Dorsomedial Medulla Research Articles

Central and peripheral effects of repeated stress and high NaCl diet on neuropeptide Y

This study was performed to investigate the influence of repeated psychological stress alone or combined with high NaCl intake on the function of the sympathetic nervous system. In addition, NPY levels have been measured in brain regions of potential importance in the central regulation of stress responses (ventrolateral and dorsomedial medulla, paraventricular and arcuate nucleus of the hypothalamus, and frontal cortex). Normotensive Wistar rats received a standard diet alone or supplemented with NaCl. To accentuate differences in sodium balance, rats on the high NaCl diet (HNa) were uninephrectomized. Half the animals on each diet were subjected to chronic stress using daily sessions (1 h) of immobilization stress. After 12 days, plasma levels of neuropeptide Y (NPY), norepinephrine (NE), and epinephrine (E) were measured basally and in response to acute footshock stress. HNa intake or chronic stress alone did not significantly alter either basal or stimulated plasma levels of NPY. However, combining the treatments produced a significant interaction, increasing the NPY response to footshock by 31% compared to HNa alone ( p = 0.039) and by 98% compared to stress alone ( p < 0.001). Chronic stress increased basal levels of NE and enhanced the response to subsequent acute stress; combining the treatments did not yield further increases. Plasma levels of E were not significantly affected by the treatments. In the brain, stress alone had no effect on the NPY levels in the structures studied. HNa intake induced a significant increase in NPY levels of the arcuate nucleus, and produced a significant interaction with stress in the dorsomedial medulla. In a supplementary experiment, to evaluate the role of the autonomic nervous system in plasma NPY responses, treatment with the ganglion blocker hexamethonium was shown to significantly attenuate stress-induced changes in NPY, NE, and E.

Robust enkephalin innervation of the locus coeruleus from the rostral medulla

Substantial evidence indicates that the noradrenergic nucleus locus coeruleus (LC) is a key target of endogenous opioid neurons, and an important structure in mediating opiate effects. However, the detailed distribution of opioid fibers and terminals in the LC, and the sources of its opioid innervation are unknown. In the present study, the enkephalin innervation of the LC was investigated in the rat using an antibody directed against the extended enkephalin peptide Met-enkephalin-Arg6-Gly7-Leu8 (ENK), which is derived exclusively from the enkephalin precursor proenkephalin A. An antibody directed against tyrosine hydroxylase (TH), the synthetic enzyme for catecholaminergic neurons, was also applied to the same tissue sections to delineate LC neurons and their dendrites. Enkephalin fibers in the LC were dense and highly varicose. In horizontal sections, ENK-like-immunoreactive (ENK-ir) fibers of considerable length coursed throughout the rostrocaudal orientation of the LC proper, whereas in frontal sections ENK-ir processes appeared punctate, suggesting a rostrocaudal orientation. Dense ENK-ir fibers were also identified in the rostromedial and caudal juxtaependymal pericoerulear regions where extranuclear dendrites of LC neurons are extensive. As previously reported, there were no ENK-ir neurons in the LC nucleus proper, but such cells were present in neighboring structures such as the parabrachial, sphenoid, and Barrington's nuclei as well as in the central gray and in the subcoeruleus area. ENK-ir neurons were also present in nuclei of the rostral medulla reported to be major afferents of the LC, the nucleus prepositus hypoglossi (PrH), and the nucleus paragigantocellularis (PGi). In the dorsomedial medulla, numerous ENK-ir neurons were identified in the medial aspect of the PrH and along the medial longitudinal fasciculus in the perifascicular reticular formation. In the ventrolateral medulla, ENK-ir neurons were distributed in a conical caudorostral column throughout the PGi. Retrograde transport of a WGA-colloidal gold conjugate (WGA-apoHRP-Au) from LC, combined with immunohistochemistry for ENK in the same tissue sections, revealed that LC afferents in the PGi and PrH were interdigitated with ENK-ir neurons. Furthermore, an unexpectedly high incidence of doubly labeled neurons were identified in both PGi and PrH. Overall, 57% and 56% of the LC-projecting neurons in PGi and PrH, respectively, were also immunoreactive for ENK, suggesting that enkephalinergic neurons of PGi and PrH are major afferents to noradrenergic LC neurons.

