Rostral Raphe Pallidus Research Articles

Dorsomedial hypothalamic and brainstem pathways controlling thermogenesis in brown adipose tissue

1. The rostral medullary raphe pallidus contains sympathetic premotor neurons controlling thermogenesis in brown adipose tissue (BAT). 2. Disinhibition of neurons in the dorsomedial hypothalamus (DMH) stimulates BAT thermogenesis through activation of neurons in raphe pallidus. 3. An increase in BAT sympathetic outflow and BAT thermogenesis following microinjection of prostaglandin E2 into the preoptic area requires activation of both DMH neurons and raphe pallidus neurons. 4. DMH contains a population of neurons receiving a tonically- active GABAergic inhibition which mediate increases in BAT thermogenesis through stimulation of BAT sympathetic premotor neurons in raphe pallidus.

Identification of sympathetic premotor neurons in medullary raphe regions mediating fever and other thermoregulatory functions.

Sympathetic premotor neurons directly control sympathetic preganglionic neurons (SPNs) in the intermediolateral cell column (IML) of the thoracic spinal cord, and many of these premotor neurons are localized in the medulla oblongata. The rostral ventrolateral medulla contains premotor neurons controlling the cardiovascular conditions, whereas rostral medullary raphe regions are a candidate source of sympathetic premotor neurons for thermoregulatory functions. Here, we show that these medullary raphe regions contain putative glutamatergic neurons and that these neurons directly control thermoregulatory SPNs. Neurons expressing vesicular glutamate transporter 3 (VGLUT3) were distributed in the rat medullary raphe regions, including the raphe magnus and rostral raphe pallidus nuclei, and mostly lacked serotonin immunoreactivity. These VGLUT3-positive neurons expressed Fos in response to cold exposure or to central administration of prostaglandin E2, a pyrogenic mediator. Transneuronal retrograde labeling after inoculation of pseudorabies virus into the interscapular brown adipose tissue (BAT) or the tail indicated that those VGLUT3-expressing medullary raphe neurons innervated these thermoregulatory effector organs multisynaptically through SPNs of specific thoracic segments, and microinjection of glutamate into the IML of the BAT-controlling segments produced BAT thermogenesis. An anterograde tracing study further showed a direct projection of those VGLUT3-expressing medullary raphe neurons to the dendrites of SPNs. Furthermore, intra-IML application of glutamate receptor antagonists blocked BAT thermogenesis triggered by disinhibition of the medullary raphe regions. The present results suggest that VGLUT3-expressing neurons in the medullary raphe regions constitute excitatory neurons that could be categorized as a novel group of sympathetic premotor neurons for thermoregulatory functions, including fever.

Medullary pathways mediating specific sympathetic responses to activation of dorsomedial hypothalamus

We sought to determine which medullary sympathetic premotor neurons mediate the cardiovascular and thermogenic effects resulting from activation of neurons in the dorsomedial hypothalamus (DMH) in urethane/chloralose-anesthetized, artificially ventilated rats. Unilateral disinhibition of neurons in the DMH with microinjection of bicuculline (2 mM, 30 nl) caused significant increases in brown adipose tissue sympathetic nerve activity (BAT SNA, +828±169% of control, n=16), cardiac SNA (+516±82% of control, n=16), renal SNA (RSNA, +203±25% of control, n=28) and, accompanied by increases in BAT temperature (+1.6±0.3 °C, n=11), end-tidal CO 2 (+0.7±0.1%, n=15), heart rate (+113±7 beats/min, n=32), arterial pressure (+19±2 mm Hg, n=32) and plasma epinephrine and norepinephrine concentrations. Inhibition of neurons in the rostral raphe pallidus (RPa) with microinjection of muscimol (6 mM, 60 nl) abolished the increases in BAT SNA and BAT temperature and reduced the tachycardia induced by disinhibition of DMH neurons. Inhibition of neurons in the RVLM with microinjection of muscimol (6 mM, 60 nl) markedly reduced the increase in RSNA, but did not affect the evoked tachycardia or the increase in arterial pressure. Combined glutamic acid decarboxylase (GAD-67) immunocytochemistry and pseudorabies viral retrograde tracing from BAT indicated close appositions between GABAergic terminals and DMH neurons in sympathetic pathways to BAT. In conclusion, these results demonstrate the existence of a tonically active, GABAergic inhibitory input to neurons in the DMH and that blockade of this inhibition increases sympathetic outflow to thermogenic and cardiovascular targets by activating functionally specific populations of sympathetic premotor neurons: the excitation of BAT SNA and BAT thermogenesis is mediated through putative sympathetic premotor neurons in the RPa, while the activation in RSNA is dependent on those in RVLM. These data increase our understanding of the central pathways mediating changes in sympathetically mediated thermogenesis that is activated in thermoregulation, stress responses and energy balance.

