gene, in the neurons containing VGLUT3 and neuronal nitric oxide synthase (nNOS) in the PBN following stimulation of cardiac sympathetic afferents. In anesthetized cats with bilateral barodenervation and cervical vagotomy, topical application of bradykinin (BK, 1-10 microg/ml, 50 microl, n = 6) on the left ventricle was performed six times, every 20 min. Repeated administration of BK elicited consistent increases in blood pressure over a 100 min period while no changes were noted in the animals treated with the vehicle for BK (0.9% saline, n=5). Compared to control cats, c-Fos expression was increased significantly in the cell bodies containing VGLUT3 as well as both VGLUT3 and nNOS in the external lateral PBN (elPBN) in BK-treated animals (all P < 0.01). In addition, using similar triple-staining method, we noted that fibers of activated neurons containing nNOS in the elPBN co-localized with vesicular glutamate transporter 2 following BK stimulation. These data suggest that glutamatergic neurons represent a cell type in the PBN that is activated by stimulation of cardiac sympathetic afferents. Nitric oxide has the potential to influence the action of glutamatergic neurons in regulation of excitatory cardiovascular responses induced by activation of cardiac sympathetic afferents.

Intracellular Neurobiotin-injections were used to label functionally identified neurons in the rostro-dorsomedial part of the trigeminal oral nucleus (Vo.r) in the cat. The labeled Vo.r neurons with the mechanoreceptive field in oral tissues innervated bilaterally either jaw-opening motoneurons or jaw-closing motoneurons. This result suggests that Vo.r neurons play an important role in sensory-motor reflexes responsible for coordination of bilaterally symmetrical jaw movements.

Barrington's nucleus contains neurones that decrease their firing during micturition contraction, as well as neurones that increase their firing during this phase. These neurones are commonly termed inverse neurones and direct neurones, respectively. The aims of the present study were to determine whether inverse neurones send descending axons to the spinal cord and to clarify how these neurones regulate bladder contractility. Forty-five single neurones were recorded from the dorsolateral pontine tegmentum. Spinal-projecting neurones were identified by antidromic stimulation of the spinal cord. More than half of inverse neurones were located outside Barrington's nucleus. Only three were spinal-projecting neurones. The results were in marked contrast with direct neurones that we studied previously: the majority of them were located within Barrington's nucleus, and 56% were spinal-projecting neurones. The firing frequency of inverse neurones ranged between 6 and 37 Hz during the relaxation phase of the micturition contraction-relaxation rhythm. The firing of all neurones began to decrease within 8 s after the onset of micturition contraction. During micturition contraction, neurones displayed little firing, being virtually silent (n = 29) or displayed weak tonic firing (3-11 Hz; n = 16). All neurones began to increase their firing within 8 seconds after the onset of bladder relaxation. These results suggest that inverse neurones do not trigger bladder contraction or relaxation, despite the finding that a few of them send descending axons to the spinal cord. One possible role of the inverse neurone is to regulate firing activities of direct neurones in Barrington's nucleus.

It has been shown that central or peripheral injections of the peptide relaxin induces water intake, not sodium intake in rats. Important inhibitory mechanisms involving serotonin and other neurotransmitters in the control of water and NaCl intake have been demonstrated in the lateral parabrachial nucleus (LPBN). In the present study, we investigated the effects of bilateral injections of methysergide (serotonergic receptor antagonist) into the LPBN on intracerebroventricular (i.c.v.) relaxin-induced water and NaCl intake in rats. Additionally, the effect of the blockade of central angiotensin AT(1) receptors with i.c.v. losartan on relaxin-induced water and NaCl intake in rats treated with methysergide into the LPBN was also investigated. Male Holtzman rats with cannulas implanted into the lateral ventricle (LV) and bilaterally in the LPBN were used. Intracerebroventricular injections of relaxin (500 ng/1 microl) induced water intake (5.1+/-0.7 ml/120 min), but not significant 1.8% NaCl intake (0.5+/-0.4 ml/120 min). Bilateral injections of methysergide (4 microg/0.2 microl) into the LPBN strongly stimulated relaxin-induced 1.8% NaCl intake (34.5+/-10.9 ml/120 min) and slightly increased water intake (10.5+/-4.9 ml/120 min). The pretreatment with i.c.v. losartan (100 microg/1 microl) abolished the effects of i.c.v. relaxin combined with LPBN methysergide on 1.8% NaCl intake (0.5+/-0.4 ml/120 min). Losartan (100 microg/1 microl) also abolished relaxin-induced water intake in rats injected with methysergide into the LPBN (1.6+/-0.8 ml/120 min) or not (0.5+/-0.3 ml/120 min). Losartan (50 microg/1 microl) partially reduced the effects of relaxin. The results show that central relaxin interacting with central angiotensinergic mechanisms induces NaCl intake after the blockade of LPBN serotonergic mechanisms.

