Brain neuropeptides: actions on central cardiovascular control mechanisms

Role of limbic peptidergic circuits in regulation of arterial pressure, relevant to development of essential hypertension

It is generally accepted that the essential hypertension (EH) is caused by interactions among congenital gene, multiple pathogenetic pressor factors, and disorder of physiologic depressor factors. The central nervous system may play a key role in the development of EH. The underlying mechanisms, however, are not well understood. Studies show that peptidergic transmitters in the limbic forebrain are involved in long-term regulation of arterial pressure and in the pathogenesis of EH. In the limbic forebrain there are peptidergic pressor and depressor circuits. The former includes corticotropin releasing factor-, substance P-, and angiotensin II-circuits; and the latter includes beta-endorphin- and atrial natriuretic peptide-circuits. These circuits extensively interconnect and interact with each other. The altered functions of them may be the pathogenesis of EH. In this review, we focus on the roles of limbic peptidergic circuits in regulation of arterial pressure, relevant to the neurogenetic mechanisms in developing EH.

Galanin messenger RNA during postnatal development of the rat brain: expression patterns in Purkinje cells differentiate anterior and posterior lobes of cerebellum

Following our initial mapping of preprogalanin messenger RNA in adult brain and its presence in a subpopulation of cerebellar Purkinje neurons [Ryan M. C. and Gundlach A. C. (1996) Neuroscience 70, 709-728], the present study examined the ontogenic expression of preprogalanin messenger RNA in the postnatal rat brain focussing on the Purkinje cells of the cerebellar cortex. Using in situ hybridization histochemistry, preprogalanin messenger RNA was detected in the developing forebrain and hindbrain from postnatal day 4 to day 60 (adult). On postnatal day 4 very light hybridization signal (labelling) was observed in cells of a number of nuclei including the central amygdaloid nucleus, the medial preoptic area, paraventricular nucleus and dorsomedial hypothalamic nucleus of the forebrain while lightly-labelled cells were detected in neurons of the nucleus of the solitary tract and locus coeruleus of the hindbrain. Hybridization signal was not apparent in other nuclei until later, with positively-labelled neurons first apparent in the dorsal cochlear nucleus at postnatal day 21. The abundance of preprogalanin messenger RNA-positive neurons and the intensity of the hybridization signal increased, in most regions, until postnatal day 28 when labelling resembled that of the mature rat. Preprogalanin messenger RNA was first detected in the cerebellum on postnatal day 10 only in Purkinje cells of lobule 10 of the posterior vermis and increased in distribution throughout Purkinje cell layers of the entire cerebellar cortex by postnatal day 13. The intensity of hybridization signal in Purkinje cells varied between lobules, with Purkinje cells in lobule 10 displaying a moderate to heavy degree of labelling, while lobules 6-9 and the more posterior lobules of the hemisphere including crus 2 of the ansiform lobule, the paramedian lobule and the copula pyramis, displayed only light labelling. The intensity of labelling in the anterior vermis and the remaining lobules of the hemisphere including crus 1 of the ansiform lobule, the simple lobule, the paraflocculus and the flocculus, was homogeneously weak. By postnatal day 21, Purkinje cell labelling reached maximum intensity in all lobules. Regional differences were still apparent, however, with labelling in the posterior vermis and hemisphere ranging from moderate to heavy, with only light to moderate labelling detected in the anterior vermis. The intensity of labelling in the posterior vermis and most lobules of the hemisphere was similar from postnatal day 21 to adulthood, while, in the anterior vermis, crus 1 of the ansiform lobule and the simple lobule, the intensity of hybridization decreased slightly by postnatal day 28 and was completely absent in Purkinje cells of the adult rat. Differential expression of preprogalanin messenger RNA in Purkinje cells of the developing rat cerebellum and transient expression in certain lobules suggests that galanin gene products may have a role in both the developing and mature rat brain and that galanin gene expression may represent a useful marker for differentiating the anterior and posterior cerebellar lobes.

Effects of sinoaortic denervation on Fos expression in the brain evoked by hypertension and hypotension in conscious rabbits

We have previously shown [Li and Dampney (1994) Neuroscience 61, 613-634] that periods of sustained hypertension and hypotension each induces a distinctive and reproducible pattern of neuronal expression of Fos (a marker of neuronal activation) in specific regions of the brainstem and forebrain of conscious rabbits. The aim of this study was to determine the contribution of afferent inputs from arterial baroreceptors to the activation of neurons in these various brain regions that is caused by a sustained change in arterial pressure. Experiments were carried out on rabbits in which the carotid sinus and aortic depressor nerves were cut in a preliminary operation. Following a recovery period of seven to 10 days, a moderate hypertension or hypotension (increase or decrease in arterial pressure of 20-30 mmHg) was induced in conscious barodenervated rabbits for 60 min by the continuous infusion of phenylephrine or sodium nitroprusside, respectively. In control experiments, barodenervated rabbits were subjected to the identical procedures except that they were infused with the vehicle solution alone. Compared with the effects seen in barointact rabbits, [Li and Dampney (1994) Neuroscience 61, 613-634] the number of neurons that expressed Fos in response to hypertension was reduced by approximately 90% in the nucleus of the solitary tract and in the caudal and intermediate parts of the ventrolateral medulla. In supramedullary regions, baroreceptor denervation resulted in a reduction of approximately 60% in hypertension-induced Fos expression in the central nucleus of the amygdala and in the bed nucleus of the stria terminalis, but no significant reduction in the parabrachial complex in the pons. Following hypotension, the number of neurons that expressed Fos in barodenervated rabbits, compared with barointact rabbits, [Li and Dampney (1994) Neuroscience 61, 613-634] was reduced by approximately 90% in the nucleus of the solitary tract, area postrema, and caudal, intermediate and rostral parts of the ventrolateral medulla. Baroreceptor denervation also resulted in a similar large reduction in hypotension-induced Fos expression in many supramedullary regions (locus coeruleus, midbrain periaqueductal grey, hypothalamic paraventricular nucleus, and in the central nucleus of the amygdala and the bed nucleus of the stria terminalis in the basal forebrain). In the supraoptic nucleus, hypotension-induced Fos expression in barodenervated rabbits was reduced by 75% compared to barointact animals, but was still significantly greater than in control animals. There was also a high level of Fos expression, much greater than in control animals, in the circumventricular organs surrounding the third ventricle (subfornical organ and organum vasculosum lamina terminalis). The results indicate that in conscious rabbits the activation of neurons that occurs in several discrete regions at all levels of the brain following a sustained change in arterial pressure is largely dependent upon inputs from arterial baroreceptors, with the exception of neurons in the circumventricular organs surrounding the third ventricle that are activated by sustained hypotension. The latter group of neurons are known to project to vasopressin-secreting neurons in the supraoptic nucleus, and may therefore via this pathway trigger the hypotension-induced release of vasopressin that occurs in the absence of baroreceptor inputs.

