The influence of bulbospinal monoaminergic pathways on sympathetic nerve activity

1. Spontaneous and reflex activity was recorded from renal and splanchnic nerves and thoracic white rami during discrete electrical stimulation within the medulla oblongata of anaesthetized cats.2. Inhibition or excitation of spontaneous sympathetic nerve activity was obtained from several medullary regions.3. The long-circuited reflex elicited in renal nerves and the spinally mediated reflex discharge produced in white rami by single shock stimulation of intercostal nerves were inhibited by stimulation within the sympatho-inhibitory areas of the medulla.4. Activation of spontaneous sympathetic nerve activity or inhibition of spontaneous and reflex sympathetic nerve activity was obtained during electrical stimulation within the lateral funiculi of the cervical spinal cord in unanaesthetized decerebrate cats, spinalized at C1.5. There was a correlation between the position of some sympatho-inhibitory regions of the medulla and spinal cord and the position of the cell bodies and axons of descending monoamine-containing neurones.6. Intravenous administration of the precursor of noradrenaline, L-DOPA, to unanaesthetized decerebrate cats, spinalized at C1, was followed by a depression of spontaneous activity in renal nerves and reflex responses elicited in renal nerves and white rami.7. Similarly the precursor of 5-hydroxytryptamine, 5-HTP, caused a depression of reflex activity elicited in renal nerves and white rami, but had no effect on spontaneous renal nerve activity.8. It is suggested that there exist both noradrenergic and tryptaminergic pathways which descend to the spinal cord from the medulla and which are inhibitory to sympathetic outflow.     

Stimulation of the lateral hypothalamus produces antinociception mediated by 5-HT1A, 5-HT1B and 5-HT3 receptors in the rat spinal cord dorsal horn

The lateral hypothalamus is part of an efferent system that modifies pain at the spinal cord dorsal horn, but the mechanisms by which lateral hypothalamus-induced antinociception occur are not fully understood. Previous work has shown that antinociception produced from electrical stimulation of the lateral hypothalamus is mediated in part by spinally projecting 5-hydroxytryptamine (5-HT) neurons in the ventromedial medulla. To further examine the role of the lateral hypothalamus in antinociception, the cholinergic agonist carbamylcholine chloride (125 nmol) was microinjected into the lateral hypothalamus of female Sprague-Dawley rats and nociceptive responses measured on the tail-flick and foot-withdrawal tests. Intrathecal injections of the selective 5-HT1A, 5-HT1B, 5-HT3 receptor antagonists, WAY 100135, SB-224289, and tropisetron, respectively, and the non-specific antagonist methysergide, were given. Lateral hypothalamus stimulation with carbamylcholine chloride produced significant antinociception that was blocked by WAY 100135, tropisetron, and SB-224289 on both the tail-flick and foot-withdrawal tests. Methysergide was not different from controls on the tail flick test, but increased foot-withdrawal latencies compared with controls. These results suggest that the lateral hypothalamus modifies nociception in part by activating spinally projecting serotonin neurons that act at 5-HT1A, 5-HT1B, and 5-HT3 receptors in the dorsal horn.     

Histochemical demonstration and mapping of 5-hydroxytryptamine- and catecholamine-containing neuron systems in the human fetal brain

