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Background: The abducens nucleus directly innervates the lateral rectus muscle and plays a role in controlling conjugate horizontal eye movements. Although the neuronal cytoarchitecture of the abducens nucleus has been extensively investigated in various species of vertebrates, few studies have been undertaken in humans, especially in fetuses or neonates., Design/subjects: We examined 12 human brains from preterm infants aged 20-43 postmenstrual weeks to document the histology and morphometry of the abducens nucleus. The brain was processed into celloidin-embedded serial sections stained with the Klüver-Barrera and other conventional methods., Results: The nucleus was identified as a mass of cells as early as 20 weeks. Its neurons were clearly distinguished from glial cells due to droplet-like, clear nuclei containing prominent nucleoli and surrounded by a basophilic perikaryon. Neurons of various sizes and shapes were intermingled within the nucleus, although larger neurons were located towards the center of the nucleus. Immature granular or reticular Nissl bodies were seen at 20-21 weeks. Tigroid, coarse Nissl bodies appeared around 28-29 weeks in larger neurons, although in smaller neurons Nissl bodies were dispersed or concentrated peripherally. Morphometric results were: (1) the nuclear volume exponentially increased with age between 20 and 43 weeks; (2) the histograms of neuronal profile areas showed a non-normal distribution trailing toward the right and widening with age; (3) the geometric average of neuronal profile areas increased linearly with age., Conclusion: Our study suggests that the human abducens nucleus enlarges more quickly toward the end of gestation, and comprises heterogeneous groups of neurons., (Copyright © 2012 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.)

During development, neurons migrate from their origin to their final destinations where they form neuronal architectures such as layers and nuclei. While the mechanisms for the formation of laminated structures have been studied extensively, little is known about nucleogenesis. Previously, we analyzed nucleogenesis in neurons from four types of mossy-fiber projecting precerebellar nuclei neurons by gene transfer, and obtained evidence suggesting that the change from tangential to radial migration occurs at the region that will develop into the nucleus (Kawauchi, D., Taniguchi, H., Watanabe, H., Saito, T., Murakami, F., 2006. Direct visualization of nucleogenesis by precerebellar neurons: involvement of ventricle-directed, radial fibre-associated migration. Development 133, 1113-1123). Here we analyzed the dynamics of these neurons using mice embryos. We electroporated genes of fluorescent proteins to the lower rhombic lip at embryonic day (E) 12.5 and carried out time-lapse analyses at E14.5, when pontine nuclei begin to be formed. We found that many labeled neurons showed transition from tangential to radial migration in the region that will develop into the nucleus. This transition occurred in two ways. One was initiated by a leading process extending radially while the second was caused by a newly developed radial process from the cell soma. Curiously, we observed that many neurons stopped tangentially migration, paused, and then began radial migration. These findings indicate that a signal to stop and cause the change in tangential to radial migration is critical for nucleogenesis by pontine neurons.

The primate lobulus petrosus (LP) of the cerebellar paraflocculus receives inputs from visual system-related pontine nuclei, and projects to eye movement-related cerebellar nuclei. To reveal a potential involvement of LP in oculomotor control, we lesioned LP unilaterally by local injections of ibotenic acid in three Macaca fuscata. We examined the effects of lesion on eye movements evoked by step (3 degrees )-ramp (5-15 degrees/s) moving target. To step-ramp moving target, the monkeys showed an initial slow eye movement and later a small catch-up saccade, which was followed by the post-saccadic pursuit nearly matching to the velocity of the ramp target motion. After LP lesioning, the velocity of post-saccadic pursuits in the ipsiversive and down-ward directions decreased by 20-40% in all three monkeys. These deficits lasted for at least 1 month, and some recovery was observed. In the amplitudes of catch-up saccades, no consistent changes were seen among the three monkeys after LP lesioning. These results suggest an involvement of LP in the primate smooth pursuit eye movement control.

The transient expression of estrogen receptor alpha (ERalpha) in the facial nucleus of rats during development was already reported. However, how and whether the receptor functions physiologically in the nucleus of developing rats are as yet unclear. In this study, we applied a retrograde tracer into one of the possible target muscles of the motoneurons in the nucleus, that is, the transverse auricular muscle (Mta), and examined whether ERalpha-immunopositive neurons take up the tracer. Because it is probable that neurogenesis, apoptosis, and maturation may be associated with the transient expression of ERalpha, we attempted to analyze the neurons expressing the receptor in the nucleus. We found that ERalpha-immunopositive neurons in the medial facial subnucleus innervate mostly the Mta. Quantitative analyses showed that the number of motoneurons projecting to the Mta remained the same throughout the ages examined, whereas that of ERalpha-immunopositive neurons decreased between postnatal days 6 and 11. Apoptosis and neurogenesis in the nucleus were not affected by the expression of ERalpha during development. ERalpha expression coincided with the maturation of neurons in the nucleus. Thus, it is possible that ERalpha expression in the facial nucleus during development plays important roles in the development of motoneurons and/or external pinna muscles.

