Nucleus Paragigantocellularis Research Articles

The projections to the spinal cord of the rat during development: a timetable of descent.

In order to establish a timetable for the developmental descent of supraspinal descending projections in the rat, a retrograde neuronal tracer was injected into the spinal cord of rat fetuses and neonates both at different gestational ages and at different levels of the spinal cord. From the results of these experiments a position interval could be deduced for the leading descending fibers of each spinal-projecting nucleus at each age studied. The chronological series of position intervals of each supraspinal descending projection (the descent pattern) depicts the descent of its fiber front during development and allows for easy comparison between the various projections. According to these descent patterns the descent sequences of the various spinal-projecting nuclei were established. At E17 fibers from the lateral vestibular nucleus, the raphe magnus nucleus and the gigantocellular reticular nucleus were present in the lumbosacral spinal cord; their descent along the spinal cord thus occurs before this stage. At E18 fibers from the parafascicular prerubral nucleus, the interstitial nucleus of Cajal, the mesencephalic reticular nucleus, the caudal pontine reticular nucleus, the laterodorsal tegmental nucleus, the subcoerulean nucleus, the spinal vestibular nucleus, the interpolar spinal trigeminal nucleus, the raphe obscurus nucleus and the ventral medullary reticular nucleus arrived in the lumbosacral cord. At the same stage fibers from the oral and caudal spinal trigeminal nucleus reached their caudalmost extent in the spinal cord, respectively, the lower and upper thoracic cord. At E19 fibers from the oral pontine reticular nucleus, the parvocellular reticular nucleus, the ventral gigantocellular reticular nucleus and the ambiguous nucleus first appeared in the lumbosacral cord. At E20 fibers from Darkschewitsch's nucleus, the paralemniscal and parabrachial nuclei, cell group A5, the locus coeruleus, the gigantocellular reticular nucleus-alpha, the raphe pallidus nucleus, the paramedian reticular nucleus, and from the dorsal medullary reticular nucleus arrived in the lumbosacral cord. Last to arrive in the lumbar cord during the prenatal period, at E21, were fibers from the posterior commissural nucleus, the red nucleus, the Edinger-Westphal nucleus, the paragigantocellular reticular nucleus, the medial vestibular nucleus, Roller's nucleus, and the solitary nucleus. Fibers from the paraventricular hypothalamic nucleus and from the lateral hypothalamic area only arrived in the lumbosacral cord at P1, followed by fibers from the incertal nucleus at P4. A transient spinal projection from an unknown group of neurons located immediately lateral to and partly intermingled with the mesencephalic trigeminal nucleus arrived in the lumbosacral spinal cord at E18 and had disappeared at P1. This cell group, called Gr?, closely resembled the mesencephalic trigeminal nucleus (Me5). Both were teardrop shaped; an oblong mass of neurons at the caudal end with a long and thin trailing edge. The trailing edge of Gr?, however, curved dorsad towards the dorsal midline raphe of the caudal mesencephalon, while the trailing edge of Me5 curved rostrad, parallel to the sulcus limitans of the sylvian aquaduct. The neurons of Gr? are mainly round, but in the caudal part of the nucleus some horizontally oriented fusiform neurons were observed. All neurons of Gr? were tiny. These results confirm that the generation sequence of the source nuclei is not a prime determinant of descent sequence along the spinal cord. The distance between the source nucleus and the entrance to the target seems of influence only in the most extreme cases (diencephalic source nuclei and the cerebral cortex). Descent velocity of the fiber fronts is not equal between different sources, nor is the descent velocity of specific fiber fronts constant over time. (ABSTRACT TRUNCATED)

Pontomedullary Efferent Projections of the Ventral Respiratory Neuronal Subsets of the Rat

The pontomedullary trajectories of projections efferent from the ventral respiratory cell group were anterogradely labelled after discrete injections of Fluoro Ruby into three morphophysiologically identified subdivisions (Bötzinger complex, rostral inspiratory, and caudal expiratory cell groups). The anterogradely labelled varicosities were located in a variety of areas involved in cardiorespiratory function: other subdivisions of the ventral respiratory cell group, the parabrachial (medial, central, and external lateral), Kölliker-Fuse, and lateral paragigantocellular nuclei, A5, and perifacial areas. Although the target areas were similar for the three studied subdivisions, some differences of the location and densities of labelled varicosities were found. Anterogradely labelled fibre bundles were found bilaterally after all of the tracer injections. Three caudally efferent bundles passed through the ventral respiratory cell group, dorsal medullary, and paramedian reticular nuclei. A labelled fibre bundle also took an ascending route through the ventral respiratory cell group: it surrounded the facial nucleus, and then followed two different pathways, one coursing towards forebrain areas and the other to the parabrachial and Kölliker-Fuse complex. Bundles of efferent axons decussated mainly at medullary levels and to a lesser extent in the pons. In the contralateral medulla and pons these labelled fibre bundles followed pathways similar to those observed ipsilaterally. The three ventral respiratory neuronal subsets sent axonal projections through similar tracts, but within them they were topographically organized. The present data are discussed with respect to the circuitry involved in the mechanisms of cardiorespiratory and other visceral functions.