Summary The distribution of monoamine neurons in the human fetal brain was studied by Falck-Hillarp fluorescence histochemistry. Catecholamine (CA)- and 5-hydroxytryptamine (5-HT)-neuron systems were found in the smallest brain studied, obtained from an embryo having a total length of 2.1 cm and a gestational age of 7 weeks. A marked proliferation and differentiation of the monoamine neuron systems took place between the 7th and 23rd week of gestation (the range covered in the present investigation) permitting a mapping of major cell groups, as well as several axon pathways and terminal innervation patterns.The basic cytoarchitectonic features of the central monoamine neurons in human fetuses were strikingly similar to those of the fetal rat. Thus, a large complex of cell bodies was found in the developing substantia nigra area, in all probability the CA neurons of the nigro-striatal dopamine system. Axons projected towards the corpus striatum. Here, the putamen and, somewhat later, the caudate nucleus became richly innervated by CA nerve terminals. Small clusters of CA nerve cells were found in the hypothalamus, e. g. in the ventral periventricular area.5-hydroxytryptamine nerve cell bodies were distributed throughout the raphe areas from the medulla oblongata to the mesencephalon forming several well delineated groups, e.g. a large group in the area of nuc. raphe dorsalis. 5-HT axons projected caudally in the ventral parts of the medulla oblongata and into the spinal cord and rostrally through the mesencephalon and into the forebrain.CA cell bodies were also found in several large complexes of the medulla oblongata and pons, where such cell bodies are of the noradrenaline type in animals. The principal locus coeruleus consisted of densely packed fluorescent cells and several loosely packed groups extended laterally, medially, dorsally and rostrally from this area. Several axon bundles ascended dorsally from this complex. Ventrally and dorsally located CA cell groups were found in the medulla oblongata, and green fluorescent axons descended into the spinal cord.Varicose nerve terminals of the CA type were found, e.g. in the spinal cord, around the third ventricle and, using brain smears, also in the developing cerebral and cerebellar cortices.There seemed to be an outflow of CA axons in ventral nerve roots of cranial and spinal nerves. The developing pineal gland showed scattered 5-HT-containing parenchymal cells. Area postrema contained a number of strongly fluorescent CA cells and some weaker fluorescent 5-HT cells.     

Co-localization of c-Fos and neurotransmitter immunoreactivities in the cat brain stem after carotid sinus nerve stimulation

To reveal neurones in the cat medulla oblongata involved in carotid baroreceptor/chemoreceptor reflexes, the distribution of c-Fos oncoprotein immunoreactivity was studied following electrical stimulation of the right carotid sinus nerve. The neurochemistry of the activated neurones was investigated using antisera to tyrosine hydroxylase, neuropeptide Y, somatostatin, and glutamate. Nitric oxide containing neurones were identified using antiserum to nitric oxide synthase (NOS) and by the histochemical localization of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase. Following sinus nerve stimulation numerous c-Fos-IR cells were detected both ipsilaterally and contralaterally in the nucleus tractus solitarii, the area postrema and throughout the ventrolateral medulla. Dual labelling studies revealed that 3.3% of c-Fos- immunoreactive cells in the nucleus tractus solitarii were also immunoreactive for tyrosine hydroxylase. The double labelled cells were scattered within the medial and ventrolateral subnuclei, predominantly rostral to obex. A higher proportion (10.3%) of c-Fos-IR cells in the ventrolateral medulla also showed tyrosine hydroxylase immunoreactivity. Caudal to obex, these were scattered in the reticular formation between the spinal trigeminal nucleus and the lateral reticular nucleus, while more rostrally they were found within the lateral reticular nucleus, the nucleus ambiguus and the lateral tegmental field. Cells expressing c-fos and reactive for glutamate, neuropeptide Y or NADPH-diaphorase (or NOS) were only rarely seen, and co-localization of c-Fos and somatostatin immunoreactivities was not seen. These results suggest that of the neurones forming pathways within the medulla activated on carotid sinus nerve stimulation, presumably mediating baro- and chemoreceptor reflexes, relatively few utilize catecholamines, glutamate, neuropeptide Y or nitric oxide as their transmitter substance.     

c-JUN-like immunoreactivity in the CNS of the adult rat: basal and transynaptically induced expression of an immediate-early gene