Activation of neurons in the rostral ventromedial medulla (RVM) directly modulates spinal nociceptive transmission by projections to the spinal cord dorsal horn and indirectly by projections to neurons in the dorsolateral pons (DLP) that project to the spinal cord dorsal horn. However, it is not known whether the same neurons in the RVM produce both direct and indirect modulation of nociception. Deposits of the retrograde tracers Fluoro-Gold (FG) in the spinal cord dorsal horn and DiI in the DLP were used to determine whether the same RVM neurons project to both of these regions. Only 0.9+/-0.1% of RVM neurons retrogradely labeled with Fluoro-Gold from the spinal cord were also labeled with DiI placed in the DLP. In addition, spinally projecting RVM neurons were significantly larger than RVM neurons that project to the DLP. Finally, spinally projecting neurons were found predominantly on the midline and within the RVM; neurons that project to the DLP had a wider distribution and were present both within and outside of the RVM. Thus, separate and morphologically distinct populations of RVM neurons appear to modulate nociception by direct and indirect descending pathways.

The excitatory and inhibitory synaptic inputs to parasympathetic preganglionic neurons in the superior salivatory (SS) nucleus were investigated in brain slices of neonatal (4-8 days old) rat using the whole-cell patch-clamp technique. The SS neurons innervating the submandibular and sublingual salivary glands and innervating the lingual artery in the anterior region of the tongue were identified by retrograde transport of a fluorescent tracer. Whole-cell currents were evoked by electrical stimulation of tissue surrounding the cell. These evoked postsynaptic currents were completely abolished by antagonists for N-methyl-D-aspartate (NMDA) glutamate, non-NMDA glutamate, gamma-aminobutyric acid type A (GABAA), and glycine receptors, suggesting that SS neurons receive glutamatergic excitatory, and GABAergic and glycinergic inhibitory synaptic inputs. In SS neurons for the salivary glands, the ratio of the NMDA component to the total excitatory postsynaptic current (EPSC) was larger than that of the non-NMDA component. This profile was reversed in the SS neurons for the tongue. In SS neurons for the salivary glands, the ratio of the GABAA component to the total IPSC was larger than the ratio of the glycine component to total inhibitory postsynaptic current (IPSC). The decay time constants of the GABAA component were slower than those for glycine. These characteristics of the excitatory and inhibitory inputs may be involved in determining the firing properties of the SS neurons innervating the salivary glands and the tongue.

After ipsilateral injections of biotinylated dextran amine (BDA) into the Kölliker-Fuse (KF) nucleus and cholera toxin B subunit (CTb) into the ventral horn in C4 to C5 segments of the spinal cord, an overlapping distribution of BDA-labeled axon terminals and CTb-labeled neurons was found in the rostral ventral respiratory group (rVRG) region ipsilateral to the injection sites. After ipsilateral injections of BDA into the KF and Fluoro-Gold (FG) into the ventral horn in C4 to C5 segments of the spinal cord, BDA-labeled axons were found to make asymmetrical synapses with the somata and dendrites of FG-labeled neurons within the neuropil of the rVRG region. Using retrograde tracing combined with immunohistochemistry for phosphate-activated glutaminase (PAG), we observed that as many as 72% of the rVRG neurons projecting to the PhN were immunoreactive for PAG and that approximately 62% and 75% of the KF neurons projecting respectively to the rVRG region and PhN contain PAG immunoreactivity. Using anterograde tracing combined with immunohistochemistry for vesicular glutamate transporter 2 (VGluT2), we further demonstrated that the KF axon terminals in the rVRG and PhN regions as well as the rVRG axon terminals in the PhN region contain VGluT2 immunoreactivity. The present results suggest that the glutamatergic pathways from the KF to the PhN directly and indirectly via the rVRG region may exist and underlie the inspiratory responses that are elicited by activation of the KF neurons.

We have examined the importance of the A5 region modulating cardiorespiratory responses evoked from the parabrachial complex (PB) in spontaneously breathing rats. Cardiorespiratory changes were analyzed in response to electrical stimulation and glutamate microinjections into the PB (10-20 nl, 1-2 nmol) before and after ipsilateral microinjection of muscimol (50 nl, 0.25 nmol) or lidocaine (50 nl, 0.5 nmol) within the A5 region. Stimulation of medial parabrachial and Kölliker-Fuse nuclei (mPB-KF) evoked a decrease in respiratory rate (P<0.001) with a rise in blood pressure (P<0.001) and heart rate (P<0.05). After muscimol or lidocaine microinjections within the A5 region, the pressor and heart rate responses to mPB-KF stimulation were reduced (P<0.05, both cases). Muscimol within the A5 region altered the respiratory response to glutamate stimulation of mPB-KF, evoking an increase in respiratory rate (P<0.05). Lidocaine abolished the respiratory response to mPB-KF stimulation. Stimulation of the lateral parabrachial nuclei (lPB) caused an increase in respiratory rate (P<0.001) with a rise in blood pressure (P<0.001) and heart rate (P<0.05). Muscimol or lidocaine microinjections within A5 region decreased heart rate (P<0.05) and pressor responses (P<0.05) evoked from lPB. The increase of respiratory rate persisted unchanged. To confirm functional interactions between A5 and PB, extracellular recordings of putative A5 neurones were obtained during PB stimulation. Eighty-three A5 cells were recorded, 35 were activated from the mPB-KF (42%). The results indicate that neurones of the A5 region participate in the cardiorespiratory response evoked from the different regions of the PB complex. The possible mechanisms involved in these interactions are discussed.