Central nervous system catecholamine content and norepinephrine release after AV3V ablation

Electrolytic ablation of the periventricular tissue surrounding the anteroventral third cerebral ventricle (AV3V-X) results in immediate increases in norepinephrine release in the paraventricular hypothalamic nucleus/anterior hypothalamus (P/A) and in the dorsomedial medulla (DM) and depletion of norepinephrine and epinephrine throughout the brain. The present study determined whether catecholamine depletion and/or altered norepinephrine release persisted after recovery from the acute effects of AV3V-X. Fourteen to eighteen days after surgery, catecholamine concentrations throughout the brain and norepinephrine release in the P/A and DM during hemorrhage were measured in control-operated and AV3V-X rats. AV3V-X decreased epinephrine content only in the midbrain, increased norepinephrine only in the cortex, and produced no differences in central nervous system dopamine. Hemorrhage-induced norepinephrine release was significantly greater in the P/A of AV3V-X rats than in control animals, whereas norepinephrine release in the DM increased equally in both groups. Thus AV3V-X does not result in chronic global central nervous system catecholamine depletion and enhances norepinephrine release in the P/A during hemorrhage.

Evidence for L-dopa systems responsible for cardiovascular control in the nucleus tractus solitarii of the rat.

Microinjections of L-DOPA (10-100 ng) into the medial area of the nucleus tractus solitarii (NTS) led to dose-dependent decreases in arterial blood pressure and heart rate in rats treated with i.p. 3-hydroxybenzylhydrazine, a central inhibitor of DOPA decarboxylase, or similarly with intraventricular 6-hydroxydopamine. D-DOPA, dopamine or noradrenaline (100 ng) produced no effect. L-DOPA methyl ester (1 microgram), a competitive antagonist for L-DOPA, microinjected into NTS, blocked the depressor and bradycardic responses to L-DOPA. High K+ (40 mM) released endogenous DOPA in a Ca(2+)-dependent manner from slices of the rat dorsomedial medulla including NTS. These results support the hypothesis that there exist systems of L-DOPA itself responsible for cardiovascular regulation in NTS of rats. This regulatory action of L-DOPA seems to be postsynaptic in nature.

Characteristics of endothelin receptors in the central nervous system of spontaneously hypertensive rats

The binding of [ 125I]sarafotoxin 6b (SRT 6b) and [ 125I]endothelin-1 (ET-1) to endothelin (ET) receptors of neuronal membranes prepared, from regions of the brain and spinal cord of 8 week-old, spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. Spontaneously hypertensive rats had significantly higher blood pressure as compared to WKY rats. Heart rate was similar in SHR and WKY rats. [ 125I]SRT 6b and 125I]ET-1 bound to the membranes of the cerebral cortex, hypothalamus, ventrolateral medulla, dorsomedial medulla and spinal cord at a single, high affinity site. The K d and B max values of the binding of [ 125I]SRT 6b were found to be similar to binding of [ 125I]ET-1 in all the regions. The concentration-dependent inhibition of binding of [ 125I]ET-1 by unlabeled ET-1, in spinal cord membranes showed an IC 50 value of 2.48 ± 0.72 nM and a K i , value of 2.35 ± 0.68 nM in WKY rats and an IC 50 value of 1.77 ± 0.49 nM and a K i value of 1.68 ± 0.46 nM in SHR rats. On the other hand, the concentration-dependent inhibition of the binding of [ 125I]SRT 6b by unlabeled ET-1, in spinal cord membranes showed an IC 50 value of 12.86 ± 3.09 pM and a K i value of 9.54 ± 2.18 pM in WKY rats, while SHR rats showed an IC 50 value of 10.30 ± 3.26 pM and a K i value of 7.46 ± 2.36 pM. The binding of [ 125I]SRT 6b and [ 125I]ET-1 in the cerebral cortex, dorsomedial medulla and spinal cord membranes was found to be similar in SHR and WKY rats. In the hypothalamus and ventrolateral medulla, the binding of both [ 125I]SRT 6b and [ 125I]ET-1 were decreased in SHR, as compared to WKY rats. The decreased binding of [ 125I]SRT 6b was due to 27.1% and 39.2% decreases in the B max values in hypothalamus and ventrolateral medulla, respectively. The decreased binding of [ 125I]ET-1 was due to 49.8% and 47.5% decreases in the B max values in hypothalamus and ventrolateral medulla, respectively. The K d values were similar in SHR and WKY rats. The endothelin receptors in the hypothalamus and ventrolateral medulla of SHR rats were down-regulated as compared to WKY rats and may be contributing to the regulation of blood pressure.