Excitatory amino acid receptor activation in the raphe pallidus area mediates prostaglandin-evoked thermogenesis

To investigate the role of excitatory amino acid neurotransmission within the rostral raphe pallidus area (RPa) in thermogenic and cardiovascular responses, changes in sympathetic nerve activity to brown adipose tissue (BAT), BAT temperature, expired CO 2, arterial pressure, and heart rate were recorded after microinjection of excitatory amino acid (EAA) receptor agonists into the RPa in urethan-chloralose-anesthetized, ventilated rats. To determine whether EAA neurotransmission within the RPa is necessary for the responses evoked by disinhibition of the RPa or by prostaglandin E 2 acting within the medial preoptic area, BAT sympathetic nerve activity, BAT temperature, expired CO 2, arterial pressure, and heart rate were measured during these treatments both before and after blockade of EAA receptors within the RPa. Microinjection of EAA receptor agonists into the RPa resulted in significant increases in all measured variables; these increases were attenuated by prior microinjection of the respective EAA receptor antagonists into the RPa. Microinjection of prostaglandin E 2 into the medial preoptic area or microinjection of bicuculline into the RPa resulted in respective significant increases in BAT sympathetic nerve activity (+approximately 190% and +approximately 235% of resting levels), in BAT temperature (approximately 1.8 °C and approximately 2 °C), in expired CO 2 (approximately 1.1% and approximately 1.1%), and in heart rate (approximately 97 beats per minute (bpm) and approximately 100 bpm). Blockade of ionotropic EAA receptors within the RPa by microinjection of kynurenate completely reversed the prostaglandin E 2 or bicuculline-evoked increases in all of the measured variables. Blockade of either N-methyl- d-aspartate (NMDA) receptors or non-NMDA receptors alone resulted in marked attenuations of the prostaglandin E 2-evoked effects on all of the measured variables. These data demonstrate that activation of an EAA input to the RPa is necessary for the BAT thermogenic and the cardiovascular effects resulting from the actions of prostaglandin E 2 within the medial preoptic area or from the disinhibition of local neurons in the RPa.

Raphe pallidus neurons mediate prostaglandin E 2-evoked increases in brown adipose tissue thermogenesis

To elucidate central neural pathways contributing to the febrile component of the acute phase response to pyrogenic insult, I sought to determine whether activation of neurons in the rostral raphe pallidus (RPa) is required for the increase in brown adipose tissue (BAT) thermogenesis evoked by i.c.v. prostaglandin E 2 (PGE 2) in urethane-chloralose-anesthetized, ventilated rats. BAT sympathetic nerve activity (SNA; +224% of control), BAT temperature (+1.8 °C), expired CO 2 (+1.3%), mean arterial pressure (+23 mm Hg), and heart rate (+73 beats per minute) were significantly increased after i.c.v. PGE 2 (2 μg). Microinjection of either the GABA A receptor agonist, muscimol (2 mM, 60 nl), or glycine (0.5M, 60 nl) into RPa resulted in a prompt reversal of the PGE 2-evoked stimulation of BAT SNA, BAT thermogenesis and heart rate, with these variables returning to control levels prior to i.c.v. PGE 2 following the long-lasting, muscimol-induced inhibition of RPa neurons. In conclusion, activation of neurons in RPa, possibly BAT sympathetic premotor neurons, is essential for the increases in BAT SNA and BAT thermogenesis stimulated by i.c.v. administration of PGE 2. The increased heart rate likely contributing to an augmented cardiac output supporting the increased BAT thermogenesis in response to PGE 2 is also dependent on neurons in RPa. These results contribute to our understanding of central neural substrates for the augmented thermogenesis during fever.

