Glutamatergic vestibular neurons express Fos after vestibular stimulation and project to the NTS and the PBN in rats

In this study, retrograde tracing method combined with phosphate-activated glutaminase (PAG) and Fos immunofluorescence histochemistry was used to identify glutamatergic vestibular nucleus (VN) neurons receiving vestibular inputs and projecting to the nucleus of the solitary tract (NTS) and the parabrachial nucleus (PBN). Conscious animals were subjected to 120 min Ferris-wheel like rotation stimulation. Neuronal activation was assessed by Fos expression in the nucleus of VN neurons. After Fluoro-gold (FG) injection into the caudal NTS, approximately 48% FG-labeled VN neurons were immunoreactive for PAG, and about 14% PAG/FG double-labeled neurons co-existed with Fos. Following FG injection into the PBN, approximately 56% FG-labeled VN neurons were double-labeled with PAG, and about 12% of the PAG/FG double-labeled neurons also expressed Fos. Careful examination of the typology and distribution pattern of these PAG-immunoreactive neurons indicated that the vast majority of these neurons were glutamatergic rather than GABAergic. These results suggest that PAG-immunoreactive VN neurons might constitute excitatory glutamatergic VN-NTS and VN-PBN transmission pathways and these pathways might be involved in vestibulo-autonomic reflexes during vestibular stimulation.     

Noradrenergic inputs to the paraventricular hypothalamus contribute to hypothalamic-pituitary-adrenal axis and central Fos activation in rats after acute systemic endotoxin exposure

Noradrenergic (NA) neurons within the nucleus of the solitary tract (NST) and caudal ventrolateral medulla (VLM) innervate the hypothalamic paraventricular nucleus (PVN) to initiate and modulate hypothalamic-pituitary-adrenal (HPA) axis responses to interoceptive stress. Systemic endotoxin (i.e. bacterial lipopolysaccharide, LPS) activates NA neurons within the NST and VLM that project to the PVN and other brain regions that receive interoceptive signals. The present study examined whether NA neurons with axonal inputs to the PVN are necessary for LPS to activate Fos expression within the PVN and other interoceptive-related brain regions, and to increase plasma corticosterone. Male Sprague-Dawley rats received bilateral stereotaxic microinjections of DSAP (saporin toxin conjugated to an antibody against dopamine-beta-hydroxylase, DbH) into the PVN to destroy NA inputs. Control rats were microinjected with vehicle into the PVN or received no PVN injections. Two weeks later, DSAP and control rats were injected i.p. with LPS (200 microg/kg BW) or saline vehicle, and perfused with fixative 2.5-3 h later. Brain tissue sections were processed to reveal nuclear Fos protein and cytoplasmic DbH immunolabeling. DSAP lesions depleted NA terminals in the PVN and bed nucleus of the stria terminalis, reduced the number of NA cell bodies in the NST and VLM, attenuated PVN Fos activation after LPS, and attenuated LPS-induced increases in plasma corticosterone. These findings support the view that NA projections from hindbrain to hypothalamus are necessary for a full HPA axis response to systemic immune challenge.     

Projections from the nucleus of the solitary tract in the rat

The axonal projections of neurons in and near the nucleus of the solitary tract have been visualized using titrated amino acid autoradiography. Axons of neurons of this nucleus ramify extensively within the nucleus itself, but much less so in the nucleus commissuralis. They also enter cranial motor nuclei within the medulla. Axons originating in the anterior part of the nucleus of the solitary tract extend to the hypoglossal, facial and probably trigeminal motor nuclei, but not to the dorsal motor nucleus of the vagus or the nucleus ambiguus. The posterior part of the nucleus of the solitary tract projects to all these motor nuclei. In the spinal cord solitary nucleus axons remain in the medial gray directly caudal to the solitary nucleus itself. The distribution becomes very weak by C₃ after some fibers spread laterally into the caudal trigeminal nucleus. Fibers are labeled in the contralateral ventral columns, but they could not be unequivocably attributed to solitary neurons. Axons ascending from the nucleus of the solitary tract extend no further rostrally than the pons, where they terminate in the caudal end of the parabrachial nuclei.Although often treated as entirely separate systems, the present results indicate that secondary gustatory neurons in the anterior solitary nucleus and secondary visceral afferent neurons in the posterior solitary nucleus have very similar rostral and caudal projections. The pontine parabrachial nuclei, the rostral termination of solitary nucleus neurons, have extensive direct connections to the thalamus, the hypothalamus and the limbic forebrain. Assuming similar connections occur in other mammals, these findings establish the existence of di-synaptic visceral afferent access to the highest autonomic integrative centers in the brain.     