Autoradiographic localization of 5HT1 binding sites in autonomic areas of the rat dorsomedial medulla oblongata.

Serotonin (5HT) binding sites in autonomic portions of the dorsomedial medulla oblongata of the rat were localized using autoradiographic techniques with radioactive ligands that express high affinity for the 5HT1 (3H-5HT), 5HT1A (3H-8OH-DPAT), or 5HT1B (125I-CYP with isoproterenol) receptor subtypes. 5HT1A sites were densely distributed in the nucleus tractus solitarius (NTS), with the highest densities localized to the interstitial subnucleus and the central subnucleus. 5HT1B sites were also found in the NTS, with the highest densities localized to the substantia gelatinosa subnucleus. The dorsal motor nucleus of the vagus nerve and nucleus ambiguus exhibited low densities of 5HT1B sites. However, the nucleus intercalatus, a cerebellar relay nucleus that also contains dendrites of vagal parasympathetic preganglionic neurons and receives autonomic forebrain afferent input, showed very dense 5HT1B sites. The promontorium, paratrigeminal islands, and the dorsomedial portion of the trigeminal nucleus (DM5), which are areas of viscerosomatic integration, exhibited high densities of both 5HT1A and 5HT1B sites. The area postrema contained low levels of both 5HT1A and 5HT1B sites. Visceral deafferentation via cervical vagotomy or nodose ganglionectomy caused a significant decrease in 5HT1A sites in the interstitial subnucleus of the NTS ipsilateral to the lesion. No changes were seen in 5HT1B sites. These studies suggest that 5HT1A and 5HT1B sites are involved in the processing of visceral sensory information in the NTS and associated areas. Based upon viscerotopic organization of the NTS, 5HT1A sites appear preferentially distributed in portions of the NTS that are associated with the coordination of swallowing, respiration, and cardiovascular function, while 5HT1B sites appear preferentially distributed in areas of the NTS associated with gastrointestinal, hepatic, pancreatic, and cardiovascular function. However, since these association were not absolute and there was a great deal of overlap between the two sites, speculation regarding their specific functions in autonomic control must await pharmacological examination.

Differential time course activation of the brain stem catecholaminergic groups following chronic adrenalectomy.

The activity of the brain stem catecholaminergic (CA) cell groups of the ventrolateral (A1C1) and dorsomedial (A2C2) medulla that are known to contain primarily nonadrenergic neurones (A1 and A2) and a smaller proportion of adrenergic cells (C1 and C2) as well as the noradrenergic group locus ceruleus (LC) in the dorsal pons was determined at various times up to 16 days following surgical adrenalectomy. The activity of the CA cell groups was estimated by the rate of tyrosine hydroxylation in vivo that was assessed by measuring the 3.4-dihydroxyphenylalanine (DOPA) accumulated 20 min following administration of DOPA decarboxylase inhibitor NSD 1015. In the medullary nuclei noradrenaline content was found around 40- up to 70-fold the adrenaline content. This result was taken as evidence that the noradrenergic cells are likely to provide the main contribution to the tyrosine hydroxylation rate that we measured. Endogenous DOPA content represented between 2 and 10% of the noradrenaline content. NSD 1015 induced an accumulation of DOPA that was linear for at least 20 min and reached at this time more than 10-fold the endogenous level. While no modification of the in vivo tyrosine hydroxylation rate was observed in the LC, a significant increase was found in both medullary groups following adrenalectomy. In the A1C1 group it was detected 8 days after surgery and was then maintained with a maximum that represented up to a 60% increase over the basal value. In the A2C2 group the activation was slightly delayed and less marked. Increase in ACTH level occurred much earlier: it was about 70% of the maximal level already 4 days following adrenalectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Organization of medullary adrenergic and noradrenergic projections to the periaqueductal gray matter in the rat.