Disinhibition of rostral raphe pallidus neurons increases cardiac sympathetic nerve activity and heart rate

We determined the cardiovascular effects of microinjecting the GABA A receptor antagonist, bicuculline, into the rostral raphe pallidus (RPa) on arterial pressure (AP), heart rate (HR) and cardiac sympathetic nerve activity (CSNA) in urethane–chloralose anesthetized, artificially-ventilated rats. In 26 animals, microinjection of the GABA A receptor antagonist, bicuculline (2 mM, 30 nl), into RPa increased CSNA (+234±64% of control), HR (+91±10 bpm) and mean AP (+16±3 mmHg). A similar tachycardia was evoked after removal of both adrenal glands, but was absent after β-adrenergic receptor blockade with atenolol. Equivalent percentage increases in CSNA and HR were evoked by disinhibition of the rostral RPa neurons after inhibition of cardiovascular sympathetic premotor neurons in the rostral ventrolateral medulla (RVLM) with bilateral microinjections of the GABA A receptor agonist, muscimol (6 mM, 50 nl) which markedly lowered CSNA, HR and AP. These results indicate that RPa contains a population of neurons, possibly sympathetic premotor neurons with direct projections to spinal cardiac sympathetic preganglionic neurons, that receive a tonic, GABAergic inhibition and thus do not contribute markedly to resting levels of CSNA and HR, but when disinhibited, they can produce large increases in CSNA and HR comparable to those seen during certain stress responses.

The rostral raphe pallidus nucleus mediates pyrogenic transmission from the preoptic area.

Fever is the widely known hallmark of disease and is induced by the action of the nervous system. It is generally accepted that prostaglandin (PG) E(2) is produced in response to immune signals and then acts on the preoptic area (POA), which triggers the stimulation of the sympathetic system, resulting in the production of fever. Actually, the EP3 subtype of PGE receptor, which is essential for the induction of fever, is known to be localized in POA neurons. However, the neural pathway mediating the pyrogenic transmission from the POA to the sympathetic system remains unknown. To identify the neuronal groups involved in the fever-inducing pathway, we first investigated Fos expression in medullary regions of rats after central administrations of PGE(2). PGE(2) application to the lateral ventricle or directly to the POA strikingly increased the number of Fos-positive neurons in the rostral part of the raphe pallidus nucleus (rRPa). Most of these neurons did not exhibit serotonin immunoreactivity. Microinjection of muscimol, a GABA(A) receptor agonist, into the rRPa blocked fever and thermogenesis in brown adipose tissue induced by intra-POA as well as by intracerebroventricular PGE(2) applications. Furthermore, neural tract tracing studies revealed a direct projection from EP3 receptor-expressing POA neurons to the rRPa. Our results demonstrate that the rRPa, which has never been associated with the fever mechanism, mediates the pyrogenic neurotransmission from the POA to the peripheral sympathetic effectors contributing to fever development.

The Rostral Raphe Pallidus Nucleus Mediates Pyrogenic Transmission from the Preoptic Area