Prosaposin is the precursor of saposins A, B, C and D, which are activators of sphingolipid hydrolases. In addition, unprocessed prosaposin functions as a neurotrophic factor in the central and peripheral nervous systems by acting to prevent neuronal apoptosis, to elongate neurites and to facilitate myelination. In this study, the expression pattern of prosaposin in the facial nerve nucleus after facial nerve transection was examined by immunohistochemistry and in situ hybridization. Prosaposin immunoreactivity in the neurons on the operated side facial nerve nucleus showed a biphasic pattern: it was significantly increased on day 3 after transection, decreased dramatically on day 7, started to increase gradually on day 14 and reached another peak on day 21 after transection. Significant increases in the levels of prosaposin mRNA were identified in the neurons on the operated side, suggesting that prosaposin was synthesized vigorously by the neurons themselves in the case of facial nerve transection. The diverse changes in prosaposin immunoreactivity during the process of facial nerve regeneration may reflect the diverse neurotrophic activities of prosaposin in facial motoneurons.

Previous studies often considered the basilar pontine nuclei (BPN) and the nucleus reticularis tegmenti pontis (NRTP) as relays of a single cerebro-(ponto)-cerebellar pathway. Conversely, the different cortical afferences to the BPN and the NRTP, as well as the anatomical and functional features of the cerebellopetal projections from these pontine nuclei, support the different, and for some aspect, complementary arrangement of the cerebrocerebellar pathways relayed by the BPN or NRTP. Both the BPN and the NRTP are innervated from the cerebral cortex, but with regional prevalence. The NRTP is principally innervated from motor or sensori-motor areas while the BPN are principally innervated from sensory, mainly teloceptive, and associative area. Projections from sensory-motor areas were also traced to the BPN. The BPN and NRTP project to all parts of the cerebellar cortex with a similar pattern. In fact, from single areas of them projections were traced to set of sagittal stripes of the cerebellar cortex. In variance to such analogies, the projections to the cerebellar nuclei differed between those traced from the NRTP and from BPN. In fact, BPN and NRTP have private terminal areas in the cerebellar nuclei with relatively little overlaps. The BPN innervated the lateroventral part of the nucleus lateralis and the caudoventral aspect of the nucleus interpositalis posterioris. The NRTP principally innervated the mediodorsal part of the nucleus lateralis, the nucleus interpositalis anterioris, the nucleus medialis. Since the single cerebellar nuclei have their specific targets in the extracerebellar brain areas, it follows that the BPN and the NRTP, passing through their cerebellar nuclei relays, are devoted to control different brain areas and thus likely to play different functional roles. From single pontine regions (of both BPN and NRTP) projections were traced to the cerebellar cortex and to the cerebellar nuclei. In some cases these projections reached areas which are likely anatomically connected (by Purkinje axons). This pattern of the pontine projections was termed as coupled projection. In some other cases, the projections reached areas of the cerebellar cortex but not the nuclear regions innervated by them. We termed this as uncoupled projection. The existence of both coupled and uncoupled projections, open new vistas on the functional architecture of the pontocerebellar pathway. More in detail, this study showed the different quantitative and topographic distribution of the coupled and uncoupled projections visualized in the cerebellar projections from BPN and NRTP. All these evidences strongly support the anatomical and the functional differences that characterise the cerebrocerebellar pathways relayed by the BPN and the NRTP.

The cerebellum dissected from neonatal rats in a block including the pons and medulla and maintained in a modified Krebs solution provides a unique preparation of brain tissue with preserved major fiber connections. Electrophysiological and optical recordings revealed that, at postnatal days 4-8 (P4-P8), Purkinje cells in the lateral portion of the cerebellum responded to the stimulation of climbing fiber afferents at the inferior olive and of parallel fibers at the posterior vermis, and that the combination of these inputs induced long-term depression. These observations and pharmacological testings indicate that certain functional features of Purkinje cells mature around P5 in the lateral portion of the cerebellum.

We aimed to clarify the overall distribution of glycinergic neurons in the midbrain, pons, and cerebellum in rats, using in situ hybridization for mRNA encoding glycine transporter 2 (GLYT2), which reliably detects glycinergic cell bodies. We combined this method with in situ hybridization for mRNA encoding glutamic acid decarboxylase isoform 67 (GAD67), and have presented for the first time global and detailed views of the distribution of glycinergic neurons in relation to GABAergic neurons. In addition to this single-detection study, we performed double-detection of GLYT2 mRNA and GAD67 mRNA to determine the distribution of neurons co-expressing these mRNAs. We have shown that many areas of the brainstem and cerebellum, not only areas where previous immunohistochemical studies have specified, involve double-labeled neurons with GLYT2 and GAD67 mRNAs. In particular, when lightly labeled GLYT2 mRNA-positive neurons were distributed within the area of GAD67 mRNA-positive neurons, almost all such GLYT2 mRNA-positive neurons were GAD67 mRNA-positive. Areas or neuron groups expressing exclusively GLYT2 mRNA or GAD67 mRNA were rather limited, such as the superior colliculus, nucleus of the trapezoid body, and Purkinje cells. The present study suggests that the corelease of glycine and GABA from single neurons is more widespread than has been reported.