Chapter 5 Cholinergic innervation and receptors in the cerebellum

We have studied the source and ultrastructural characteristics of ChAT-immunoreactive fibers in the cerebellum of the rat, and the distribution of muscarinic and nicotinic receptors in the cerebellum of the rat, rabbit, cat and monkey, in order to define which of the cerebellar afferents may use ACh as a neurotransmitter, what target structures are they, and which cholinergic receptor mediate the actions of these pathways. Our data confirm and extend previous observations that cholinergic markers occur at relatively low density in the cerebellum and show not only interspecies variability, but also heterogeneity between cerebellar lobules in the same species. As previously demonstrated by Barmack et al. (1992a,b), the predominant fiber system in the cerebellum that might use ACh as a transmitter or a co-transmitter is formed by mossy fibers originating in the vestibular nuclei and innervating the nodulus and ventral uvula. Our results show that these fibers innervate both granule cells and unipolar brush cells, and that the presumed cholinergic action of these fibers most likely is mediated by nicotinic receptors. In addition to cholinergic mossy fibers, the rat cerebellum is innervated by beaded ChAT-immunoreactive fibers. We have demonstrated that these fibers originate in the pedunculopontine tegmental nucleus (PPTg), the lateral paragigantocellular nucleus (LPGi), and to a lesser extent in various raphe nuclei. In both the cerebellar cortex and the cerebellar nuclei these fibers make asymmetric synaptic junctions with small and medium-sized dendritic profiles. Both muscarinic and nicotinic receptor could mediate the action of these diffuse beaded fibers. In the cerebellar nuclei the beaded cholinergic fibers form a moderately dense network, and could in principle have a significant effect on neuronal activity. For instance, the cholinergic fibers arising in the PPTg may modulate the excitability of the cerebellonuclear neurons in relation to sleep and arousal (e.g. McCormick, 1989). Studies on the distribution of cholinergic markers in the cerebellum have proven valuable besides the issue whether cholinergic mechanism play a role in the cerebellar circuitry, because they illustrate a complexity of the cerebellar anatomy that extends beyond its regular trilaminar and foliar arrangement. For instance, AChE histochemistry has been shown to preferentially stain the borders of white matter compartments (the 'raphes', Voogd, 1967), and therefore is useful in topographical analysis of the cortico-nuclear and olivocerebellar projections (Hess and Voogd, 1986; Tan et al., 1995; Voogd et al., 1996; see Voogd and Ruigrok, 1997, this Volume). ChAT-immunoreactivity, at least in rat, appears to be a good marker to outline the morphological heterogeneity of mossy fibers, and m2-immunocytochemistry could be used to label (subpopulations of) Golgi cells, subsets of mossy fibers and, in the rabbit, a specific subset of Purkinje cells (Jaarsma et al., 1995).

Barosensitive and chemosensitive neurons in the rat medulla: A double labeling study with c-Fos/glutamate, GAD, PNMT and calbindin

The purpose of this study was to survey distribution and density of the barosensitive and chemosensitive neurons in the medulla of rats anesthetized with fentanyl/midazolam, using immunohistochemical methods. After stimulation of the arterial baroreceptor or the chemoreceptor, we identified c-Fos-labeled neurons with immunoreactions to antisera of glutamate, PNMT, GAD and calbindin in the nucleus tractus solitarii (NTS) and the ventrolateral medulla (VLM). The double-labeled neurons were located in the medial part of the NTS, and in the lateral part of the paragigantocellular reticular nucleus and the ventral division of the ambiguus nucleus. Main findings were as follows: (1) No significant difference was found in distribution and density of glutamatergic, adrenergic and calbindin-containing neurons between the barosensitive and chemosensitive types; (2) a few GABAergic neurons were distributed almost evenly in the NTS and VLM, and in these neurons the barosensitive type outnumbered the chemosensitive one; (3) glutamatergic and calbindin-containing neurons were dominant in the NTS; adrenergic neurons in the VLM; (4) as for the adrenergic neurons in the NTS, the chemosensitive type significantly outnumbered the barosensitive one. This study showed that distribution and density of the barosensitive neurons, either glutamatergic, adrenergic, or calbindin-containing neurons, overlapped with those of the chemosensitive corresponding neurons, suggesting presence of the neural matrix of the cardiopulmonary interaction. Exceptionally, the number of the barosensitive GABAergic neurons was significantly larger than that of the chemosensitive GABAergic ones.