Fever is the widely known hallmark of disease and is induced by the action of the nervous system. It is generally accepted that prostaglandin (PG) E(2) is produced in response to immune signals and then acts on the preoptic area (POA), which triggers the stimulation of the sympathetic system, resulting in the production of fever. Actually, the EP3 subtype of PGE receptor, which is essential for the induction of fever, is known to be localized in POA neurons. However, the neural pathway mediating the pyrogenic transmission from the POA to the sympathetic system remains unknown. To identify the neuronal groups involved in the fever-inducing pathway, we first investigated Fos expression in medullary regions of rats after central administrations of PGE(2). PGE(2) application to the lateral ventricle or directly to the POA strikingly increased the number of Fos-positive neurons in the rostral part of the raphe pallidus nucleus (rRPa). Most of these neurons did not exhibit serotonin immunoreactivity. Microinjection of muscimol, a GABA(A) receptor agonist, into the rRPa blocked fever and thermogenesis in brown adipose tissue induced by intra-POA as well as by intracerebroventricular PGE(2) applications. Furthermore, neural tract tracing studies revealed a direct projection from EP3 receptor-expressing POA neurons to the rRPa. Our results demonstrate that the rRPa, which has never been associated with the fever mechanism, mediates the pyrogenic neurotransmission from the POA to the peripheral sympathetic effectors contributing to fever development.

Differential regulation of sympathetic outflows to vasoconstrictor and thermoregulatory effectors.

The medullary premotor neurons determining the sympathetic outflow regulating cardiac function and vasoconstriction are located in the rostral ventrolateral medulla (RVLM). The present study sought evidence for differential characteristics and baroreceptor reflex sensitivities between the sympathetic nerve activity (SNA) controlling brown adipose tissue (BAT) metabolism and thermogenesis and cardiovascular SNA such as that controlling mesenteric vasoconstriction via the splanchnic (SPL) nerve. The tonic discharge of sympathetic nerves is determined by the inputs to functionally specific sympathetic preganglionic neurons from supraspinal populations of premotor neurons. Under normothermic conditions, BAT SNA was nearly silent, while SPL SNA exhibited sustained, large-amplitude bursts. Disinhibition of neurons in the rostral raphe pallidus (RPa), a potential site of sympathetic premotor neurons controlling BAT SNA, or icv injection of prostaglandin E2, a pyrogenic stimulus, elicited a dramatic increase in BAT SNA. SPL SNA was strongly influenced by the baroreceptor reflex as indicated by a high coherence to the arterial pressure, while activated BAT SNA exhibited no correlation with the arterial pressure. Since these characteristics and reflex responses in sympathetic outflow have been shown to arise from the ongoing or altered discharge of sympathetic premotor neurons, the marked differences between SPL SNA and BAT SNA provide strong evidence supporting the hypothesis that vasoconstriction and thermogenesis (metabolism) are controlled by distinct populations of sympathetic premotor neurons, the former in the RVLM and strongly baroreceptor-modulated and the latter potentially in the RPa exhibiting little influence of baroreceptor reflex activation.

Differential regulation of brown adipose and splanchnic sympathetic outflows in rat: roles of raphe and rostral ventrolateral medulla neurons.

1. The medullary premotor neurons determining the sympathetic outflow regulating cardiac function and vasoconstriction are located in the rostral ventrolateral medulla (RVLM). The present study sought evidence for an alternative location for the sympathetic premotor neurons determining the sympathetic nerve activity (SNA) controlling brown adipose tissue (BAT) metabolism and thermogenesis. 2. The tonic discharge on sympathetic nerves is determined by the inputs to functionally specific sympathetic preganglionic neurons from supraspinal populations of premotor neurons. Under normothermic conditions, BAT SNA was nearly silent, while splanchnic (SPL) SNA, controlling mesenteric vasoconstriction, exhibited sustained large-amplitude bursts. 3. The rostral raphe pallidus (RPa) contains potential sympathetic premotor neurons that project to the region of sympathetic preganglionic neurons in the thoracic spinal cord. Disinhibition of neurons in RPa elicited a dramatic increase in BAT SNA, with only a small rise in SPL SNA. 4. Splanchnic SNA was strongly influenced by the baroreceptor reflex, as indicated by a high coherence with the arterial pressure wave, a significant amplitude modulation over the time-course of the cardiac cycle and a marked inhibition of SPL SNA during a sustained increase in arterial pressure. When activated, the bursts in BAT SNA exhibited no correlation with arterial pressure and were not affected by increases in arterial pressure. 5. Because these characteristics and reflex responses in sympathetic outflow have been shown to arise from the on-going or altered discharge of sympathetic premotor neurons, the marked differences between SPL and BAT SNA provide strong evidence supporting the hypothesis that vasoconstriction and thermogenesis (metabolism) are controlled by distinct populations of sympathetic premotor neurons, the former in the RVLM and the latter, potentially, in the RPa.