The periaqueductal or midbrain central gray matter (CG) in the rat contains a dense network of adrenergic and noradrenergic fibers. We examined the origin of this innervation by using retrograde and anterograde axonal tracers combined with immunohistochemistry for the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT). Following injections of the fluorescent tracers Fast Blue or Fluorogold into the CG, double-labeled neurons in the medulla were identified mainly in the noradrenergic A1 group in the caudal ventrolateral medulla (VLM) and A2 group in the medial part of the nucleus of the solitary tract (NTS); and in the adrenergic C1 group in the rostral ventrolateral medulla and C3 group in the rostral dorsomedial medulla. Injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) into these cell groups resulted in a distinct pattern of axonal labeling in various subdivisions of the CG. Anterogradely labeled fibers originating in the medial NTS were predominantly found in the lateral portion of the dorsal raphe nucleus and in the adjacent part of the lateroventral CG (CGlv). Following PHA-L injections into the C3 region the anterogradely labeled fibers were diffusely distributed in the CGlv and the dorsal raphe nucleus at caudal levels, but rostrally tended to be located laterally in the CGlv. In contrast, ascending fibers from the caudal and rostral VLM terminated in the rostral dorsal part of the CGlv and in the dorsal nucleus of the CG, whereas ventral parts of the CG, including the dorsal raphe nucleus, contained few afferent fibers. Double-label studies with antisera against DBH and PNMT confirmed that noradrenergic neurons in the A1 and A2 groups and adrenergic neurons in the C1 and C3 groups contributed to these innervation patterns in the CGlv. Noradrenergic and adrenergic projections from the medulla to the CG may play an important role in a variety of autonomic, sensory and behavioral processes.

Midbrain periaqueductal gray projections to the dorsomedial medulla in the rabbit

The present study sought to determine the existence of projections from the midbrain periaqueductal gray (PAG) to the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus nerve (DMN) in the rabbit. Fast Blue injections into the NTS/DMN complex revealed a population of retrogradely labeled cells within the ventrolateral PAG. Deposits of wheat germ agglutinin/horseradish peroxidase (WGA/HRP) into the ventrolateral PAG revealed terminal label within the dorsomedial, lateral, ventrolateral, intermediate, and commissural subnuclei of the NTS. Label was also observed within the DMN and a heavy concentration encapsulated this nucleus. These data suggest that the projection from the PAG to the NTS/DMN complex may represent a substrate by which the PAG may influence autonomic and cardiovascular regulation, particularly during emotional arousal.

Enhanced drinking after excitotoxic lesions of the parabrachial nucleus in the rat

Previous reports indicate the lateral parabrachial nucleus (IPBN) is important in the regulation of fluid intake. After electrolytic lesions of the IPBN, rats consume increased amounts of water when challenged with pharmacological stimuli that mimic depletion of the extracellular fluid space. Nonetheless, it is possible that neurons within the IPBN are not responsible for the overingestion of water during extracellular thirst challenges, since electrolytic lesions damage fibers of passage as well as neurons within the IPBN. Thus we used the excitatory neurotoxin ibotenic acid to lesion cell bodies within the IPBN. After recovery from surgery, water consumption by lesioned rats was significantly greater than consumption by vehicle or uninjected control rats when challenged with subcutaneous angiotensin II or isoproterenol to stimulate drinking. However, when injected with subcutaneous hypertonic saline to produce cellular dehydration, or when water deprived for 24 h, the water intake of rats with lesions was not different from the intake of control rats. Anatomical examination of the lesion sites revealed that ibotenic acid injection caused a notable loss of neurons in the IPBN with little or no damage to surrounding structures. Moreover, injection of an anterograde tracer into the dorsomedial medulla resulted in labeling of fibers that traverse the ibotenic acid lesion site. Together, these data suggest neurons within the IPBN are involved in the regulation of fluid intake, particularly challenges that involve depletion of the extracellular fluid space.