Extracellular recordings were taken from preganglionic superior salivatory nucleus (SSN) neurons projecting to submandibular and intra-lingual ganglia, in order to study the action of SSN neurons resulting from ionophoretic application of ionotropic NMDA receptor agonist in urethane-chloralose anaesthetized rats. Single SSN neurons were identified by their antidromic spike responses following stimulation of the chorda-lingual nerve (CLN), chorda tympani branches (CTBs) and the lingual nerve (LN). About one-third (33%, 10/30) of the identified SSN neurons were induced to fire by ionophoretic application of the NMDA receptor agonists used, dl-homocysteic acid (DLH) and N-methyl-D-aspartic acid (NMDA). More than half exhibited firing at high frequencies, often exceeding 40 Hz. About one-fifth (20%; 6/30) of the identified SSN neurons exhibited orthodromic spike responses to the combination of NMDA receptor agonist application and sensory nerve (CLN or LN) stimulus. These excitatory responses evoked by application of NMDA receptor agonist were attenuated (n = 4) by ionophoretic application of DL-2-amino-5-phosphonovaleric acid (AP5; NMDA receptor antagonist). About half (47%) of the neurons did not respond to any combination of NMDA receptor agonist and sensory nerve stimuli. No differences were observed between SSN neurons with B fibre axons and those with C fibre axons in response to ionophoresis of the NMDA receptor agonists. The NMDA-sensitive neurons, which exhibited high frequency firing, were predominantly found in the rostral part of the SSN. In summary, activation of ionotropic NMDA receptors exerts an excitatory effect on about half of the SSN neurons. These data support the view that NMDA receptors are involved in information processing and transmission on SSN neurons.

Activation of the chemoreflex with potassium cyanide (KCN, 40 microg/rat, i.v.) in awake rats produces pressor and bradycardic responses as well as a tachypneic response. In the present study, we evaluated the involvement of the periaqueductal gray matter (PAG) and the parabrachial nucleus (PBN) in the neural pathways of the cardiovascular responses to chemoreflex activation. The cardiovascular responses to chemoreflex activation were evaluated before and after bilateral microinjection of 2% lidocaine, a local anesthetic, into the PBN or PAG in order to block in a reversible manner the neuronal activity and axonal conduction of fibers of passage in these areas. The data show that the pressor response to chemoreflex activation 3 min after bilateral microinjection of lidocaine into the dorsolateral aspect of the PBN was significantly reduced in comparison to the control response (32 +/- 5 vs. 48 +/- 4 mm Hg, n = 7), with no significant changes in the bradycardic responses. The effect of lidocaine was reversible since the pressor response was back to control levels 15 min after microinjection of this anesthetic. Bilateral microinjections of lidocaine into the dorsolateral (n = 11) or lateral (n = 8) columns of the PAG in distinct groups of rats produced no significant changes in the pressor or bradycardic responses of the chemoreflex. These data indicate that the PBN is part of the neuronal pathways involved in the sympathoexcitatory component of the chemoreflex while the PAG is not.

Hypotension produces a reflex increase in the activity of sympathetic vasomotor nerves. Studies in anaesthetised animals have established that neurons in the rostral ventrolateral medulla (RVLM) that project directly to sympathetic vasomotor preganglionic neurons in the spinal cord are a critical component of the central pathways mediating this reflex response. There are also neurons in supramedullary regions (the A5 area in the pons and the paraventricular nucleus (PVN) in the hypothalamus), however, that project directly to the sympathetic vasomotor outflow. The aim of this study was to identify and map neurons within the A5 area and PVN, as well as in the RVLM, which may contribute to the reflex sympathoexcitatory response to a hypotensive challenge in conscious rabbits. In a preliminary operation, a retrogradely transported tracer was injected into a site centred on the intermediolateral cell column in the upper lumbar spinal cord. After a waiting period of at least 1 week, a moderate hypotension (decrease in arterial pressure of approximately 20 mm Hg) was induced in conscious rabbits for 60 min by continuous infusion of sodium nitroprusside. In confirmation of previous studies, hypotension resulted in the expression of Fos in the RVLM, the A5 area and PVN. There were also retrogradely labelled neurons in all these regions. In both the RVLM and A5 area, approximately 40% of the retrogradely labelled neurons were also immunoreactive for Fos. In contrast, in the PVN the proportion of retrogradely labelled neurons that were also Fos-positive was much less (approximately 6%). This study has demonstrated that, in the conscious rabbit, a significant proportion of spinally projecting neurons within discrete regions in the RVLM and A5 area are activated by hypotension (as indicated by Fos expression). In the PVN, only a very small proportion of spinally projecting neurons are activated by hypotension, and thus these neurons appear to be regulated primarily by inputs other than baroreceptor inputs.