Contrasting effects of systemic and central sibutramine administration on the intake of a palatable diet in the rat

Sibutramine hydrochloride monohydrate is the only centrally active weight-modifying agent currently approved by the FDA for long-term use in the treatment of obesity. Systemic sibutramine treatment has been shown to reduce food intake in humans and rodent models in a manner that is consistent with the enhancement of satiety mechanisms. Although it is generally assumed that the hypophagic effects of the drug are mediated by actions within the brain, the locus or loci of these effects remains unclear. These experiments compared the effects of systemic and intracranial injections of sibutramine on the intake of a palatable diet in non-deprived animals. Consistent with prior reports, systemic injections of sibutramine hydrochloride (at 0, 0.5, 1.0, or 3.0 mg/kg sibutramine i.p.) dose-dependently reduced feeding on a high fat/high sucrose diet across a 2-h feeding session, but did not alter water intake or locomotor activity. In contrast, bilateral injections of sibutramine (at 0.0, 2.0, 4.0 and 10.0 μg/0.5 μl/side) into either the paraventricular nucleus of the hypothalamus (PVN) or the medial nucleus accumbens shell (ACb) significantly and dose-dependently increased food intake of the sweetened fat diet. ACb treatment also modestly inhibited locomotor behavior; intracranial injections had no effect on water consumption. These experiments are the first to suggest that sibutramine treatment may have distinct actions upon separate neural circuits that modulate food intake behavior in the rat.     

Anatomical interactions between the central amygdaloid nucleus and the hypothalamic paraventricular nucleus of the rat: a dual tract-tracing analysis

Axonal connections between the amygdala and the hypothalamic paraventricular nucleus were examined by combined anterograde-retrograde tract tracing. Iontophoretic injections of the retrograde tracer Fluorogold were placed in the paraventricular nucleus, and the anterograde tracer PHA-L in the ipsilateral central or medial amygdaloid nuclei. Single and double-label immunohistochemistry were used to detect tracers. Single label anterograde and retrograde tracing suggest limited evidence for direct connections between the central or medial amygdala and the paraventricular nucleus. In general, scattered PHA-L-positive terminals were seen in autonomic subdivisions of the paraventricular nucleus (lateral parvocellular, dorsal parvocellular and ventral medial parvocellular subnuclei) following central or medial amygdaloid nulcleus injection. Double-label studies indicate that central and medial amygdaloid nucleus efferents contact paraventricular nucleus -projecting cells in several forebrain nuclei. In the case of central nucleus injections, PHA-L positive fibers occasionally contacted Fluorogold-labeled neurons in the anteromedial, ventromedial and preoptic subnuclei of the bed nucleus of the stria terminalis. Overall, such contacts were quite rare, and did not occur in the bed nucleus of the stria terminalis regions showing greatest innervation by the central amygdaloid nucleus. In contrast, medial amygdala injections resulted in a significantly greater overlap of PHA-L labeling and Fluorogold-labeled neurons, with axosomatic appositions observed in medial divisions of the bed nucleus of the stria terminalis, anterior hypothalamic area and preoptic area. The results provide anatomical evidence that a substantial proportion of amygdaloid connections with hypophysiotrophic paraventricular nucleus neurons are likely multisynaptic, relaying in different subregions of the bed nucleus of the stria terminalis and hypothalamus.     

Neuropeptides in the human dorsal vagal complex: An immunohistochemical study

The distribution of twelve biologically active neuropeptides, i.e., thyrotropin-releasing hormone, corticotropin-releasing factor, pro-opiomelanocortin-derived peptides (adrenocorticotropic hormone, β-endorphin, α-melanocyte-stimulating hormone), leucine-enkephalin, dynorphin A, dynorphin B, cholecystokinin, substance P, galanin and calcitonin gene-related peptide, was examined by immunohistochemistry in the human dorsal vagal complex including the nucleus of the solitary tract, the dorsal motor nucleus of the vagus and the area postrema. Immunoreactivity of all the twelve neuropeptides was found widely distributed in the various subdivisions of the nucleus of the solitary tract, showing a unique distribution for every peptide. Neuronal cell bodies immunostained with leucine-enkephalin, galanin and dynorphin B were found in this region. There were no immunopositive perikarya for any of the peptides in the other structures studied. Fibers containing galanin, corticotropin-releasing factor, substance P, dynorphin B, thyrotropin-releasing hormone and calcitonin gene-related peptide were observed at a relatively high density in the nucleus of the solitary tract. In the same structure, a moderately dense network of fibers immunostained with dynorphin A, cholecystokinin and leucine-enkephalin, but only solitary pro-opiomelanocortin-derived peptides-containing fiber fragments were observed. In the dorsal motor nucleus of the vagus the most prominent network of fibers was found to contain thyrotropin-releasing hormone, galanin and substance P. In contrast to these, no β-endorphin immunoreactivity was detected. The area postrema contained only moderate to low densities of galanin-, substance P-, calcitonin gene-related peptide-, dynorphin B- and cholecystokinin-immunoreactive fibers.     

