The antidromic activation of tectal neurons by electrical stimuli applied to the caudal medulla oblongata in the toad,Bufo bufo L.

In order to specify the tectal projection to the bulbar/spinal regions, the antidromic responses of the physiologically identified tectal neurons as well as the gross antidromic field responses in the optic tectum to electrical stimuli applied to the caudal medulla were examined in the paralyzed common toad, Bufo bufo. The antidromic field potential was recorded in the optic tectum in response to electrical stimuli applied to the ventral paramedian portion of the contralateral caudal medulla (where the crossed tecto-spinal pathway of Rubinson (1968) and Lázár (1969) runs), but generally not when they were applied to various parts of the ipsilateral caudal medulla. The antidromic field potential was largest at the superficial part of Layer 6 or at the border between Layers 6 and 7 of the optic tectum, indicating that neurons in these layers project to the contralateral caudal medulla. Mapping experiments of the antidromic field potential over the optic tectum showed that the antidromic field potential was recorded mainly in the lateral part of it, indicating that this part of the optic tectum is the main source of projection neurons to the contralateral caudal medulla. Various classes of tectal neurons as well as retinal ganglion neurons were identified from the characteristics of the response properties to moving visual stimuli and the properties of the receptive fields. Of these, the Class T1, T2, T3, T4, T5(1), T5(2), T5(3), and T5(4) tectal neurons were activated antidromically by stimuli applied to the contralateral caudal medulla. Only a limited proportion of the Class T5(1) neurons was activated antidromically by stimuli applied to the ipsilateral caudal medulla. On the other hand, the Class T7 and T8 neurons, as well as the Class R2, R3, and R4 retinal neurons, were not activated antidromically by stimuli applied to the caudal medulla of either side. These results suggest a possibility that these tectal neurons which project to the medullary regions form the substrate of the sensorimotor interfacing and contribute to the initiation or coordination of the visually guided behavior, such as prey-catching.     

MSG effects on beta-endorphin and alpha-MSH in the hypothalamus and caudal medulla

Monosodium glutamate (MSG) was given to neonatal male rats to determine its effects on neurons containing beta-endorphin (beta-END) and alpha-melanocyte stimulating hormone (alpha-MSH) within the basal hypothalamus (arcuate nucleus) and caudal medulla [nucleus tractus solitarius (NTS)] and on the levels of beta-END and alpha-MSH within these areas. Immunocytochemical studies demonstrated a reduction in the number of cells within the medial hypothalamic area (arcuate nucleus) among MSG-treated animals versus saline controls. MSG did not reduce the number of cell bodies within the caudal medulla (NTS). MSG significantly reduced beta-END and alpha-MSH immunoreactive levels in the basal hypothalamus as determined by radioimmunoassay. Whereas a significant reduction in the level of beta-END occurred in the ventral caudal medulla (VCM), none occurred in the dorsal caudal medulla (DCM). In contrast, levels of alpha-MSH increased significantly in the DCM among animals receiving MSG compared to control animals. This study documents the contribution of beta-endorphin containing neurons of the basal hypothalamus to areas of the caudal medulla. The effect of MSG on beta-endorphin and alpha-MSH neurons in these areas and their differential effects on levels in the caudal medulla areas raises questions about the sites of origin of these peptides.     

The motor nuclei of the glossopharyngeal-vagal and the accessorius nerves in the rat