The pontine storage centre (PSC) and the pontine micturition centre (PMC) are known to be critical for urinary filling and emptying, respectively. In the present study, firing patterns of 45 neurons in the PSC area where electrical stimulation induced inhibition of the micturition reflex were analyzed in 20 male decerebrated and paralyzed cats. The electrically determined PSC area was widespread in the dorsolateral pontine reticular formation (P0-P4), ventrolateral to the PMC. Four major types of neurons were detected according to urinary storage/micturition cycles: tonic storage neurons (38%), phasic storage neurons (40%), tonic micturition neurons (9%) and phasic micturition neurons (13%). These four types of neurons were intermingled in the PSC. However, the tonic and phasic micturition neurons tended to be located within a limited area (P2-P3). These neurons were further classified into augmenting, constant and decrementing firing patterns. Some increased their firing prior to the storage/micturition phase initiation. Such preceding pattern was more frequently found in the tonic neurons than in the phasic neurons. In conclusion, the PSC neurons with diverse heterogeneous discharge patterns suggest that these neurons may organize a complex neuronal circuitry, which is critical in the neural control of the urinary continence.

Relationships between age-related changes in sleep patterns and neuronal activity have received scant attention. In the present study, reticularis pontis oralis (RPO) and ventral tegmental nucleus of Gudden (VTN) neurons were recorded in unanesthetized restrained young (3 months) and old (23 months) Sprague-Dawley rats during wakefulness (W), slow wave sleep (SWS) and rapid eye movement (REM) sleep. All RPO neurons displayed a tonic activity. Firing rates were similar during W in young and old rats. In contrast, firing rates were higher during SWS in old rats (P < 0.001). In both young and old rats, firing rates increased significantly during REM sleep as compared to W and SWS but this increase was markedly greater in old rats. Neurons recorded from VTN displayed bursting activity at theta frequencies during W and REM sleep. The frequency of VTN bursting neurons was higher during REM sleep as compared to W in both groups of age. This difference was significantly more pronounced in old as compared to young rats (P < 0.001). Sleep-related hyperactivity of pontine neurons is discussed in terms of a possible deficit in inhibitory processes in old rats.

The paratrigeminal nucleus, which receives sensory input from trigeminal, glossopharyngeal and vagus nerves, has efferent projections to bulbar, pontine and possibly to thalamic structures associated with nociception, thermoregulation and cardiovascular control. Anterograde neuronal tracers were used to study paratrigeminal efferent connections. Labeled terminal fibers, evidencing bilateral efferent paratrigeminal projections were observed in the medial and caudal solitary tract (sol), lateral reticular nucleus (LRt), ambiguus nucleus (Amb), rostroventrolateral reticular nucleus (RVL), while ipsilateral projections were found in the parabrachial (PB) nuclei and ventral portion of the ventral posteromedial thalamic nucleus (VPM). This extends other findings that describe paratrigeminal projections. Retrograde neuronal transport tracers, microinjected in the defined projection areas were used to map distribution of the paratrigeminal neurons originating different efferent connections. Microinjection of latex microspheres containing fluorescein or rhodamine and Fluoro-gold in the ventral VPM, PB, RVL, Amb, LRt and NTS revealed sets of labeled paratrigeminal nucleus neurons respectively organised in a rostral-caudal sequence. The largest extent of the paratrigeminal nucleus (medial portion) contained neurons projecting to the RVL/Amb, structures associated with cardiovascular regulation. The data show a segmented topographical organization of the nucleus, with different sets of neurons within delimited segments, projecting to neuronal structures associated with different functions. This points to a complex and extensive role for the paratrigeminal nucleus in the integration of somatosensory reflexes related to cardiovascular, respiratory and pain mechanisms. The nucleus may act as a medullary relay interposed between sensory afferents and different structures related to homoeostatic functions.

It is well known that the intermediate layer (SGI) of the mammalian superior colliculus (SC) receives cholinergic inputs originating from the pedunculopontine tegmental nucleus (PPTN). The action of the cholinergic input on the SGI neurons was investigated using whole-cell patch-clamp recording technique in slice preparations obtained from rats. Application of acetylcholine (ACh) induced fast inward currents mediated by nicotinic ACh receptors in the SGI neurons. Depolarization induced by nicotine enhanced the N-methyl-D-aspartate receptor-mediated excitatory postsynaptic potential component and lowered the threshold of bursting response in the SGI neurons to stimulation of the superficial layer. Thus, the cholinergic input to the SGI facilitates the signal transmission through the direct visuomotor pathway in the SC. The behavioral correlate of this observation was explored by microinjection of nicotine into the SC of awake monkeys during visually guided saccade task; injection of nicotine increased frequency of express saccades, the saccades with extremely short reaction times (<120 ms). Analysis of single unit activity of the PPTN neurons revealed that a population of the PPTN neurons increased firing preceding saccades in a particular direction and also during the GAP period between the offset of fixation point and onset of the saccade target. Thus, PPTN neurons may be involved in execution and preparation of saccades. All these results explain the mechanisms of how the brainstem cholinergic system facilitates initiation of saccades presumably depending on attention or vigilance level of the animal.

