Neuroprotective effects of R,R-tetrahydrochrysene against glutamate-induced cell death through anti-excitotoxic and antioxidant actions involving estrogen receptor-dependent and -independent pathways

Glutamate-induced neural cell death is mediated by excitotoxicity and oxidative stress. Treatment of glutamate toxicity with estrogen and its related compounds for neuroprotection remains controversial. In this study, we examined the effects of selective estrogen receptor (ER) ligands on glutamate toxicity and found that R,R-tetrahydrochrysene (R,R-THC), an antagonist of ERbeta and agonist of ERalpha, has neuroprotective effects against glutamate-induced death in primary rat cortical cells and mouse N29/4 hypothalamic cells. The protective effect of R,R-THC was dose-dependent and was maintained even when added several hours after the initial glutamate exposure. R,R-THC blocked glutamate-induced depletion of intracellular glutathione, increased superoxide dismutase activity, and protected cells from hydrogen peroxide-induced death. R,R-THC also prevented glutamate-induced nuclear translocation of apoptotic inducing factor and release of mitochondrial cytochrome c. The protective effect of R,R-THC was blocked by methyl-piperidino-pyrazole (MPP; an ERalpha antagonist) in glutamate-treated cortical cells, and pretreatment with MK-801 (an NMDA receptor antagonist) but not CNQX (an AMPA/kainate receptor antagonist) increased cell survival. On the other hand, MPP did not block the protective effect of R,R-THC in glutamate-treated N29/4 cells, and neither MK-801 nor CNQX conferred protection. Activation of ERalpha and/or ERbeta with 17beta-estradiol (E2), propyl-pyrazole-triol or diarylpropionitrile did not provide effective neuroprotection, and pretreatment with ICI 182,780 did not inhibit the protective effect of R,R-THC in either type of cell. These results suggest that the use of ER agonists (including E2) has limited beneficial effects when both excitotoxicity and oxidative stress occur. In contrast to agonists of ERs, R,R-THC, which possesses anti-excitotoxic and antioxidant actions via ER-dependent and -independent pathways, provides significant neuroprotection.

Differential neuronal activation in the hypothalamic paraventricular nucleus and autonomic/neuroendocrine responses to I.C.V. endotoxin

The paraventricular nucleus (PVN) of the hypothalamus is a key site for regulating neuroendocrine and autonomic activities. To study the role of the PVN activation in brain inflammation-induced autonomic/endocrine responses, lipopolysaccharide (LPS; 0.5 or 5 microg) was administered i.c.v. and rats were killed 1, 3 or 6 h after the injection. I.c.v. LPS-0.5 microg did not cause changes in mean arterial pressure (MAP) over 6 h, whereas LPS-5 micro induced a temporary decrease in MAP approximately 30 min after the injection. LPS at either dose increased heart rate. Whereas induction of Fos-like immunoreactivity was confined to the dorsal medial parvocellular division (mpd) of the PVN with the lower dose, labeling was found throughout the PVN with the higher dose. At 3 h, LPS-5 microg also stimulated increases in arginine vasopressin (AVP) heteronuclear RNA levels in the posterior magnocellular and dorsal parvocellular divisions of the PVN at 3 h, and activation of catecholaminergic neurons in the hypothalamus and brainstem. Increases in tyrosine hydroxylase (TH) mRNA levels were found in the locus coeruleus at 6 h. LPS at both doses elevated plasma ACTH levels and corticotropin-releasing factor gene expression in the mpd of the PVN. I.c.v. LPS induced IL-1beta mRNA in the meninges and ventricular ependymal lining at 1 h, and in the periventricular PVN at 3 h. Induction of IL-1beta mRNA was found in the lung at 1 h, and a significant increase in plasma LPS binding protein occurred at 3 h. These findings suggest that PVN activation induced by the lower dose of LPS is related primarily to increases in activity of the HPA axis, whereas the higher dose of LPS more widely activates autonomic regulatory centers including the PVN and also stimulates changes in sympathetic output and hypothalamic AVP synthesis. Activation of the PVN by i.c.v. LPS likely occurs through both central and systemic routes. Differential neuronal activation in the PVN is functionally related to autonomic/endocrine responses elicited by brain inflammation.

Receptor activity modifying protein 2 distribution in the rat central nervous system and regulation by changes in blood pressure

The neuropeptide, adrenomedullin, acts in the central nervous system (CNS) to regulate blood pressure, at least partly through an adrenomedullin receptor which is composed of receptor activity modifying protein 2 (RAMP-2) and calcitonin receptor-like receptor (CRLR). We used in situ hybridization to localize RAMP-2 mRNA throughout the brain, and we performed reverse transcription-polymerase chain reaction to detect CRLR mRNA in the brain. We found that RAMP-2 mRNA is expressed in numerous areas, including autonomic nuclei such as the paraventricular, supraoptic, arcuate and ventromedial nuclei, as well as the nucleus of the solitary tract (NTS), area postrema and dorsal motor nucleus of the vagus. Many regions expressing RAMP-2 mRNA also express low levels of CRLR mRNA. We examined changes in the mRNA expression of RAMP-2 and preproadrenomedullin in the brain in response to blood pressure manipulations. Rats received intravenous infusions of nitroprusside or phenylephrine to decrease or increase blood pressure, respectively. Decreased blood pressure elicited an increase in RAMP-2 mRNA expression in the NTS and a decrease in preproadrenomedullin mRNA expression in the paraventricular nucleus (PVN). Increased blood pressure elicited a decrease in RAMP-2 mRNA expression in the PVN and NTS. The CNS distribution and modulation of adrenomedullin signalling components by changes in blood pressure provide anatomical and physiological evidence for a homeostatic role for adrenomedullin in the brain.

Intracerebroventricular adrenomedullin stimulates the hypothalamic-pituitary-adrenal axis, the sympathetic nervous system and production of hypothalamic nitric oxide

We tested the hypothesis that central adrenomedullin stimulates activity of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic output from the brain, and we assessed the effects of central adrenomedullin on the nitric oxide (NO) system in the brain. In conscious rats, intracerebroventricular (i.c.v.) injections of adrenomedullin (2 nmol/kg) increased arterial pressure and heart rate, with return to baseline values within 20 min and 65 min of injections, respectively. Adrenomedullin injections augmented expression of tyrosine hydroxylase mRNA in the locus coeruleus after 4 h. Plasma concentrations of adrenocorticotropic hormone, measured with radioimmunoassay, were also increased by adrenomedullin. i.c.v. Adrenomedullin stimulated Fos expression in neurones within autonomic centres including the paraventricular nucleus (PVN) of the hypothalamus, arcuate nucleus, locus coeruleus, nucleus of the tractus solitarius and area postrema. In the PVN, large proportions of corticotropin releasing factor- and NO-producing neurones were activated (Fos positive). NO production, measured with nitrate/nitrite assays, was elevated in the hypothalamus, but not brainstem, of adrenomedullin-treated rats compared to controls. We conclude that centrally administered adrenomedullin stimulates activity of the HPA axis, the sympathetic nervous system, and the hypothalamic NO system.

Gamma(2)-melanocyte-stimulating hormone suppression of systemic inflammatory responses to endotoxin is associated with modulation of central autonomic and neuroendocrine activities

Central autonomic and neuroendocrine activities are important components of the host response to bacterial inflammation. We demonstrate that intravenous infusion of gamma(2)-melanocyte-stimulating hormone (gamma(2)-MSH), a potent autonomic regulating peptide, prevents lipopolysaccharide (LPS)-induced hypotension and tachycardia, and modulates the ACTH response to endotoxin. In the hypothalamic paraventricular nucleus, a major neuroendocrine and autonomic center, gamma(2)-MSH inhibits LPS-induced increases in CRF mRNA levels, but does not suppress LPS-augmented arginine vasopressin heteronuclear RNA expression. In the locus coeruleus, a brainstem noradrenergic center, gamma(2)-MSH inhibits LPS-induced increases in tyrosine hydroxylase mRNA levels. Gamma(2)-MSH inhibits LPS-induced IL-1beta gene expression in the brain, pituitary and thymus, and prevents increases in plasma NO levels. These findings reveal that gamma(2)-MSH attenuates systemic inflammatory responses to endotoxin and suggest that modulation of central autonomic and neuroendocrine activities by gamma(2)-MSH contributes to its anti-inflammatory effects.