Central nervous system norepinephrine release during hypotension and hyperosmolality in conscious rats

Extracellular norepinephrine (NE) levels in the paraventricular/anterior hypothalamic area (P/A) and in the dorsomedial medulla (DM) in conscious Sprague-Dawley rats were estimated by in vivo microdialysis before, during, and after sustained hypotension (75 mmHg mean arterial pressure) produced either by hemorrhage (Hem) or by 2-chloroadenosine infusion (2-Cl-ADO, 2.6-26.0 micrograms/min iv). P/A and DM NE were also measured before, during, and after hypertonic saline infusion (HTS; 1.5 M NaCl at 10 microliters.100 g-1.min-1 iv). P/A and DM NE increased during both Hem and 2-Cl-ADO and returned to baseline after reinfusion of hemorrhaged blood or after 2-Cl-ADO was stopped. However, Hem caused greater increases in P/A NE than 2-Cl-ADO despite equivalent decreases in blood pressure. Hem and 2-Cl-ADO produced equivalent changes in DM NE. HTS did not change P/A or DM NE despite increases in blood pressure of approximately 15 mmHg and plasma osmolality of approximately 30 mosmol/kgH2O. We conclude that 1) hypotension increases P/A and DM NE, which may mediate compensatory responses, 2) Hem is a more potent stimulus for NE release in the P/A than isovolemic hypotension induced by 2-Cl-ADO, and 3) the hypertensive response to HTS does not involve changes in P/A or DM NE.

Adrenergic innervation of the rat nucleus locus coeruleus arises predominantly from the C1 adrenergic cell group in the rostral medulla

Focal iontophoretic injections of the retrograde tracer Fluoro-Gold into the locus coeruleus were combined with immunocytochemistry for phenylethanolamine N-methyltransferase, the final enzyme in the synthesis of epinephrine. Retrograde labeling confirmed recent findings that the major afferents to the locus coeruleus are present in the ventrolateral (nucleus paragigantocellularis) and dorsomedial medulla (nucleus prepositus hypoglossi), areas containing the C1 and C3 adrenergic cell groups, respectively. The Fluoro-Gold label revealed morphologic details of locus coeruleus afferent cells. Labeled neurons in the prepositus hypoglossi region were typically round (10 μm diameter) or ellipsoidal and compressed against the ventricle wall ( 10 × 20μm), while those in the paragigantocellularis were most often multipolar and ellipsoidal or triangular in shape ( 10 × 20−20 × 30μm). Double labeling in the same tissue sections revealed that locus coeruleus afferent neurons are intercalated among phenylethanolamine N-methyltrans-ferase-positive C1 and C3 neurons. Twenty-one per cent of locus coeruleus afferent neurons in paragigantocellularis stained for phenylethanolamine N-methyltransferase while only 4% of locus coeruleus afferents in the prepositus hypoglossi area exhibited phenylethanolamine N-methyltransferase immunoreactivity. In paragigantocellularis, doubly labeled neurons were usually the smaller locus coeruleus afferents, while in the prepositus hypoglossi phenylethanolamine N-methyltransferase labeling was found in all cell types that project to the locus coeruleus. Phenylethanolamine N-methyltransferase-positive fibers from the C1 and C3 cell groups form an adrenergic fiber bundle in the dorsomedial medulla; in the pons, these fibers appear to exit this bundle and innervate the locus coeruleus. Fibers from the neurons of the C3 cell group also appear to ascend on the dorsal surface of the medulla to innervate the locus coeruleus. The phenylethanolamine N-methyltransferase fiber innervation in the locus coeruleus was dense and highly varicose. Phenylethanolamine N-methyltransferase innervation in the dorsal pons was not restricted to the locus coeruleus but was also prominent in neighboring areas such as Barrington's nucleus and the lateral dorsal tegmental nucleus of Gudden.