Barosensitive and chemosensitive neurons in the rat medulla: A double labeling study with c-Fos/glutamate, GAD, PNMT and calbindin

The purpose of this study was to survey distribution and density of the barosensitive and chemosensitive neurons in the medulla of rats anesthetized with fentanyl/midazolam, using immunohistochemical methods. After stimulation of the arterial baroreceptor or the chemoreceptor, we identified c-Fos-labeled neurons with immunoreactions to antisera of glutamate, PNMT, GAD and calbindin in the nucleus tractus solitarii (NTS) and the ventrolateral medulla (VLM). The double-labeled neurons were located in the medial part of the NTS, and in the lateral part of the paragigantocellular reticular nucleus and the ventral division of the ambiguus nucleus. Main findings were as follows: (1) No significant difference was found in distribution and density of glutamatergic, adrenergic and calbindin-containing neurons between the barosensitive and chemosensitive types; (2) a few GABAergic neurons were distributed almost evenly in the NTS and VLM, and in these neurons the barosensitive type outnumbered the chemosensitive one; (3) glutamatergic and calbindin-containing neurons were dominant in the NTS; adrenergic neurons in the VLM; (4) as for the adrenergic neurons in the NTS, the chemosensitive type significantly outnumbered the barosensitive one. This study showed that distribution and density of the barosensitive neurons, either glutamatergic, adrenergic, or calbindin-containing neurons, overlapped with those of the chemosensitive corresponding neurons, suggesting presence of the neural matrix of the cardiopulmonary interaction. Exceptionally, the number of the barosensitive GABAergic neurons was significantly larger than that of the chemosensitive GABAergic ones.

Expression of insulin receptor-related receptor in the rat brain examined by in situ hybridization and immunohistochemistry

Insulin receptor-related receptor (IRR) is a member of the insulin receptor family. However, its endogenous ligand and physiological roles are unknown. To elucidate the physiological roles of IRR, an orphan receptor, in the brain, we examined its expression at mRNA and protein levels in the brain by in situ hybridization and immunohistochemistry, respectively. The expression of IRR mRNA in the brain was highly restricted to the forebrain including the nucleus of the diagonal band, medial septal nucleus, ventral pallidum, accumbens nucleus and caudate putamen, and the brainstem including the prepositus hypoglossal nucleus, medial vestibular nucleus, gigantocell reticular nucleus, paragigantocellular nucleus and ventral cochlear nucleus. Most IRR mRNA-positive cells in the forebrain but not in the brainstem were cholinergic neurons. However, most IRR mRNA in the forebrain and brainstem was coexpressed with that of trkA, a high-affinity receptor for nerve growth factor. IRR-immunoreactive cell bodies were also detected in the forebrain and brainstem. The pattern of IRR immunoreactivity was similar to that of IRR mRNA. Its restricted pattern indicates that IRR plays unique roles in the brain, in contrast to insulin and insulin-like growth factor-I receptors, other members of the insulin receptor family, which are widely expressed in the brain.

Anatomical distribution of somatostatin receptors in the brainstem of the human fetus.