An immunocytochemical study of dorsal root ganglia, spinal cord and medulla oblongata was performed with antisera against the c-jun proto-oncogene encoded protein. The c-JUN-like immunoreactivity was restricted to the cell nucleus. In the CNS of untreated rats a basal c-JUN-like immunoreactivity was present in the nuclei of two types of neurons: motor and autonomic. Labelled nuclei could be seen in many motoneurons of the ventral horn of the entire length of spinal cord and the lower medulla oblongata, as well as in the area of the nucleus hypoglossus, the dorsal motor nucleus of nucleus vagus, nucleus ambiguus, nucleus facialis, nucleus abducens and motor nucleus of nucleus trigeminus. Additionally, labelled nuclei were found in the preganglionic sympathetic and preganglionic parasympathetic cells of the nucleus intermediolateralis and nucleus intercalatus in the spinal cord. In the medulla oblongata we found a cluster of cells with c-JUN-like immunoreactivity in an area between the dorsomedial part of the oral nucleus spinalis trigeminalis and the lateral border of the knee of facial nerve. Additionally, a second cluster of c-JUN-like immunoreactivity cells was visible between the ventromedial part of the oral nucleus spinalis trigeminalis and the lateral border of the rostral nucleus facialis. Examination of the characteristics of all cell groups with a basal c-JUN-like immunoreactivity in the spinal cord and lower brainstem revealed an overlapping distribution with cholinergic cell groups. Basal c-JUN-like immunoreactivity was also seen in the dorsal root ganglion cells. We examined the factors which can effect the expression of the c-JUN protein. Maximal expression of c-JUN-like immunoreactivity was observed after electrical stimulation of primary afferents. Stimulation of sciatic nerve at a strength sufficient to recruit A delta- and C-fibres produced c-JUN-like immunoreactivity in many nuclei of the ipsilateral dorsal horn of the lumbar spinal cord. c-JUN-like immunoreactivity was first detectable at 30 min following the end of stimulation, reached a maximum after 1 h, remained unchanged for another 1 h and declined to the basal level after 16 h. The distribution of c-JUN-like immunoreactivity in the lumbar cord coincided with the region of termination of sciatic nociceptive afferents. Contralateral c-JUN-like immunoreactivity appeared after 4 h. After noxious mechanical stimulation of the plantar hindpaw c-JUN-like immunoreactivity occurred in the spinal area of termination of nociceptive afferents of the tibial nerve. Noxious stimulation did not provoke additional c-JUN-like immunoreactivity in dorsal root ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evidence for colocalization of substance P and 5-hydroxytryptamine in spinally projecting neurons from the cat medulla oblongata

Substance P (SP)- and 5-hydroxytryptamine (5-HT)-like immunoreactivities were localized in bulbospinal neurons of the raphe nuclei and ventrolateral medulla (VLM). In raphe pallidus and raphe obscurus virtually all of the spinally projecting neurons contained SP and/or 5-HT. Furthermore, SP and 5-HT were colocalized in half of these spinal-raphe neurons. In raphe magnus few spinally projecting neurons contained either SP or 5-HT. Half of the bulbospinal neurons in the caudal VLM contained SP and/or 5-HT and in 50% of these SP and 5-HT were colocalized. However, no SP-containing neurons in the rostral VLM projected to the spinal cord.     

Inhibitory serotonergic effects on rostral ventrolateral medullary neurons

In rats anaesthetised with urethane, iontophoretic application of 5-hydroxytryptamine (5-HT) and the 5-HT_1A agonists buspirone, flesinoxan and 8-hydroxy-2-(di-n-propylamino)-tetralin inhibited ongoing or amino-acid-evoked activity of neurons in the rostral ventrolateral medulla (RVLM) including barosensitive cells with spinally projecting axons. More than 90% of cells tested were inhibited by these agonists. In 5/9 cells the inhibition was reduced after intravenous spiperone (0.6 mg/kg). These results suggest that the sympathoinhibitory effects produced by microinjection of 5-HT_1A agonists into the RVLM are due to a direct inhibitory action on neurons that send excitatory projections to the spinal sympathetic outflow.On leave from the Department of Physiology, Shanghai Medical University, Shanghai 200032, China     

The spinal route of sympatho-inhibitory pathways descending from the medulla oblongata

1. The effect of making discrete lesions in the cervical spinal cord on the brainstem elicited inhibition of a spinal somato-sympathetic reflex response has been studied in anaesthetized cats. 2. Electrical stimulation within three areas of the medulla caused an inhibition of the spinal component of the reflex response elicited in thoracic white rami communicantes by stimulation of intercostal nerves. The three medullary areas studied were the ventrolateral medulla and the caudal rephe nucleus, from where bulbospinal monoamine neurones originate, and the ventromedial reticular formation. 3. The inhibitory effects of stimulation in the ventrolateral medulla and raphe nucleus were abolished by the destruction of parts of the ipsilateral dorsolateral funiculus of the cervical spinal cord, whereas the inhibition produced by ventromedial reticular formation stimulation was abolished by lesions which included part of the ventral quadrant of the cord. 4. The time course of the inhibitory effects of electrical stimulation of descending sympatho-inhibitory tracts in the cervical spinal cord was studied in unanaesthetized decerebrate cats spinalized at C1. Inhibition obtained from the dorsolateral funiculus characteristically had a longer time to onset than inhibition obtained from the ventrolateral and ventral funiculi.     