Le noyau du faisceau solitaire : Aspects neuroanatomiques, neurochimiques et fonctionnels

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)

Tonic cardiovascular effects of angiotensin II in the ventrolateral medulla.

The rostral and caudal parts of the ventrolateral medulla play a major role in the control of blood pressure. Both regions contain a high density of receptor binding sites for angiotensin II, and it has been shown previously that microinjection of angiotensin II into the rostral ventrolateral medulla causes a rise in blood pressure. The aims of this study were to determine the cardiovascular effects of microinjection of angiotensin II and its specific antagonist [Sar1Thr8]angiotensin II into the caudal ventrolateral medulla and to characterize the regional vascular effects elicited by both compounds in the rostral ventrolateral medulla. Microinjections of angiotensin II (0.2-20 pmol) into histologically verified sites in the caudal ventrolateral medulla of anesthetized baroreceptor-denervated rabbits produced dose-dependent decreases in blood pressure and renal sympathetic nerve activity, whereas microinjection of [Sar1Thr8]angiotensin II (40 pmol) produced increases in these variables. In the rostral ventrolateral medulla, angiotensin II (0.02-20 pmol) elicited a dose-dependent increase in blood pressure, iliac vascular resistance, and renal sympathetic nerve activity, whereas [Sar1Thr8]angiotensin II (40 pmol) produced decreases in these variables. The effects on heart rate elicited by either compound in the rostral or caudal ventrolateral medulla were small but were in the same direction as the other cardiovascular variables. In contrast, angiotensin II had no detectable effect on sympathoexcitatory neurons within the rostral dorsomedial medulla, a region that lacks angiotensin II receptor binding sites. The results indicate that endogenous angiotensin II acts on specific receptors within the rostral and caudal parts of the ventrolateral medulla and has a tonic excitatory action on sympathoexcitatory and sympathoinhibitory neurons within these respective regions.

Angiotensin II and angiotensin (1–7) excite neurons in the canine medulla in vitro

Our group showed previously that the heptapeptide angiotensin (1–7) [Ang-(1–7)] is a bioactive product of the renin-angiotensin system, and produces dose-dependent cardiovascular effects similar to those evoked by Ang II when microinjected into the nucleus tractus solitarii (nTS) of the rat. The effects of Ang II were compared with those of Ang-(1–7) on single neuron activity recorded from the medial nTS or dorsal motor nucleus of the vagus (dmnX) in perifused horizontal slices of the canine dorsomedial medulla. Ang II excited 48% of 31 medial nTS neurons, but only activated 14% of 22 dmnX cells. Ang-(1–7) also excited half of the medial nTS cells and 14% of the dmnX neurons. Although most medial nTS neurons excited by Ang II were also activated by Ang-(1–7), two cells were excited by Ang II but not by Ang-(1–7), and one cell was excited by Ang-(1–7) but not by Ang II. Because Ang-(1–7) lacks direct vasoconstrictor effects, neurons in the dorsomedial medulla may have different receptor characteristics than peripheral tissues. The observation of a few medial nTS neurons excited by only one Ang peptide suggests that there may be a separate Ang-(1–7) receptor that participates in the physiological effects of Ang peptides mediated by the brain.

Local effects of substance P on respiratory regulation in the rat medulla oblongata