Cardiovascular responses to subseptic doses of endotoxin contribute to differential neuronal activation in rat brain

The contribution of cardiovascular activity in the early central responses to systemic inflammation was assessed in rats following intravenous administration of subseptic doses of lipopolysaccharide (LPS). LPS at 12.5 microg/kg increased heart rate (HR) but did not alter mean arterial pressure (MAP), and induced interleukin-1 beta (IL-1 beta) gene expression at 1 h in circumventricular organs (CVOs), choroid plexus, meninges, blood vessels, and pituitary gland. IL-1 beta mRNA levels were attenuated at 2 h in most regions studied. LPS at 50 microg/kg caused a biphasic change in MAP, increased HR, increased levels of arginine vasopressin heteronuclear RNA in the hypothalamic paraventricular nucleus (PVN), and induced IL-1 beta gene expression in the nucleus of the solitary tract (NTS) at 1 h. LPS (both doses) induced Fos-like immunoreactivity (FLI) in the area postrema, organum vasculosum of the lamina terminalis, NTS, preoptic area, supraoptic nucleus, and PVN at 1 h. In the PVN, neurons with FLI were found primarily in the dorsal and dorsal medial parvocellular divisions after 12.5 microg/kg of LPS whereas neurons with FLI were found throughout the PVN after 50 microg/kg of LPS. After 2 h, FLI was widespread throughout the brain. Plasma ACTH levels were elevated at 1 and 2 h in response to both doses of LPS, and levels of CRF mRNA were increased after 2 h in the parvocellular PVN. Our results reveal that central responses to increasing doses of LPS show different patterns which are related to activation of distinct immune and viscerosensory pathways, and that cardiovascular responses contribute to early neuronal activation as LPS concentrations are increased.

Distribution of preproadrenomedullin mRNA in the rat central nervous system and its modulation by physiological stressors

Adrenomedullin (ADM), encoded by the preproadrenomedullin (ppADM) gene, exerts multiple effects in a wide variety of peripheral and central tissues. Although ADM-like immunoreactivity has been shown to be widely distributed throughout the rat central nervous system (CNS), the detailed distribution of ppADM gene expression in the CNS and its modulation by physiological stimuli remain unknown. In our study, in situ hybridization was used to localize ppADM mRNA in the rat brain and to quantify its levels after exposure to different stressors including lipopolysaccharide (LPS; 100 microg/kg, iv), restraint stress (2 cycles of 1 hour restraint/1 hour rest), and 24 hours of dehydration. In addition, Fos immunoreactivity was used to identify the activation of neurons in response to LPS. Our results show that ppADM mRNA is widely distributed throughout the rat CNS, with especially high levels in autonomic centers including the hypothalamic paraventricular nucleus (PVN), hypothalamic supraoptic nucleus (SON), locus coeruleus, ventrolateral medulla, and intermediolateral cell column of the spinal cord. Furthermore, LPS inhibits ppADM gene expression in the parvocellular PVN (pPVN), magnocellular PVN (mPVN), SON, dorsal motor nucleus of the vagus, and area postrema among examined regions; restraint stress reduces ppADM mRNA levels in the pPVN, mPVN, SON, nucleus of the solitary tract, dorsal motor nucleus of the vagus, area postrema, and subfornical organ; 24 hours of water deprivation decreases ppADM gene expression only in the mPVN and SON. Taken together, our results suggest that ADM is involved in the regulation of the hypothalamo-neurohypophysial system, the hypothalamo-pituitary-adrenal axis, and central autonomic functions.

Nitric oxide regulates body temperature, neuronal activation and interleukin-1 beta gene expression in the hypothalamic paraventricular nucleus in response to immune stress

An immune challenge initiates a complex cascade of events in the body including important responses from the central nervous system. As nitric oxide (NO) has been implicated in the central regulation of neuroendocrine and autonomic responses, this study was performed to determine if NO regulates physiological responses, neuronal activation, and/or interleukin-1 beta (IL-1 beta) gene expression in the paraventricular nucleus of the rat hypothalamus (PVN) in response to intravenous endotoxin, lipopolysaccharide (LPS, 100 microg/kg). Intracerebroventricular injections of NO synthase (NOS) inhibitors (7-nitroindazole sodium salt for neuronal NOS, N(G)-nitro-L-arginine for neuronal NOS and endothelial NOS, and aminoguanidine for inducible NOS) in LPS-treated rats showed that inhibition of NOS eliminated the drop in body temperature and led to increased neuronal activation in the PVN as assessed by immunohistochemistry for Fos-like immunoreactivity. Activation of NO-producing PVN neurons was also increased in these rats suggesting that NO influences neuronal NOS activity in PVN neurons. Finally, increased IL-1 beta gene expression in the PVN of LPS-treated rats receiving N(G)-nitro-L-arginine showed that NO regulates brain IL-1 beta gene expression. The results obtained with the NOS inhibitors support the hypothesis that NO produced from eNOS in the brain participates in temperature regulation, and inhibits PVN neuronal activity and IL-1 beta gene expression during immune stress.

Area postrema ablation attenuates activation of neurones in the paraventricular nucleus in response to systemic adrenomedullin

Adrenomedullin (ADM) is a potent vasodilator in the periphery which also acts centrally to increase blood pressure and inhibit drinking, feeding and salt appetite. This study was designed to study the effects of circulating ADM on neuronal activation in autonomic centres in the rat brain and to examine whether neuronal nitric oxide (NO) may participate in these processes. We identified activated neurones 1 h after intravenous (i.v.) injections of ADM (2 nmol/kg) using immunohistochemistry for Fos. The nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemical reaction was used to localize putative NO-producing neurones and double labelling for Fos and NADPH-d was used to identify activated NO producing neurones. To separate baroreceptor-induced neuronal activation in autonomic centres by ADM from other effects which it may have, i.v. infusions of sodium nitroprusside (NP) were used to mimic the hypotensive effects of ADM in control rats. Significantly greater numbers of activated neurones were found in the paraventricular nucleus of the hypothalamus (PVN) and especially in the dorsolateral medial parvocellular division, the nucleus of the solitary tract, and the area postrema (AP) of ADM-treated rats compared to control rats. In addition, the number of activated NO-producing neurones in the PVN was significantly higher in ADM-treated rats compared to rats treated with NP. To determine whether AP is one of the possible routes through which systemic ADM enters the brain to exert its central effects, the APs of rats were ablated by aspiration. One hour after i.v. injections of ADM, significantly fewer PVN neurones were activated in AP ablation rats compared to AP sham ablation rats. Similarly, the number of activated NO-producing neurones in the PVN was significantly lower in AP ablation rats compared to AP sham ablation rats. In conclusion, our results suggest that systemic ADM gains access to the brain through the AP to regulate neuronal activity in autonomic centres and that neuronal NO might be involved in central autonomic and/or neuroendocrine regulation by ADM.

Effects of restraint stress and spontaneous hypertension on neuropeptide Y neurones in the brainstem and arcuate nucleus

Neuropeptide Y (NPY) is found in autonomic neurones and participates in regulation of autonomic functions. To investigate the role of NPY in the stress response in normo- and hypertensive rats, activation of brainstem and arcuate nucleus (ARC) NPY neurones and levels of NPY mRNA in the ARC were measured in response to restraint stress in adult spontaneously hypertensive rats (SHRs) and two strains of normotensive rats. Controls from each strain were not restrained. Sections of the brain were prepared for Fos immunohistochemistry and NPY in-situ hybridization to identify activated NPY neurones in the nucleus of the tractus solitarii (NTS), ventrolateral medulla (VLM), and ARC. NPY mRNA levels were quantified in the ARC. In the NTS and VLM of restrained rats, approximately 33% and 75%, respectively, of NPY neurones were activated. No differences among strains were found. In the ARC, about 36% of neurones activated by restraint contained NPY mRNA with no differences found among strains. In unrestrained rats, NPY mRNA levels were significantly elevated in SHRs compared to the normotensive rats. Restraint led to significant decreases in mRNA levels in all strains and mRNA levels among strains were no longer different from one another. These data show that NPY likely participates as a neurotransmitter in the autonomic pathways utilized during stress and originating in the NTS, VLM, and ARC. On the other hand, the decreased gene expression of NPY in the ARC in response to restraint stress argues against a role for activation of autonomic pathways or the hypothalamo-pituitary-adrenal (HPA) axis by NPY from the ARC of stressed rats. The elevated NPY gene expression in resting SHRs compared to normotensive rats is abrogated after restraint, suggesting that this gene is differentially regulated in SHRs compared to normotensive rats.