Distribution of bombesin-like immunoreactivity in the nucleus of the solitary tract and dorsal motor nucleus of the rat and human: colocalization with tyrosine hydroxylase

Bombesin is a peptide neurotransmitter/neuromodulator with important autonomic and behavioral effects that are mediated, at least in part, by bombesin-containing neurons and nerve terminals in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV). The distribution of bombesin-like immunoreactive nerve terminals/fibers and cell bodies in relation to a viscerotopically relevant subnuclear map of this region was studied by using an immunoperoxidase technique. In the rat, bombesin fiber/terminal staining was heavy in an area that included the medial subnucleus of the NTS and the DMV over their full rostral-caudal extent. Distinctly void of staining were the gelatinous, central, and rostral commissural subnuclei and the periventricular area of the NTS, regions to which gastric, esophageal, cecal, and colonic primary afferents preferentially project. The caudal commissural and dorsal subnuclei had light bombesin fiber/terminal staining, as did the intermediate, interstitial, ventral, and ventrolateral subnuclei. With colchicine pretreatment, numerous cell bodies were stained in the medial and dorsal subnuclei, with fewer neurons in the caudal commissural, intermediate, interstitial, ventral, and ventrolateral subnuclei. Bombesin-like immunoreactive neurons were found in numerous other areas of the brain, including the ventrolateral medulla, the parabrachial nucleus, and the medial geniculate body. In the human NTS/DMV complex, the distribution of bombesin fiber/terminal staining was very similar to the rat. In addition, occasional bombesin-like immunoreactive neurons were labeled in a number of subnuclei, with clusters of neurons labeled in the dorsal and ventrolateral subnuclei. Double immunofluorescence studies in rat demonstrated that bombesin colocalizes with tyrosine hydroxylase in neurons in the dorsal subnucleus of the NTS. Bombesin does not colocalize with tyrosine hydroxylase in any other location in the brain. In conclusion, the distribution of bombesin in the NTS adheres to a viscerotopically relevant map. This is the anatomical substrate for the effects of bombesin on gastrointestinal function and satiety and its likely role in concluding a meal. The anatomic similarities between human and rat suggest that bombesin has similar functions in the visceral neuraxis of these two species. Bombesin coexists with catecholamines in neurons in the dorsal subnucleus, which likely mediate, in part, the cardiovascular effects of bombesin.

Peptidase inhibitor-induced antidiuresis mediated through angiotensin and opioid receptors in the rat hypothalamus

We examined the effects on urine outflow rate after microinjections of thiorphan (a carboxypeptidase inhibitor) and bestatin (an aminopeptidase inhibitor) into the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei of anesthetized hydrated rats to determine the possible role of neuropeptides in the regulation of urine production. After individual microinjection of the peptidase inhibitors into the nuclei, only thiorphan at 100 nmol administered into the PVN significantly decreased the urine outflow rate. Two consecutive microinjections of the peptidase inhibitors at 100 nmol each into the nuclei induced potent antidiuresis. These effects after microinjections of the peptidase inhibitors into the PVN and SON were diminished by pretreatment with [Sar1,Ile8]angiotensin (ANG) II (an ANG II receptor antagonist) and naloxone (an opioid receptor antagonist) in the PVN and with [Sar1,Ile8]ANG II in the SON, respectively. A vasopressin (AVP) receptor antagonist, d(CH2)5-D-Tyr(Et)VAVP (i.v.), completely blocked the antidiuresis by microinjections of the peptidase inhibitors into both the nuclei. Urinary osmotic pressure was significantly increased by consecutive microinjections of the peptidase inhibitors into the PVN and SON. These results suggest that endogenously-released ANG II and opioid peptides in the PVN and ANG II in the SON regulate urine production mediated through increased AVP release.

Localization of preprogalanin messenger RNA in rat brain: identification of transcripts in a subpopulation of cerebellar Purkinje cells

Galanin, a 29 amino acid peptide, is widely distributed throughout both the peripheral and central nervous systems and is thought to be involved in multiple physiological functions including smooth muscle relaxation, stimulation of feeding, blood pressure regulation, control of hormone secretion and modulation of nociception. Galanin has been shown to co-exist with several neurotransmitters throughout the neuroaxis and in some cases to modify their presynaptic and postsynaptic actions. In the present study, the anatomical distribution of preprogalanin messenger RNA in rat brain was examined by in situ hybridization histochemistry using specific 35S-labelled oligonucleotide probes. Neurons expressing preprogalanin messenger RNA were found throughout the brain and were particularly abundant in the hypothalamus. High densities of preprogalanin messenger RNA-positive neurons were found in the anteroventral preoptic, supraoptic, paraventricular and dorsomedial nuclei of the hypothalamus, in the locus coeruleus and in the nucleus of the solitary tract. Moderate densities of preprogalanin messenger RNA-positive cells were apparent in the periventricular and arcuate nuclei of the hypothalamus, in the dorsal raphe and dorsal cochlear nuclei. Low densities of preprogalanin messenger RNA-expressing neurons were observed in the piriform cortex, medial septum and the retrochiasmatic area. These findings are consistent with results of previous in situ localization studies of preprogalanin messenger RNA and also with studies reporting the distribution of galanin-like immunoreactivity in rat brain. A novel finding, however, was the detection of preprogalanin messenger RNA in Purkinje cells in the caudal cerebellar vermis (lobules 6 to 10) and the flocculus and paraflocculus of the lateral hemispheres of the cerebellum. Galanin is presumably co-localized in these cells with GABA, which is normally present in Purkinje cells and possibly with tyrosine hydroxylase, which has recently been detected in a similar subpopulation of cerebellar Purkinje cells in both rat and mouse. Thus, the present study reveals a previously unreported site of galanin gene expression in the cerebellum which represents a novel, putative site of action for galanin to add to its already varied physiological roles.