Retrograde cobalt labeling was performed by incubating the rootlets of cranial nerves IX, X and XI, or the central stumps of the same nerves, in a cobaltic lysine complex solution, and the distribution of efferent neurons sending their axons into these nerves was investigated in serial sections of the medulla and the cervical spinal cord in young rats. The following neuron groups were identified. The inferior salivatory nucleus lies in the dorsal part of the tegmentum at the rostral part of facial nucleus. It consists of a group of medium-sized and a group of small neurons. Their axons make a hair-pin loop at the midline and join the glossopharyngeal nerve. The dorsal motor nucleus of the vagus situates in the dorsomedial part of the tegmentum. Its rostral tip coincides with the first appearance of sensory fibres of the glossopharyngeal nerve, the caudal end extends into the pyramidal decussation. The constituting cells have globular or fusiform perikarya and they are the smallest known efferent neurons. The ambiguous nucleus is in the ventrolateral part of the tegmentum. The rostral tip lies dorsal to the facial nucleus, and the caudal tip extends to the level of the pyramidal decussation. The rostral one third of the ambiguous nucleus is composed of tightly-packed medium sized neurons, while larger neurons are arranged more diffusely in the caudal two thirds. The long dendrites are predominantly oriented in the dorsoventral direction. The dorsally-oriented axons take a ventral bend anywhere between the ambiguous nucleus and dorsal motor nucleus of the vagus. The motoneurons of the accessorius nerve are arranged in a medial, a lateral and a weak ventral cell column. The medial column begins at the caudal aspect of the pyramidal decussation and terminates in C2 spinal cord segment. The lateral and ventral columns begin in C2 segment and extend into C6 segment. The neurons have large polygonal perikarya and characteristic cross-shaped dendritic arborizations. The axons follow a dorsally-arched pathway between the ventral and dorsal horns. The accessorius motoneurons have no positional relation to any of the vagal efferent neurons. It is concluded that the topography and neuronal morphology of accessorius motoneurons do not warrant the designation of a bulbar accessorius nucleus and a bulbar accessorius nerve.     

Novel axonal projection from the caudal end of the ventrolateral medulla to the intermediolateral cell column

We used an optical imaging technique to investigate whether axons of neurons in the caudal end of the ventrolateral medulla (CeVLM), as well as axons of neurons in the rostral ventrolateral medulla (RVLM), project to neurons in the intermediolateral cell column (IML) of the spinal cord. Brain stem-spinal cord preparations from neonatal normotensive Wistar-Kyoto and spontaneously hypertensive rats were stained with a voltage-sensitive dye, and responses to electrical stimulation of the IML at the Th2 level were detected as changes in fluorescence intensity with an optical imaging apparatus (MiCAM-01). The results were as follows: 1) depolarizing responses to IML stimulation during low-Ca high-Mg superfusion were detected on the ventral surface of the medulla at the level of the CeVLM, as well as at the level of the RVLM, 2) depolarizing responses were also detected on cross sections at the level of the CeVLM, and they had a latency of 24.0 +/- 5.5 (SD) ms, 3) antidromic action potentials in response to IML stimulation were demonstrated in the CeVLM neurons where optical images were detected, and 4) glutamate application to the CeVLM increased the frequency of excitatory postsynaptic potentials (EPSPs) and induced depolarization of the IML neurons. The optical imaging findings suggested a novel axonal and functional projection from neurons in the CeVLM to the IML. The increase in EPSPs of the IML neurons in response to glutamate application suggests that the CeVLM participates in the regulation of sympathetic nerve activity and blood pressure and may correspond to the caudal pressor area.     

肾性高血压大鼠延髓尾端神经元型一氧化氮合酶表达的改变

实验采用免疫组织化学方法观察两肾一夹肾性高血压大鼠延髓尾端两个区域（延髓腹面降压区和尾端加压区）内神经元型一氧化氮合酶（neuronal oxide synthase,nNOS）表达的变化。肾性高血压大鼠延髓尾端这两个区域的nNOS的表达均增加,说明高血压对L-Arg-NO通路活性增强。NO的前体L-Arg能增强nNOS的表达,nNOS抑制剂L-NAME则降低nNOS的表达。以上两个区域nNOS表达变化的特点在肾性高血压4周和7周的动物相同,肾性高血压7周的nNOS表达和4周比较,未见明显差异。     

Galanin-like immunoreactivity in the chicken brain

The anatomical distribution of neurons containing galanin has been studied in the central nervous system of the chicken by means of immunocytochemistry using antisera against rat galanin. Major populations of immunostained perikarya were detected in several brain areas. The majority of galanin-immunoreactive cell bodies was present in the hypothalamus and in the caudal brainstem. Extensive groups of labeled perikarya were found in the paraventricular, periventricular, dorsomedial and tuberal hypothalamic nuclei, and in the nucleus of the solitary tract in the medulla oblongata. In the telencephalon, immunoreactive perikarya were observed in the preoptic area, in the lateral septal nucleus and in the hippocampus. The mesencephalon contained only a few galanin-positive perikarya located in the interpeduncular nucleus. Immunoreactive nerve fibers of varying density were detected in all subdivisions of the brain. Dense accumulations of galanin-positive fibers were seen in the preoptic area, periventricular region of the diencephalon, the ventral hypothalamus, the median eminence, the central gray of the brainstem, and the dorsomedial caudal medulla. The distributional pattern of galanin-immunoreactive neurons suggests a possible involvement of a galanin-like peptide in several neuroregulatory mechanisms.     