Localization of the spinal nucleus of accessory nerve in rat: a horseradish peroxidase study

The spinal nucleus of the accessory nerve (SNA) comprises the group of somata (perikarya) of motor neurons that supply the sternocleidomastoid and trapezius muscles. There are many conflicting views regarding the longitudinal extent and topography of the SNA, even in the same species, and these disagreements prompted the present investigation. Thirty Sprague-Dawley rats (15 males, 15 females) were used. The SNA was localized by retrograde axonal transport of horseradish peroxidase. Longitudinally, the SNA was found to be located in the caudal part (caudal 0.9-1.2 mm) of the medulla oblongata, the whole lengths of cervical spinal cord segments C1, C2, C3, C4, C5 and rostral fourth of C6. In the caudal part of the medulla oblongata, the SNA was represented by a group of perikarya of motor neurons lying immediately ventrolateral to the pyramidal fibres that were passing dorsolaterally after their decussation. In the spinal cord, the motor neuronal somata of the SNA were located in the dorsomedial and central columns at C1, in the dorsomedial, central and ventrolateral columns at C2 and in the ventrolateral column only at C3, C4, C5 and rostral quarter of C6. The perikarya of motor neurons supplying the sternocleidomastoid were located in the caudal part (caudal 0.9-1.2 mm) of the medulla oblongata ventrolateral to the pyramidal fibres that were passing dorsolaterally after their decussation. They were also located in the dorsomedial and central columns at C1, in the dorsomedial, central and ventrolateral columns at C2 and only in the ventrolateral column at the rostral three-quarters of C3. The perikarya of motor neurons supplying the trapezius muscle were located in the ventrolateral column only in the caudal three-quarters of C2, the whole lengths of C3, C4 and C5, and in the rostral quarter of C6.     

Evidence for the involvement in the baroreceptor reflex of a descending inhibitory pathway

1. The onset and time course of baroreceptor inhibition of pre- and post-ganglionic sympathetic reflex activity has been examined in the anaesthetized cat.2. The shortest time to the onset of inhibition of an intercostal evoked reflex response in cardiac and renal nerve was less than 90 msec following a rise in pressure in a carotid sinus blind sac, and around 55 msec following stimulation of the ipsilateral sinus nerve. The cardiac nerve response was completely inhibited before the renal nerve response.3. Because of the long delays in the somato-sympathetic reflex pathway it is argued that these minimum times will be much less than the real central delay of baroreceptor inhibition. These were estimated by adding on the central times for the somato-sympathetic reflexes to give latencies of 94-143 msec for the inhibition.4. A spinal sympathetic reflex was inhibited by 30-75% following a rise in pressure in a carotid sinus blind sac or sinus nerve stimulation. The minimum time for this inhibition was around 100 msec.5. The baroreceptor inhibition of the spinal sympathetic reflex was abolished following section of a restricted region in the dorsolateral part of the lateral funiculus of the cervical spinal cord.6. Both pre- and post-ganglionic reflexes could be inhibited when stimulating within three regions of the medulla oblongata. The latency to inhibition elicited from the ventromedial reticular formation was short, some 5-30 msec, whereas that elicited from a ventrolateral region or the mid line raphe nucleus was long, some 90-160 msec.7. The possibility is discussed that the baroreceptor inhibition of both the pre- and post-ganglionic reflexes examined in this study is occurring at the spinal level via a pathway from either the raphe nuclei or ventrolateral medulla.     

Effects of carotid sinus nerve transection on changes in neuropeptide Y and indolamines induced by long-term hypoxia in rats

 Long-term hypoxia induces changes in neuropeptide-Y-like immunoreactivity (NPY-LI) and/or in the content of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) at the central level. To determine whether these alterations depend on the integrity of carotid body (CB) chemoreceptors, intact rats or those whose carotid sinus nerve was transected (CSNT) were exposed to hypoxia (10% O₂) or to normoxia for 14 days. Thereafter, NPY-LI, 5-HT and 5-HIAA levels in discrete brain regions were determined. The increase in NPY-LI in the ventrolateral medulla oblongata (VLM) of intact hypoxic rats was mostly abolished after CSNT and therefore is mainly mediated by CB chemoreceptors. In contrast, other hypoxia-induced changes were similar or even enhanced in CSNT as compared to intact rats and therefore do not depend on the integrity of CB chemoreceptors. This was the case for the increase of NPY-LI in the striatum and the caudal dorsomedian medulla oblongata (DMM), as well as for all the changes in 5-HT and 5-HIAA in the DMM, the VLM, the raphe nuclei, the striatum and the frontal cortex. We propose that long-term hypoxia alters brain NPY-LI and indolamine content through the stimulation of CB chemoreceptors or ancillary chemoreceptors, as well as through local biochemical or morphological mechanisms. Received: 5 May 1998 / Received after revision: 27 July 1998 / Accepted: 3 September 1998     