Previous studies showed that nicotine suppresses the ponto-geniculo-occipital (PGO) spikes of rapid eye movement (REM) sleep in cats. This effect may depend on stimulation of dorsal raphe nucleus (DRN) serotoninergic neurons that inhibit the pedunculopontine (PPT) and laterodorsal tegmental (LDT) cholinergic neurons, generators of PGO spikes. For testing this hypothesis 37 experiments were performed in rat midbrain slices. Nicotine (2 mM), administered locally into DRN, significantly increased the firing rate of 81.1% DRN neurons and serotonin release while simultaneously and significantly decreasing the firing rate of 80.8% LDT neurons and of 81.8% PPT neurons. The inhibition of LDT neurons by nicotine administered into DRN was blocked by the 5-HT1A receptor antagonist WAY-100635 (140 nM) administered into LDT. These results indicate that nicotine inhibits the activity of LDT and PPT neurons and consequently the generation of PGO spikes through stimulation of DRN serotoninergic neurons.

Changes in the masseteric monosynaptic reflex (MMR) and jaw-opening reflex (JOR) responses resulting from conditioning stimulation in the hypothalamus were studied in anesthetized rabbits. Stimulation of the lateral hypothalamus evoked a facilitation of the MMR and an inhibitory or facilitatory effect on the JOR. The facilitatory effect on JOR was stronger than that on the MMR. The facilitatory effective site for the JOR was in the dorsal and lateral directions as compared to the inhibitory field. The results suggest two functionally distinct regions in the lateral hypothalamus that separately project to the jaw-opening muscles.

It has been reported that calcium-binding proteins are good markers for different sets of neurons in various brain regions. We examined expression of the main calcium-binding proteins in projection neurons in the rat medullary dorsal horn (MDH) by combining immunofluorescence histochemistry for calbindin D28k (CB), calretinin (CR) and parvalbumin (PV) with the retrograde tract-tracing method. A fluorescence tracer, tetramethylrhodamine-dextran amine (TMR-DA), was injected into the parabrachial, thalamic or hypothalamic region. After such injections, a number of PV-, CR-, and/or CB-immunoreactive MDH neurons were labeled retrogradely with TMR-DA. Triple-immunofluorescence histochemistry further revealed that a number of CB-, CR-, or PV-immunoreactive TMR-DA-labeled MDH neurons showed immunoreactivity for substance P receptor (NK1), and that they expressed immunoreactivity for c-fos protein in the rats which were injected with formalin into the lips. Thus, it was indicated that some of CB-, CR-, or PV-containing projection neurons in the MDH might be involved in the transmission of nociceptive stimuli.

In an in vitro model system based on purified target cerebellar granule neurons and explants of afferents, pontine mossy fiber afferents stop growing through contact-mediated mechanisms when they encounter granule neurons. Here we studied the developmental regulation of the stop signal posed by granule cells and the response of mossy fibers to the stop signal in two culture systems. Granule neurons presented in slices or as dissociated cells from postnatal day (P) 4 and P7 cerebellum were more potent in the arrest of P0 pontine neurites than younger (P0-P2) or older (up to P14) granule neurons. In contrast, pontine neurites at embryonic day (E) 18, during their period of normal growth toward the cerebellum, grew extensively on both cerebellar slices of all ages from P0 to P10 and dissociated P4 granule neurons. When E18 explants were maintained for 2 days before plating in medium conditioned by neonatal cerebellar cells, E18 pontine explants were rendered more responsive to the stop signal from P4 granule cells. These results indicate that the stop signal, and the response of afferents to it, are developmentally regulated. Moreover, factors within the target region may initiate these interactions.