Central actions of nitric oxide in regulation of autonomic functions

The identification of nitric oxide (NO) as a gaseous, nonconventional neurotransmitter in the central nervous system has led to an explosion of studies aimed at learning about the roles of NO, not only at a cellular level, but also in regulating the activity of specific physiological systems that are coordinated by the brain. In the 1980s, publications began to appear which pointed to a role for NO in regulating peripheral autonomic function. In the 1990s, it became apparent that NO also acts centrally to affect autonomic responses. In this review, I will discuss the state of the current knowledge about the central role of NO in physiological functions which are related specifically to the control of sympathetic output. Studies which do not differentiate a central from a peripheral role for NO in these functions have not been included. After a brief discussion about the cellular events in which NO is involved, the distribution of NO-producing neurons in central autonomic areas of the brain will be presented. The more general actions of central NO in regulating sympathetic activity, as assessed with i.c.v. injections of pharmacological agents, will be followed by more specific sites of action achieved with microinjections into discrete brain areas. The review will be concluded with discussions about central NO in two physiological states of sympathetic imbalance, hypertension and stress.

Immune stress activates putative nitric oxide-producing neurons in rat brain: cumulative effects with restraint

Immune and restraint stresses induce changes in the hypothalamo-pituitary-adrenal axis activity and autonomic function. In the hypothalamus, the paraventricular nucleus (PVN) plays an integral role, and nitric oxide (NO) is hypothesized to participate in this process. We used 1) intravenous injections of lipopolysaccharide (LPS, 125 microg/kg) to identify activated (Fos-positive) putative NO-producing neurons, 2) retrograde tracing to determine if autonomic medullary regions signal the PVN to mediate this activation, and 3) intravenous LPS injections plus restraint stress to determine if responses to restraint are altered by the presence of immune stress. At 2 hours after LPS injections, approximately 15% of putative NO-producing neurons were activated in the nucleus of the tractus solitarius (NTS) and ventrolateral medulla (VLM); about half of the putative NO neurons in the PVN were activated. In LPS + restraint rats, the percentage of activated putative NO neurons in the PVN was not significantly different from LPS-treated rats, but the numbers of putative NO neurons and activated NO neurons per section increased significantly. Retrogradely labeled neurons were found mostly in the middle NTS and VLM, and about 75% were activated. No neurons in the NTS or VLM were triple labeled. The results show that putative NO-producing neurons in the PVN, NTS, and VLM are activated by circulating LPS. However, the LPS-induced signaling to the PVN likely occurs through pathways other than the NO network of neurons in NTS or VLM. Finally, superimposition of restraint stress onto animals already exposed to immune stress stimulates the NO system in the PVN to a greater extent than either stress alone.

Hypertensive rats exhibit heightened expression of corticotropin-releasing factor in activated central neurons in response to restraint stress

To test the hypothesis that chronically elevated sympathetic drive is associated with hyperreactiveness of autonomic centers in the brain to stress, adult spontaneously hypertensive rats (SHRs) and two strains of normotensive rats (Wistar Kyoto [WKY] and Sprague Dawley [SD] rats) were acutely exposed to restraint stress; controls from each strain were not stressed. Brain sections were prepared for Fos immunohistochemistry to identify activated neurons in the paraventricular nucleus of the hypothalamus, Barrington's nucleus of the pons, nucleus of the tractus solitarius, and ventrolateral medulla, or for combined Fos immunohistochemistry and corticotropin-releasing factor (CRF) in situ hybridization in the paraventricular nucleus and Barrington's nucleus. Restraint led to increased activation of neurons in all nuclei. Strain differences were found only in the caudal and rostral paraventricular nucleus where restraint resulted in greater numbers of activated neurons in SHRs compared to either normotensive strain. Levels of CRF mRNA in Barrington's nucleus of unrestrained rats were similar among strains. After restraint, mRNA levels and double labeled neurons were increased in Barrington's nucleus of SHRs. In unstressed rats, CRF mRNA levels were elevated in some regions of the paraventricular nucleus in SHRs. After restraint, mRNA levels increased throughout the paraventricular nucleus of SHRs. Significantly greater numbers of double labeled neurons were found in the dorsolateral medial and ventral medial parvocellular paraventricular nucleus of stressed SHRs compared to WKY or SD rats. These data show that chronic elevation in sympathetic activity, present in SHRs, is associated with hyperreactiveness of the paraventricular and Barrington's nucleus including recruitment of neurons to express CRF, and may have important implications for the response of the hypothalamo-pituitary-adrenal axis during stress.

Central regulation of autonomic function: no brakes?

1. Nitric oxide (NO) is formed by neuronal NO synthase (nNOS) and acts as a non-conventional neurotransmitter in the brain. A growing body of evidence supports the hypothesis that NO acts to decrease sympathetic output to the periphery; these effects may occur at several autonomic sites. The present review describes studies from our laboratory that address this hypothesis. 2. Restraint stress activates putative NO-producing neurons in many autonomic centres: preoptic area, medial septum, amygdala, hypothalamus, including the paraventricular nucleus (PVN), raphe nuclei, nucleus tractus solitarius (NTS) and ventrolateral medulla (VLM). These results suggest that NO is directly or indirectly involved in regulating sympathetic output to the periphery. 3. Systemic angiotensin II (AngII) activates putative NO-producing neurons in the PVN. These neurons may be activated either by the increases in arterial pressure that accompany AngII injections or due to activation of AngII-containing neural pathways. 4. Hypotension is associated with the activation of putative NO-producing PVN neurons, small numbers of which also project to the NTS or VLM. As the majority of activated neurons is in the magnocellular division, NO production may be related to the production of vasopressin. 5. Adult spontaneously hypertensive rats (SHR) show increased gene expression of nNOS in the hypothalamus, dorsal medulla and caudal VLM. These differences are not present in young prehypertensive SHR, suggesting that the changes in gene expression in adult rats are associated with the increased sympathetic nerve activity found in these rats. 6. Gene expression of nNOS is altered in the hypothalamus and caudal VLM of renal hypertensive rats at 3 and 6 weeks after surgical induction of hypertension. Contrasting results at the two time points may be due to differing underlying physiological processes that characterize the two stages of renal hypertension. 7. Nitric oxide may affect sympathetic output through several possible mechanisms. These include affecting production of the second messenger cGMP and interactions with more classical neurotransmitters or with neurohormonal systems in the brain.

Activation by systemic angiotensin II of neurochemically identified neurons in rat hypothalamic paraventricular nucleus

Using the immunohistochemical localization of the protein product of the immediate early gene, c-fos, to localize activated neurons in the paraventricular nucleus of the hypothalamus (PVN), we studied the chemical phenotypes of neurons activated by circulating angiotensin II (AII). We determined the proportions of activated PVN neurons that expressed AII type I receptor-like immunoreactivity (AT1-L) or the neurohormones vasopressin (VP) and oxytocin (OXY). In addition, we identified activated PVN neurons that putatively produce nitric oxide (NO) on the basis of histochemical staining for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d). Conscious rats received intravenous AII infusions at a rate sufficient to elevate mean arterial pressure by 40-60 mmHg for 90 min; control rats received infusions of vehicle. Brains were prepared for double immunohistochemistry [Fos-like immunoreactivity (FLI)/AT1-L, FLI/VP or FLI/OXY] or FLI/ NADPH-d histochemistry. Systemic AII infusions led to activation of 149+/-14 PVN neurons per section. In contrast, control animals showed activation of 21+/-6 PVN neurons per section. AII infusions elicited the activation of the following numbers of chemically identified PVN neurons per section: AT1-L, 24+/-5; VP, 26+/-5; OXY, 11+/-2; NADPH-d, 22+/-4. Control animals had few activated PVN neurons per section. For each of the chemically identified populations of PVN neurons, the following proportions were activated: AT1-L, 12.5%; VP, 15.2%; OXY, 7.2%; NADPH-d, 17.3%. The results suggest that PVN neurons producing the AT1 receptor, VP, OXY, and NO, participate in the mediation of the central responses to circulating AII.