Neurotensin projections to subfornical organ from arcuate nucleus

Two series of experiments were done in the rat to investigate whether neurons in arcuate nucleus of the hypothalamus (Arc) containing neurotensin (NT)-like immunoreactivity projected to subfornical organ (SFO). In the first series, the anterograde tract-tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was microiontrophoresed into the region of Arc that contains NT neurons. After a 9-12 day survival period the animals were sacrificed and forebrain sections that contained SFO were processed for combined PHA-L and NT immunoreactivity. In the second series of experiments, unilateral or bilateral electrolytic lesions of Arc were made and after a 10-17 day survival period SFO was examined to determine the relative contribution of NT Arc neurons to NT immunoreactivity within SFO. PHA-L labelled fibers with terminal-like boutons were found in SFO primarily on the side ipsilateral to the site of injection. A small number of the PHA-L labelled fibers in the lateral aspect of SFO was also immunoreactive to NT. Unilateral lesions reduced, whereas bilateral lesions of Arc eliminated most of the NT-like immunoreactivity within SFO. These data demonstrate the existence of a direct pathway from Arc to SFO that contains the putative neurotransmitter NT. These results suggest that this pathway may function in the modulation of neural and/or humoral events related to cardiovascular regulation and body fluid homeostasis by influencing the activity of SFO neurons.

Fos expression in neurons projecting to the pressor region in the rostral ventrolateral medulla after sustained hypertension in conscious rabbits

Previous studies in anaesthetized animals have shown that the baroreflex control of sympathetic vasomotor activity is mediated to a large extent by inhibitory inputs to sympathoexcitatory pressor neurons in the rostral part of the ventrolateral medulla. The aim of this study was to determine, in conscious rabbits, the distribution of neurons within the brain that have two properties characteristic of interneurons conveying baroreceptor signals to the rostral ventrolateral medulla: (i) they are activated by an increase in arterial pressure; and (ii) they project specifically to the rostral ventrolateral medulla pressor region. In a preliminary operation, an injection of the retrogradely transported tracer, fluorescent-labelled microspheres, was made into the physiologically identified pressor region in the rostral ventrolateral medulla. After a waiting period of one to eight weeks, hypertension was produced in the conscious rabbit by continuous intravenous infusion of phenylephrine at a rate sufficient to increase arterial pressure by approximately 20 mmHg, maintained for a period of 60 min. A control group of animals was infused with the vehicle solution alone. In confirmation of our previous study, hypertension produced by phenylephrine resulted in the neuronal expression of Fos (a marker of neuronal activation) in the nucleus of the solitary tract, area postrema, the intermediate and caudal parts of the ventrolateral medulla parabrachial complex, and in the central nucleus of the amygdala. Approximately 50% of the Fos-immunoreactive neurons in both the caudal and intermediate parts of the ventrolateral medulla were also retrogradely labelled from the rostral ventrolateral medulla pressor region; such double-labelled neurons were confined to a discrete longitudinal column located just ventrolateral to the nucleus ambiguus. Significant numbers of double-labelled neurons were also found in the nucleus of the solitary tract and area postrema, although these represented a much lower proportion (13-16%) of the total number of Fos-immunoreactive neurons in these regions. In the parabrachial complex, Fos-immunoreactive and retrogradely labelled neurons were largely separate populations, while in the amygdala they were entirely separate populations. In the control group of rabbits, virtually no double-labelled neurons were found in any of these regions. The results indicate that putative baroreceptor interneurons that project to the pressor region of the rostral ventrolateral medulla are virtually confined to the lower brainstem. In particular, they support the results of previous studies in anaesthetized animals indicating that neurons in the intermediate and caudal ventrolateral medulla convey baroreceptor signals to the rostral ventrolateral medulla pressor region, and extend them by demonstrating the precise anatomical distribution of these neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of substance P on cardiovascular regulation in the rabbit

The effect of substance P on blood pressure and aortic reflex was investigated in rabbits. Microinjections of substance P and Sar9, Met(O2)11-SP (a selective NK1-receptor agonist) into the floor of the fourth ventricle led to a dose-dependent increase of blood pressure and a sharp enhancement of the baroreflex. These effects were abolished by pretreatment with SR 140333 (a selective NK1-receptor antagonist). Intraventricular injection of the antagonist alone significantly decreased the amplitude of the aortic reflex. After bivagotomy, the amplitude of the parasympathetic component of the baroreflex decreased dramatically and substance P injections were no longer effective. Our results demonstrate that substance P activation of NK1 receptors plays a major role in the modulation of the parasympathetic component of the baroceptor reflex.

Neurotransmitters and neuropeptides in the baroreceptor reflex arc: connections between the nucleus of the solitary tract and the ventrolateral medulla oblongata in the rat

The primary baroreceptor area (nucleus of the solitary tract-NTS) is anatomically interconnected with the rostral ("vasomotor area") and the caudal ("vasodepressor area") ventrolateral medulla by a well-defined arc of neuronal pathways. The chemical character and the direction of these pathways have been investigated with immunohistochemical and neurochemical techniques in intact and brainstem-operated rats. The transection of the neuronal arc resulted in an accumulation of tyrosine hydroxylase immunoreactivity in a small group of cells in the NTS adjacent to the area postrema, ipsilateral to the knife cut. Decreased angiotensinogen mRNA and atrial natriuretic peptide concentrations were measured in the ventrolateral medulla after the cut, and an accumulation of angiotensin II-immunoreactivity was found in neuronal perikarya in the ipsilateral NTS. Intracranial vagotomy caused marked depletions in glutamate levels in the subcommissural portion of the NTS and in the caudal ventrolateral medulla but nowhere else in the brainstem investigated including the rostral ventrolateral medulla.

Local and commissural neuropeptide-containing projections of the nucleus of the solitary tract to the dorsal vagal complex in the pigeon

The neuropeptide content of neurons of the nucleus of the solitary tract (NTS), which have local and commissural projections to the dorsal motor nucleus of the vagus (DMNX) and to NTS, were demonstrated in the pigeon (Columba livia) by using a combined fluorescein-bead retrograde-transport-immunofluorescence technique. The specific peptides studied were bombesin, cholecystokinin, enkephalin, galanin, neuropeptide Y, neurotensin, and substance P. Perikarya immunoreactive for bombesin were located in medial tier subnuclei of NTS and the caudal NTS. Most galanin- and substance P-immunoreactive cells were found in subnucleus medialis ventralis. Cells immunoreactive for neuropeptide Y were found in the medial tier of NTS and in the lateral tier, especially in subnucleus lateralis dorsalis intermedius. The majority of enkephalin- and neurotensin-immunoreactive cells were found centrally in subnuclei medialis dorsalis and medialis intermedius. Cells immunoreactive for cholecystokinin were located in subnuclei lateralis dorsalis pars anterior, medialis superficialis, and the caudal NTS. Based on the presence of retrogradely labeled cells, numerous neurons of the medial tier of NTS, but extremely few lateral tier NTS neurons, had projections to the ipsilateral and contralateral DMNX and NTS. The number of retrogradely labeled NTS cells was always greater ipsilaterally than contralaterally. The percentages of peptide-immunoreactive NTS cells that projected to the ipsilateral and contralateral DMNX were in the ranges of 29-61% and 10-48%, respectively. The percentages of peptide-immunoreactive NTS cells that projected to the contralateral NTS ranged from 13 to 60%. Peptide-immunoreactive NTS cells that have local and commissural projections to DMNX and NTS may act as interneurons in vagovagal reflex pathways and in the integration of visceral sensory and forebrain input to NTS and DMNX.