The synaptic organization of afferents to the parafascicular nucleus (Pf) of the thalamus was studied in rats. In the Pf, three types of axon terminals were identified: the first type was a small terminal with round synaptic vesicles forming an asymmetric synapse, the second type was a large terminal with round synaptic vesicles forming an asymmetric synapse, and the third type was a terminal with pleomorphic vesicles forming a symmetric synapse. They were named SR, LR and P boutons, respectively. In order to determine the origin of these axon terminals, biotinylated dextran amine (BDA) was injected into the main afferent sources of the Pf, the superior colliculus (SC) and the pedunculopontine tegmental nucleus (PPN). Axon terminals from the SC were both SR and LR boutons which made synaptic contacts with somata and dendrites. PPN afferents were SR boutons, which made synaptic contacts with somata and smaller dendrites. Double-labeled electron microscopic studies, in which a retrograde tracer (wheat germ agglutinin conjugated to horseradish peroxidase: WGA-HRP) was injected into the striatum and an anterograde tracer (BDA) into the SC revealed that SC afferent terminals made synapses directly with Pf neurons that projected to the striatum. Another experiment was performed to find out whether two different afferents converged onto a single Pf neuron. To address this question, two different tracers were injected into the SC and PPN in a rat. Electron microscopically, both afferent terminals from the SC and PPN made synaptic contacts with the same dendrite. Our results prove that a single neuron of the rat Pf received convergent projections from two different sources.

The present study was undertaken to explore the neuronal mechanisms of hypocretin actions on neurons in the nucleus pontis oralis (NPO), a nucleus which plays a key role in the generation of active (REM) sleep. Specifically, we sought to determine whether excitatory postsynaptic potentials (EPSPs) evoked by stimulation of the laterodorsal tegmental nucleus (LDT) and spontaneous EPSPs in NPO neurons are modulated by hypocretin. Accordingly, recordings were obtained from NPO neurons in the cat in conjunction with the juxtacellular microinjection of hypocretin-1 onto intracellularly recorded cells. The application of hypocretin-1 significantly increased the mean amplitude of LDT-evoked EPSPs of NPO neurons. In addition, the frequency and the amplitude of spontaneous EPSPs in NPO neurons increased following hypocretin-1 administration. These data suggest that hypocretinergic processes in the NPO are capable of modulating the activity of NPO neurons that receive excitatory cholinergic inputs from neurons in the LDT.

A previously undescribed subgroup of A7 neurons was identified and named globosa neurons. Morphologically, these neurons exhibit strong TH staining, are larger and globularly shaped, and are situated more laterally compared with the main group of A7 neurons. They have prominent dendritic processes that are oriented transversely and extend into the lateral lemniscus. These neurons are activated during underwater diving in rats, but at present their function is unknown.

Projections to the parabrachial nucleus (PBN) from the nucleus of the solitary tract (NST) carry afferent signals from both the oral cavity and gastrointestinal tract. Although physiological studies suggest the convergence of oral and gastrointestinal sensory signals in the parabrachial nucleus, anatomical studies have emphasized the segregation of these pathways. To more precisely determine the anatomical relationship between gastric distension and oral afferent representation in PBN, small deposits of two anterograde tracers were made into the NST under physiological guidance in the same rat. Gastric terminations were dense and separate from taste projections in the rostral portion of the external lateral and dorsal lateral subnuclei. Gustatory projections were densest and separate from gastric terminations in the ventral lateral and central medial subnuclei of the caudal waist region, but were intermingled with gastric projections in these subnuclei and the external subnuclei at slightly more rostral levels. Patterns of segregation and overlap often appeared as 'patches' within or across subnuclear boundaries. In a second set of experiments, physiological evidence for overlap in PBN was evaluated from single unit extracellular responses evoked by gastric distension and orosensory (taste and orotactile) stimulation. Neurophysiological recordings verified that a small proportion of single cells within the waist and external subnuclei could be activated by both gastric and orotactile stimulation. The anatomical experiments further revealed intranuclear projections from the caudal NST injections that extended rostrally to sites at which responses to oral stimulation had been recorded. Although existing physiological data suggest such interactions are more limited than those in PBN, these anatomical data suggest that gastric/oral interactions may also exist in the NST.

Stimulation of the lateral hypothalamus (LH) produces antinociception that is modified by intrathecal alpha-adrenergic antagonists. Spinally-projecting noradrenergic neurons in the LH have not been identified, suggesting that the LH may innervate brainstem noradrenergic neurons, such as the A7 catecholamine cell group in the dorsolateral pontine tegmentum, that modify nociception at the level of the spinal cord dorsal horn. Recently we demonstrated in neuroanatomical studies that substance P-immunoreactive neurons in the LH project the A7 area. To identify a functional connection between substance P neurons in the LH and the A7 cell group, the cholinergic agonist carbachol (125 nmol) was microinjected into the LH of female Sprague-Dawley rats and antinociception was obtained on the tail flick or foot withdrawal test. Cobalt chloride (100 nM) was then microinjected near the A7 cell group to block synaptic activation of spinally-projecting A7 neurons, which were identified using tyrosine-hydroxylase immunoreactivity. Within 5 min of the cobalt chloride injection, the antinociceptive effect of carbachol stimulation was blocked. In another set of experiments, the NK(1) receptor antagonist L-703-606 (5 microg) was microinjected near the A7 cell group following LH stimulation with carbachol. L-703-606 also abolished LH-induced antinociception. These results support the conclusion that antinociception produced by activating substance P neurons in the LH is mediated in part by the subsequent activation of spinally-projecting noradrenergic neurons in the A7 cell group.