Increased gene expression of neuronal nitric oxide synthase in brain of adult spontaneously hypertensive rats

Neuronal nitric oxide is hypothesized to participate in regulation of autonomic function by decreasing sympathetic output to the periphery. This hypothesis predicts that gene expression of neuronal nitric oxide synthase is increased during states of heightened sympathetic activity. To test the hypothesis, we measured gene expression in the spontaneously hypertensive rat (SHR), a genetic model of hypertension in which sympathetic activity is correlated with increasing pressure. SHRs and two strains of control rats (Wistar-Kyoto [WKY] and Sprague-Dawley [SD]) at 4 weeks (pre-hypertensive) and 14 weeks (established hypertension) of age were used to measure gene expression in hypothalamus, dorsal pons, dorsal medulla, rostral ventrolateral medulla, and caudal ventrolateral medulla. Semi-quantitative reverse transcription-polymerase chain reactions and in situ hybridization were used to measure changes in neuronal nitric oxide synthase mRNA. No significant differences were found in any of the areas studied among the three strains of rats in the 4-week rats. At 14 weeks significant increases in gene expression were found in the hypothalamus (73% compared to WKYs, 104% compared to SDs), dorsal medulla (31% and 45%), and caudal ventrolateral medulla (24% and 27%) of SHRs. In situ hybridization revealed that neurons expressing the synthase gene in the hypothalamus were found primarily in the paraventricular (both parvo- and magnocellular divisions) and supraoptic nuclei. These data show that gene expression of neuronal nitric oxide synthase is increased in central autonomic centers in animals with increased sympathetic activity and they support the hypothesis that nitric oxide plays an important role in maintenance of homeostatic balance through modulation of sympathetic activity.

Activation by hypotension of neurons in the hypothalamic paraventricular nucleus that project to the brainstem

To investigate the involvement of neuronal nitric oxide (NO) in the response of the brain to changes in blood pressure, we studied the activation of putative NO-producing neurons in the paraventricular nucleus of the hypothalamus (PVN) in rats whose mean arterial pressures (MAPs) were decreased by 40-50% with hemorrhage (HEM) or infusion of sodium nitroprusside (NP). Activation was assessed on the basis of expression of the immediate early gene, c-fos; putative NO-producing neurons were identified with the histochemical stain for nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d); and the proportions of neurons projecting to the nucleus of the tractus solitarius (NTS) and/or caudal ventrolateral medulla (CVLM) were determined with retrograde tracing techniques. No differences were found for results obtained from HEM and NP animals. Three to four percent of activated PVN neurons projected to the NTS or CVLM. Conversely, approximately 33% and 16% of neurons projecting to the NTS and CVLM, respectively, were activated. About 43% of NADPH-d neurons in the PVN were activated. Of PVN neurons projecting to the NTS or CVLM, 38% and 32%, respectively, were NADPH-d positive. About 11% of NADPH-d PVN neurons projected to the NTS or CVLM. An average of 3 NADPH-d neurons per section were activated and projected to either target. Finally, 7 PVN cells per section sent collateral branches to the NTS and CVLM; 2 or 3 of these cells per section were also activated by decreases in arterial pressure. No NADPH-d cells were found that sent collateral branches to the NTS and CVLM. This study shows that decreases in MAP activate PVN neurons that project, singly and through collaterals, to the NTS and CVLM. A relatively high proportion of the singly projecting neurons is NADPH-d positive. These results support the contention that descending projections from the PVN to the brainstem play an important role in the physiological response to decreases in arterial pressure and suggest that NO may participate in this response.

Stress-induced activation of nitric oxide-producing neurons in the rat brain

Nitric oxide (NO) is a gaseous neurotransmitter that may mediate a decrease in sympathetic output to the periphery. This implication predicts that NO-producing neurons in the brain are activated in animals experiencing increased levels of sympathetic activity. To test this prediction, we subjected three groups of experimental rats to differing levels of environmental stimulation for 1 hour: minimal stimulation, moderate stimulation, and restraint stress. NO-producing neurons were histochemically visualized in sections of the brain, and activation of these neurons was assessed according to the neuronal expression of the immediate early gene c-fos. Constitutive activation of NO-producing neurons was found in the hypothalamus (paraventricular and supraoptic nuclei), dorsal raphe nuclei, and spinal nucleus of the trigeminal nerve of minimally stimulated rats. When animals were subjected to a novel environment (moderate stimulation), additional NO-producing neurons were activated in the medial septum, medial amygdala, hypothalamic nuclei (lateral, periventricular, and posterior), colliculi, nucleus raphe obscurus, medial vestibular nucleus, nucleus of the tractus solitarius, and several components of the ventrolateral medulla. Restraint stress caused the activation of NO-producing neurons in all of these areas, often in increasing numbers, and the activation of additional NO-producing neurons in the diagonal band of Broca, lateral and medial preoptic areas, basomedial and basolateral amygdalar nuclei, hypothalamic nuclei (dorsomedial, retrochiasmatic supraoptic, and circularis), nucleus raphe pontus, lateral parabrachial nucleus, and pontine nuclei. Expressed as a proportion of NO-producing neurons per section, the largest percentages (>20%) of double-stained neurons were found in the basolateral amygdala (46%), hypothalamic paraventricular nucleus (35%), corpora quadrigemina (estimated at 40%), dorsal raphe (45%), nuclei raphe pontus (33%) and obscurus (63%), lateral parabrachial nucleus (22%), medial vestibular nucleus (25%), lateral division of the nucleus paragigantocellularis (26%), and lateral reticular nucleus (35%). Evidence from other studies increasingly supports the concept that NO plays a generalized role in autonomic regulation by decreasing sympathetic output. Our results show that more NO-producing neurons were activated during stress than during minimal or moderate levels of stimulation. Together, the evidence suggests that NO is a neurochemical messenger that is utilized by individual autonomic neurons as the organism responds to increased levels of sympathetic activity.

Decreased gene expression of neuronal nitric oxide synthase in hypothalamus and brainstem of rats in heart failure

Nitric oxide may act at autonomic sites in the brain to regulate sympathetic outflow. Our goal was to determine whether gene expression of the neuronal isoform of nitric oxide synthase (nNOS) is altered in discrete autonomic brain regions of rats in the chronic phase of heart failure compared to sham-operated control rats. Experiments were performed in rats 4 to 5 weeks after left coronary artery ligation. Histological data indicated that there was a 39% outer and a 45% inner infarct of the left ventricular myocardium in the heart failure group. The myocardium in sham-operated rats showed no observable damage. Total RNA was purified from microdissected brain tissue blocks containing hypothalamus, dorsal pons, dorsal medulla, rostral ventrolateral medulla, and caudal ventrolateral medulla. Changes in nNOS mRNA were semiquantified in each region using reverse transcription-polymerase chain reactions in which known concentrations of deletion mutant of the gene were coamplified as an internal standard. Compared with controls, significant decreases in nNOS mRNA levels were found in hypothalamus (19%), dorsal pons (43%) and dorsal medulla (34%) of rats with heart failure. There were no statistically significant differences in nNOS mRNA levels in rostral or caudal ventrolateral medulla between the control and heart failure groups. Concomitant with the changes nNOS gene expression in central sites, the plasma concentration of norepinephrine was significantly elevated in rats with heart failure compared to sham-operated control rats. Our results show that heart failure is associated with decreases in nNOS gene expression in at least three regions of the brain and with increased sympathetic outflow to the periphery. The decreased NO production that is likely associated with the decreases in nNOS gene expression may lead to the increased sympathetic drive seen in chronic heart failure.

Connectivity between brainstem autonomic structures and expression of c-fos following electrical stimulation of the central nucleus of the amygdala in rat

Combinations of retrograde tracing with detection of Fos (the protein product of the immediate early gene c-fos) following electrical stimulation of the central nucleus of the amygdala were used to explore: (1) the connectivity of activated (Fos-positive) neurons in the ventrolateral medulla with the nucleus of the solitary tract; (2) the connectivity of activated neurons in the nucleus of the solitary tract with the ventrolateral medulla; (3) the proportion of activated catecholaminergic neurons that project to the nucleus of the solitary tract or to the ventrolateral medulla. Retrograde tracer was injected into the nucleus of the solitary tract or the ventrolateral medulla. After 5 days, stimulation for 60 min induced a statistically significant increase in the number of Fos-immunoreactive neurons in the ventrolateral medulla that project to the nucleus of the solitary tract and in the number of Fos-positive neurons in the nucleus of the solitary tract that project to the ventrolateral medulla. Of the neurons activated by stimulation of the central nucleus of the amygdala, 20% in the ventrolateral medulla and 3% in the nucleus of the solitary tract contained the retrograde tracer and were also immunopositive for tyrosine hydroxylase, the enzyme responsible for synthesis of catecholamines.