Topographical projections from the cerebral cortex to the nucleus of the solitary tract in the cat

Summary The distribution of cerebral cortical neurons sending projection fibers to the nucleus of the solitary tract (NST), and the topographical distribution of axon terminals of cortico-NST fibers within the NST were examined in the cat by two sets of experiments with horseradish peroxidase (HRP) and HRP conjugated with wheat germ agglutinin (WGA-HRP). First, HRP was injected into the NST. In the cerebral cortex of these cats, neuronal cell bodies were labeled retrogradely in the deep pyramidal cell layer (layer V): After HRP injection centered on the rostral or middle part of the NST, HRP-labeled neuronal cell bodies were distributed mainly in the orbital gyrus and caudal part of the infralimbic cortex, and additionally in the rostral part of the anterior sylvian gyrus. After HRP injection centered on the caudal part of the NST, labeled neuronal cell bodies were seen mainly in the caudoventral part of the infralimbic cortex, and additionally in the orbital gyrus, posterior sigmoid gyrus and rostral part of the anterior sylvian gyrus. The labeling in the infralimbic cortex, orbital gyrus and anterior sylvian gyrus was bilateral with a predominantly ipsilateral distribution, while that in the posterior sigmoid gyrus was bilateral with a clear-cut contralateral dominance. In the second set of experiments, WGA-HRP was injected into the cerebral cortical regions where neuronal cell bodies had been retrogradely labeled with HRP injected into the NST: After WGA-HRP injection into the orbital gyrus, presumed axon terminals in the NST were labeled in the rostral two thirds of the nucleus bilaterally with an ipsilateral predominance. After WGA-HRP injection into the rostral part of the anterior sylvian gyrus, a moderate number of presumed axon terminals were labeled throughout the whole rostrocaudal extent of the NST bilaterally with a slight ipsilateral dominance. After WGA-HRP injection into the middle and caudal parts of the anterior sylvian gyrus, no labeling was found in the NST. After WGA-HRP injection into the caudal part of the infralimbic cortex, presumed terminal labeling in the NST was seen throughout the whole rostrocaudal extent of the nucleus bilaterally with a dominant ipsilateral distribution. After WGA-HRP injection into the posterior sigmoid gyrus, however, no terminal labeling was found in the NST. The results indicate that cortico-NST fibers from the orbital gyrus terminate in the rostral two thirds of the NST, while those from the infralimbic cortex and the rostral part of the anterior sylvian gyrus project to the whole rostrocaudal extent of the NST.     

Up-regulation of substance P binding sites in the vagus nerve projection area of the cat brainstem after nodosectomy. A quantitative autoradiographic study

Substance P (SP) regulates visceral functions in the nucleus of the solitary tract (NST) area. High affinity SP binding sites labelled with [³H]SP or [¹²⁵I]SP show a heterogeneous distribution in the cat medulla with high densities in the rostral and dorso-caudal parts of both the median subnucleus of NST and the dorsal motor nucleus (DMN). We previously observed a significant loss of SP immunoreactivity in the vagal area of the cat after an ipsilateral nodosectomy. It was thus important to study the correlated plasticity of SP binding in the context of the regulation of receptor function. Whichever labelled ligand was used, a unilateral nodose excision was followed by an ipsilateral increase in SP binding in the NST (200%) and the DMN (300%) after 30 days of survival. This increase was region-specific and did not match exactly the decrease in SP immunoreactivity following nodosectomy. This SP receptor density up-regulation could be due to long-term deprivation of SP afferent fibres in the NST and partly in the DMN. In the latter the increase of SP receptors occurred in both the cytoplasm of large neurons and the neuropile and did not affect the glia. The up-regulation phenomenon seems to be specific for SP receptors in the cat (at least in the DMN) and may constitute a reactive mechanism against the injury of axotomy of DMN neurons.     