RVLM and raphe differentially regulate sympathetic outflows to splanchnic and brown adipose tissue.

To determine whether neurons in the rostral raphe pallidus (RPa) specifically control the sympathetic nerve activity to brown adipose tissue (BAT SNA), thereby regulating adipocyte metabolism and BAT thermogenesis, the responses in BAT SNA to disinhibition of RPa neurons and to disinhibition of neurons in the vasomotor region of the rostral ventrolateral medulla (RVLM) were compared with those in splanchnic (Spl) SNA, which primarily regulates visceral vasoconstriction. In urethan-chloralose-anesthetized ventilated rats, both acute hypothermia and microinjection of bicuculline into RPa produced significantly larger increases in BAT SNA (542 and 1,949% of control) than in Spl SNA (19 and 24% of control). The enhanced burst discharge in BAT SNA was not coherent with that in Spl SNA or with the arterial pressure (AP) at any frequency except the central respiratory frequency. Microinjections of bicuculline into RVLM evoked increases in Spl SNA (86% of control) and AP (32 mmHg), but reduced BAT SNA to low, normothermic levels. Microinjections of muscimol into RVLM reduced Spl SNA (-82% of control) and AP (-59 mmHg), but did not prevent the increase in BAT SNA after disinhibition of RPa neurons. These results indicate that the neural networks generating BAT SNA in response to disinhibition of RPa neurons are independent of those generating basal Spl SNA and support a model in which sympathetic outflow to tissues involved in thermoregulation and metabolism is regulated by central pathways, including neurons in RPa, that are distinct from those involved in the sympathetic control of the cardiovascular system.

GABA-mediated inhibition of raphe pallidus neurons regulates sympathetic outflow to brown adipose tissue.

Sympathetic nerve activity to brown adipose tissue (BAT) regulates adipocyte metabolism of its stored lipid fuel and thus the thermogenesis in BAT. To determine if the discharge of neurons in the rostral raphe pallidus (RPa) can influence BAT thermogenesis, changes in sympathetic nerve activity to BAT were recorded after microinjection (60 nl) of the GABAA receptor antagonist bicuculline (500 microM) into the RPa in chloralose-urethan-anesthetized, ventilated rats. Bicuculline caused a large, rapid rise in the sympathetic nerve activity to BAT (which had also increased during acute hypothermia) from very low, normothermic control levels to maximum values (mean: 1,949 +/- 604% control; n = 13) after 4-6 min. The sympathetic nerve discharge to BAT had a mean burst frequency (3. 5 +/- 0.3 Hz) that was significantly less than the heart rate (7.3 +/- 0.2 beats/min), and it was not inhibited during baroreceptor reflex activation. Bicuculline-stimulated increases in the sympathetic nerve activity to BAT and cold-evoked increases in neuronal fos expression were localized to the RPa at the level of the caudal half of the facial nucleus. This dramatic increase in sympathetic nerve activity to BAT after disinhibition of neurons in rostral RPa is consistent with a major role for RPa neurons, perhaps as sympathetic premotoneurons for BAT, in medullary control of BAT thermogenesis.

Afferent projections to the rat nuclei raphe magnus, raphe pallidus and reticularis gigantocellularis pars α demonstrated by iontophoretic application of choleratoxin (subunit b)