Expression of Fos-like protein in brain following sustained hypertension and hypotension in conscious rabbits

The purpose of this study was to examine comprehensively and quantitatively the effects of sustained hypertension and hypotension on neuronal expression of Fos, the protein product of the proto-oncogene c-fos, in the brain of conscious rabbits. Hypertension or hypotension was produced by continuous intravenous infusion of phenylephrine or nitroprusside, at a rate sufficient to increase or decrease, respectively, arterial pressure by 20-30 mmHg, maintained for a period of 60 min. In comparison with a sham control group of rabbits that were infused with the vehicle solution alone, hypertension induced a significant increase in Fos immunoreactivity in the area postrema, the nucleus tractus solitarii, the caudal and intermediate ventrolateral medulla, the lateral parabrachial nucleus and the central nucleus of the amygdala. Double-labelling for tyrosine hydroxylase and Fos immunoreactivity showed that few (approximately 5%) of the Fos-positive neurons in the caudal and intermediate ventrolateral medulla in this group of animals were also positive for tyrosine hydroxylase. Hypotension also produced a significant increase in Fos immunoreactivity in the above regions, as well as in the rostral ventrolateral medulla, the A5 area, the locus coeruleus and subcoeruleus, the paraventricular nucleus, the supraoptic nucleus, the arcuate nucleus and the medial preoptic area. Approximately 65% of neurons in the rostral, intermediate and caudal ventrolateral medulla that expressed Fos following hypotension were also positive for tyrosine hydroxylase. Similarly, in the pons, approximately 75% of Fos-positive cells in the locus coeruleus, subcoeruleus and A5 area were positive for tyrosine hydroxylase. In the hypothalamus, 92% of Fos-positive neurons in the supraoptic nucleus, and 37% of Fos-positive neurons in the paraventricular nucleus, were immunoreactive for vasopressin. Our results demonstrate that hypertension and hypotension induce reproducible and specific patterns of Fos expression in the brainstem and forebrain. The distribution patterns and chemical characteristics of Fos-positive neurons following sustained hypertension or hypotension are significantly different. In particular, hypotension, but not hypertension, caused Fos expression in many tyrosine hydroxylase-positive cells within all pontomedullary catecholamine cell groups.

Regional haemodynamic effects of carbachol injected into the hypothalamic paraventricular nuclei of conscious, unrestrained rats

Carbachol was injected into the hypothalamic paraventricular nuclei (PVN) of conscious, unrestrained Long Evans rats, chronically instrumented with intravascular catheters and pulsed Doppler probes to assess changes in regional haemodynamics. Bilateral microinjections of carbachol (1 ng-1 microgram) produced increases in blood pressure, bradycardias and vasoconstrictions in renal, superior mesenteric and hindquarters vascular beds. In the presence of phentolamine, the bradycardic and hindquarters vasoconstrictor responses to carbachol were unchanged while the pressor response was smaller due to a reduction in the renal and the superior mesenteric vasoconstriction. In the presence of propranolol, the bradycardic response was reduced, but the pressor and renal vasoconstrictor responses were potentiated, whereas the superior mesenteric and hindquarter vasoconstrictions were not changed significantly. In the presence of phentolamine and propranolol, the heart rate and pressor responses, as well as the renal vasoconstriction, were unchanged, whereas the superior mesenteric vasoconstriction was reduced and the hindquarters vasoconstriction was potentiated. Together these results are consistent with an involvement of the sympathoadrenal system in the pressor response to carbachol injected into the PVN of untreated animals. They indicate that alpha-adrenoceptor-mediated vasoconstriction in the superior mesenteric vascular bed is a particularly important component in that regard. In the presence of the vasopressin antagonist, d(CH2)5(Tyr(Et))DAVP, alone or in combination with phentolamine and propranolol, the pressor response to carbachol was substantially reduced, while the renal and superior mesenteric vasoconstrictor effects were completely abolished; the bradycardia was not significantly affected by this treatment. These results indicate an important involvement of vasopressin in the cardiovascular responses to carbachol injected into the PVN of untreated animals. Moreover, in the presence of the vasopressin antagonist the hindquarters vascular bed showed a vasodilatation following PVN injection of carbachol; this effect was reversed to a vasoconstriction following combined i.v. pretreatment with the vasopressin antagonist, phentolamine and propranolol and hence was possibly due to circulating adrenaline acting on vasodilator beta 2-adrenoceptors. However, there was a residual hindquarters vasoconstriction raising the possibility that non-adrenergic, non-vasopressinergic vasoconstrictor mechanisms were influencing that vascular bed.

Effects of central angiotensin II and angiotensin III on baroreflex regulation

In the present study the cardiovascular effects of intracerebroventricularly (i.c.v.) applied angiotensin II (AN II) and angiotensin III (AN III) were analysed in conscious Wistar rats. The baroreceptor heart reflex (BHR) was elicited by intravenous bolus injection of both phenylephrine (1 microgram) and sodium nitroprusside (5 micrograms) before and after i.c.v. administration (1.5 and 15 min) of the peptides. Administration of 20 ng and 200 ng AN II produced a short increase in inter-beat interval (IBI) and a long-lasting increase in mean blood pressure (MBP), inclusive of a drinking response. Only after the high dose of 200 ng AN II we found a continuous impairment in the BHR for reflex bradycardia. Inversely, the small doses of both 100 pg AN II and 100 pg AN III were without effects on IBI and MBP; they induced an enhancement in BHR for the reflex bradycardia and after 100 pg AN II it was also found for the reflex tachycardia. Pretreatment with 20 nmol amastatin (AM), a specified aminopeptidase A inhibitor, followed by 100 pg An II suppressed the enhancement in BHR. AM alone was without effects in this respect. These findings suggest that: 1) the influence of central angiotensin on the BHR could be dose-dependent in the opposite way and 2) AN III seems to be the active form and involved in the central blood pressure regulatory mechanism.