Medullary catecholamine inputs to the anteroventral third ventricular cardiovascular regulatory region in the rat

Lesions in the tissue at the anteroventral end of the third ventricle (AV3V area) prevent the development of a variety of forms of experimental hypertension. This region receives afferents from several cell groups which have been implicated in cardiovascular regulation, including the nucleus of the solitary tract and neurons in the ventrolateral medulla. About 70% of the nucleus of the solitary tract neurons which could be retrogradely labeled from the AV3V area stained immunohistochemically for tyrosine hydroxylase, but not phenylethanolamine-N-methyltransferase, and were therefore presumably noradrenergic. About half of the neurons in the rostral part of the ventrolateral medulla which innervated the AV3V area stained for both enzymes, and thus were apparently adrenergic. These medullary catecholaminergic inputs to the AV3V area may be of importance in explaining recent data concerning the roles of both regions in experimental hypertension.     

Synaptic organization of afferent projections to the supramammillary nucleus of the rat

We studied the fine structure of afferent terminals from the preoptic area, the nucleus of the diagonal band of Broca, the infralimbic cortex and the laterodorsal tegmental nucleus within the supramammillary nucleus (SUM) using the anterograde tracing method of horse-radish peroxidase conjugated with wheat germ agglutinin (WGA-HRP). Injection of WGA-HRP into the preoptic area permitted ultrastructural recognition of many anterogradely labeled terminals in the SUM. Almost all labeled terminals (99%) contained clear round synaptic vesicles and formed asymmetric synaptic contacts (Gray's type I). About 86% of labeled terminals from the nucleus of the diagonal band were asymmetric (Gray's type I), whereas 14% contained pleomorphic synaptic vesicles and formed symmetric synaptic contacts (Gray's type II). Almost all labeled terminals from the infralimbic cortex were located in the ventral part of the SUM, and 95% of labeled terminals were Gray's type I. The majority of labeled terminals (90%) from the laterodorsal tegmental nucleus were Gray's type I, and the remaining (10%) were Gray's type II. The percentage of labeled terminals with dense-cored vesicles was very high in terminals from the preoptic area (70%), and low in terminals from the infralimbic cortex (19%). Labeled terminals in all cases contacted mainly intermediate-sized dendrites (0.5–1.0 m diameter). All cases had only a few labeled axosomatic terminals. The cases of injections into the preoptic area and the diagonal band nucleus had some reciprocal connections at the ultrastructural level.     

大鼠孤束核-臂旁核-中央杏仁核间接纤维联系的超微结构观察

目的 :研究孤束核 臂旁核 中央杏仁核间接纤维联系方式 ,并对臂旁核内一氧化氮的作用途径进行了探讨。方法 :利用直流电损毁孤束核顺行溃变 ,结合中央杏仁核注射辣根过氧化物酶逆行追踪技术 ,在超微结构水平上 ,观察大鼠臂旁核内溃变终末及逆行标记结构的形态分布及其相互关系。结果 :分布于臂旁核内孤束核的轴突终末 ,可与投射至中央杏仁核的神经元及其他结构形成十分密切的并列关系。结论 :臂旁核内的突触并列结构可能是一氧化氮发挥有效生物信使与信息分子作用的结构基础。     

Co-expression of vasopressin and androgen-binding protein in the rat hypothalamus

In previous studies we have observed the expression of androgen binding protein (ABP) in the rat hypothalamo-neurohypophysial system. With immunocytochemical double staining we found partial co-localization with oxytocin. In the present study we used antibodies to the anti-diuretic hormone arginine vasopressin (AVP) for co-localization with ABP in the rat hypothalamus. Both antigens were seen in the magnocellular paraventricular and supraoptic nuclei. Dense fiber networks with varicosities containing both AVP and ABP immunoreactivity were visible throughout the hypothalamus, the median eminence and in the posterior pituitary lobe. Double immunostaining revealed also co-existence in the parvocellular portion of the paraventricular nucleus and in the suprachiasmatic nucleus. ABP immunoreactive neurons in the preoptic region were devoid of AVP staining, AVP neurons in the bed nucleus of the stria terminalis stained only occasionally for ABP. We conclude that both the magnocellular and the parvocellular hypothalamic vasopressin systems are capable of expressing the steroid binding globulin, which is probably subject to axonal transport, along with the peptide hormone. Intrahypothalamic expression of ABP may be among the mechanisms necessary for rapid actions of steroids on hypothalamic neuroendocrine systems.     