Parabrachial nucleus projection to the amygdala in the rat: electrophysiological and anatomical observations

The amygdala, an important limbic forebrain centre, is the recipient of projections from a number of autonomic brainstem nuclei including the pontine parabrachial nucleus. This study examined the influence of electrical stimulation of the parabrachial nucleus on the excitability of amygdala neurons and their response to two cardiovascular stimuli, namely baroreceptor activation and the administration of systemic angiotensin II. We also defined the chemical identity of some amygdala neurons that receive parabrachial nucleus projections by combining the transport of the anterograde tracer Phaseolus vulgaris leucoagglutinin injected into the parabrachial nucleus with immunocytochemical labelling of neurotensin and galanin profiles within the amygdala. In urethane-anesthetized rats, stimulation of parabrachial nucleus evoked four basic types of synaptic responses in amygdala cells: (1) a short duration (< 100 ms) excitation in 75 of 167 neurons, (2) a longer duration (> 100 ms) excitatory response in 36 neurons, (3) an inhibitory response in 32 cells, and (4) more complex responses consisting of excitation-inhibition or inhibition-excitation sequences in the remainder of the cells. Thirty-seven of 72 amygdala neurons activated synaptically by parabrachial nucleus stimulation also responded to baroreceptor activation or intravenous angiotensin II. Anatomical data revealed the presence of Phaseolus vulgaris leucoagglutinin labelled terminals predominantly within the lateral, medial, and capsular subdivisions of the central nucleus of amygdala. Phaseolus vulgaris leucoagglutinin varicosities and boutons were observed apposed to the neurotensin and galanin neuronal perikarya within the central nucleus of amygdala. The electrophysiological results provide a framework whereby parabrachial nucleus efferents influence the activity of amygdala neurons that are responsive to cardiovascular stimuli. Furthermore, the anatomical data indicate that a portion of the parabrachial nucleus input is directed toward galanin and neurotensin neurons within the central nucleus of amygdala.

Convergent influence of the central nucleus of the amygdala and the paraventricular hypothalamic nucleus upon brainstem autonomic neurons as revealed by c-fos expression and anatomical tracing

Combinations of anatomical tracing with detection of Fos (the protein product of the immediate early gene c-fos) consequent to the stimulation of the central nucleus of the amygdala were used to explore the possibility that the hypothalamic paraventricular nucleus participates in the activation of brainstem neurons in the nucleus of the solitary tract and ventrolateral medulla. After injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin in the paraventricular nucleus, labeled fibers and varicosities were found to impinge on catecholaminergic and non-catecholaminergic Fos-positive neurons in the brainstem. After injections of a retrograde tracer in the nucleus of the solitary tract or ventrolateral medulla, we observed that some of the Fos-positive neurons within the parvocellular paraventricular nucleus that project to the brainstem were catecholaminergic or oxytocinergic. The results indicate that direct and indirect inputs from the amygdala may influence the activity of autonomic neurons in the brainstem. The paraventricular nucleus, via its direct projections onto catecholaminergic and non-catecholaminergic neurons, may participate in activation of brainstem neurons. Activated catecholaminergic and oxytocinergic parvocellular neurons in the paraventricular nucleus may be involved in the transmission of autonomic signals from the amygdala toward the brainstem.

Changes in blood volume and pressure induce c-fos expression in brainstem neurons that project to the paraventricular nucleus of the hypothalamus

Immunohistochemistry for c-fos was combined with retrograde tracing techniques to study the effects of acute reductions in arterial blood pressure due to hemorrhage (HEM) in conscious rats on activated neurons in the brainstem nucleus of the tractus solitarius (NTS) or ventrolateral medulla (VLM) which project to the paraventricular nucleus (PVN) of the hypothalamus. In an attempt to separate blood pressure effects from those associated with changes in blood volume, a similar approach was used to study the effects of drug-evoked hypotension using peripheral infusions of sodium nitroprusside (NP). Few differences were found in patterns or numbers of activated neurons (Fos-immunoreactive) in the NTS or VLM after HEM or NP treatment; only in the NTS at the level of the area postrema were significantly higher numbers of neurons that expressed Fos found in NP rats. In addition, a large proportion of PVN-projecting neurons in the NTS and VLM was activated whereas many activated neurons in the NTS and VLM did not project to the PVN. These results show that a decrease in blood pressure leads to the activation of NTS and VLM neurons but that a change in blood volume does not activate significantly greater numbers of neurons in these areas that project to the PVN or to other targets. Whereas substantial numbers of neurons in the NTS and VLM appear to transmit cardiovascular information to the PVN, many others likely transmit this information to other central targets.

Gene expression of brain nitric oxide synthase and soluble guanylyl cyclase in hypothalamus and medulla of two-kidney, one clip hypertensive rats

Nitric oxide may act at autonomic sites in the brain to regulate arterial blood pressure. Our goal was to determine whether gene expressions of the brain isoform of nitric oxide synthase and of the beta subunit of soluble guanylyl cyclase, the target of nitric oxide, were altered in discrete autonomic brain regions after induction of hypertension in rats. The two-kidney, one clip model was used to induce hypertension, and measurements were made 3 and 6 weeks after the left renal artery was clipped. Only experimental rats with blood pressures elevated by at least 25 mm Hg were used. Total RNA was purified from microdissected tissue blocks containing hypothalamus, dorsal medulla, rostral ventrolateral medulla, and caudal ventrolateral medulla. Changes in nitric oxide synthase and guanylyl cyclase mRNA were semiquantified in each region by use of reverse transcription-polymerase chain reactions in which known concentrations of deletion mutants of the two genes were coamplified as internal standards. Compared with controls, significant decreases and increases in nitric oxide synthase mRNA were found in the hypothalamus (x 2.2) and caudal ventrolateral medulla (x 6.4), respectively, of hypertensive rats 3 weeks after clipping. These alterations were reversed in hypertensive rats at 6 weeks; levels increased (x 4.6) in the hypothalamus and decreased (x 5.5) in the caudal ventrolateral medulla. Changes in guanylyl cyclase expression paralleled those for nitric oxide synthase in some but not all areas at both time points.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypotension induces Fos immunoreactivity in NADPH-diaphorase positive neurons in the paraventricular and supraoptic hypothalamic nuclei of the rat

Double staining for Fos and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-D) was used to study the distribution of activated neurons that synthesize nitric oxide in the paraventricular (PVN) and supraoptic nuclei (SON) following hypotensive stimulation in conscious rats. Fos was detected in many magno- and parvocellular NADPH-D positive neurons in response to haemorrhage or drug-evoked hypotension using i.v. infusions of sodium nitroprusside. However, quantitative analysis did not reveal any differences in the number of Fos positive PVN neurons following either mode of stimulation. These results suggest that a subpopulation of hypothalamic NADPH-D positive neurons is activated following hypotensive challenge. This activation of NADPH-D neurons may occur indirectly through other CNS structures that influence the excitability of hypothalamic SON and PVN. Furthermore, the lack of a difference in activated neurons within the PVN following either haemorrhage or nitroprusside infusion suggests that while a drop in blood pressure causes activation of neurons that produce nitric oxide, a decrease in blood volume, which accompanies haemorrhage, does not.