The distribution of somatostatin binding sites was studied in the pons and medulla oblongata of three human fetuses (gestional ages 26, 28 and 30 weeks). The study was carried out by in vitro quantitative autoradiography using either [125I-Tyr0,D-Trp8]somatostatin-14 or [125I-Tyr11]somatostatin-14 as radioligands. Somatostatin binding sites were observed in a number of nuclei subserving sensory, motor or integrative functions within the pons and medulla. In addition, discrete tracts also contained significant amounts of binding sites. Among structures involved in sensory processes, a high density of binding sites (40-60 fmol/ mg wet tissue) was measured in the dorsal cochlear nucleus and in the nucleus tractus spinalis trigemini caudalis. Moderate to high levels of binding sites (30-40 fmol/mg wet tissue) were detected in the other sensory cranial nerve nuclei. A moderate density of sites (15-30 fmol/mg wet tissue) was measured in most motor nuclei, the highest concentrations being observed in the dorsal motor nucleus of the vagus nerve, the facial nucleus, the hypoglossal nucleus and the nucleus ambiguus. The griseum pontis and the nucleus corporis pontobulbaris contained very high (> 60 fmol/mg wet tissue) and high concentrations of somatostatin binding sites, respectively, while the other relay nuclei contained low to moderate levels of binding. In monoaminergic nuclei, very high and moderate to high concentrations of somatostatin binding sites were measured in the nucleus locus coeruleus and in its dorsal subnucleus, respectively. Moderate densities of sites were detected in the ventral subnucleus of the nucleus locus coeruleus and in the different parts of the raphe. In the white matter, low levels of binding were measured in the inferior cerebellar peduncle, the lateral and median lemnisci and the tractus solitarius. Conversely, moderate to high concentrations of somatostatin binding sites were measured in the median and superior cerebellar peduncles. The pyramis contained a very high density of recognition sites. A marked heterogeneity in the density of binding sites was observed within a few structures particularly in the medial accessory olivary of nucleus and the medial longitudinal fasciculus. Selective ligands were used to determine the pharmacological profile of the [Tyr11]somatostatin-14 binding sites in various brainstem regions. In the dorsal cochlear nucleus and the pyramis, all somatostatin binding sites belonged to the SSA subtype. Conversely, in the lateral paragigantocellular nucleus, all somatostatin binding sites belonged to the SSB subtype. The other regions studied contained various proportions of SSA and SSB subtypes. In conclusion, the present study shows that high concentrations of somatostatin receptors are present in many regions of the human fetus brainstem. These data support the concept that somatostatin could be involved in the maturation of brain structures.

Anatomy and physiology of saccadic long-lead burst neurons recorded in the alert squirrel monkey. I. Descending projections from the mesencephalon.

1. The intra-axonal recording and horseradish peroxidase injection technique together with spontaneous eye movement monitoring has been employed in alert behaving monkeys to study the discharge pattern and axonal projections of mesencephalic saccade-related long-lead burst neurons (LLBNs). 2. Most of the recovered axons (N = 21) belonged to two classes of neurons. The majority (N = 13) were identified as efferents of the superior colliculus and had circumscribed movement fields typical of collicular saccade-related burst neurons. This discharge pattern, their responses to electrical stimulation of one or both superior colliculi, and their morphological appearance identified them as members of the T class of tectal efferent neurons. 3. Axons of these T cells deployed terminal fields within several saccade-related brain stem areas including the nucleus reticularis tegmenti pontis, which projects to the cerebellum; the nucleus reticularis pontis oralis and caudalis, which contains excitatory premotor burst neurons; the nucleus raphe interpositus, which contains omnipause neurons; the nucleus paragigantocellularis, which contains inhibitory premotor burst neurons, as well as other less differentiated parts of the brain stem reticular formation. 4. The other class of LLBNs (N = 4) had their somata in the medullary reticular formation just lateral to the interstitial nucleus of Cajal. They projected primarily to the raphe nuclei, the medullary reticular formation, and the paramedian reticular nucleus. Discharges were of the directional type with up ON directions (N = 3) and down ON directions (N = 1). 5. Other fibers, which project to pontine and medullary oculomotor structures but whose somata were not recovered (N = 4), illustrate that there are also other types of LLBNs that contribute to the generation and control of saccadic eye movements. 6. Our findings complement previous data about the axonal trajectories of T-type superior colliculus efferents. They also demonstrate the existence of LLBNs located in the mesencephalic reticular formation and their target areas in the brain stem. Implications of these findings for current concepts of oculomotor control are discussed.

Substance P-induced respiratory excitation is blunted by delta-receptor specific opioids in the rat medulla oblongata.

The effects of substance P (SP) and the naturally occurring met-enkephalin and the synthetic mu-specific opioid agonist, DAGO (Tyr-D-Ala-Gly-N-Methy-Phe-Gly-ol) and the delta-specific opioid agonist DADL (Tyr-D-Ala-Gly-Phe-D-Leu) on basal ventilation were investigated in halothane-anaesthetized rats. Local injections of SP (0.75-1.5 nmol) in the ventrolateral medulla oblongata (VLM), e.g. nucleus paragigantocellularis, and nucleus reticularis lateralis increased ventilation because of an elevation of tidal volume. Met-enkephalin induced a short-lasting ventilatory depression mainly because of a depression of tidal volume. Activation of delta- and mu-opioid receptors in the VLM by local application of DADL and DAGO, respectively, induced ventilatory depression, which was later in onset and more long-lasting. Local administration of met-enkephalin into the VLM also produced a long-lasting inhibition of the SP-induced ventilatory excitation. A similar blockade of the SP-induced excitatory ventilatory response could be elicited by DADL but not by DAGO. This antagonistic effect was attenuated by local application of the delta-opioid receptor antagonist ICI 154. 129. We conclude that the naturally occurring met-enkephalin as well as synthetic mu- and delta-specific enkephalin analogues (DAGO and DADL, respectively) in VLM depress basal ventilation by an effect on inspiratory drive. There is a functional antagonism between activation of delta-opioid receptors and SP receptors into the VLM in respect to respiratory regulation.