Fos immunocytochemistry was combined with immunolabeling for dopamine-beta-hydroxylase (DBH) to examine neuronal activation in the medulla and pons after administration of polyethelene glycol (PEG), which produces volume depletion without altering arterial blood pressure. Increased Fos immunoreactivity was observed in the area postrema, nucleus of the solitary tract, rostral ventrolateral medulla, lateral parabrachial nucleus, and the dorsomedial pons at the level of the locus coeruleus. Fos immunolabeling in the caudal nucleus of the solitary tract, rostral ventrolateral medulla, and the dorsomedial pons occurred primarily in neurons that did not contain DBH. Thus, PEG activates non-catecholaminergic neurons in medullary and pontine areas associated with cardiovascular and body fluid regulation., (Copyright 2002 Elsevier Science B.V.)

The pedunculopontine tegmental nucleus (PPT) has been implicated in the generation and/or maintenance of both active sleep (AS) and wakefulness (W). GABAergic neurons are present within this nucleus and recent studies have shown that these neurons are active during AS. In order to examine the role of mesopontine GABAergic processes in the generation of AS, the GABA(A) agonist muscimol and the GABA(A) antagonist bicuculline were microinjected into the PPT of chronic cats that were prepared for recording the states of sleep and wakefulness. Muscimol increased the time spent in AS by increasing the frequency and duration of AS episodes; this increase in AS was at the expense of the time spent in wakefulness. A decrease in PGO density during AS was also observed following the microinjection of muscimol. On the other hand, bicuculline decreased both AS and quiet sleep and increased the time spent in wakefulness. These data suggest that GABA acts on GABA(A) receptors within the PPT to facilitate the generation of AS by suppressing the activity of waking-related processes within this nucleus.

In order to study the importance of two pontine regions modulating laryngeal resistance, electrical current or microinjections of glutamate (10-30 nl, 1-3 nmol) were made into the pontine parabrachial complex and the A5 region in spontaneously breathing anaesthetized rats. Two distinct patterns of laryngeal and respiratory responses were elicited. An increase of subglottal pressure was accompanied with an expiratory facilitatory response consisted of a decrease in both respiratory rate and phrenic nerve activity. A decrease of subglottal pressure was accompanied with an inspiratory facilitatory response consisted of an increase in both respiratory rate and phrenic nerve activity. The modification of laryngeal calibre occurred during both respiratory phases in most cases. The concomitant cardiovascular changes of these responses were also analyzed. Controls using guanethidine to block autonomic responses which might interact with respiratory control were also made. Histological analysis of stimulation sites showed a topographical organization of these responses: laryngeal constriction was evoked from Kölliker-Fuse, medial parabrachial nuclei and A5 region, whilst the laryngeal dilation was evoked from the lateral parabrachial nucleus.

We examined the morphological changes in two pontine noradrenergic neuronal groups, area A5 and the locus coeruleus (LC), in neonatal Sprague-Dawley rats between postnatal day 1 and day 10. The volume of the unilateral LC exhibited no significant developmental change. Meanwhile, the number of A5 neurones counted unilaterally was significantly larger on days 1-2 than on days 3-4 or day 10.

The neurons synthesizing nitric oxide (NO) that are part of the renal sympathetic pathways were located by double-staining for the neuronal isoform of nitric oxide synthase (nNOS) using immunocytochemistry to identify NO-synthesizing neurons and transneuronal tracing following infection of the left kidney with pseudorabies virus (PRV). Following kidney injection with PRV, the animals survived 4-day post-inoculation prior to sacrifice and tissue processing. PRV-infected neurons that double-stained for nNOS were found in the paraventricular hypothalamic nucleus (PVN), the raphe obscurus nucleus (ROb), the ventromedial medulla (VMM), the rostral ventrolateral medulla (rVLM) and the A5 cell group. In the thoracolumbar spinal cord, nNOS neurons co-localized with PRV-infected cells in the dorsal horn in laminae I, III-V ipsilateral to the injected kidney and in lamina X, the intermediolateral cell column, the lateral funiculus, the intercalated nucleus and the central autonomic area. We conclude that NO synthesizing cells may significantly affect renal autonomic pathways in the rat by interacting with the renal sensory and sympathomotor circuitry at multiple sites.

In urethane anesthetized rats, the laterodorsal tegmental area was stimulated systematically with a carbon fiber electrode to clarify regions regulating the urinary bladder and/or the external urethral sphincter. Contraction of the former was monitored by bladder pressure and that of the latter by electromyogram. Stimulation of a small area around the ventrolateral edge of the central gray in a plane at the junction of the mesencephalon and pons, where cholinergic neurons in the laterodorsal tegmental nucleus formed the largest mass, induced contraction only of the bladder. Arranged in tandem rostrocaudally with this bladder site, a very small area whose stimulation induced contraction only of the sphincter was found also at the ventrolateral edge of the central gray in a plane slightly caudal to the above. Slightly lateral and caudal to this sphincter site, there were sites the stimulation of which induced contraction of both the bladder and sphincter. It was thus shown physiologically that there were discrete sites in the laterodorsal tegmental area regulating the bladder and sphincter independently.