Is the cranial accessory nerve really a portion of the accessory nerve? Anatomy of the cranial nerves in the jugular foramen

The accessory nerve is traditionally described as having both spinal and cranial roots, with the spinal root originating from the upper cervical segments of the spinal cord and the cranial root originating from the dorsolateral surface of the medulla oblongata. The spinal rootlets and cranial rootlets converge either before entering the jugular foramen or within it. In a recent report, this conventional view has been challenged by finding no cranial contribution to the accessory nerve. The present study was undertaken to re-examine the accessory and vagus nerves within the cranium and jugular foramen, with particular emphasis on the components of the accessory nerve. These nerves were traced from their rootlets attaching to the spinal cord and the medulla and then through the jugular foramen. The jugular foramen was exposed by removing the dural covering and surrounding bone. A surgical dissecting microscope was used to trace the roots of the glossopharyngeal nerve (CN IX), vagus nerve (CN X) and accessory nerve (CN XI) before they entered the jugular foramen and during their travel through it. The present study demonstrates that the accessory nerve exists in two forms within the cranial cavity. In the majority of cases (11 of 12), CN XI originated from the spinal cord with no distinct contribution from the medulla. However, in one of 12 cases, a small but distinct connection was seen between the vagus and the spinal accessory nerves within the jugular foramen.     

The distribution of infrahyoid motoneurons in the cat: a retrograde horseradish peroxidase study

Summary The distribution of cell bodies and the peripheral course of axons of infrahyoid motoneurons were examined in the cat by the retrograde horseradish peroxidase method after application of the enzyme to the peripheral nerve branches supplying the infrahyoid muscles. Infrahyoid motoneurons were observed to constitute a slender cell column, which extended from a level of the caudal part of the hypoglossal nucleus usually to the most caudal level of the C1 cord segment, or occasionally to the lower levels of the C2 cord segment. The cell column was located immediately lateral to that of motoneurons of the spinal accessory nerve. In the cell column, thyrohyoid motoneurons were distributed in the medulla oblongata; sternohyoid motoneurons were located somewhat more cranially than sternothyroid motoneurons in the medulla oblongata and cervical cord. However, the level of craniocaudal distribution of thyrohyoid, sternohyoid or sternothyroid motoneurons highly overlapped. The experiments involving severance of the hypoglossal and/or cervical nerves indicated that axons of thyrohyoid and sternohyoid motoneurons passed via the roots of both hypoglossal and C1 nerves, that axons of sternohyoid motoneurons passed via the C1 nerve roots, and that axons of infrahyoid motoneurons innervating the conjugated part of the sternohyoid and sternothyroid muscles passed usually via the C1 nerve roots, or occasionally via the roots of both C1 and C2 nerves.     

Mapping of monoamine neurones and fibres in the cat lower brainstem and spinal cord

Summary The localization of monoaminergic neurones in the medulla oblongata and the pons, and the distribution of catecholaminergic fibres in the spinal cord of the cat were investigated by means of formaldehyde-induced (FIF) or glyoxylic-acid-induced (GIF) fluorescence. Four groups of catecholamine (CA)-containing neurones were found in the following regions: (1) in the ventrolateral medulla oblongata within and adjacent to the lateral reticular nucleus, beginning slightly rostral to the medullo-spinal junction and extending rostrally to the cranial third of the inferior olive; (2) in the commissural, medial and lateral nucleus of the solitary tract; (3) cranial to the first group, closely adjacent to the facial nucleus and the superior olive; and (4) in the dorsolateral pons distributed to different nuclei, namely the nucleus coeruleus and subcoeruleus, the Koelliker-Fuse nucleus, and the medial and lateral parabrachial nuclei. The indoleamine (IA)-containing cell bodies were in general confined to the raphe nuclei, namely the nucleus raphe pallidus, nucleus raphe obscurus, nucleus raphe magnus, nucleus raphe pontis, nucleus raphe dorsalis and the central superior nucleus. A few IA-neurones were located more laterally, especially dorsal and lateral of the cranial half of the inferior olive, around the root of the hypoglossal nerve, in the lateral tegmental field and the pontine central gray. In the spinal cord most CA-fibres were found in the intermediolateral cell column. Another dense accumulation of CA-fibres was located dorsally and laterally of the central canal. The ventral and dorsal horns also contained CA-nervefibres which were slightly more numerous in the sacral spinal cord than in the more rostral parts of the spinal cord.     