Distribution of c-Fos in guinea-pig brain following morphine withdrawal

The distribution of the immediate-early gene and transcription factor protein, c-Fos, was examined in the brains of guinea-pigs following treatment with morphine, naloxone or naltrexone, or the induction of morphine withdrawal by these opioid antagonists. Guinea-pigs were given subcutaneous injections of morphine sulphate or tartrate three times per day in increasing doses for three days (total dose 690 mg/kg as base). Control animals received saline injections. Naloxone hydrochloride (30 mg/kg), naltrexone hydrochloride (15 mg/kg) or saline was administered subcutaneously 1 h after the last dose of morphine or saline, and the animals killed 1.5 h later by perfusion-fixation under deep sodium pentobarbitone anaesthesia. In the animals that were treated with morphine and withdrawn with either naloxone or naltrexone, c-Fos was expressed in neurons in many brain areas, including the frontal and cingulate cortices, olfactory tubercles, ventral pallidum, nucleus accumbens, habenular, paraventricular thalamic nucleus, septal and arcuate nuclei, lateral and posterior hypothalamic areas, ventral tegmental area, central grey, dorsal raphe nucleus, locus coeruleus, raphe magnus, lateral paragigantocellular nucleus and solitary tract nucleus. In contrast, only low levels of c-Fos were found in brains of animals that had been treated for three days with morphine followed by saline, or with saline followed by naltrexone or naloxone. The widespread distribution of c-Fos induced by morphine withdrawal reflects the complexity of the accompanying behavioural and autonomic responses.

Analysis of projections from the cochlear nucleus to the lateral paragigantocellular reticular nucleus in the rat.

Golgi-staining, retrograde and anterograde tract-tracing, and a two-color immunoperoxidase technique have been employed, at the light- and electron-microscopic levels, to analyze the auditory projections from the cochlear nucleus (CN) to the lateral paragigantocellular reticular nucleus (LPGi) in the rat. We have found that the auditory input originates predominantly in the posteroventral and cochlear root nuclei. The auditory axons terminate in the cell-poor, ventral portion of the LPGi, which is strongly invaded by beaded dendritic profiles, originating from parent cell bodies located in the dorsal half of the LPGi. Ultrastructural analysis has revealed that the anterogradely labeled auditory axons form functional synapses preferentially with dendritic shafts. These axo-dendritic contacts are apparently excitatory in nature. By means of a sequential two-color immunoperoxidase staining method, we have further characterized potential postsynaptic neurons in the LPGi. Black-stained auditory fibers intermingle with brown-stained serotonergic or adrenergic neurons. Varicose auditory axons are often closely apposed to immunoreactive dendritic profiles of serotonergic and adrenergic neurons, indicating the presence of possible synaptic contacts of auditory terminal fibers with these transmitter-classified cells. The monosynaptic auditory in- put from the CN may modulate the activity of B3 sero-tonergic and C1 adrenergic cells in the LPGi and may thus induce adaptive changes in response to acoustic stimuli.

Lower brainstem catecholamine afferents to the rat dorsal raphe nucleus.

A large body of data suggests that the activation of alpha 1 receptors by a tonic noradrenergic input might be responsible for the tonic discharge of the serotonergic neurons of the dorsal raphe nucleus (DRN). To test this hypothesis, it was necessary to determine the origin of the noradrenergic and adrenergic innervation of these neurons. For this purpose, we combined small iontophoretic injections of the sensitive retrograde tracer cholera toxin b subunit (CTb) in the different subdivisions of the DRN with tyrosine hydroxylase immunohistochemistry. After CTb injections in the ventral or dorsal parts of the central DRN, a small number of double-labeled cells was observed in the locus coeruleus (A6 noradrenergic cell group), the A5 noradrenergic group, the dorsomedial medulla (C3 adrenergic cell group), and the lateral paragigantocellular nucleus (C1 adrenergic cell group). After CTb injections in the lateral wings or the dorsal part of the rostral DRN, a similar number of double-labeled cells was seen in C3. Slightly more double-labeled cells were seen in A6 and A5. In addition, a substantial to large number of double-labeled cells appeared in C1, the commissural part of the nucleus of the solitary tract (A2 noradrenergic cell group) and the caudoventrolateral medulla (A1 noradrenergic cell group). These results indicate that the noradrenergic and adrenergic inputs to the DRN arise from all the catecholaminergic cell groups of the lower brainstem except the A7 noradrenergic group. They further reveal the existence of a topographical organization of these afferents to the different subdivisions of the DRN.