Vasopressin (VP) acts on both the locus coeruleus (LC) neurons and the neighbouring dorsal pontine reticular formation (PRF) neurons by exciting them. Experiments performed in precollicular decerebrate cats have shown that microinjection of 0.25 x 10(-11) micrograms VP into the LC complex of one side increased the extensor rigidity of the ipsilateral limbs, while rigidity of the contralateral limbs remained unmodified or slightly decreased. The amplitude of modulation and thus the response gain of both the ipsilateral and the contralateral forelimb extensor triceps brachii to sinusoidal roll tilt of the animal (at 0.15 Hz, +/- 10 degrees), leading to stimulation of labyrinth receptors, decreased significantly, while there was only a slight decrease in phase lead of the responses. These effects occurred 5-10 min after the injection, were fully developed within 30 min and disappeared in about 2 h. VP activation of presumed noradrenergic LC neurons had a facilitatory influence on ipsilateral limb extensor motoneurons, either directly through the coeruleospinal (CS) pathway, or indirectly by inhibiting the dorsal PRF and the related medullary inhibitory reticulospinal (RS) neurons. Moreover, because the facilitatory CS neurons fire out-of-phase with respect to the excitatory VS neurons, we postulated that the higher the firing rate of the CS neurons in the animal at rest, the greater the disfacilitation affecting the limb extensor motoneurons during side-down animal tilt. These motoneurons would then respond less efficiently to the excitatory VS volleys elicited for the same direction of animal orientation, leading to a reduced gain of the EMG responses of the forelimb extensors to labyrinth stimulation. In contrast to these findings, unilateral injections of the same dose of VP immediately ventral to the LC, i.e., in the peri-LC alpha and the surrounding dorsal PRF, where presumed cholinergic neurons are located, decreased extensor rigidity in the ipsilateral limbs while that of the contralateral limbs either decreased or increased. The same injection also produced either a moderate or a marked increase in gain of the multiunit EMG response of the ipsilateral triceps brachii to animal tilt. In the first instance the response gain of the contralateral triceps brachii to animal tilt increased slightly, while the corresponding response pattern remained unmodified, as shown for the ipsilateral responses (increased EMG activity during ipsilateral tilt and decreased activity during contralateral tilt). In the second instance, however, the response gain of the contralateral triceps brachii showed only slight changes, while the pattern of response was reversed. These effects occurred 5-20 min after the injection, developed fully within 20-60 min and disappeared in 2-3 h. We postulated that VP increased the discharge of the dorsal PRF neurons and the related medullary inhibitory RS neurons of the injected side, leading to reduced postural activity of the ipsilateral limbs. However, because these inhibitory RS neurons fire out-of-phase with respect to the excitatory VS neurons, it appeared that the higher the firing rate of the RS neurons in the animal at rest, the greater the disinhibition affecting the limb extensor motoneurons during ipsilateral tilt. These motoneurons would then respond more efficiently to the same excitatory VS volleys elicited by given parameters of stimulation, leading to an increased gain of the EMG responses. The contralateral effects could be attributed to crossed excitation by dorsal PRF neurons of one side, either of medullary inhibitory RS neurons or of excitatory CS neurons of the opposite side, respectively. We conclude that VP controls posture and gain of the VS reflex by acting on LC neurons as well as on dorsal PRF and the related medullary inhibitory RS neurons.

Responses of parabrachial nucleus (PBN) neurons (n = 43) to chemical stimulation of the posterior tongue were recorded in chorda tympani (CT)-sectioned rats and compared with those (n = 45) in CT-intact. The chemical stimuli used were 0.5 M sucrose, 0.5 M sodium chloride (NaCl), 0.03 M hydrochloric acid (HCl), 0.01 M quinine hydrochloride, and distilled water. These stimuli were applied to an area posterior to the intermolar eminence of the tongue. Neurons of CT-sectioned rats responsive to the chemical stimuli were located in more caudal areas of the PBN compared with those of CT-intact. Numbers of responses to the five stimuli and breadth of responsiveness to the four basics were not different between both groups of rats. However, average response magnitudes of the neurons in CT-sectioned rats were lower than those in CT-intact. In both groups of rats, the response magnitudes to NaCl and HCl were larger than those to the other three stimuli, and responses to NaCl and those to HCl were highly correlated. It is suggested that glossopharyngeal fibers responding strongly to acids and salts are likely to be the main source of PBN responses from the posterior tongue.

In some behavioral-lesion experiments involving animals, ibotenic acid (IBO) is used as a means of damaging brain structures. Occasionally one needs to assess the status of fibers coursing through the damaged area to determine whether the deficits observed are the result of destruction of neurons rather than fibers. In such cases, IBO, is considered to be the method of choice since it destroys cell bodies but leaves fibers of passage intact. However, if the IBO dose injected in a given area is too high, both cell bodies and fibers of passage could be damaged. The anterograde and retrograde tracer wheat germ agglutinin-horseradish peroxidase (WGA-HRP) is a useful technique to verify that fibers are intact, and is a more powerful tool in comparison with a tracer, such as HRP, which has been used in previous studies.