Chemically defined collateral projections from the pons to the central nucleus of the amygdala and hypothalamic paraventricular nucleus in the rat

Triple fluorescence labelling was employed to reveal the distribution of chemically identified neurons within the pontine laterodorsal tegmental nucleus and dorsal raphe nucleus which supply branching collateral input to the central nucleus of the amygdala and hypothalamic paraventricular nucleus. The chemical identity of neurons in the laterodorsal tegmental nucleus was revealed by immunocytochemical detection of choline-acetyltransferase or substance P; in the dorsal raphe nucleus, the chemical content of the neurons was revealed with antibody recognizing serotonin. The projections were defined by injections of two retrograde tracers, rhodamine- and fluorescein-labelled latex microspheres, in the central nucleus of the amygdala and paraventricular nucleus, respectively. Neurons projecting to both the central nucleus of the amygdala and the paraventricular nucleus were distributed primarily within the caudal extensions of the laterodorsal tegmental nucleus and dorsal raphe nucleus. Approximately 11% and 7% of the labelled cells in the laterodorsal tegmental nucleus and dorsal raphe nucleus projected via branching collaterals to the paraventricular nucleus and central nucleus of the amygdala. About half of these neurons in the laterodorsal tegmental nucleus were cholinergic, and one-third were substance-P-ergic; in the dorsal raphe nucleus, approximately half of the neurons containing both retrograde tracers were serotonergic. These results indicate that pontine neurons may simultaneously transmit signals to the central nucleus of the amygdala and paraventricular nucleus and that several different neuroactive substances are found in the neurons participating in these pathways. This coordinated signalling may lead to synchronized responses of the central nucleus of the amygdala and paraventricular nucleus for the maintenance of homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of c-fos protein in rat brain elicited by electrical and chemical stimulation of the hypothalamic paraventricular nucleus

The functional connectivity of the paraventricular nucleus of the hypothalamus (PVN) was studied by assessing the expression of the immediate early gene, c-fos, after unilateral stimulation of this structure in urethane-anesthetized rats. Electrical stimulation for 1 h (10 s on, 10 s off; 15-40 microA at 20 Hz) was accompanied by increases in mean arterial pressure (13-29 mm Hg). In these animals, ipsilateral increases in numbers of neurons with Fos-like immunoreactivity (FLI) were immunohistochemically demonstrated in the insular cortex, lateral septum, medial amygdala, hypothalamus, lateral division of the parabrachial nucleus (PBN) of the pons and the nucleus of the tractus solitarius (NTS) and ventrolateral medulla (VLM). Numbers of cells with FLI were quantitated in five areas known for their roles in autonomic function: arcuate nucleus, ventromedial hypothalamus, lateral PBN, NTS (at three levels) and VLM (caudal and rostral). In each case, stimulation of the PVN led to significant differences in number of neurons with FLI on the side ipsilateral to the stimulation compared to the contralateral side. To eliminate effects associated with stimulation of fibers of passage in the vicinity of the PVN, the results after electrical stimulation were compared to those obtained in animals in which the PVN was chemically stimulated unilaterally with the excitatory amino acid L-glutamate (5 one-minute infusions of 50 nl, 0.5 M glutamate over 1 h). Mean arterial pressure was increased after each injection (7-13 mm Hg), and significant differences in numbers of neurons with FLI between sides were maintained in all five areas except the NTS caudal to, and at, the level of the area postrema. An increase in neurons with FLI in the piriform cortex of all animals including controls may be due to injury-induced activation of target neurons from the PVN. These data illustrate that electrical and chemical stimulation of the PVN leads to simultaneous activation of neurons in many targets. All of the target areas studied receive direct projections from the PVN, although multisynaptic projections may also contribute to activation of target neurons.

Electrical stimulation of the central nucleus of the amygdala induces fos-like immunoreactivity in the hypothalamus of the rat: a quantitative study

The effect of electrical stimulation of an important forebrain autonomic structure, the central nucleus of the amygdala (CNA), on c-fos expression in three hypothalamic nuclei was studied in rat with immunocytochemistry to reveal the protein (Fos) encoded by the immediate early gene (IEG). Image analysis was used to quantify the Fos immunoreactive neurons within the supraoptic (SON), paraventricular (PVN), and arcuate (AN) nuclei. Stimulation for 60 min induced a statistically significant increase of the number of Fos immunoreactive neurons in all three nuclei ipsilateral to the CNA stimulation site. Double immunocytochemical staining (Fos and vasopressin or Fos and oxytocin) was employed to evaluate the participation of different subpopulations of neurons within the SON and PVN in response to CNA stimulation. In the SON, the increased number of Fos immunoreactive nuclei following the stimulation was observed in the vasopressin and oxytocin-secreting cells within this nucleus. In the PVN, the increase in the number of Fos immunoreactive neurons was predominantly within the parvocellular compartment. These studies demonstrate that IEG expression in hypothalamic neurons can be evoked as a result of afferent stimulation from the CNA. Activation of peptide- and hormone-containing neurons within the SON, PVN and AN, through mono- or multisynaptic pathways, may play a role in hormonal and autonomic responses.

Reinnervation of isolated islets of Langerhans transplanted beneath the kidney capsule in the rat

Neural regulation of islets of Langerhans mediates responses to stress and food ingestion. Transplantation of isolated islets offers hope to patients with insulin dependent diabetes mellitus but denervation of isolated islets may affect the capacity for appropriate metabolic control. Previous examination of the endocrine response to stress in islet autografted dogs revealed differences consistent with loss of neural regulation. Therefore, in the present study, islets grafted in rats were examined for extent and nature of reinnervation. Islets isolated from syngeneic donors were grafted under the kidney capsule of Wistar-Furth rats (n = 7) after 3 wk of streptozotocin induced diabetes. After 4 mo, graft-bearing kidneys were recovered and processed for double immunofluorescence. Antibodies were directed against (a) neuron associated proteins: synapsin (SYN) and L1; (b) neurotransmitters; tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), and calcitonin gene-related peptide (CGRP); and (c) islet hormones: insulin and somatostatin. SYN and L1 immunoreactivities in nerve fibres suggested reinnervation of the grafted islets although fibres were not associated with structures within the transplanted islets as in intact islets. CGRP immunoreactivity was observed in fibres and in a subpopulation of cells within intact islets but only in cells of the grafted islets. VIP, TH, and NPY immunoreactivities were found in nerve fibres of intact islets but only VIP was observed in fibres of grafted islets suggesting an absence of sympathetic reinnervation. In conclusion, transplanted islets of Langerhans become reinnervated but with a distribution and complement of neurotransmitters distinct from intact islets.

Distribution of the tight junction-associated protein ZO-1 in circumventricular organs of the CNS

The immunofluorescent distribution of ZO-1, a tight junction-associated protein, was studied in murine circumventricular organs. These regions generally express a less restrictive blood-brain barrier than is found in other areas of the CNS. In the remaining brain parenchyma, where a characteristic blood-brain barrier exists, ZO-1 was localized in discrete, continuous lines along blood vessels, presumably in association with endothelial cell tight junctions. The ependymal cells in the ventricular walls displayed a more punctate pattern of ZO-1 distribution, indicative of discontinuous tight junctions. In two of the circumventricular organs examined, the median eminence and the subfornical organ, many capillaries lacked detectable ZO-1 immunoreactivity while the apical aspects of the specialized ependymal cells (tanycytes) revealed an unbroken ZO-1 distribution. Scant labelling of ZO-1 in blood vessels was found in the area postrema, and only weak and discontinuous ZO-1 labelling was present in the ventricular wall. Capillaries of the organum vasculosum laminae terminalis expressed ZO-1 immunoreactivity which was comparable to the pattern observed in CNS regions with typical blood-brain barrier. The subcommissural organ, known to contain a blood-brain barrier, also displayed continuous ZO-1 staining in blood vessels. Unbroken ZO-1 distribution was observed in the specialized ependymal cells adjacent to both the organum vasculosum laminae terminalis and subcommissural organ. These immunocytochemical data demonstrate a distribution of ZO-1 in CNS parenchyma outside the circumventricular organs that is consistent with an organization of tight junctions which prevent free paracellular exchange of substances between blood and neuropil but which allow for continuity between CSF and the neuronal environment. The ZO-1 staining pattern in blood vessels and ventricular walls of the circumventricular organs is heterogeneous despite the prevalent absence of a functional blood-brain barrier.

Alterations in brain hexokinase activity associated with heart failure in rats

This study examined the activity of discrete regions of the brain as assessed with histological localization and photodensitometric quantification of the metabolic enzyme hexokinase in a group of rats with coronary occlusion (HF) and in sham-operated control rats. Three weeks after surgery, the mean left ventricular end diastolic pressure and right atrial pressure were elevated, and left ventricular peak systolic pressure was decreased in the HF group compared with the sham group; these findings are also observed during heart failure. In addition, histological data indicated that there was a 37.6 +/- 2.8% outer and 40.8 +/- 3.1% inner infarct of the myocardium in the group of rats with HF (n = 6). Rats in the control group had no observable damage to the myocardium (n = 6). Accompanying these symptoms of heart failure were significant increases in hexokinase activity in the parvocellular (pPVN, 16.3%) and magnocellular (mPVN, 17.6%) divisions of the paraventricular nucleus of the hypothalamus, and in the locus ceruleus (LC, 17.1%). No changes in hexokinase activity were observed in the median preoptic area, supraoptic nucleus (SON), subfornical organ, or posterior hypothalamus. These results reinforce the idea that heart failure (with coronary occlusion) is associated with changes in specific areas in the brain and that metabolic alterations in the pPVN, mPVN, and LC are likely related to alterations in vasopressin production, blood volume regulation, and sympathoexcitation observed in the heart failure state.