Neurokinin-1 receptor-expressing neurons in the ventral medulla are essential for normal central and peripheral chemoreception in the conscious rat.

Neurokinin-1 receptor immunoreactive (NK1R-ir) neurons and processes are widely distributed within the medulla, prominently at central chemoreceptor sites. Focal lesions of NK1R-ir neurons in the medullary raphe or the retrotrapezoid nucleus partially reduced the CO(2) response in conscious rats. We ask if NK1R-ir cells and processes over a wide region of the ventral medulla are essential for central and peripheral chemoreception by cisterna magna injection of SSP-SAP, a high-affinity version of substance P-saporin. After 22 days, NK1R-ir cell loss was -79% in the retrotrapezoid nucleus and -65% in the A5 region, which lie close to the ventral surface, and -38% in the medullary raphe and -49% in the pre-B?tzinger complex/rostral ventral respiratory group, which lie deeper. Dorsal chemoreceptor sites, the caudal nucleus tractus solitarius and the A6 region, were unaffected. At 8 and 22 days, these lesions produced 1) hypoventilation during air breathing in wakefulness ( approximately 8%) and in non-rapid eye movement (NREM) ( approximately 9%) and rapid eye movement ( approximately 14%) sleep, as measured over a 4-h period; 2) a substantially reduced ventilatory response to 7% CO(2) by 61% in wakefulness and 46-57% in NREM sleep; and 3) a decreased ventilatory response to 12% O(2) by 40% in wakefulness and 35% in NREM sleep at 8 days, with partial recovery by 22 days. NK1R-ir neurons in the ventral medulla are essential for normal central chemoreception, provide a drive to breathe, and modulate the peripheral chemoreceptor responses. These effects are not state dependent.     

Parvalbumin in respiratory neurons of the ventrolateral medulla of the adult rat

A column of parvalbumin immunoreactive neurons is closely associated with the location of respiratory neurons in the ventrolateral medulla of the rat. The majority (66%) of bulbospinal neurons in the medullary ventral respiratory column (VRC) that were retrogradely labeled by tracer injections in the phrenic nucleus were also positive for parvalbumin. In contrast, only 18.8% of VRC neurons retrogradely labeled after a tracer injection in the VRC, also expressed parvalbumin. The average cross-sectional area of VRC neurons retrogradely labeled after VRC injections was 193.8 μm² ± 6.6 SE. These were significantly smaller than VRC parvalbumin neurons (271.9 μm² ± 12.3 SE). Parvalbumin neurons were found in the Bötzinger Complex, the rostral ventral respiratory group (VRG), and the caudal VRG, areas which all contribute to the bulbospinal projection. In contrast, parvalbumin neurons were sparse or absent in the preBötzinger Complex and in the vicinity of the retrotrapezoid nucleus, areas that have few bulbospinal projections. Parvalbumin was rarely colocalized within Neurokinin-1 receptor positive (NK1R) VRC neurons, which are found in the preBötzinger complex and in the anteroventral part of the rostral VRG. Parvalbumin neurons in the Bötzinger Complex and rostral VRG help define the rostrocaudal extent of these regions. The absence of parvalbumin neurons from the intervening preBötzinger complex also helps establish the boundaries of this region. Regional boundaries described in this manner are in good agreement with earlier physiological and anatomical studies. Taken together, the distributions of parvalbumin, NK1R and bulbospinal neurons suggest that the rostral VRG may be subdivided into distinct, anterodorsal, anteroventral, and posterior subdivisions.     