Role of superior laryngeal nerve and Fos staining following dehydration and rehydration in the rat

Immunohistochemistry for Fos was used to determine the role of the superior laryngeal nerve in conscious rats following water deprivation and rehydration. Adult male rats were subjected to either unilateral superior laryngeal nerve section (SLNX) or sham surgery. Two weeks later rats from each surgical group were water deprived for 48 h or water deprived for 46 h and given access to water for 2 h prior to perfusion. Controls were allowed ad libitum access to water. Brains were processed for Fos using a commercially available antibody. Changes in plasma osmolality and hematocrit were not significantly different between SLNX and sham following any of the treatments. Water intake in rats was not significantly affected by SLNX. In the supraoptic nucleus (SON) of sham rats, water deprivation significantly increased Fos staining while water intake following dehydration prevented this increase. Water deprivation significantly increased Fos staining in the SON of SLNX rats. Following water intake after 46 h water deprivation in SLNX rats, Fos staining in the ipsilateral SON was significantly greater than the contralateral SON and significantly lower than 48 h water deprivation. In the nucleus of the solitary tract (NTS) of sham rats, both water deprivation and water intake produced significant increases in Fos staining bilaterally compared to euhydrated controls. In SLNX rats, water deprivation significantly increased Fos in both ipsilateral and contralateral NTS that was not different from sham rats. SLNX significantly decreased Fos staining in the ipsilateral NTS of rats given access to water after dehydration compared to the corresponding sham treated rats. Fos staining was not affected in the contralateral NTS of SLNX rats given access to water after dehydration. This suggests that the superior laryngeal nerve contributes to changes in Fos staining in the NTS and SON following water intake in dehydrated rats.     

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 tracer 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.Abbreviations CVL Caudal ventrolateral medulla - DAO dorsal accessory olive - F fornix - FDP fastigial depressor response - FG Fluoro-Gold - FPR fastigial pressor response - LC locus ceruleus - LHA lateral hypothalamic area - LPB lateral parabrachial nucleus - LPGi lateral paragigantocellular nucleus - LRN lateral reticular nucleus - MAO medial accessory olive - MN medial nucleus of the cerebellum - NTS nucleus of the tractus solitarius - PVH paraventricular nucleus of the hypothalamus - RVL rostral ventrolateral medulla - SCP superior cerebellar peduncle - SFO subfornical organ - V ₃ third ventricle - V ₄ fourth ventricle - WGA-HRP wheat germ agglutinin-conjugated horseradish peroxidase     

An electrophysiological study of the medial prefrontal cortical projection to the nucleus of the solitary tract in rat

The medial prefrontal cortex (MPFC) has been described as a visceromotor cortical area, since autonomic effects such as depressor responses may be elicited from this area. The central circuitry which mediates these depressor responses may include a projection from the MPFC to the nucleus of the solitary tract (NTS). Neurones were recorded extracellularly in the MPFC and were tested for antidromic (AD) activation from the NTS. These were all tested for (1) constant spike latency, (2) ability to follow high-frequency stimulation to more than 200 Hz, and (3) where possible, collision of stimulation-evoked spike with spontaneous spike or spikes evoked by iontophoretic application of glutamate. Of the 34 cells studied, all had constant AD latency (30±1 ms, range 16–46 ms); they followed high-frequency stimulation up to 354±19 Hz, and only seven cells were spontaneously active (range 1–19 spikes/s). The threshold stimulation intensity for AD activation was 102±9 A (n=34, range 8–200 A). Depth-threshold curves (n=7) showed minimum-threshold AD activation currents that corresponded to the dorsal and ventral sub-divisions of the NTS. Small shifts in AD latency were found in the depth-threshold curves, suggesting axonal branching. Analysis of recording sites showed that NTS-projecting MPFC neurones were predominantly found in the infralimbic and ventral prelimbic regions of the MPFC. These findings indicate that there is a population of neurones in the MPFC that projects to, and probably terminates within, the NTS. It is possible that this projection may, in part, mediate the cardiovascular response to MPFC stimulation.     