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<h3>Abstract</h3> Stress increases vulnerability to psychiatric disorders, partly by affecting brain monoamine systems, such as the locus coeruleus (LC)-norepinephrine system. During stress, LC activity is coregulated by corticotropin-releasing factor (CRF) and endogenous opioids. This study identified neural circuitry that regulates LC activity of intruder rats during the resident–intruder model of social stress. LC afferents were retrogradely labeled with Fluorogold (FG) and rats were subjected to one or five daily exposures to an aggressive resident. Sections through the nucleus paragigantocellularis (PGi) and central amygdalar nucleus (CNA), major sources of enkephalin (ENK) and CRF LC afferents, respectively, were immunocytochemically processed to detect c-fos, FG, and CRF or ENK. In response to a single exposure, intruder rats assumed defeat with a relatively short latency (SL). LC neurons, PGI-ENK LC afferents, and CNA-CRF LC afferents were activated in these rats as indicated by increased c-fos expression. With repeated stress, rats exhibited either a SL or long latency (LL) to defeat and these strategies were associated with distinct patterns of neuronal activation. In SL rats, LC neurons were activated, as were CNA-CRF LC afferents but not PGI-ENK LC afferents. LL rats had an opposite pattern, maintaining activation of PGi-ENK LC afferents but not CNA-CRF LC afferents or LC neurons. Together, these results indicate that the establishment of different coping strategies to social stress is associated with changes in the circuitry that regulates activity of the brain norepinephrine system. This may underlie differential vulnerability to the consequences of social stress that characterize these different coping strategies.

Chapter 10 The ventro-medial medullary projections to spinal motoneurons: ultrastructure, transmitters and functional aspects

Publisher Summary This chapter considers the ventro-medial medullary projections to spinal motoneurons in detail with respect to their ultrastructure, transmitters and function. In general terms, the ventro-medial medulla comprises the area ranging from the caudal part of the inferior olive to the caudal part of the trapezoid body. At the level of the inferior olive it also comprises the nucleus raphe obscurus, the ventral part of the nucleus raphe pallidus and the area immediately overlying the inferior olive and immediately laterals to it. More rostrally it comprises the nucleus raphe magnus and laterally adjacent areas up to the medial border of the facial nucleus. In the rat, according to the nomenclature of Andrezik and Beitz, the ventro-medial medulla includes the ventral part of the paramedian reticular nucleus, the gigantocellular nucleus-ventral part and the ventro-medial part of the paragigantocellular nucleus at the level of the inferior olive. It is important to note that the more dorsally located gigantocellular nucleus, which comprises many spinal projecting cells, including giant cells, is not considered part of the ventro-medial medulla.