Distribution of glycine/GABA neurons in the ventromedial medulla with descending spinal projections and evidence for an ascending glycine/GABA projection

The ventromedial medulla (VM), subdivided in a rostral (RVM) and a caudal (CVM) part, has a powerful influence on the spinal cord. In this study, we have identified the distribution of glycine and GABA containing neurons in the VM with projections to the cervical spinal cord, the lumbar dorsal horn, and the lumbar ventral horn. For this purpose, we have combined retrograde tracing using fluorescent microspheres with fluorescent in situ hybridization (FISH) for glycine transporter 2 (GlyT2) and GAD67 mRNAs to identify glycinergic and/or GABAergic (Gly/GABA) neurons. Since the results obtained with FISH for GlyT2, GAD67, or GlyT2 + GAD67 mRNAs were not significantly different, we concluded that glycine and GABA coexisted in the various projection neurons. After injections in the cervical cord, we found that 29% ± 1 (SEM) of the retrogradely labeled neurons in the VM were Gly/GABA (RVM: 43%; CVM: 21%). After lumbar dorsal horn injections 31% ± 3 of the VM neurons were Gly/GABA (RVM: 45%; CVM: 12%), and after lumbar ventral horn injections 25% ± 2 were Gly/GABA (RVM: 35%; CVM: 17%). In addition, we have identified a novel ascending Gly/GABA pathway originating from neurons in the area around the central canal (CC) throughout the spinal cord and projecting to the RVM, emphasizing the interaction between the ventromedial medulla and the spinal cord. The present study has now firmly established that GABA and glycine are present in many VM neurons that project to the spinal cord. These neurons strongly influence spinal processing, most notably the inhibition of nociceptive transmission.     

Immunocytochemical localization of GABA containing neurons in the ventrolateral medulla oblongata of the rat

Localization of gamma-aminobutyric acid (GABA) in the ventrolateral medulla oblongata of the rat was studied, using antisera directed against GABA molecule fixed to bovine serum albumin. Within the rostral portion of the ventrolateral medulla, GABA-like immunoreactive neurons were found in the lateral wing of the raphe magnus and in the region of the paragigantocellular reticular nucleus. In the caudal portion of the ventrolateral medulla, a lesser number of GABA-stained neurons were found in the region around the nucleus reticularis lateralis. GABA-like immunoreactive punctate structures were also found throughout the ventrolateral medulla. These results provide further evidence for the existence of GABAergic neurons in the ventrolateral medulla oblongata of the rat.     

Substance P in the ventrolateral medulla oblongata regulates ventilatory responses.

Local injection of substance P (SP) into the ventral portion of the nucleus gigantocellularis, nucleus reticularis lateralis, and nucleus retrofacialis of the ventrolateral medulla oblongata (VLM) or direct application on the ventral surface of the medulla oblongata caused marked stimulation of tidal volume (VT) and/or minute ventilation (VE). The ventilatory response to hypoxia was significantly blunted after SP in the VLM but not in the dorsal medulla oblongata (DM) (nucleus tractus solitarius). The SP antagonist [D-Pro2,D-Trp7,9]SP almost completely inhibited this response when applied locally to a wide area of the superficial layer of the VLM but not of the DM. Unilateral or bilateral application of 0.3-1.5 nmol of the SP antagonist in the VLM (corpus trapezoideum and the caudal region extending from the rootlets of the nucleus hypoglossus to the first cervical segment) markedly attenuated the response to a 5% CO2 inhalation. The inhibition of the CO2 response was seen after [D-Pro2,D-Trp7,9]SP in the rostral areas of the medulla oblongata corresponding to the corpus trapezoideum and the caudal region extending from the rootlets of the nucleus hypoglossus to the first cervical segment of the cervical cord. Electric somatosensory-induced ventilatory stimulation could be depressed by approximately 70% by [D-Pro2,D-Trp7,9]SP locally applied on the surface of the VLM. We conclude that SP is involved in the hypoxic, hypercapnic, and somatosensory ventilatory responses in the rat. However, these respiratory reflexes are mediated via different neuronal pools in the medulla oblongata, mainly the VLM.     