The aim of the present study was to identify the specific afferent projections to the rostral and caudal nucleus raphe magnus, the gigantocellular reticular nucleus pars α and the rostral nucleus raphe pallidus. For this purpose, small iontophoretic injections of the sensitive retrograde tracer choleratoxin (subunit b) were made in each of these structures. In agreement with previous retrograde studies, after all injection sites, a substantial to large number of labeled neurons were observed in the dorsal hypothalamic area and dorsolateral and ventrolateral parts of the periaqueductal gray, and a small to moderate number were found in the lateral preoptic area, bed nucleus of the stria terminalis, paraventricular hypothalamic nucleus, central nucleus of the amygdala, lateral hypothalamic area, parafascicular area, parabrachial nuclei, subcoeruleus area and parvocellular reticular nucleus. In addition, depending on the nucleus injected, we observed a variable number of retrogradely labeled cells in other regions. After injections in the rostral nucleus raphe magnus, a large number of labeled cells were seen in the prelimbic, infralimbic, medial and lateral precentral cortices and the dorsal part of the periaqueductal gray. In contrast, after injections in the other nuclei, fewer cells were localized in these structures. Following raphe pallidus injections, a substantial to large number of labeled cells were observed in the medial preoptic area, median preoptic nucleus, ventromedial part of the periaqueductal gray, Kölliker-Fuse and lateral paragigantocellular reticular nuclei. Following injections in the other areas, a small to moderate number of cells appeared. After gigantocellular reticular pars α injections, a very large and substantial number of labeled neurons were found in the deep mesencephalic reticular formation and oral pontine reticular nucleus, respectively. After the other injections, fewer cells were seen. Following rostral raphe magnus or raphe pallidus injections, a substantial number of labeled cells were observed in the insular and perirhinal cortices. Following caudal raphe magnus or gigantocellular reticular pars α injections, fewer cells were found. After raphe magnus or gigantocellular reticular pars α injections, a moderate to substantial number of cells were localized in the fields of Forel, lateral habenular nucleus and ventral caudal pontine reticular nucleus. Following raphe pallidus injections, only a small number of cells were seen. Our data indicate that the rostral and caudal parts of the nucleus raphe magnus, the gigantocellular reticular nucleus pars α and the nucleus raphe pallidus receive afferents of comparable strength from a large number of structures. In addition, a number of other afferents give rise to stronger inputs to one or two of the four nuclei studied. Such differential inputs might be directed to populations of neurons with different physiological roles previously recorded specifically in these nuclei.

Immunocytochemical studies of the 5-HT1A receptor in ventral medullary neurons that project to the intermediolateral cell column and contain serotonin or tyrosine hydroxylase immunoreactivity

Activation of serotonin-1A receptors (5-HT(1A)R) in the medulla oblongata lowers sympathetic nerve discharge and blood pressure. Binding sites for 5-HT(1A)R ligands are present in ventral medullary nuclei [e.g., rostral ventrolateral medulla (RVLM), raphe pallidus (RPa), and parapyramidal region (PPR)] that project to sympathetic preganglionic neurons in the intermediolateral cell column (IML). However, the projections and the neurochemical contents of the ventral medullary neurons that are likely to be involved in the hypotensive actions of 5-HT(1A) agonists are unclear. Using a sheep antibody to a fragment of the third intracellular loop of the 5-HT(1A)R, we localized 5-HT(1A)R immunoreactivity (ir) to IML-projecting neurons that were retrogradely labeled with rhodamine beads injected into the IML of adult male rats. The percentages of IML-projecting neurons containing 5-HT(1A)R-ir were 49% in RPa, 34% in PPR, and 44% in RVLM. Using multiple-immunofluorescence labeling, we also demonstrated 5-HT(1A)R-ir in serotonergic (5-HT) and in catecholaminergic (tyrosine hydroxylase; TH-ir) neurons of the ventral medulla. The percentages of 5-HT-ir neurons containing 5-HT(1A)R-ir were 28% in RPa, 18% in PPR, and 31% in raphe obscurus. In addition, 5-HT(1A)R-ir was present in 14% of TH-ir neurons of the RVLM. Moreover, some IML-projecting neurons in the PPR and RPa were doubly immunolabeled for 5-HT(1A)R-ir and 5-HT, and some IML-projecting neurons in the RVLM were doubly immunolabeled for 5-HT(1A)R-ir and TH-ir. These data provide anatomical evidence for the presence of 5-HT(1A)R on serotonergic and catecholaminergic bulbospinal neurons and for their potential role in directly modifying the activity of these ventral medullary neurons.