The present study was undertaken to reveal spatio-temporal changes in the distribution of Fos-like immunoreactive (-IR) neurons in the parabrachial nucleus (PBN), one of the important relay nuclei for processing autonomic and somatosensory information from the oro-facial regions, following the induction of experimental tooth movement in rat upper molars. The experimental tooth movement was induced by the insertion of elastic rubber between the first and second upper molars. In normal animals, the PBN contained a smaller number of Fos-IR neurons. Following experimental tooth movement, the Fos-IR neurons increased in number significantly on both the ipsilateral and contralateral PBN, reaching a maximum at 4 h (about 10 times that of normal animals), and then decreased gradually. However, a significant number of Fos-IR neurons remained at 24 h post-operation. Remarkable side-by-side differences in the number of Fos-IR neurons were recognized at 1 to 4 h following the experimental tooth movement. Their number returned to normal (basal) levels at 5 days post. All subnuclei of PBN showed similar temporal changes in the number of Fos-IR neurons, this being particularly apparent in lateral PBN. Administrations of morphine (3 and 10 mg/kg, i.p.) drastically reduced the induction of Fos-IR neurons in all subnuclei of both the ipsilateral and contralateral PBN in a dose-dependent manner, and its effect was antagonized by pretreatment with naloxone (2 mg/kg, i.p.). The reduction of Fos-IR neurons by morphine pretreatment suggests that the appearance of Fos-IR neurons in the PBN may be partly due to the noxious stimulation and/or stress arising from tooth movement. The bilateral expression of Fos-IR neurons in the PBN indicates that the experimental tooth movement causes the activation of PBN neurons for the processing of somatosensory as well as autonomic information. The prolonged expression of Fos-IR neurons in all the subnuclei of bilateral PBN reflects clinical features of the transient discomfort and/or abnormal sensations, which many patients often complain about during orthodontic treatment.

The organization of corticotectal projections from the medial agranular cortex (AGm), which has been considered to contain rat's frontal eye field, was examined using anterograde and retrograde tracing techniques. When biotinylated dextranamine (BDA) injections were made into the rostral part of the AGm, small numbers of BDA-labeled axons were found in the rostral two-thirds of the superior colliculus (SC) while some labeled axons were seen in the caudal one-third of the SC. These labeled axons were distributed mainly in the lateral part of the stratum griseum intermediale. On the other hand, after BDA injections into the caudal part of the AGm, moderate to dense plexuses of labeled axons were found in the rostral two-thirds of the SC while some labeled axons were seen in the caudal one-third of the SC. These labeled axons were distributed in the ventromedial and dorsolateral marginal zones of the stratum griseum intermediale as well as in the stratum griseum profundum. The corticotectal projections were largely uncrossed. After combined injections of BDA into the caudal part of the AGm on one side and cholera toxin B subunit (CTb) into the paramedian pontine reticular formation on the opposite side or into the interstitial nucleus of Cajal on the same side, the overlapping distributions of BDA-labeled axons and CTb-labeled neurons were found in the ventromedial marginal zone of the stratum griseum intermediale ipsilateral to the site of BDA injection. These results suggest that the caudal part of the AGm plays a more significant role in the oculomotor function than does the rostral part of the AGm.

Anatomical data demonstrate a dense projection, in the cat, from hypocretin (orexin) neurons in the hypothalamus to the laterodorsal tegmental nucleus (LDT), which is a critical pontine site that is involved in the regulation of the behavioral states of sleep and wakefulness. The present study was therefore undertaken to explore the hypocretinergic control of neurons in the LDT vis-à-vis these behavioral states. Accordingly, hypocretin-1 was microinjected into the LDT of chronic, unanesthetized cats and its effects on the percentage, latency, frequency and duration of wakefulness, quiet (non-REM) sleep and active (REM) sleep were determined. There was a significant increase in the time spent in wakefulness following the microinjection of hypocretin-1 into the LDT and a significant decrease in the time spent in active sleep. The increase in the percentage of wakefulness was due to an increase in the duration of episodes of wakefulness; the reduction in active sleep was due to a decrease in the frequency of active sleep episodes, but not in their duration. These data indicate that hypocretinergic processes in the LDT play an important role in both of the promotion of wakefulness and the suppression of active sleep.

The laterodorsal and pedunculopontine tegmental nuclei (LDT-PPT) are involved in the generation of active sleep (AS; also called REM or rapid eye movement sleep). Although the LDT-PPT are composed principally of cholinergic neurons that participate in the control of sleep and waking states, the function of the large number of GABAergic neurons that are also located in the LDT-PPT is unknown. Consequently, we sought to determine if these neurons are activated (as indicated by their c-fos expression) during active sleep induced by the microinjection of carbachol into the rostro-dorsal pons (AS-carbachol). Accordingly, immunocytochemical double-labeling techniques were used to identify GABA and Fos protein, as well as choline acetyltransferase (ChAT), in histological sections of the LDT-PPT. Compared to control awake cats, there was a larger number of GABAergic neurons that expressed c-fos during AS-carbachol (31.5+/-6.1 vs. 112+/-15.2, P<0.005). This increase in the number of GABA+Fos+ neurons occurred on the ipsilateral side relative to the injection site; there was a small decrease in GABA+Fos+ cells in the contralateral LDT-PPT. However, the LDT-PPT neurons that exhibited the largest increase in c-fos expression during AS-carbachol were neither GABA+ nor ChAT+ (47+/-22.5 vs. 228.7+/-14.0, P<0.0005). The number of cholinergic neurons that expressed c-fos during AS-carbachol was not significantly different compared to wakefulness. These data demonstrate that, during AS-carbachol, GABAergic as well as an unidentified population of neurons are activated in the LDT-PPT. We propose that these non-cholinergic LDT-PPT neurons may participate in the regulation of active sleep.