Nucleus of the solitary tract and dorsal motor nucleus of the vagus nerve of the pigeon: localization of peptide and 5-hydroxytryptamine immunoreactive fibers

The distribution of peptide and serotonin fibers in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus nerve (DMNX) in the pigeon (Columba livia) was investigated immunocytochemically. This information was correlated with the viscerotopic organization of the nuclei and with central NTS circuitry to suggest the role of the neurochemical containing fibers in the regulation of organ function. The distribution of fibers containing cholecystokinin (CCK), calcitonin gene-related peptide (CGRP), enkephalin (ENK), neuropeptide Y (NPY), neurotensin (NT), substance P (SP), somatostatin (SS), vasoactive intestinal peptide (VIP), and 5-hydroxytryptamine (5-HT) was determined. Each substance had a distinct distribution within the subnuclei of NTS-DMNX, but certain generalities can be deduced. In the DMNX, fibers immunoreactive for ENK, NT, and SP were found in greatest concentration, while CGRP and 5-HT immunoreactive fibers were the least dense. This suggests that ENK, NT, and SP may have a significant modulatory effect on gastrointestinal functions. In the NTS overall, ENK, NT, SP, and VIP fibers were found in high density, CCK, NPY, SS, and 5-HT fibers were found in moderate density, and CGRP fibers were found in low density. However, some individual NTS subnuclei were found to contain moderate to high concentrations of each of the substances, including CGRP. Fibers containing CCK, ENK, NT, SP, SS, and VIP in the medial dorsal NTS subnuclei may regulate gastroesophageal functions. The caudal part of subnucleus lateralis parasolitarius did not contain most of the substances, which suggests that pulmonary function is not modulated by these neurochemicals. The boundaries of a subnucleus could sometimes be demarcated by a change in density of immunoreactive fibers between adjacent subnuclei. This was particularly evident in NTS subnuclei medialis dorsalis anterior centralis and lateralis parasolitarius, and in DMNX subnucleus posterior dorsalis magnocellularis. The selective distribution of peptide and serotonin immunoreactive fibers in various subnuclei of NTS-DMNX suggests that these substances may be differentially involved in neural circuits that mediate cardiovascular and gastrointestinal functions.

Opioid peptide gene expression in the nucleus tractus solitarius of rat brain and increases induced by unilateral cervical vagotomy: implications for role of opioid neurons in respiratory control mechanisms

Neurons expressing messenger RNA encoding the opioid peptide precursors, preproenkephalin and preprodynorphin were localized in the medulla oblongata of the rat by in situ hybridization of specific DNA oligonucleotide probes. Neurons containing preproenkephalin messenger RNA were found throughout the medullary reticular formation in the gigantocellular and paragigantocellular reticular nuclei, the parvicellular and lateral reticular nuclei; commissural, medial and ventrolateral subnuclei in the nucleus tractus solitarius and the nucleus of the spinal trigeminal tract. Labelled cells were also concentrated in the more medial regions of the area postrema. In contrast, neurons containing preprodynorphin messenger RNA had a more restricted distribution and were detected in the commissural and ventrolateral nucleus tractus solitarius and nucleus of the spinal trigeminal tract, especially in the more dorsal regions. Expression of preproenkephalin and preprodynorphin messenger RNA was also examined in the dorsal vagal complex of rats that had undergone a unilateral nodose ganglionectomy or cervical vagotomy. Twenty-four hours after both cervical vagotomy and nodose ganglionectomy, there was a specific 1.5-2-fold elevation in preproenkephalin and preprodynorphin messenger RNA levels in the ventrolateral subnucleus of the contralateral nucleus tractus solitarius relative to levels in the ipsilateral nucleus tractus solitarius and in the nucleus tractus solitarius of sham-operated animals. Previous immunohistochemical studies demonstrating the co-localization of enkephalin and dynorphin in the ventrolateral nucleus tractus solitarius suggest that these changes occurred in the same population of neurons. In light of the suggested role of the ventrolateral nucleus tractus solitarius as a central respiratory centre and the activation of the intact pulmonary afferents that innervate this area following a unilateral vagotomy (which increases inspiration volume and expiratory time by affecting the Hering-Breuer reflex), our results suggest a specific involvement of enkephalin- and dynorphin-containing neurons in the ventrolateral nucleus tractus solitarius in central respiratory control mechanisms.

Intracerebroventricular treatment with vasopressin V1-receptor antagonist inhibits centrally-mediated pressor response to clonidine in conscious rats

The effect of intracerebroventricular (i.c.v.) treatment with a vasopressin (AVP) V1-receptor antagonist on the pressor response to i.c.v. injection of clonidine was investigated in conscious rats with chronic i.c.v. guide cannulas and an arterial catheter. In conscious rats, i.c.v.-injected clonidine (5 and 10 micrograms) dose-dependently produced a pressor response with a decrease in heart rate. No significant depressor response was induced by clonidine. The i.c.v. pretreatment with an AVP V1-receptor antagonist ([d(CH2)5-Tyr(Me)]-AVP) at 0.5-2.5 micrograms dose-dependently inhibited the pressor response to 10 micrograms of i.c.v.-injected clonidine, while systemic (i.v.) pretreatment with the antagonist (2.5 micrograms) had no effect. In pentobarbital-anesthetized rats, 10 micrograms of i.c.v.-injected clonidine caused a marked depressor response associated with bradycardia. However, i.c.v. pretreatment with the antagonist (2.5 micrograms) did not affect cardiovascular responses to i.c.v.-injected clonidine. These results suggest that endogenous AVP in the brain is involved in the mechanisms underlying the pressor response to i.c.v.-injected clonidine in conscious rats.

Pressor response to microinjection of clonidine into the hypothalamic paraventricular nucleus in conscious rats

We have reported that intracerebroventricular (i.c.v.) injection of clonidine causes pressor response in conscious rats. To determine the effective brain site, cardiovascular responses induced by unilateral microinjection of clonidine into various hypothalamic nuclei of conscious rats were studied. Microinjection of clonidine (5-20 micrograms/0.5 microliter) into the paraventricular nucleus (PVN) of conscious rats dose-dependently produced a long-lasting pressor response with a decrease in heart rate, which mimicked the response to i.c.v. injection of clonidine. However, clonidine (10 micrograms) injection into various hypothalamic nuclei (anterior, posterior, ventromedial and dorsomedial nucleus) caused a small or no pressor response. In anesthetized rats, clonidine injected into the PVN induced a long-lasting depressor response concomitant with bradycardia. PVN pretreatment with the alpha 2-adrenoceptor antagonist, yohimbine (1 and 10 micrograms), dose-dependently inhibited the pressor response to PVN injected clonidine, but the alpha 1-adrenoceptor antagonist, prazosin (1 microgram), had no significant effect. Central (i.c.v.) pretreatment with the vasopressin (AVP) V1-receptor antagonist, [d(CH2)5Tyr(Me)]-AVP (0.5 and 2.0 micrograms), dose-dependently inhibited the pressor response to PVN injection of clonidine (10 micrograms), while systemic (i.v.) and local (intra-PVN injection) pretreatments with V1-receptor antagonist (2.0 micrograms) had no effect. These results suggest that the pressor response to microinjection of clonidine into the PVN of conscious rats is mediated by endogenous brain AVP, which is released by activation of alpha 2-adrenoceptors. It is also suggested that the PVN is a possible brain site for the pressor response to i.c.v. injected clonidine.