The principal target nuclei of nigrothalamic projections in the rat are the mediodorsal (MD) and ventromedial (VM) nuclei. The present study examined the patterns of distribution and collateral projections of the two major groups of nigrothalamic neurons, i.e., nigro-MD and nigro-VM neurons. Retrograde fluorescent labeling with Fluoro-Gold was used to examine whether the distribution areas of nigro-MD and nigro-VM neurons might be overlapped with or segregated from each other in the substantia nigra pars reticulata. A clear tendency was observed that nigro-MD neurons were distributed more ventrally than nigro-VM neurons. It was further examined by retrograde fluorescent double labeling with Fluoro-Gold and Fluoro-Ruby whether or not these nigrothalamic neurons might provide axon collaterals to the superior colliculus or the pontine reticular formation. The nigro-MD neurons were found to send axon collaterals to the superior colliculus more frequently than the nigro-VM neurons. Additionally, a small number of nigrothalamic neurons were found to send axon collaterals to the pontine reticular formation. The functional significance of the two major populations of nigrothalamic neurons was discussed on the basis of their collateral projections to the superior colliculus or the pontine reticular formation.

To study the iron, transferrin, and ferritin distribution at subcellular levels in response to acute dietary iron deficiency, we tested the hypothesis that early post-weaning iron deficiency can change iron and iron regulatory protein concentrations in rat brain. Male Sprague-Dawley rats were fed diets containing either 2 or 35 micrograms iron/g for 2, 3 or 4 wk starting at 21 d of age. Brain iron, transferrin and ferritin concentrations in cytosolic and microsomal fractions of either whole brain or pons and cerebellum were then determined. After 14 d of dietary iron restriction, brain iron concentrations were 50% lower in the microsomal fraction and 30% lower in cytosol compared with controls. Brain cytosolic transferrin concentration almost doubled in the same animals. Brain ferritin concentration in fractions from rats fed the iron-deficient diet for 14 d was lower than in controls, but then remained fairly constant. Absolute brain weight and total brain protein contents were unaffected by iron restriction. This study extends previous research by demonstrating that the brain responds to changes in body iron status with a change in transferrin concentration. If the dietary restriction is quite severe, this adaptation is insufficient. This study also notes that brain ferritin decreases with decreasing body iron status, though it was less responsive than nonheme iron in liver. The concept that iron enters the brain through a highly regulated endocytotic process at the blood brain barrier, that undoubtedly involves the regulation of transferrin receptors in capillary endothelial cell, is supported by our observation of elevated transferrin concentrations in brain of iron-deficient rats.

By in situ hybridization histochemistry, fibroblast growth factor receptor gene (flg)-expressing neurons were newly identified in the basal magnocellular nuclei (the vertical and horizontal limbs of the diagonal band, and Meynert's nucleus). The present study also confirmed flg localization in the laterodorsal tegmental nucleus and the pedunculopontine tegmental nucleus of the pons. Immuno- and in situ hybridization histochemistry on the same sections demonstrated that choline acetyltransferase and flg were colocalized in single neurons of the diagonal band, Meynert's nucleus and the pontine tegmental areas. The results suggest that a significant number of the basal magnocellular and a majority of the mesopontine cholinergic neurons are directly affected by fibroblast growth factors (FGF) via FGF receptor gene.

The distribution and development of ferritin-containing cells were studied in the pons and cerebellum of human fetuses up to adults, using an immunohistochemical method. The predominant cell type labeled with antiserum to ferritin in the pons and cerebellum was morphologically oligodendrocytes. In the pons, positive cells appeared at 21 weeks of gestation in the reticular formation, and longitudinal and transverse fibers, and at 25 weeks of gestation in pontine nuclei. They increased with age from 33 weeks to infancy. In the cerebellum, positive cells appeared at 25 weeks of gestation in the cerebellar white matter and granular layer. They increased from 29 to 40 weeks of gestation in the white matter, and to childhood in the granular layer. The time of appearance of positive cells in the pons and cerebellum is earlier than in the cerebrum, like myelination. This development of ferritin-positive glia may be related to maturation of oligodendrocytes as well as being the basis of myelination.

By utilizing an anterograde neural tracer, Phaseolus vulgaris leucoagglutinin (PHA-L), pontomedullary reticuloreticular connections and reticulospinal connections were studied, including their fiber trajectories and distribution of PHA-L labeled terminals in close apposition to target reticular and spinal neurons, and branching patterns of axon collaterals at the levels of the cervical and upper thoracic cord. PHA-L was focally microinjected into the medial pontine reticular formation corresponding to the nucleus reticularis pontis oralis. A great number of PHA-L labeled thin fibers descended bilaterally coursing through the medial part of the pontine and medullary reticular formation with an ipsilateral predominance. Labeled terminal boutons were closely apposed to somata of various sized pontomedullary reticular neurons. Labeled thick fibers descended ipsilaterally coursing through the ventral half of the medial longitudinal fasciculus, and further descended through the ventral funiculus of the spinal cord. At the levels of the cervical and upper thoracic cord, these reticulospinal fibers gave off axon collaterals sending terminal fibers to small- to large-sized neurons in Rexed's laminae VII and VIII. Some of the axon collaterals innervated not only ipsilateral but also contralateral gray matter. By reconstructing branching patterns of axon collaterals, each axon collateral was found to innervate spinal neurons located in a disk-like spinal segment with a width less than 1 mm.