Neuropeptide FF2 receptor distribution in the human brain. An immunohistochemical study

Human neuropeptide FF2 (hFF2) receptor has been postulated to mediate central autonomic regulation by virtue of its ability to bind with high affinity to many amidated neuropeptides. In the present immunohistochemical study, we identified hFF2 positive neurons in the forebrain and medulla oblongata of individuals, who died suddenly of mechanical trauma or hypothermia. Morphologically, these neurons demonstrated features identified with both projection neurons and interneurons. In the forebrain, the highest density of hFF2 expressing neurons was observed in the anterior amygdaloid area and dorsomedial hypothalamic nucleus, especially in its caudal part. A lesser density of hFF2 neurons was identified in the ventromedial hypothalamic nucleus, lateral and posterior hypothalamic areas whereas few cells were visualized in the paraventricular hypothalamic nucleus, perifornical nucleus, horizontal limb of the diagonal band, ventral division of the bed nucleus of the stria terminalis, nucleus basalis of Meynert and ventral tegmental area. In the medulla, significant numbers of hFF2 neurons were observed in the dorsal motor nucleus of vagus and to a lesser extent in the area of catecholaminergic cell groups, A1/C1. These data provide first immunohistochemical evidence of hFF2 localization in the human brain, which is consistent with that reported for tissue distribution of FF2 mRNA and FF2 binding sites within the brain of a variety of mammalian species. The distribution of hFF2 may help in identifying the role of amidated neuropeptides in the human brain within the context of central autonomic and neuroendocrine regulation.     

Changes in gas composition of expired air during electric stimulation of the ventral medulla oblongata]

The experiments on urethane-anesthetized cats with the electrically stimulated ventral brain stem revealed that caudal ventral medulla at the depth of 1500 microns possesses structures whose electrical activation increases the level of carbon dioxide in arterial blood and in the end portion of expirate, on the one hand, and decreases the oxygen content in expirate and arterial blood, on the other hand.     

Immunocytochemical localization of GABA containing neurons in the ventrolateral medulla oblongata of the rat

Summary Localization of -aminobutyric acid (GABA) in the ventrolateral medulla oblongata of the rat was studied, using antisera directed against GABA molecule fixed to bovine serum albumin. Within the rostral portion of the ventrolateral medulla, GABA-like immunoreactive neurons were found in the lateral wing of the raphe magnus and in the region of the paragigantocellular reticular nucleus. In the caudal portion of the ventrolateral medulla, a lesser number of GABA-stained neurons were found in the region around the nucleus reticularis lateralis. GABA-like immunoreactive punctate structures were also found throughout the ventrolateral medulla. These results provide further evidence for the existence of GABAergic neurons in the ventrolateral medulla oblongata of the rat.     

Sympathoinhibitory pathway from caudal midline medulla to RVLM is independent of baroreceptor reflex pathway

Glutamate stimulation of the caudal midline medulla (CMM) causes profound sympathoinhibition due to GABAergic inhibition of presympathetic neurons in the rostral ventrolateral medulla (RVLM). We investigated whether the sympathoinhibitory pathway from CMM to RVLM, like the central baroreceptor reflex pathway, includes a glutamatergic synapse in the caudal ventrolateral medulla (CVLM). In pentobarbital sodium-anesthetized rats, the RVLM on one side was inhibited by a muscimol microinjection. Then the response evoked by glutamate microinjections into the CMM or by baroreceptor stimulation was determined before and after 1) microinjection of the GABA receptor antagonist bicuculline into the RVLM on the other side or 2) microinjections of the glutamate receptor antagonist kynurenate bilaterally into the CVLM. Bicuculline in the RVLM greatly reduced both CMM- and baroreceptor-evoked sympathoinhibition. Compared with the effect of vehicle solution, kynurenate in the CVLM greatly reduced baroreceptor-evoked sympathoinhibition, whereas its effect on CMM-evoked sympathoinhibition was not different from that of the vehicle solution. These findings indicate that the output pathway from CMM sympathoinhibitory neurons, unlike the baroreceptor and other reflex sympathoinhibitory pathways, does not include a glutamatergic synapse in the CVLM.     