The central autonomic network: functional organization, dysfunction, and perspective

The central autonomic network (CAN) is an integral component of an internal regulation system through which the brain controls visceromotor, neuroendocrine, pain, and behavioral responses essential for survival. It includes the insular cortex, amygdala, hypothalamus, periaqueductal gray matter, parabrachial complex, nucleus of the tractus solitarius, and ventrolateral medulla. Inputs to the CAN are multiple, including viscerosensory inputs relayed on the nucleus of the tractus solitarius and humoral inputs relayed through the circumventricular organs. The CAN controls preganglionic sympathetic and parasympathetic, neuroendocrine, respiratory, and sphincter motoneurons. The CAN is characterized by reciprocal interconnections, parallel organization, state-dependent activity, and neurochemical complexity. The insular cortex and amygdala mediate high-order autonomic control, and their involvement in seizures or stroke may produce severe cardiac arrhythmias and other autonomic manifestations. The paraventricular and other hypothalamic nuclei contain mixed neuronal populations that control specific subsets of preganglionic sympathetic and parasympathetic neurons. Hypothalamic autonomic disorders commonly produce hypothermia or hyperthermia. Hyperthermia and autonomic hyperactivity occur in patients with head trauma, hydrocephalus, neuroleptic malignant syndrome, and fatal familial insomnia. In the medulla, the nucleus of the tractus solitarius and ventrolateral medulla contain a network of respiratory, cardiovagal, and vasomotor neurons. Medullary autonomic disorders may cause orthostatic hypotension, paroxysmal hypertension, and sleep apnea. Neurologic catastrophes, such as subarachnoid hemorrhage, may produce cardiac arrhythmias, myocardial injury, hypertension, and pulmonary edema. Multiple system atrophy affects preganglionic autonomic, respiratory, and neuroendocrine outputs. The CAN may be critically involved in panic disorders, essential hypertension, obesity, and other medical conditions.

Effects of central substance P on baroreflex regulation

The effects of intracerebroventricularly (i.c.v.) administered Substance P (100 pg, 1 microgram, 10 micrograms) on mean blood pressure (MBP), inter-beat interval (IBI) and the baroreceptor heart reflex (BHR) were studied in conscious Wistar rats. The BHR was induced by intravenous injection of both phenylephrine (1 microgram) and sodium nitroprusside (5 micrograms) before and after SP administration (3 and 15 min). The dose of 100 pg SP was without effect on the resting values of both MBP and IBI but enhanced the BHR sensitivity by about + 0.5 ms/mm Hg in the phenylephrine test 3 min after i.c.v. SP. 1 microgram and 10 micrograms SP caused a long-lasting dose dependent increase in MBP and changed the IBI. In contrast to the results obtained with 100 pg, the BHR sensitivity was impaired-1 microgram SP: -0.2 ms/mm Hg (phenylephrine) and -0.45 ms/mm Hg (nitroprusside), 10 micrograms SP: -0.35 ms/mm Hg (phenylephrine). These changes in BHR sensitivity were only recognised 3 min, but not 15 min, after i.c.v. treatment even hough changes in the resting values of MBP and IBI were still present at 15 min. These data suggest that SP through the cerebrospinal fluid may participate in central cardiovascular control and, moreover, it may influence the baroreflex regulation.

Neonatally administered capsaicin induces functional disturbances in the carotid afferent pathway to the nucleus tractus solitarius

The effect of neonatal capsaicin treatment on chemo- and/or barosensory input to the medulla was studied in 35-40-day-old rats. By means of responses evoked in the nucleus tractus solitarius by stimulating the ipsilateral sinusal nerve, the excitability of slow-conducting carotid afferent fibers and the effect of substance P microinjection into the fourth ventricle were evaluated. Neonatal capsaicin resulted in reduced amplitude of the late component of the evoked responses, increased chronaxie values in the strength-duration paradigm, and increased sensitivity of evoked responses to the inhibitory effect of intracerebroventricular administered substance P. The results indicate that capsaicin given early in life leads to functional disturbances of chemo- and/or barosensory input to the nucleus tractus solitarius, involving both the slow-conducting primary afferents and the receptors for substance P of the second-order cells of the sensory pathway.

Immunohistochemical localization of serotonin, leu-enkephalin, tyrosine hydroxylase, and substance P within the visceral sensory area of cartilaginous fish

We examined the distribution of immunoreactivity to serotonin (5-HT), leu-enkephalin (LENK), tyrosine-hydroxylase (TH), and substance P (SP) within the primary visceral sensory region of cartilaginous fish. Two genera of sharks, Squalus and Heterodontus, a skate, Raja, a ray, Myliobatis, and a holocephalian, Hydrolagus, were used. Cranial nerves, VII, IX, and X enter the visceral sensory complex from the lateral aspect and divide it into lobes. Based on sagittally cut sections, there are four lobes in Hydrolagus and five in Squalus, corresponding to the number of gill arches. The neurochemicals are differentially distributed within each lobe. LENK+ and 5-HT+ fibers are located in all regions within the visceral sensory complex. SP+ fibers are extremely dense in a dorsolateral subdivision and do not extend as far ventrally as 5-HT+ and LENK+ fibers. The lobes lack 5-HT+ cells, but contain a few LENK+ and SP+ cells. Many TH+ cells are distributed in dorsomedial portions of the complex, but there are few TH+ fibers. Thus, the visceral sensory area of cartilaginous fish contains several divisions that can be distinguished by their neurochemical content.