The parabrachial complex, which plays an important role in respiratory regulation, has been reported to send projection fibers to the phrenic nucleus, but the synaptic organization between the parabrachial fibers and the phrenic motoneurons has not been examined. Using anterograde and retrograde tracing methods, we found in the rat that the parabrachial fibers originating mainly from the Kölliker-Fuse nucleus (KF) terminated not only within the phrenic nucleus but also on the radial dendritic bundles of the phrenic motoneurons. It was further revealed that the KF fibers made asymmetrical synapses predominantly with dendrites and partly with somata of the phrenic motoneurons. These data suggest that output signals from the KF may exert excitatory influence directly upon the phrenic motoneurons.

Serotonergic neurons of the dorsal raphe nucleus (DRN) cease firing during active sleep (AS, also called rapid-eye-movement sleep). This cessation of electrical activity is believed to play a 'permissive' role in the generation of AS. In the present study we explored the possibility that GABAergic cells in the DRN are involved in the suppression of serotonergic activity during AS. Accordingly, we examined whether immunocytochemically identified GABAergic neurons in the DRN were activated, as indicated by their expression of c-fos, during carbachol-induced AS (AS-carbachol). Three chronically-prepared cats were euthanized after prolonged episodes of AS that was induced by microinjections of carbachol into the nucleus pontis oralis. Another four cats (controls) were maintained 2 h in quiet wakefulness before being euthanized. Thereafter, immunocytochemical studies were performed on brainstem sections utilizing antibodies against Fos, GABA and serotonin. When compared with identically prepared tissue from awake cats, the number of Fos+ neurons was larger in the DRN during AS-carbachol (35.9+/-5.6 vs. 13.9+/-4.4, P<0.05). Furthermore, a larger number of GABA+ Fos+ neurons were observed during AS-carbachol than during wakefulness (24.8+/-3.3 vs. 4.0+/-1.0, P<0.001). These GABA+ Fos+ neurons were distributed asymmetrically with a larger number located ipsilaterally to the site of injection. There was no significant difference between control and experimental animals in the number of non-GABAergic neurons that expressed c-fos in the DRN. We therefore suggest that activated GABAergic neurons of the DRN are responsible for the inhibition of serotonergic neurons that occurs during natural AS.

Injections into the pedunculopontine nucleus (PPN) of the cholinergic receptor agonist, carbachol (CAR), were found to reduce the amplitude of the vertex-recorded, sleep state-dependent P13 midlatency evoked potential in a dose- and time-dependent manner. This effect was blocked or reduced by pretreatment with the muscarinic receptor antagonist, scopolamine, injected into the PPN.

Benzodiazepines have been reported to induce eating when administered into the brainstem of rats (either the fourth ventricle or the parabrachial nucleus). Benzodiazepines in the brainstem also have been reported to enhance the hedonic impact of taste, as measured by hedonic/aversive taste reactivity patterns, when administered to the fourth ventricle. The present study examined whether the parabrachial nucleus in particular is a brainstem site of the benzodiazepine-produced enhancement of eating and palatability. Food intake (cereal mash) was measured after brainstem microinjections of midazolam or vehicle (0.0, 7.5, and 15.0 microg) into the parabrachial nucleus, the nucleus of the solitary tract, the pedunculopontine tegmental nucleus, or the fourth ventricle (60 microg). We used the taste reactivity paradigm to measure hedonic/aversive affective reactions elicited from rats by oral infusions of a bittersweet solution (7% sucrose-0.01% quinine). Positive hedonic reactions and negative aversive reactions to sucrose-quinine were also measured after microinjections of midazolam (0.0, 7.5, and 15 microg) into the parabrachial nucleus. Midazolam increased food intake and selectively enhanced positive hedonic taste reactivity patterns to the bittersweet solution when microinjections were delivered to the parabrachial nucleus. When administered to the other brainstem sites at the same doses, however, midazolam had no effect. We therefore conclude that the parabrachial nucleus can mediate the benzodiazepine-induced enhancement of the hedonic impact of taste as well as mediating the enhancement of eating behavior.