2012 Parabrachial unit responses to taste stimuli in acutely sodium-deficient rats

We have used the evoked expression of the immediate early gene-encoded proteins (c-Fos, Fos B, Jun B, Jun D, c-Jun and Krox-24) to monitor sensory processing in the hindbrain structures of rats undergoing somatic inflammation. Experiments were performed on freely moving animals that did not experience constraints other than those imposed by the disease itself. Local injections of chemicals were used to cause subcutaneous inflammation of the plantar foot or monoarthritis by intracapsular injection. Labelling was studied at survival times that corresponded either to the time points of maximum labelling in the spinal cord (4 h for the subcutaneous model, 24 h and two weeks for the monoarthritis model) or at survival times that corresponded to the chronic phase of monoarthritis evolution (six, nine and 15 weeks). Controls consisted of freely moving, unstimulated animals. Basal expression was observed for all immediate early genes and in a variety of stuctures, but always remained moderate. All immediate early gene-encoded protein expressions except c-Jun were evoked, but except for c-Fos, and to a lesser extent Jun D, intensities of staining always remained faint. The following results will be mainly based on c-Fos expression, as this protein proved to be the most effective marker for all the survival times studied.Somatic pain evoked c-Fos expression in a subset of discrete subrogions of both the caudal medulla oblongata and transitional areas of the pontomesencephalic junction. In the caudal medulla oblongata, structures involved were the caudal intermediate reticular nucleus, the subnucleus reticularis dorsalis, the ventrolateral reticular formation and the lateral paragigantocellular nucleus. Structures involved at the pontomesencephalic junction level mostly included the superior and dorsal lateral subnuclei of the parabrachial area, the nucleus cuneiformis and the most caudal portions of the lateral central gray, also including the laterodorsal tegmental nucleus; labelling in other lateral subnuclei of the parabrachial area always remained moderate. Staining in the caudal reticular areas was evident only at short survival times (4 and 24 h survival times in subcutaneous and monoarthritis models, respectively). Staining in nuclei of the pontomesencephalic junction was evident in all cases except for the very long survival periods (six to 15 weeks) of monoarthritis. In all cases staining was bilateral with contralateral predominance with regard to the stimulated limb.The present work demonstrates that hindbrain stuctures involved in somatic pain processing can be effectively identified in behaving animals and that c-Fos is the most reliable activity marker in this case. The structures involved only partially overlap with those implicated in anaesthesia or visceronociceptive processing as demonstrated previously, thus suggesting that a certain degree of specificity could exist for some of them. Nuclei of the caudal medulla oblongata would be more involved in eliciting cardiovascular behaviours that acute pain elicits while nuclei of the pontomesencephalic junction would be more involved in mediating pain of inflammatory origin.

Saccadic premotor neurons in the brainstem: functional neuroanatomy and clinical implications

Saccadic eye movements are generated by immediate premotor excitatory (EBN) and inhibitory (IBN) medium-lead burst neurons, long-lead burst neurons (LBN), and omnipause neurons (OPN) in the brainstem. The histological identification of the functional neuron populations is essential for performing any neuropathological analysis of clinical cases with saccadic disorders. This paper describes the localization of some premotor saccadic neurons in human brain and their neurochemistry, based on monkey data. In humans, the EBNs for horizontal saccades (EBNH) lie in the paramedian pontine reticular formation in the nucleus reticularis pontis caudalis (nrpc) and form a compact group of medium-sized neurons. The medium-sized IBNs lie caudal to the nucleus abducens in the nucleus paragigantocellularis dorsalis (pgd). The EBNs for vertical saccades (EBNV) are medium-sized neurons in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) in the rostral mesencephalon. The OPNs are located at the...

An investigation of a possible direct projection from the medial nucleus of the cerebellum to the paraventricular nucleus of the hypothalamus in the rat: a study using retrograde WGA-HRP and Fluoro-Gold tracing techniques.

Retrograde transport of lectin-conjugated horseradish peroxidase and Fluoro-Gold was used in an attempt to obtain data to confirm the existence, predicted from physiological studies, of a direct, monosynaptic projection from the medial nucleus of the cerebellum (MN) to the paraventricular nucleus of the hypothalamus (PVH) in the rat. Injections of these two tracers that included the PVH and surrounding diencephalic structures, or that in the case of Fluoro-Gold were localized to the PVH, resulted in retrograde neuronal labeling in widely separated nuclei known to project to the areas included in the injection sites. Thus, effective uptake and transport of both tracers occurred under the experimental conditions employed in this study. However, injections confined to the PVH and regions of the hypothalamus adjacent to it, or to the PVH alone, produced no retrograde neuronal labeling in the medial nucleus, indicating that the MN does not project directly to the PVH. Alternative explanations for the findings from physiological experiments were sought. The possibility that electrical stimulation of fibers of passage through the region of the MN might produce a monosynaptic response in the contralateral PVH was discarded, because retrogradely labeled neurons in nuclei such as the locus ceruleus and lateral parabrachial nucleus were distributed mainly ipsilateral to hypothalamic injection sites. However, tracer injections into the MN produced retrograde labeling of neurons in the same region of the lateral paragigantocellular nucleus (LPGi) in which labeled cells were found following tracers injections into the PVH. Axon collaterals of individual neurons in the LPGi might, therefore, project both to the MN and to the PVH. The possibility that such a circuit could, in the absence of a direct MN to PVH projection, provide the basis to explain the physiological findings is discussed.

Histological identification of premotor neurons for horizontal saccades in monkey and man by parvalbumin immunostaining.