Effects of renal denervation and reinnervation on ganglionic gene expression of neurotransmitter proteins and c-fos in rat

To investigate the molecular basis for reno-renal interactions, Northern blot analyses of sympathetic ganglia were used to study the changes in levels of mRNA encoding tyrosine hydroxylase (TH), neuropeptide Y (NPY), and c-fos at 4, 14, 21, and 56 days after denervation of the left kidney, and of c-fos mRNA at 1 and 4 h after denervation. Ganglia included in the study were right and left paravertebral chain ganglia (PVG, T11 to L2), celiac-mesenteric plexus (CMP), and right and left superior cervical ganglia (SCG). Levels of TH mRNA in the left PVG and CMP were decreased at 4 and 14 days compared to controls. Levels were elevated at 21 days and similar to control levels at 56 days. In the right PVG, TH mRNA levels were elevated at 4 and 14 days, diminished from this elevated level at 21 days, and similar to control levels at 56 days. No differences were found in TH mRNA levels of left or right SCG compared to controls. In long-term experiments (days), no differences in NPY or c-fos mRNA levels were found in any of the ganglia from experimental rats compared to controls. Levels of c-fos mRNA in the left PVG and CMP were decreased at 1 hour compared to control levels. By 4 h, differences in mRNA levels were no longer apparent. In the right PVG, c-fos mRNA levels were elevated at 1 hour and no longer different from control levels at 4 h. No differences were found in c-fos mRNA levels of left or right SCG compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Branching projections of catecholaminergic brainstem neurons to the paraventricular hypothalamic nucleus and the central nucleus of the amygdala in the rat

In this study, we have employed triple fluorescent-labelling to reveal the distribution of catecholaminergic neurons within three brainstem areas which supply branching collateral input to the central nucleus of the amygdala (CNA) and the hypothalamic paraventricular nucleus (PVN): the ventrolateral medulla (VLM), the nucleus of the solitary tract (NTS) and the locus coeruleus (LC). The catecholaminergic identity of the neurons was revealed by immunocytochemical detection of the biosynthetic enzyme, tyrosine hydroxylase. The projections were defined by injections of two retrograde tracers, rhodamine- and fluorescein-labelled latex microspheres, in the CNA and PVN, respectively. In the VLM and NTS, the greatest incidence of neurons which contained both retrograde tracers was found at the level of the area postrema. These neurons were mainly located within the confines of the A1/C1 (VLM) and A2 (NTS) catecholaminergic neuronal groups. Double-projecting neurons in the LC (A6) were distributed randomly within the nucleus. It was found that 15% in the VLM, 10% in the NTS and 5% in the LC of the retrogradely labelled cells projected via branching collaterals to the PVN and CNA. One half of these neurons in the VLM and NTS were catecholaminergic, in contrast to the LC where virtually all double-retrogradely labelled neurons revealed tyrosine hydroxylase immunoreactivity. In the other brainstem catecholaminergic cell groups (A5, A7, C3), no catecholaminergic neurons were found that supplied branching collaterals to the CNA and PVN. Our results indicate that brainstem neurons may be involved in the simultaneous transmission of autonomic-related signals to the CNA and the PVN. Catecholamines are involved in these pathways as chemical messengers. Brainstem catecholaminergic and non-catecholaminergic neurons, through collateral branching inputs may provide coordinated signalling of visceral input to rostral forebrain sites. This may lead to a synchronized response of the CNA and PVN for the maintenance of homeostasis.

Efferent projections from the parabrachial nucleus demonstrated with the anterograde tracer Phaseolus vulgaris leucoagglutinin

Efferent projections from the parabrachial complex (PBN) were studied in the rat using the anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHA-L). Projections to the hypothalamus (ventromedial, dorsomedial, paraventricular, and supraoptic nuclei) originate primarily in the lateral PBN (1PBN). The amygdalar central nucleus (ACE) receives strong projections from all parts of the PBN although the external 1PBN projects primarily to the lateral ACE. Whereas the projections to the lateral bed nucleus of the stria terminalis, median preoptic nucleus, diagonal band of Broca, and lateral preoptic area originate primarily from the 1PBN, those to the insular cortex arise from the medial PBN (mPBN). The mPBN projects to the ventral posteromedial thalamus and the 1PBN and mPBN project to the zona incerta. Descending projections from the mPBN and Kölliker-Fuse area target the commissural nucleus tractus solitarius (NTS); the mPBN projects to the more rostral NTS. Similarly, the caudal parvicellular reticular formation (RF) receives projections from the mPBN and 1PBN, whereas input to the rostral RF arises from the former. All compartments of the PBN project to the ventrolateral medulla, although the projections arising from the 1PBN are densest. Finally, the raphe nuclei and periaqueductal gray receive some projections from most PBN divisions. These pathways provide a potential means whereby autonomic information can be relayed through the PBN to other structures important in regulating autonomic functions.

Expression of c-fos protein in rat brain after electrical stimulation of the aortic depressor nerve

To reveal central nervous system (CNS) structures involved in the baroreceptor reflex we studied the distribution of Fos protein-like immunoreactivity in the rat brain after one hour of electrical stimulation of the aortic depressor nerve (ADN). In 13 male Wistar rats under urethane the ADN was cut on both sides and the central ends were placed on stimulating electrodes. Intermittent (11 s on, 6 s off) electrical stimulation at parameters set to elicit a drop in mean arterial pressure of 15-30 mmHg was applied to one, both or neither ADNs for 1 h. CNS sections were incubated for 48 h in anti-Fos antibody and prepared for visualization of the reaction product using the ABC immunoperoxidase technique. Label was found in several discrete brain nuclei primarily on the side ipsilateral to the side of stimulation. In the medulla labelled nuclei were found in the nucleus tractus solitarius, area postrema, rostral and caudal ventrolateral medulla, nucleus ambiguus and medullary reticular formation. In the pons labelled neurons were found in the lateral and ventrolateral parabrachial nucleus, locus coeruleus, pontine reticular field and A5 region. In the forebrain labelled nuclei were observed in the peri- and paraventricular hypothalamus, supraoptic nucleus, subfornical organ, preoptic area, central nucleus of the amygdala, median preoptic area, horizontal limb of the diagonal band, bed nucleus of the stria terminalis and islands of Calleja. In control animals moderate amounts of label were present in the supraoptic nucleus and periventricular hypothalamus bilaterally. These results define central pathways involved in mediating the baroreceptor reflex.

Characterization of peptidergic efferents from the lateral parabrachial nucleus to identified neurons in the rat dorsal raphe nucleus

The peptidergic content of the lateral parabrachial nucleus (LPB) efferents to the dorsal raphe nucleus (DRN) was studied by combining visualization of the anterogradely transported tracer Phaseolus vulgaris leucoagglutinin within fibers that were immunocytochemically stained for neurotensin (NT), calcitonin gene-related peptide (CGRP) or galanin (GAL). The identity of DRN target neurons was determined with simultaneous immunocytochemical labelling for serotonin, the major transmitter within the nucleus. Within the DRN, we estimated that about two-thirds of the anterogradely labelled fibers arising from the LPB also showed peptidergic immunoreactivity. NT was the most commonly observed neuropeptide in LPB neuronal efferents directed to the DRN, followed by CGRP and GAL. The peptidergic afferents in the DRN were oriented preferentially in the dorsoventral plane. Peptidergic fibers from the LPB possessed varicosities (diameters not exceeding 3 microns) and were apposed on serotoninergic neuronal somata. Some of the anterogradely labelled peptidergic fibers were not associated with cells showing immunoreactivity for serotonin. The present results suggest that NT-ergic, CGRP-ergic and GAL-ergic neurons within the LPB are in contact with serotoninergic and non-serotoninergic neurons within the DRN. Since the DRN is known to project to the LPB, it is likely that bi-directional interconnections between these nuclei exist. Such linkages may provide anatomical substrates for coordinated autonomic responses.