211 NMDA receptor-dependent activation of map kinase in cultured rat hippocampal neurons

Disinhibition of DMH neurons with the GABAA receptor antagonist, bicuculline, increases heart rate (HR) and augments both brown adipose tissue sympathetic nerve activity (BAT SNA) and renal SNA (RSNA) contributing to the evoked increases in BAT thermogenesis and arterial pressure (AP). We determined the role of glutamate receptor activation in the rostral raphe pallidus (RPa) in mediating the sympathoexcitatory responses in HR, BAT SNA and RSNA following disinhibition of DMH neurons in urethane/chloralose anesthetized, artificially ventilated rats. Microinjections of either the selective NMDA receptor agonist, NMDA, or the selective non-NMDA receptor agonist, kainic acid (KA), into the RPa produced increases in BAT SNA (peak: +502% and +408% of control, respectively) and BAT temperature (peak: +0.6 °C and +1.0 °C) accompanied by rises in HR (peak: +38 and +63 bpm), RSNA (peak: +57% and +58% of control) and MAP (peak: +12 and 15 mmHg). These responses were reversed by subsequent microinjection into RPa of the respective selective glutamate receptor antagonists, AP5 and CNQX. Microinjections of the non-selective glutamate receptor antagonist, kynurenic acid (Kyn), the NMDA receptor antagonist, AP5, or the non-NMDA receptor antagonist, CNQX, were effective in reversing the increases in BAT SNA (for Kyn, from peak of +419% of control to +9% of control) and BAT temperature, but not those in HR, MAP or RSNA (for Kyn, from peak of +143% of control to +124% of control) evoked by unilateral microinjection of bicuculline into the DMH. These results indicate that both NMDA and non-NMDA glutamate receptors in the RPa play a significant role in mediating the excitatory synaptic transmission producing the activation of BAT thermogenesis following disinhibition of DMH neurons. Glutamate receptors in the RPa may not be important for transmitting cardiovascular responses induced by activation of the DMH neurons.

Catecholaminergic input to spinally projecting serotonin neurons in the rostral ventromedial medulla oblongata of the rat

The midline of the rostral ventral medulla (RVM) is the portion in which many serotonin (5-HT) neurons of the nucleus raphe magnus and the rostral nucleus raphe pallidus are located and where dense catecholaminergic (CA) fibers are distributed. In this study, we investigated the connection between spinally projecting 5-HT neurons and CA fibers in the rat RVM by light and electron microscopic immunocytochemistry. First, light microscopic immunocytochemistry using a triple labeling method revealed that the 5-HT-immunoreactive (IR) neuron containing retrograde tracer from the cervical cord was intimately surrounded by tyrosine hydroxylase (TH)-IR fibers. Second, silver-gold intensified TH-IR axon terminals were found to make synaptic contacts with 5-HT-IR neuronal perikarya and dendrites by double labeling immunoelectron microscopy. These morphological findings suggest that spinally projecting 5-HT neurons, presumed to be involved in pain modulation or sympathetic autonomic control, are directly regulated by CA neurons at the level of the RVM.

Evidence for projections from the rostral medullary raphe onto medullary catecholamine neurons in the rat

Following the iontophoretic deposition of Phaseolus vulgaris leucoagglutinin (PHA-L) into the rostral medullary raphe, which included portions of the caudal nucleus raphe magnus, rostral nucleus raphe pallidus, rostral nucleus raphe obscurus and rostral nucleus reticularius paragigantocellularis, two-color immunoperoxidase staining was employed to demonstrate continguity between PHA-L-immunoreactive (PHA-LI) varicose fibers and boutons and medullary catecholamine (CA) cells. Raphe projections were contiguous with phenylethanolamine N-methyltransferase-immunoreactive (PNMTI) neurons in the C1, C2 and C3 cell groups and with tyrosine hydroxylase-immunoreactive (THI) neurons in the A1 and A2 cell groups. Contiguity between PHA-LI processes and medullary CA cells was observed most frequently in the C1 cell group. Preliminary findings of this study have been presented previously.