Distribution of P2 Antigen in Neural and Non-Neural Bovine Tissues

Rabbit antisera to bovine nerve preparations were used to study the tissue distribution in the ox of P₂, an antigen specific for the peripheral nervous system. Double diffubion gel precipitation tests were able to demonstrate P₂ in spinal nerves, trigeminal nerve, spinal cord, medulla oblongata. and pons, but not in higher centers of the CNS, optic nerve, or non-neural tissues. A highly sensitive inhibition of enzyme immunoassay was developed to detect and quantities low levels of P₂ By this assay, P₂ was found to be most concentrated in peripherai nerves. with decreasing amounts found in the spinal cord, medulla oblongata, pons, cerebellum, and cerebral peduncle. No P₂ was found in the thalamus, cerebrum, or optic nerve; however, low levels of P₂ were detected in the adrenal meaulla, a non-neural tissue composed largely of cells derived from the embryonic neural crest region.     

Stimulation of 5-hydroxytryptamine nerve cells in dorsal and median raphe nuclei elevates blood glucose in rats

The role played by dorsal or median raphe nuclei in glucoregulation was investigated by stimulating these nuclei in normal rats and in rats with chemical ablation of the hydroxytryptamine (5-HT) nerve cells in these nuclei. Electrical stimulation of either dorsal or median raphe nuclei increased blood glucose or the in vivo voltammetric signal of hypothalamic 5-OH-indole in normal rats; the increase in blood glucose level or the hypothalamic 5-OH-indole release was proportional to the intensity of stimulation. Microinjection of kainic acid or l-glutamate at the same sites also produced hyperglycemia or stimulated the hypothalamic 5-OH-indole release. This stimulation-induced hyperglycemia was significantly reduced by pretreatment of animals with spinal transection or adrenalectomy. In addition, selective destruction of the hypothalamic 5-HT nerve fibers, produced by administration of 5,7-di-hydroxytryptamine (a 5-HT nerve depletor) into both dorsal and median raphe regions, reduced the magnitude of the hyperglycemic responses to electrical stimulation of either dorsal or median raphe nuclei. The data indicate that stimulation of ascending 5-HT pathways in the rat's brain increases the adrenal-sympathetic efferent activity and leads to hyperglycemia.     

Participation of ventrolateral medullary neurons in the renal-sympathetic reflex in rabbits

In an effort to locate medullary structures that mediate the renal-sympathetic reflex, the effect, on the excitatory (E) and inhibitory (I) components of that reflex, of certain drugs applied to the ventral surface of the medulla was investigated in urethane-anesthetized and vagotomized rabbits. Application of bicuculline, a GABA receptor antagonist, selectively abolished the I component of the renal-sympathetic reflex as well as the sympathoinhibition elicited by stimulation of the aortic nerve. The E component, on the other hand, was specifically eliminated by kynurenic acid, a glutamate receptor antagonist. Strychnine or atropine sulfate did not affect either reflex appreciably. Subsequently, within the region of the ventrolateral medulla (VLM) subjacent to the site of drug applications, we searched for neurons which responded to stimulation of the renal nerve and/or the aortic nerve. Of 68 responsive VLM neurons found, 50 (73.5%) responded to stimulation of both nerves. Of the 50 neurons, 40 were tested for their antidromic activation to stimulation of the spinal cord. Twenty-four neurons (60%) were antidromically activated. Responses of these reticulospinal neurons to stimulation of the renal nerve preceded that of renal nerve activity (RNA) by about 100 ms. All the antidromically activated, VLM neurons which responded to stimulation of the renal nerve also responded to stimulation of the aortic nerve. In conclusion, the renal-sympathetic reflex appears to be mediated by the same pool of bulbospinal neurons in the ventrolateral medulla that mediates the arterial baroreceptor reflex, and the E and I components of that reflex can be selectively abolished by pharmacological intervention of the subjacent ventral surface of the medulla.     