Expression of c-fos and NGFI-A messenger RNA in the medulla oblongata of the anaesthetized rat following stimulation of vagal and cardiovascular afferents

Messenger RNA encoding the immediate early genes (IEGs) c-fos and NGFI-A was localized by in situ hybridization of specific 35S-labelled oligonucleotides to detect activated neurones in the medulla oblongata following unilateral electrical stimulation of the vagus (nX) and aortic depressor nerve (ADN), and following mechanical stimulation of the left carotid sinus (CS). In electrically stimulated rats, c-fos and NGFI-A mRNA was strongly expressed in the nucleus tractus solitarius (NTS) (predominantly ipsilaterally), area postrema (AP) and in a dorsal subregion of the paratrigeminal nucleus (PTN). Lower levels of c-fos and NGFI-A mRNA were seen in the ipsilateral NTS and PTN following mechanical stimulation of the left CS. In general these data correlate with the topography of innervation by the different nerve afferents, although the expression in the PTN (and in some cases the AP) would not be predicted on the basis of neuronal innervation patterns reported for the rat. Expression of these IEGs also occurred in the rostral and caudal ventrolateral medulla and inferior olive of both stimulated and sham-operated rats; presumably due to effects of the anaesthesia and surgical procedures. In conclusion the localization of the expression of c-fos and NGFI-A mRNAs represents a useful neuroanatomical technique for detecting the cell bodies of neurones that are activated by cardiovascular nerve afferents and should allow the further characterization of the neurochemical identity of these neurones.

Substance P depresses bioelectrical responses evoked in the nucleus tractus solitarii: interaction with gamma-aminobutyric acid-ergic neurons

The effects of intracerebroventricular (i.c.v.) administration of substance P (SP) and gamma-aminobutyric acid (GABA) on responses evoked in the nucleus tractus solitarii (NTS) by electrical stimulation of the ipsilateral sinusal nerve were studied in alpha-chloralose-anesthetized rats. Both SP (0.01-10 micrograms) and GABA (100 micrograms) significantly depressed the presumably C-fiber mediated, late negative wave of the response. The effects were almost completely prevented by bicuculline (10 micrograms i.c.v.). It is concluded that i.c.v. administered SP induces dose-dependent depression of baro- and/or chemosensory transmission in the NTS, via a mechanism involving interactions with GABAergic neurons of the NTS.

Preprogastrin-releasing peptide messenger ribonucleic acid: neuroanatomical localization in rat brain by in situ hybridization with synthetic oligodeoxynucleotide probes

Gastrin-releasing peptide (GRP) is a 27 amino acid peptide that is present in both the central and peripheral nervous systems and that shares immunological and functional properties with the amphibian peptide, bombesin. GRP has multiple putative biological functions including effects on feeding behaviour and carbohydrate metabolism, body temperature, and effects on hormone release, but little is known about the regulation of GRP gene expression in the brain. This study examined the distribution of neurones expressing preproGRP mRNA in rat brain by in situ hybridization of [35S]-labelled DNA oligonucleotides. PreproGRP mRNA was detected in several regions of brain, with highest concentrations in the parvocellular paraventricular and suprachiasmatic nuclei of the hypothalamus, the lateral and basolateral nuclei of the amygdala, the amygdaloid-hippocampal area and the ventral part of the granule cell layer of the dentate gyrus. Moderate levels were seen in layers II and III of the cingulate and retrosplenial cortex, the medial and mediobasal nuclei of the amygdala, the anteroventral thalamic nucleus; medial geniculate nucleus and the parabrachial nucleus. These findings are largely consistent with the cellular localization of GRP-like immunoreactivity in rat brain and recent studies of preproGRP mRNA localization using cRNA probes. The distribution of preproGRP mRNA observed further suggests the involvement of GRP in the central regulation of several functions including regulation of hypothalamic/pituitary hormone release.

Enkephalins, substance P and acetylcholine microinjected into the nucleus ambiguus elicit vagal bradycardia in rats

Little is known about putative transmitters in the nucleus ambiguus (NA) mediating parasympathetic control of the heart, although Met-enkephalin (m-ENK), Leu-enkephalin (l-ENK), substance P (SP) and acetylcholine (Ach) have been detected in the cell bodies and fibers of this nucleus. The effects of these substances on arterial pressure (AP) and heart rate (HR) were studied by microinjecting them (4-20 nl) into the NA. Experiments were done in 26 spinal (high cervical) rats that were anesthetized with urethane and artificially ventilated. L-Glutamate (GLU) was microinjected into the right NA to identify the location of cell bodies from which decreases in HR and AP could be elicited. m-ENK, l-ENK, SP or Ach was then microinjected into these sites. Microinjection of 1 nmol of GLU elicited significant decreases in HR (-72.2 +/- 9.7 bpm, n = 15) which were not accompanied by significant decreases in mean AP. Microinjection of m-ENK (15-200 pmol; n = 7), l-ENK (15-200 pmol; n = 6), SP (0.9-15 pmol; n = 7) and Ach (2.0-20 pmol; n = 7) into the NA decreased HR in a dose-dependent manner but did not affect AP. The magnitudes of HR responses to m-ENK, l-ENK, SP and Ach were smaller but of longer duration than the changes in HR to microinjection of GLU. These results suggest a physiological role for GLU, enkephalins, SP and Ach in the vagal control of HR mediated by the NA.

Somatostatin inhibits the centrally mediated hypertensive response to clonidine in freely moving rats

The effect of somatostatin on the hypertensive response induced by intracerebroventricular (i.c.v.) injection of clonidine was investigated in freely moving rats. A 10 micrograms i.c.v. injection of clonidine produced a marked pressor response and a decrease in heart rate. No depressor response was induced by clonidine. The i.c.v. pretreatment with somatostatin (2 and 5 micrograms) dose-dependently inhibited the pressor response to i.c.v. injected clonidine (10 micrograms), and a long-lasting depressor response was observed. Systemic (i.v.) treatment with somatostatin had no such effect. These results suggest that brain somatostatin modulates the centrally-mediated pressor response to clonidine.

Neurotransmitter plasticity in the sympathetic nervous system: influence of external factors and possible physiological implications

Neuronal function can be modulated by a variety of neuronal, environmental and hormonal stimuli. One form of neuronal modulation is the change in the biosynthesis of specific neurotransmitters. This is of particular interest since neurotransmitters are the agents responsible for neuronal communication. The analysis of the long-term modulation of neurotransmitter expression in response to external factors could be a suitable model to study the possible biochemical mechanisms involved in learning and memory. Furthermore, understanding the molecular mechanisms involved in the regulation of norepinephrine synthesis in the sympathetic nervous system may be relevant for understanding stress and diseases of the cardiovascular system.

Central interaction between endothelin and brain natriuretic peptide on pressor and hormonal responses

Interaction between intracerebroventricular (i.c.v.) administration of endothelin (ET) and brain natriuretic peptide (BNP) on pressor and hormonal responses was examined in unanesthetized, freely moving rats. I.c.v. administered ET (5, 20 or 40 pmol/2 microliters) dose-dependently increased arterial pressure. Plasma catecholamine levels were elevated by 40 pmol of ET, and plasma ACTH level was also elevated by centrally administered ET in a dose-dependent manner. I.c.v. administration of BNP (0.2, 1 nmol/3 microliters) dose-dependently attenuated central ET (40 pmol/2 microliter)-induced pressor response, plasma catecholamine and ACTH secretion. These results indicate that ET may be one of the neuropeptides which stimulate both sympathetic nervous system and hypothalamo-pituitary-adrenal axis, and that BNP and ET interact in the central nervous system (CNS) to regulate cardiovascular and hormonal functions. Furthermore, these results raise a possibility that BNP antagonizes the effect of not only angiotensin II but also other neuropeptides in the CNS.