The internal lateral nucleus (IL) of the parabrachial nucleus receives information from the spinal cord. The IL perhaps relays nociceptive signals to the intralaminar nuclei of the thalamus, apparently being implicated in the motivational-affective component of pain reactions. However, cells of origin of spinal fibers to the IL have not been investigated enough. We intended to clarify these cells, as well as their shapes, by retrograde double-labeling techniques. Fast blue and diamidino yellow dyes were injected, respectively, into the left and right ILs. The distribution of double-labeled cells was almost the same as that of single-labeled cells on both sides of the spinal cord. The total number of bilateral double-labeled cells was highest in the dorsolateral part of the lateral funiculus (DL), followed, in order, by lamina I, the dorsomedial part of the lateral funiculus (DM), lamina V and lamina VII. A few double-labeled cells were seen in laminae II-IV, VI, VIII and X. The ratio of the total number of bilateral double-labeled cells to the total number of bilateral single-labeled cells through the spinal cord was 43% in the DL, 37% in the DM, 28% in lamina V and 24% in lamina I. The ratio was 10% or less in the other remaining laminae. No marked differences were observed between the shapes of double- and single-labeled cells.

Immunohistochemical localization of a neural cell adhesion molecule (NCAM) was examined in the subpial pontine migratory stream of the fetal rat with a monoclonal antibody specific for the rat NCAM, MAb-AF11. Although the pontine cell strand showed weaker expression of NCAM than the parenchymal areas of the brainstem, within the cell strand, NCAM-immunoreactivity was somewhat greater in the anterior part of the stream near the neurons' destination than the caudal part. The weak NCAM gradient in the pontine migratory stream may contribute to formation of the pontine cell strand and the basal pontine gray.

Subcortical connections of an 'oculomotor' region in the ventral bank of the anterior ectosylvian sulcus (AESo), where eye movements were evoked by intracortical microstimulation, were studied in cats using a wheatgerm agglutinin horseradish peroxidase (WGA-HRP) tracing method. Following injection of WGA-HRP into the AESo, both anterogradely-labeled terminals and retrogradely-labeled cells were found with the highest concentration in the suprageniculate nucleus and the medial zone of the lateroposterior nucleus of the thalamus. In the brainstem, anterogradely-labeled terminals were found in the superior colliculus, the pontine reticular formation, the pontine tegmental reticular formation and the pontine nuclei.

The dorsal nucleus of the lateral lemniscus (DLL) in the mouse was studied using the rapid Golgi method. Three types of neurons were observed in the DLL. Type I neurons had a piriform or triangular cell body with a mean diameter of 14 by 19 micron, and emitted 3-5 primary dendrites. The cell bodies of type II neurons were either spindle or piriform in shape and were, on the average, 17 by 26 micron in diameter with 2-4 primary dendrites. Type III neurons had polygonal or triangular cell bodies which were 24 by 31 micron in average diameter and there were 4-6 primary dendrites. The axons of the DLL neurons most frequently traveled medially or ventromedially, and only a few could be followed dorsally among the fibers composing the lateral lemniscus (LL). The afferent fibers of the DLL were separated into three groups: ascending afferents, descending afferents and afferents from the medial aspect. The ascending afferents were collaterals of the LL fibers distributed mainly in the inferior colliculus. The descending afferents were also collaterals arising from the descending LL fibers. The afferents from the medial aspect ran across the tegmental area to distribute in the DLL. In addition, numerous LL fibers gave off terminal collaterals to the DLL. The ascending or descending nature of these LL fibers was not determined. Thus, the DLL is considered to be one of the commissural relay nuclei in the auditory system.

The activity of the pontine nucleus (PN) neuron was recorded in 3 monkeys moving a handle alternately from start to target zones in a simple extension-flexion movement at the wrist. Of 73 PN neurons related to the task, 44 were related to movement, 19 to handle holding and 5 to both movement and holding of the handle. Of the 44 movement-related neurons, 16 were related to flexion, 22 to extension, and 6 to both. In 37 of 54 analyzed movements of the PN neurons which were related to movements, or to both movements and handle holding, the change of the activity occurred before the movement. However, in most of these cases (24/37), discharge occurred less than 100 ms earlier than the start of the movement. In the remaining one-third of movements (17/54), neurons discharged after the onset of the movement. Locations of the 73 neurons were histologically verified in the pontine nucleus. Somewhat similar observations were made of 14 cells located in the nucleus reticularis tegmenti pontis (NRTP). Considering that the majority of movement-related PN and NRTP neurons discharged immediately before or even after the onset of movement, these neurons may play a role in the execution of movement, at least of a simple movement, rather than in the initiation or planning of movement.