The microinjection of nerve growth factor (NGF) and neurotrophin-3 (NT-3) into the rostral pontine tegmentum of adult cats rapidly induces long-lasting episodes of rapid eye movement (REM) sleep [J. Yamuy, F.R. Morales, M.H. Chase, Induction of rapid eye movement sleep by the microinjection of nerve growth factor into the pontine reticular formation of the cat, Neuroscience 66 (1995) 9-13]. Because this effect may be mediated by neurotrophin receptors, we sought to determine the distribution of neurons that contain low- and high-affinity neurotrophin receptors in regions of the feline pons and mesencephalon which are involved in the generation of REM sleep as well as neuronal groups that are involved in the control of REM sleep-related patterns of physiological activity. Using antibodies directed against p75, trkA, trkB and trkC, immunolabeled neurons were present in the latero-dorsal and pedunculo-pontine tegmental nuclei, the peribrachial nuclei, medial and lateral pontine reticular formation, the raphe nuclei, and the locus coeruleus. Giant reticular cells and large neurons in the mesencephalic trigeminal nucleus were immunoreactive for p75 and all trk receptors. Neurons that were devoid of neurotrophin-receptor immunoreactivity were intermingled with immunostained neurons in all explored structures. Thus, both low- and high-affinity neurotrophin receptors are conspicuously present in neurons located in mesopontine regions of adult cats. These data underscore the importance of neurotrophin-induced trophic actions on mesopontine neurons. Furthermore, the results support the hypothesis that NGF and NT-3 may modulate the electrical activity of neurons in the rostral pontine tegmentum that are responsible for the generation of REM sleep by acting on one or more of the neurotrophin receptors.

The ventrolateral periaqueductal gray (PAG) and pontine reticular formation (PRF) are implicated in the neuronal network for audiogenic seizures (AGS). The AGS of genetically epilepsy-prone rats (GEPR-9s) culminate in tonic hindlimb extension (TE), and elevated acoustically evoked neuronal firing and burst firing, immediately preceding TE, have been observed in PAG and PRF. This study examined changes in PAG and PRF neuronal firing and behavior in GEPR-9s, following phenytoin administration. Recordings involved 16 PAG and nine PRF neurons in GEPR-9s. Phenytoin in doses (mean, 6. 3 mg/kg) that suppressed TE selectively did not consistently alter PAG neuronal firing. However, these doses of phenytoin resulted in significant (51.6% of control) suppression of PRF neuronal firing. Doses of phenytoin (mean, 8.3 mg/kg), which completely blocked AGS, significantly reduced PAG neuronal firing (64.6% of control), and more greatly suppressed PRF firing (25.8% of control). These results are consistent with a critical role for PRF neurons in generation of TE not evident for PAG. The suppression of PAG and PRF neuronal firing induced by phenytoin with complete seizure blockade is consistent with vital roles for both structures in the seizure network. The differential effects of phenytoin on structures requisite to the seizure network indicate that this experimental approach may be able to identify the most sensitive therapeutic target for anticonvulsant drugs, which could be critical to pharmacological suppression of specific seizure behaviors manifest in various types of convulsions, potentially including human epilepsy.

The localization of glial cell line-derived neurotrophic factor (GDNF) family receptor alpha-1 (GFRalpha-1) was investigated in rat brain by immunohistochemistry using a polyclonal antibody against a specific sequence of the rat protein. For raising the antisera in rabbits, we synthesized the oligopeptide SDVFQQVEHISKGN that corresponds to residues 139 to 152 of rat GFRalpha-1. On immunospot assay, 0.5 microg/ml of an affinity-purified antibody was capable of detecting 7.8 pmol of the rat GFRalpha-1 oligopeptides. When rat brain homogenates were examined by Western blots, the antibody revealed two main bands with molecular weights of approximately 47 kDa and 53 kDa, corresponding to the known sizes of GFRalpha-1. Immunohistochemistry in rat brain demonstrated that GFRalpha-1-like immunoreactivity was present in neurons but not in glial cells. The localization of GFRalpha-1-like immunoreactivity was largely consistent with that of the corresponding GFRalpha-1 mRNA. Positive neurons were distributed widely in various brain regions, but were particularly abundant in such regions as the olfactory bulb, diagonal band, substantia innominata, zona incerta, substantia nigra, cerebellar cortex, nuclei of the cranial nerves including auditory system and spinal motoneurons. The present study showed that GFRalpha-1 in the normal central nervous system is expressed preferentially in certain multiple neuronal systems that include cholinergic system as well as dopaminergic system and motor neurons. As GFRalpha-1 protein was found in numerous brain structures, GDNF family ligands may have therapeutic application not only in degenerative diseases affecting in specific nervous systems, such as Parkinson's disease, amyotrophic lateral sclerosis and multiple system atrophy, but in diffusely damaging diseases like cerebrovascular diseases.

The distribution of labeled neurons in the brain and spinal cord was studied after injecting the Bartha strain of pseudorabies virus (PRV) into the sciatic nerve to provide a baseline for studying neural circuitry after spinal cord injury (SCI) and regeneration. Following a single injection of viral particles into the left sciatic nerve, PRV labeling was found in the spinal cord at 2 days post-injection (p.i.). Increasing complexity in viral labeling from the spinal cord to supraspinal regions became apparent with increasing survival time. In brain regions, several neuronal groups that regulate sympathetic outflow, such as the rostroventrolateral medulla, the lateral paragigantocellular nuclei, and the A5 cells, were densely labeled. However, relatively sparse labeling was noticed in the lateral vestibular nuclei, the red nucleus and the motor cortex whose spinal projections regulate somatic motor function, although those areas were abundantly labeled with Fast blue (FB) in a double-labeling experiment in which FB was co-injected into the lumbar cord. The pattern of viral labeling became more complex beyond 5 days p.i. when increased numbers of cell groups were labeled with PRV but not FB. In addition, some infected neurons started to lyse, as evidenced by a decrease in viral labeling at 7 days p.i. Thus, the 5th day post-viral injection would appear to be an appropriate survival time to obtain maximal labeling with acceptable specificity. We suggest that transneuronal labeling using PRV should be appropriate for studying multi-neural circuitry after SCI and regeneration.