The effect of substance P (SP) and the SP antagonist [D-Pro2,D-Trp7,9]-SP on basal ventilation was investigated in halothane-anesthetized rats. Microinjections of SP (0.4-1.5 nmol) into the ventrolateral medulla oblongata (VLM), (nuclei gigantocellularis, facialis, ambiguus, and reticularis lateralis) or into the dorsomedial medulla oblongata (DM, nucleus tractus solitarius) and its ventral surroundings dose dependently increased tidal volume (VT) and/or minute ventilation. In sensitive areas, the ventilatory stimulation was initiated within minutes, peaked around 8-10 min, and slowly returned to normal over 30-45 min after the injection. In the VLM sites, the increase in VT was generally accompanied by a decrease in respiratory frequency (f), whereas in the DM, f increased in parallel with VT. Furthermore, within the VLM, the respiratory response patterns differed with the definite location of the SP injection. A shortening of inspiratory time was observed in the ventromedial part, the ventrolateral portion of the nucleus paragigantocellularis and ventral to the nucleus facialis. In contrast, a lengthening of expiratory time was seen when SP was injected or applied more laterally along the ventral portion of nucleus facialis and near or directly on the ventral medullary surface. Application of [D-Pro2, D-Trp7,9]SP before or after SP completely antagonized the excitatory effects of SP on ventilation. The SP antagonist administered into the VLM decreased the ventilatory response to hypoxic breathing but caused no change during hyperoxic conditions.

Distribution of Catecholamine-Synthesizing Enzymes in Goldfish Brains: Presumptive Dopamine and Norepinephrine Neuronal Organization

The organization of presumptive dopamine- and norepinephrine-synthesizing neurons in the brains of goldfish is described by using antibodies to tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) with avidin-biotin immunocytochemical techniques. In the hindbrain, TH-immunoreactive (IR) and DBH-IR cell bodies are located together in the following three regions: (1) dorsomedial medulla in the postobecular region, (2) medullary tegmentum from the level of the greatest expansion of the vagal lobes to the medullospinal transition, and (3) isthmal tegmentum dorsolateral to the medial longitudinal fasciculus. Elsewhere in the brain, TH-IR neurons were visualized in eight distinct forebrain neuronal groups; DBH-IR cell bodies were not observed. Fibers and terminals IR for TH and DBH were most dense in forebrain periventricular regions, i.e. adjacent to the third ventricle, and specifically around the lateral and preoptic recesses. In the telencephalon, a dense innervation of TH- and DBH-IR fibers was noted within the area dorsalis, pars lateralis and pars dorsalis. Within the area dorsalis, pars centralis TH-IR fibers were dense; DBH-IR fibers were not visualized in this region. The presence of both dopamine- and norepinephrine-synthesizing neurons in the isthmal and medullary tegmentum and in the dorsomedial medulla provides evidence indicating that these regions are homologous to the locus ceruleus, medullary reticular nucleus and area postrema, respectively, in tetrapod brains. In addition, the remarkably dense innervation of TH-IR and DBH-IR fibers and terminals in periventricular regions of the hypothalamus and within the telencephalon suggests that there are potential similarities in the catecholaminergic innervation of forebrain regions of teleost and mammalian brains.

Pertussis toxin treatment counteracts intramembrane interactions between neuropeptide Y receptors and α2-adrenoceptors

The effect of intracerebroventricular injections of pertussis toxin were investigated on the neuropeptide Y-induced modulation of α 2-adrenoceptor binding in membranes from the dorsomedial medulla oblongata of the rat. Concentration-response experiments showed that neuropeptide Y reduced the binding affinity of the α 2-agonist, p-[ 3H]aminoclonidine, with a maximal effect of 30% at 3–30 nM. Pertussis toxin treatment (10 μg, 24 h) counteracted this modulation, without reducing the binding of neuropeptide Y to its own receptor. The results indicate that pertussis toxin-sensitive G-proteins are essential for the mediation of the intramembrane interaction between neuropeptide Y receptors and α 2-adrenoceptors.

Dorsomedial medulla stimulation activates rat supraoptic oxytocin and vasopressin neurones through different pathways.