Distribution of NT-IR perikarya in the brain of the guinea pig with special reference to cardiovascular centers in the medulla oblongata

The occurrence and distribution of neurotensin-immunoreactive (NT-IR) perikarya was studied in the central nervous system of the guinea pig using a newly raised antibody (KN 1). Numerous NT-IR perikarya were found in the nuclei amygdaloidei, nuclei septi interventriculare, hypothalamus, nucleus parafascicularis thalami, substantia grisea centralis mesencephali, ventral medulla oblongata, nucleus solitarius and spinal cord. The distribution of NT-IR perikarya was similar to that previously described in the rat and monkey. In the gyrus cinguli, hippocampus and nucleus olfactorius, though, no NT-IR neurons were detected in this investigation. Additional immunoreactive perikarya, however, were observed in areas of the ventral medulla oblongata, namely in the nucleus paragigantocellularis, nucleus retrofacialis and nucleus raphe obscurus. The relevance of the NT-IR perikarya within the ventral medulla oblongata is discussed with respect to other neuropeptides, which are found in this area, and to cardiovascular regulation.     

Sympathoexcitatory CVLM neurons mediate responses to caudal pressor area stimulation

Neurons in the caudal pressor area (CPA) are a source of tonic sympathoexcitation that is dependent on activation of cardiovascular sympathetic premotor neurons in the rostral ventrolateral medulla (RVLM). In the present study, we sought to clarify the mechanism through which CPA neurons elicit increases in RVLM neuronal discharge, vasoconstrictor sympathetic tone, and arterial pressure. In urethan-chloralose-anesthetized, paralyzed, and artificially ventilated rats, bilateral disinhibition of CPA with bicuculline (Bic) after bilateral disinhibition of caudal ventrolateral medulla (CVLM) caused increases in splanchnic sympathetic nerve activity (+277% control) and arterial pressure (+54 mmHg). Inhibition of CVLM neurons with muscimol abolished the pressor response to activation of CPA neurons, suggesting that neurons within CVLM mediate the excitatory responses from CPA. Disinhibition of CVLM and CPA with Bic enhanced the sympathoexcitatory responses to stimulation of CPA with DL-homocysteic acid, which were blocked by microinjections of kynurenic acid into CVLM. We conclude that the pathway from CPA to RVLM involves an obligatory glutamatergic activation of sympathoexcitatory neurons in the vicinity of CVLM.     

Organization of histamine-containing neurons in the brain of the crested newt,Triturus carnifex

The distribution of immunoreactivity for histamine was studied in the brain of the urodele Triturus carnifex using the indirect immunofluorescence method. Histamine-immunoreactive cell bodies were localized in the caudal hypothalamus within the dorsolateral walls of the infundibular recesses. These immunoreactive cell bodies were pear-shaped, bipolar and frequently of the cerebrospinal-fluid-contacting type. Histaminergic nerve fibers were detected in almost all parts of the brain. Dense innervation was seen in the telencephalic medial pallium and ventral striatum, the neuropil of the preoptic area, the septum, the paraventricular organ, the posterior commissure, the caudal hypothalamus, the ventral and lateral mesencephalic tegmentum. Medium density innervation was observed in the lateral mesencephalic tegmentum and optic tectum. Poor innervation was present in the telencephalic dorsal pallium and in the central gray of the medulla oblongata. Few fibers occurred in the olfactory bulbs and in the telencephalic lateral pallium. Double immunofluorescence staining, using an antibody against tyrosine hydroxylase, showed that histamine-immunostained somata and those containing tyrosine-hydroxylase-like immunoreactivity were co-distributed in the tuberal hypothalamus. No co-occurrence of histamine-like and tyrosine hydroxylase-like immunostaining was seen in the same neuron. The pattern of histamine-immunoreactive neurons in the newt was similar to that described in other vertebrates. Our observations, carried out on the apparently simplified brain of the newt confirm that the basic histaminergic system is well conserved throughout vertebrates.     

Origin of autonomic nerve fibers innervating the parathyroid gland in the rabbit

The cells of origin of nerve fibers innervating the parathyroid gland were studied in the rabbit using the HRP-retrograde transport method. Numerous labeled neurons were observed in the caudal half of the ipsilateral superior cervical ganglion following HRP injection into the parathyroid gland. Furthermore, in the medulla oblongata, labeled neurons were found in the dorsal nucleus of the vagus and many of them were distributed caudal to the level of the obex.