alpha-Adrenoreceptors are present in the ventricular (VZ) and subventricular (SVZ) zones of the mammalian embryonic forebrain, and contribute towards cell cycle controls in the germinal neuroepithelium [Pabbathi et al., Brain Res. 760 (1997) 22-33.]. Since noradrenaline-containing fibres from the locus coeruleus (LC) and other brainstem nuclei innervate many parts of the CNS from an early stage of embryogenesis, we have used heterochronic cocultures to investigate whether noradrenergic innervation may be the source of trophic support. Dorsal neopallium from E13 rat embryo was cultured in proximity to E15 rostral pons (RP), enabling rapid innervation of the neuroepithelium by differentiated noradrenergic neurons of the LC. The projection of interconnecting fibres into germinal areas of the cortex was established in vitro by retrograde tracing and dopamine beta-hydroxylase (DBH) immunocytochemistry. When functional innervation was prevented by transection of axons connecting the explants, the number of apoptotic (TUNEL-positive) cells in the neopallium was increased. Bromodeoxyuridine (BrdU) double-labelling confirmed that germinal cells were amongst those which underwent apoptosis. When cortical explants were innervated by a source of non-monoaminergic (cholinergic) axons from the E18 basal forebrain diagonal band/septum complex (DS), numbers of apoptotic cells were comparable to those in non-innervated cultures. alpha1 and alpha2 adrenoreceptor antagonists included in the medium of cortical cocultures innervated by noradrenergic axons reversed the survival-promoting effect of innervation. Blockade of alpha1 but not of alpha2 receptors also reduced the numbers of S-phase nuclei in the cortex. The results provide evidence that local delivery of neurotransmitter from embryonic noradrenergic axons terminating in the neocortex can regulate survival and proliferation of neuroepithelial cells.

By immunostaining, neurons expressing peptides (dynorphin and corticotropin-releasing factor, CRF) and glutamate decarboxylase (GAD), a GABA-synthesizing enzyme, were precisely mapped in the rat lateral lemniscal nuclei. While GAD neurons were numerous and preferably localized in the dorsal (DLL) and ventral (VLL) nuclei, neurons expressing these peptides were less numerous and localized primarily in the intermediate (ILL) nucleus of the lateral lemniscus. The ILL nucleus was shown to project to the inferior colliculus and to express Fos rapidly in response to peripheral acoustic stimulation, suggesting that the ILL nucleus may take part in non-GABAergic relay of acoustic information in the lateral lemniscus.

The parabrachial region of the brainstem reticular formation projects to the dorsal lateral geniculate nucleus of the thalamus and to the intermediate gray layer of the superior colliculus. We used the retrograde axonal transport of two fluorescent labels to demonstrate that individual parabrachial cells project to both structures. The results suggest that cholinergic cells of the parabrachial region may coordinate the relay of visuosensory information to the cortex with the onset of orienting movements.

Single-unit neuronal activity was recorded from the cerebellar interpositus nucleus and lateral pontine nuclei during conditioned inhibition of the eyeblink response in rats. Conditioned inhibition training sessions included 100 trials/day for 12 days. During each training session, the rats were given 50 presentations of a tone conditioned stimulus (CS) that was paired with a brief periocular shock unconditioned stimulus (US). They were also given 50 presentations of a compound stimulus that included the tone-CS and a light-CS. The compound-CS was not paired with the US. The two types of trials were mixed throughout the session and presented in an irregular sequence. This training procedure resulted in significant inhibition of the eyeblink response during the compound-CS. Neurons in the interpositus and lateral pontine nuclei exhibited significantly less activity during the compound-CS relative to the tone-CS. The suppression of cerebellar and pontine learning-related neuronal activity during the inhibitory CS may be critical for inhibiting the conditioned eyeblink response., (Copyright 1999 Elsevier Science B.V.)

The parabrachial nucleus (PB) is a major relay of noxious and non-noxious visceral sensory information from the nucleus of the solitary tract, spinal cord, and spinal trigeminal nucleus to the forebrain. The nucleus of the solitary tract, spinal cord, and trigeminal dorsal horns contain many enkephalin- and dynorphin-immunoreactive neurons that project to the PB. To study the role of mu-opioid receptors in relaying these inputs, we examined the distribution of mu-opioid receptor immunoreactivity in the PB. The most intense staining was in the external lateral parabrachial subnucleus (PBel), including dendrites extending from the PBel into the lateral crescent subnucleus. Because the Pbel is a major source of projections to the amygdala, we combined retrograde tracing from the central nucleus of the amygdala with immunohistochemistry for mu-opioid receptors. These experiments showed that mu-opioid receptors are expressed by Pbel neurons that project to the amygdala, including those Pbel neurons whose dendrites extend into the lateral crescent subnucleus. These results indicate that mu-opioid receptors in the PB may mediate or modulate nociceptive information relayed to the amygdala from medullary or spinal cord neurons that terminate not only in the Pbel, but also in the adjacent lateral crescent parabrachial subnucleus., (Copyright 1999 Elsevier Science B.V.)