Role of central tachykinin peptides in cardiovascular regulation in rats

The mechanisms of action of tachykinin peptides thought to be involved in central cardiovascular regulation were examined. Intracerebroventricular injections (i.c.v.) of tachykinin peptides caused dose-dependent increases in blood pressure and heart rate. The pressor responses to substance P (SP) (10 micrograms, i.c.v.) and neurokinin A (NKA) (10 micrograms, i.c.v.) were blocked by peripheral administration of pentolinium or phentolamine, and partially attenuated by adrenalectomy. In contrast, the only initial pressor response to the neurokinin B (NKB) analogue senktide (10 micrograms, i.c.v.) was blocked by pentolinium or phentolamine. The pressor response to senktide was inhibited by pretreatment with a vasopressin V1 receptor antagonist (d(CH2)5OMe(Tyr)AVP) (10 micrograms/kg, i.v.), and senktide (10 micrograms, i.c.v.) caused an increase in plasma vasopressin level. However, the vasopressin antagonist did not influence the SP- and NKA-induced pressor responses. These results suggest that central SP and NKA increase the blood pressure and heart rate via sympathetic nerve activity, whereas central NKB increases the blood pressure mainly via release of vasopressin from the hypothalamus.

Localization of preprogalanin mRNA in rat brain: in situ hybridization study with a synthetic oligonucleotide probe

Galanin is a peptide containing 29 amino acid residues that is present in both the central and peripheral nervous systems. Galanin has multiple putative biological functions including regulation of hormone release, stimulation of feeding behaviour, and effects on blood pressure. This study examined the distribution of neurones expressing preprogalanin mRNA in the rat brain by in situ hybridization of a specific 35S-labelled oligonucleotide. Preprogalanin mRNA was detected in several regions of brain, with high concentrations in the paraventricular, periventricular, supraoptic, dorsomedial and arcuate nuclei of the hypothalamus; the locus coeruleus and dorsal raphe nucleus in the pons; and the nucleus tractus solitarii and ventrolateral reticular nucleus in the medulla. These findings are consistent with studies of the cellular localization of galanin-like immunoreactivity in rat brain, and further suggest the involvement of galanin in the regulation of several functions ranging from water balance to blood pressure control.

Neuropeptides and catecholamines in efferent projections of the nuclei of the solitary tract in the rat

This study focuses on the involvement of catecholamines and nine different peptides in efferents of the nucleus of the solitary tract to the central nucleus of the amygdala, the bed nucleus of the stria terminalis, and different parabrachial and hypothalamic nuclei in the rat. A double-labeling technique was used that combines a protein-gold complex as the retrograde tracer with immunohistochemistry. Catecholaminergic projection neurons were the most numerous type observed and projected mainly ipsilaterally to all targets studied. Most projections arose from areas overlying the dorsal motor nucleus, mainly the medial nucleus. Neurons synthesizing somatostatin, met-enkephalin-Arg-Gly-Leu, dynorphin B, neuropeptide Y, and neurotensin projected to all structures examined. Somatostatin and enkephalin immunoreactive projection cells were the most numerous. They were located in close proximity to each other, including all subnuclei immediately surrounding the solitary tract, bilaterally. Most dynorphin and neuropeptide Y immunoreactive projection cells were found rostral to that of enkephalinergic and somatostatinergic projections, and mainly in the ipsilateral medial nucleus. Neurotensinergic projections were sparse and from dorsal and dorsolateral nuclei. Substance P and cholecystokinin contribute to parabrachial afferents. The location of substance P immunoreactive projection cells closely resembled that of enkephalinergic and somatostatinergic projections. Projecting cholecystokinin immunoreactive cells were observed in dorsolateral nucleus. Bombesin immunoreactive cells in dorsal nucleus projected to either the parabrachial or hypothalamic nuclei. No vasoactive intestinal polypeptide-containing cells were detected. Thus, most catecholaminergic and neuropeptidergic efferents originated from different populations of cells. It is proposed that catecholaminergic neurons constitute the bulk of solitary efferents and that they may contribute to autonomic neurotransmission. Peptidergic neurons mainly form other subgroups of projections and may play a role in modulating the physiological state of the target nuclei.

Cardiovascular instability induced by intracerebroventricular administration of vasopressin or corticotrophin-releasing factor in conscious long evans and brattleboro rats

Abstract Conscious Long Evans and Brattleboro rats, chronically instrumented with pulsed Doppler probes around left renal and superior mesenteric arteries and the distal abdominal aorta, had vasopressin or corticotrophin-releasing factor administered intracerebroventricularly. In Long Evans rats, vasopressin caused no cardiovascular instability, but in Brattleboro rats, vasopressin caused the development of marked oscillations in blood pressure and heart rate. Under the latter conditions, falls in blood pressure were accompanied by increases in hindquarter blood flow. Similar oscillations in blood pressure, heart rate and regional haemodynamics were seen in Long Evans and Brattleboro rats given corticotrophin-releasing factor. These results indicate that centrally-administered vasopressin and corticotrophin-releasing factor can have an important influence on the control of regional haemodynamics. In some respects the effects of the peptides resemble the changes seen during the defence reaction.

Steroid hormones and the cardiovascular system: direct actions of estradiol, progesterone, testosterone, gluco- and mineralcorticoids, and soltriol [vitamin D] on central nervous regulatory and peripheral tissues

Knowledge of steroid hormone sites of action and related effects in cardiovascular and neural regulatory tissues is reviewed. Evidence for nuclear receptor sites is derived mainly from autoradiographic studies with relatively intact tissues and some biochemical studies with tissue homogenates. In the heart and in the walls of blood vessels, estradiol, dihydrotestosterone, corticosterone, aldosterone, dexamethasone, and soltriol (vitamin D) show nuclear binding. In the brain and spinal cord, neuronal regions associated with cardiovascular regulation contain nuclear receptors in specific patterns for each steroid hormones, including progesterone and soltriol. These data indicate that all steroid hormones exert direct actions on the cardiovascular system at its different levels of organization, thus enabling adjustment to the changing demands during reproduction (gonadal steroids), stress (adrenal steroids), and solar seasons (vitamin D-soltriol).