1. This study utilized retrograde anatomical tracer techniques and in vivo extracellular electrophysiological studies to examine caudal ventrolateral and dorsomedial medulla afferents to supraoptic nucleus neurosecretory neurones in male Long-Evans rats. 2. In one series of experiments, pentobarbitone-anaesthetized animals were subjected to ventral exposure of the hypothalamus and rhodamine-tagged latex microspheres (0.05-0.2 microliter) were injected into one supraoptic nucleus. Following perfusion with paraformaldehyde-glutaraldehyde 18-24 h later, cell counts were obtained of rhodamine- and/or catecholamine-labelled neurones in the caudal ventrolateral and dorsomedial medulla both ipsi- and contralateral to the injection site. 3. In the caudal ventrolateral medulla, each injection labelled fewer than 15% of the catecholaminergic neurones; with small injections, most (68-100%) of the rhodamine-labelled neurones also displayed catecholamine histofluorescence. In the caudal nucleus tractus solitarii, one-half to one-third as many rhodamine-labelled cells were observed, but a higher percentage (13-100%) of these were non-catecholaminergic. 4. Extracellular recordings were obtained from antidromically identified supraoptic neurones classified as vasopressin (n = 106) or oxytocin (n = 26) secreting. Single cathodal pulses (0.2 ms duration, 0.02-0.08 mA) applied in the caudal half of the ipsilateral nucleus tractus solitarii evoked a transient (30-50 ms) activation of 63% of both vasopressin- and oxytocin-secreting neurones. Mean latencies (+/- S.E.M.) for vasopressin and oxytocin cells were 49.8 +/- 1.0 and 46.5 +/- 2.4 ms respectively; these were not significantly different. Similar responses were noted to contralateral stimuli applied to four vasopressin and two oxytocin cells. 5. Vasopressin neurones activated by caudal nucleus tractus solitarii stimulation displayed similar patterns of response to stimulation in the caudal ventrolateral medulla. However, latencies from the nucleus solitarius (mean 47.6 +/- 1.4 ms; n = 59) were significantly longer (P less than 0.05) than from the ventrolateral medulla (41.5 +/- 2.0 ms; n = 17). In eight out of eleven vasopressin neurones tested, interruption of synaptic transmission through the ventrolateral medulla reduced or abolished the caudal nucleus tractus solitarii-evoked excitation but had no effect on their response to baroreceptor activation. This manoeuvre affected zero out of five oxytocin cells similarly excited by nucleus solitarius stimulation. 6. These observations indicate that visceral input mediated through the nucleus tractus solitarii is transmitted differentially to supraoptic vasopressin- and oxytocin-secreting neurones.

Distribution of phenylethanolamine N-methyltransferase cell bodies, axons, and terminals in monkey brainstem: an immunohistochemical mapping study.

Adrenaline (epinephrine) is an important candidate transmitter in descending spinal control systems. To date intrinsic spinal adrenergic neurons have not been reported; thus adrenergic input is presumably derived from brainstem sites. In this regard, the localization of adrenergic neurons in the brainstem is an important consideration. Maps of adrenergic cell bodies and to a lesser extent axons and terminal fields have been made in various species, but not in monkeys. Thus, the present study concerns the organization of adrenergic systems in the brainstem of a monkey (Macaca fascicularis) immunohistochemically mapped by means of an antibody to the enzyme phenylethanolamine N-methyltransferase (PNMT). PNMT-immunostained cell bodies are distributed throughout the medulla in two principal locations. One concentration of labeled cells is in the dorsomedial medulla and includes the nucleus of the solitary tract (NTS), the dorsal motor nucleus of the vagus (X), and an area ventral to X in a region of the reticular formation (RF) known as the central nucleus dorsalis (CnD) of the medulla. A few scattered cells are observed in the periventricular gray just ventral to the IVth ventricle and on midline in the raphe. The second major concentration of PNMT-immunostained cells is located in the ventrolateral RF, lateral and dorsolateral to the inferior olive (IO), including some cells in the rostral part of the lateral reticular nucleus (LRN). Terminal fields are located in the NTS, X, area postrema (AP), and the floor of the IVth ventricle in the medulla and pons. A light terminal field is also observed in the raphe, particularly raphe pallidus (RP). A heavy terminal field is present in locus coeruleus (LC). Fibers labeled for PNMT form two major fiber tracts. One is in the dorsomedial RF extending as a well-organized bundle through the medulla, pons, and midbrain. A second tract is located on the ventrolateral edge of the medulla and caudal pons. Fibers in this tract appear to descend to the spinal cord. A comparison with maps of other catecholamine neurons in primates is discussed, confirming that the distribution of the adrenergic system in monkeys is similar to that described in the human.