Connections of the caudal ventrolateral medullary reticular formation in the cat brainstem

 A region of the caudal ventrolateral medullary reticular formation (CVLM) participates in baroreceptor, vestibulosympathetic, and somatosympathetic reflexes; the adjacent retroambigual area is involved in generating respiratory-related activity and is essential for control of the upper airway during vocalization. However, little is known about the connections of the CVLM in the cat. In order to determine the locations of terminations of CVLM neurons, the anterograde tracers Phaseolus vulgaris leucoagglutinin and tetramethylrhodamine dextran amine were injected into this region. These injections produced a dense concentration of labeled axons throughout the lateral medullary reticular formation (lateral tegmental field), including the retrofacial nucleus and nucleus ambiguus, regions of the rostral ventrolateral medulla, the lateral and ventrolateral aspects of the hypoglossal nucleus, nucleus intercalatus, and the facial nucleus. A smaller number of labeled axons were located in the medial, lateral, and commissural subnuclei of nucleus tractus solitarius, the A5 region of the pontine reticular formation, the ventral and medial portions of the spinal and motor trigeminal nuclei, locus coeruleus, and the parabrachial nucleus. We confirmed the projection from the CVLM to both the rostral ventrolateral medulla and lateral tegmental field using retrograde tracing. Injections of biotinylated dextran amine or Fluorogold into these regions resulted in retrogradely labeled cell bodies in the CVLM. However, the neurons projecting to the lateral tegmental field were located mainly dorsal to those projecting to the rostral ventrolateral medulla, suggesting that these neurons form two groups, possibly with different inputs. Injections of retrograde tracers into the lateral tegmental field and rostral ventrolateral medulla also produced labeled cell bodies in other regions, including the medial and inferior vestibular nuclei and nucleus solitarius. These data are consistent with the view that the CVLM of the cat is a multifunctional area that regulates blood pressure, produces vocalization, affects the shape of the oral cavity, and elicits contraction of particular facial muscles. Received: 18 February 1997 / Accepted: 27 March 1997     

Serotonin(3) receptor stimulation in the nucleus tractus solitarii activates non-catecholaminergic neurons in the rat ventrolateral medulla

The present study was performed to determine whether or not the increased arterial pressure triggered by 5-HT(3) receptor stimulation in the nucleus tractus solitarii and underlain by a sympathoexcitation is associated with the activation of ventromedullary cells known to be involved in vascular regulation, i.e. the C1 and A1 catecholaminergic cells. For this purpose, double immunohistochemical labeling for tyrosine hydroxylase and c-fos protein was performed all along the ventrolateral medulla after microinjection of 1-(m-chlorophenyl)-biguanide, a selective and potent 5-HT(3) receptor agonist, into the nucleus tractus solitarii of alpha-chloralose/urethane-anaesthetized rats. This treatment produced a significant elevation of arterial pressure ( approximately +35 mm Hg). Concomitantly, a significant increase in the number of c-fos expressing neurons was observed in the rostral ventrolateral medulla (+63%), in particular in its most anterior part (+78%), and in the medullary region surrounding the caudal part of the facial nucleus (+91%). Retrograde labeling with gold-horseradish peroxidase complex showed that at least some of these activated c-fos expressing cells project to the spinal cord. However, the number of double-stained neurons, i.e. c-fos and tyrosine hydroxylase positive neurons, did not increase at any level of the ventrolateral medulla. In contrast, under the same alpha-chloralose/urethane anesthesia, systemic infusion of sodium nitroprusside appeared to produce a hypotension and a marked increase in the density of such double c-fos and tyrosine hydroxylase expressing cells in the rostral ventrolateral medulla and the caudal medullary region surrounding the caudal part of the facial nucleus.These data indicate that medullary catecholaminergic C1 and A1 neurons are not involved in the pressor effect elicited by 5-HT(3) receptor stimulation in the nucleus tractus solitarii. However, this 5-HT(3) receptor-mediated effect is clearly associated with the excitation of (non-catecholaminergic) neurons within the pressor region of the ventral medulla.