大鼠脑干星形胶质细胞在应激性胃黏膜损伤中的作用

研究大鼠迷走神经背核（DMV）和孤束核（NTS）星形胶质细胞在应激性胃黏膜损伤中的作用。将36只雄性 Wistar 大鼠随机分为对照组和束缚－浸水应激组（RWIS 0．5、1、2、3、5h）,通过免疫组织化学技术,检测胶质纤维酸性蛋白（GFAP）的表达。将12只雄性 Wistar 大鼠随机分为生理盐水对照组和 L －AA （星形胶质细胞的抑制剂）组,束缚－浸水应激1 h,检测 Fos 蛋白和 GFAP 蛋白的表达及胃黏膜损伤情况。与对照组相比,应激组大鼠在 DMV 和 NTS 的不同区段 GFAP 有不同程度的增加。束缚－浸水应激条件下,星形胶质细胞抑制剂 L －AA 可显著抑制 GFAP 的表达及神经元的 Fos 蛋白的表达,同时胃黏膜损伤明显减轻。星形胶质细胞可能通过调节神经元的激活,参与了束缚－浸水应激,影响了胃肠机能,导致胃黏膜损伤。     

Ascending noradrenergic projections from the brainstem: Evidence for a major role in the regulation of blood pressure and vasopressin secretion

Summary The role of projections from the lateral tegmental (A₁, A₂) and coeruleal (A₆) noradrenergic cell groups in the control of arginine vasopressin (AVP) secretion was studied following lesions to the ventral (VNAB) and dorsal (DNAB) noradrenergic bundles by 6-hydroxydopamine. These lesions were associated with the expected, large reductions in cortical (DNAB) and hypothalamic (VNAB) noradrenaline concentrations. Vehicle injected, control animals and VNAB lesioned animals showed a similar AVP secretory response to haemorrhage, whilst the DNAB group showed a markedly diminished release of AVP in response to this challenge. Following Clonidine injection, both controls and VNAB animals showed major reductions in plasma AVP concentrations, but again the DNAB group behaved in a different manner, with a marked attenuation of the inhibitory effect of Clonidine on AVP secretion. In addition, the DNAB group had a significantly lower basal blood pressure, a greater initial agonist response to Clonidine and a loss of the hypotensive response to Clonidine in comparison to sham and VNAB lesioned groups. All three groups showed a similar AVP response to intravenous nicotine. These data suggest that noradrenergic projections originating in the locus coeruleus, or in the lateral tegmental NA groups but which ascend together with coeruleal axons in the DNAB, modulate the vasopressin response to visceral stimuli and to Clonidine, and that they also play an important role in mediating the hypotensive effect of Clonidine.This work was supported by a grant from the Wellcome Trust (SL) and a programme grant (No. PG 733722) from the Medical Research Council (BJE)     

Topographic principles in the spinal projections of serotonergic and non-serotonergic brainstem neurons in the rat

The spinal projections from the raphe-associated brainstem areas containing serotonergic neurons were studied with aldehyde-induced fluorescence in combination with the retrograde fluorescent tracer True Blue in the rat. This technique makes it possible to determine simultaneously the projections of individual neurons and to detect whether serotonin is present in the same neurons. After tracer injections into the spinal cord retrogradely labeled serotonergic and non-serotonergic neurons were found in the medullary raphe nuclei and adjacent regions and to a lesser extent in association with the dorsal and median raphe nuclei in the mesencephalon. Large True Blue injections that covered one side of the spinal cord at mid-cervical level labeled about 60% of the ipsilaterally situated serotonergic neurons in the medullary raphe regions while the corresponding figure contralaterally was about 25%. On both sides a larger number of labeled non-serotonergic neurons were found; these were sometimes located dorsal to, but often intermingled with, the serotonergic cells. While the serotonergic projection from the mesencephalon could not be labeled from injections below cervical levels, the labeling in more caudal brainstem regions exhibited only minor variations depending on the rostrocaudal level of the spinal segment injected. Furthermore, quantitative data from injections at different levels indicate that the majority of the spinal-projecting neurons traverse most of the length of the cord. Summarizing the results obtained from small injections restricted to subregions of the cord we feel that it is possible to distinguish three fairly distinct pathways for spinal projections from the medullary raphe and adjacent regions: The dorsal pathway originates mainly from cells in the caudal pons and rostral medulla oblongata (rostral part of nucleus raphe magnus, nucleus raphe magnus proper, nucleus reticularis gigantocellularis pars alpha and nucleus paragigantocellularis). This pathway, which contains a large non-serotonergic component, descends through the dorsal part of the lateral funiculus and terminates mainly in the dorsal horn at all spinal cord levels. The intermediate pathway is largely serotonergic with its cell bodies located within the arcuate cell group (situated just ventral and lateral to the pyramids very close to the ventral surface of the brainstem) and in the nucleus raphe obscurus and pallidus and terminates in the intermediate grey at thoracolumbar and upper sacral levels.(ABSTRACT TRUNCATED AT 400 WORDS)