The premotor excitatory and inhibitory burst neurons are essential for horizontal saccades. In the monkey, excitatory burst neurons lie in the ipsilateral paramedian pontine reticular formation, and the inhibitory burst neurons lie more caudally in the contralateral nucleus paragigantocellularis dorsalis. For a neuropathological analysis of degenerative changes in saccadic disorders of patients, the histological identification of the burst neuron areas in man is important. Here, we show that this is possible with parvalbumin immunostaining as a histological marker. First, in monkeys, the premotor burst neurons were backlabeled by injections of wheat germ agglutinin-horseradish peroxidase or cholera toxin subunit B into the abducens nucleus or tetanus toxin fragment C into the lateral rectus muscle and shown by double labeling to contain parvalbumin. Then, human brainstem sections were immunoreacted for parvalbumin, and, by comparing the resulting staining pattern to that in the monkey, the homologous burst neuron areas were defined in man. In the monkey, excitatory burst neurons were confirmed to the nucleus reticularis pontis caudalis and did not extend farther rostrally into the nucleus reticularis pontis oralis. All retrogradely labeled cells in both burst neuron areas were parvalbumin positive, and approximately 70% of the parvalbumin-positive cells were retrogradely labeled. Both burst neuron areas were highlighted by their parvalbumin staining pattern and could be outlined in man as well. The putative excitatory burst neuron area in man is in the medial part of the nucleus reticularis pontis caudalis (extending 2.5 mm mediolaterally), immediately rostral (250 microns) to the omnipause neurons and extending 2.2 mm rostrally, and the putative inhibitory burst neuron area lies in the medial part of the paragigantocellular nucleus caudal to the abducens nucleus, extending 1.8 mm caudally. The location of the burst neuron areas, including the burst neurons themselves, via parvalbumin immunostaining will help in the analysis of clinical cases with slow saccades.

Distribution of natriuretic peptide precursor mRNAs in the rat brain.

Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) represent members of a recently discovered neuropeptide family involved in central regulation of endocrine and autonomic functions. The present study employed an in situ hybridization approach to provide the first detailed comparative mapping of ANP, BNP, and CNP mRNAs in brain. Results indicate that ANP mRNA is highly expressed in anterior olfactory nuclei, limbic cortices, dorsal endopiriform nucleus, hippocampal subfield CA1, cortical amygdaloid nuclei, medial habenula, anteroventral periventricular and arcuate nuclei, periventricular stratum, zona incerta, mammillary nuclei, inferior olive, nucleus ambiguus, and pontine paragigantocellular nuclei. CNP mRNA is expressed at highest levels in olfactory nuclei, limbic cortices, dorsal endopiriform nucleus, hippocampal subfields CA1-3, anteroventral periventricular and arcuate nuclei, and numerous brainstem regions (including the pontine, lateral reticular, solitary tract, prepositus hypoglossal, and spinal trigeminal nuclei). Positive labeling for BNP mRNA was not observed in brain. The presence of both ANP and CNP mRNA in the same regions of distinct nuclei (e.g., the anteroventral periventricular and arcuate nuclei) suggests the potential for coexpression. Overall, the present data are consistent with a prominent role for both ANP and CNP in neuroendocrine regulation and central cardiovascular integration. The extensive localization of ANP and/or CNP mRNA in olfactory nuclei, limbic cortex, hippocampus, amygdala and diencephalic limbic relays further indicate a putative role for ANP and CNP as neuromodulators of olfactory/limbic information processing.

Internal connections in the rostral ventromedial medulla of the rat

Physiological and pharmacological data suggest that the rostral ventromedial medulla (RVM) is an important site where integration between somatic and visceral functions might occur. The aim of the present study was to describe the interconnections between various nuclei of the rostral ventromedial medulla and thus reveal the possible anatomical basis for such functional interactions. The topography of anterogradely labelled internal projections was examined following iontophoretic microinjections of Phaseolus vulgaris leucoagglutinin (PHA-L). The results revealed that the nuclei of the rostral ventromedial medulla have strong interconnections and, to varying degrees, they also have bilateral projections into the rostral ventrolateral medulla. A particularly dense projection to widespread regions of the ventral medulla was traced from the raphe obscurus. Terminals, originating from the raphe pallidus were similarly dispersed but very low density in comparison. The focus of the projections of the gigantocellular nucleus pars ventralis and pars alpha shifted from the lateral paragigantocellular nucleus towards the RVM in rostral direction. Connections from the raphe magnus were altogether restricted to the RVM and the medial aspects of the lateral paragigantocellular nucleus. The diffuse and dense intramedullary connections of the raphe obscurus suggest that it might have an important role in coordinating the activity of rostral ventral medullary cells. The raphe pallidus and the ventral gigantocellular nuclei, areas that were innervated from widespread regions of the rostral ventral medulla but gave only limited projections there, are more likely to be involved in the direct descending control of spinal activities.