Expression of c-fos protein in rat brain elicited by electrical stimulation of the pontine parabrachial nucleus

The expression of Fos, the protein product of the primary response gene c-fos, was used metabolically to map the short-term (1 hr) effects of urethane and sodium pentobarbital anesthesia in rat. Subsequently, urethane-anesthetized rats were used to study the integrated response to electrical stimulation (1-1.5 hr) of the pontine parabrachial nucleus (PBN), an important center for relay of autonomic information in the brain. Immunohistochemistry was used to localize Fos-like immunoreactivity (FLI) in the brain. To approximate amounts of FLI in the conscious animal, rats were killed immediately after attaining surgical anesthesia with sodium pentobarbital (50 mg/kg) or urethane (1.2-1.7 gm/kg). No FLI was found in the brains of these rats. In rats killed 1 hr after anesthesia with sodium pentobarbital, FLI was found only in the habenulae. After 1 h of urethane anesthesia, low levels of FLI were found in the following areas: nucleus of the tractus solitarius (NTS); caudal and rostral ventrolateral medulla (VLM); lateral PBN; ventromedial, paraventricular, and supraoptic nuclei (SON) of the hypothalamus; medial preoptic area; central nucleus of the amygdala (ACE); endopiriform cortex; insular cortex; piriform cortex; and islands of Calleja. Electrical stimulation of the PBN (10 sec on, 10 sec off; 15-50 microA at 20 Hz for 60-90 min) in rats anesthetized with urethane led to increases in mean arterial pressure (10-30 mm Hg) and to ipsilateral increases of FLI in the lateral PBN, dorsal division of SON, ACE, endopiriform nucleus, insular cortex, piriform cortex, and islands of Calleja. In two animals, ipsilateral increases were found in the ventromedial hypothalamus and medial amygdaloid nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the parabrachial nucleus input to the hypothalamic paraventricular nucleus in the rat

The brainstem parabrachial nucleus (PBN) is viewed as an increasingly important site for the transfer of autonomic-related information to more rostral structures in the forebrain including the hypothalamus. In this study, we examined electrophysiologically in vivo and anatomically the nature of PBN input to the hypothalamic paraventricular nucleus (PVN) and particularly to the vasopressin-and oxytocin-secreting magnocellular neurosecretory cells within this nucleus. In urethane-anaesthetized rats, extracellular recordings from 108 antidromically identified neurosecretory PVN cells revealed an excitatory (37/43 cells) and less frequently an inhibitory (6/43 cells) response consequent to electrical stimulation in the PBN. Both vasopressin (12/37 cells)-and oxytocin (9/37 cells)-secreting neurons appear to respond to the PBN stimulus. Four cells projecting to the neurohypophysis could also be antidromically activated from PBN, and this observation may be indicative of collateral branching in some PVN neurosecretory neurons. In addition, recordings from 60 non-magnocellular (i.e. non-neurohypophysially-projecting) PVN cells revealed a facilitatory response (43/60 cells) following PBN stimulation, Iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) were made within the rat lateral PBN and brains prepared for immunocytochemical examination of projections to the PVN region. PHA-L-labelled fibres and terminals were visualized within both the parvocellular and magnocellular divisions of the PVN. In addition, labelled fibres were also seen in a region immediately dorsal to the PVN. PHA-L-labelled fibres with axonal varicosities and boutons were visualized over immunocyto-chemically-identified vasopressin and oxytocin neurons within the magnocellular PVN. These convergent electrophysiological and anatomical data provide evidence for a PBN projection to the PVN that is predominantly excitatory to both magnocellular neurosecretory and non-magnocellular cells. Moreover, with respect to vasopressin-and oxytocin-secreting cells, the PBN input appears to be directed at both populations of peptidergic neurons.

The hypothalamic paraventricular and lateral parabrachial nuclei receive collaterals from raphe nucleus neurons: a combined double retrograde and immunocytochemical study

Retrograde tracer injections of fluorescein- and rhodamine-labelled latex microspheres centered in the parvicellular zone of the hypothalamic paraventricular nucleus and pontine lateral parabrachial nucleus revealed that 36% of the labelled neurons in the dorsal raphe nucleus send collaterals to both structures. These cells were organized in a well-distinguishable cluster within the dorsal raphe nucleus. By combining retrograde tracing with immunocytochemistry, it was found that less than 8% of the double-labelled cells stained positively for serotonin. Of the remaining raphe nuclei that were examined, only the median raphe nucleus contributed a minor nonserotoninergic projection to the paraventricular or lateral parabrachial nuclei. Few of the retrogradely labelled cells in the median raphe nucleus contained both tracers. These results suggest that nonserotoninergic and serotoninergic neurons in the dorsal raphe nucleus, via collateral branching, may simultaneously influence the activity of two central nervous system nuclei involved in autonomic control.

Neurons in the rat medulla oblongata containing neuropeptide Y-, angiotensin II-, or galanin-like immunoreactivity project to the parabrachial nucleus

Projections from the medulla to the parabrachial complex of the rat were examined for their content of neuropeptide Y-, angiotensin II- or galanin-like immunoreactivity using combined retrograde tracing and immunohistochemical techniques. Rhodamine-labelled latex microspheres were stereotaxically injected into discrete nuclei of the parabrachial complex. After survival of two to five days, colchicine (100 micrograms in 10 microliters saline) was injected into the cisterna magna. One day later, rats were perfused and the brainstems were prepared for visualization of the retrograde tracer and immunoreactivity of one of the three peptides. Retrograde labelling verified that the area postrema, nucleus of the tractus solitarius, caudal spinal nucleus of the trigeminal nerve, parvocellular reticular nucleus, and ventrolateral medulla including the rostral ventrolateral medulla and nucleus paragigantocellularis project to the lateral parabrachial and Kölliker-Fuse nuclei. While most projections were primarily ipsilateral, a small proportion of the projections from the ventrolateral medulla was bilateral. Neurons containing neuropeptide Y-like immunoreactivity were found in the caudal and intermediate nucleus of the tractus solitarius, dorsal to the lateral reticular nucleus and in the nucleus paragigantocellularis. After bilateral microsphere injections into the lateral parabrachial and Kölliker-Fuse nuclei, double-labelled neurons were found dorsal to the lateral reticular nucleus of caudal and intermediate medullary levels, at the ventral surface of the medulla at intermediate levels and in the nucleus paragigantocellularis at rostral levels. Neurons with angiotensin II-like immunoreactivity were observed at the dorsomedial border of the caudal and intermediate nucleus of the tractus solitarius, in the area postrema and in the lateral reticular nucleus and nucleus paragigantocellularis. Of these neurons, small numbers in the nucleus of the tractus solitarius and ventrolateral medulla also projected to the lateral parabrachial and Kölliker-Fuse nuclei. Neurons containing galanin-like immunoreactivity were found in the caudal nucleus of the tractus solitarius, the area postrema, the spinal trigeminal nucleus, the raphe nuclei (pallidus and obscurus), the nucleus paragigantocellularis and dorsal to the lateral reticular nucleus. Of these cells, double-labelled neurons were found in the commissural and medial subdivisions of the caudal nucleus of the tractus solitarius and in the rostral ventrolateral medulla including the ventral surface and the nucleus paragigantocellularis. The results suggest that neuropeptide Y, angiotensin II and galanin may serve as neurochemical messengers in pathways from the medulla to the parabrachial complex. The location of double-labelled neurons suggests that the information relayed by these neurons is related to autonomic activity.

Gene expression of tyrosine hydroxylase and neuropeptide Y in prevertebral ganglia of renal hypertensive rats

The gene expression of tyrosine hydroxylase (TH) and neuropeptide Y (NPY) was studied in prevertebral ganglia and adrenal glands of adult male rats during the development of renal hypertension (removal of 1 kidney/constriction of other kidney). Only tissues from rats with arterial pressures significantly elevated by day 3 were compared with those from controls. At 4 or 5 days after renal surgery, superior cervical ganglia, celiac-mesenteric plexus, adrenal glands, and stellate ganglia were surgically removed from nonfixed rats for Northern blot analysis or from perfusion-fixed rats for in situ hybridization. In all tissues, levels of TH mRNA were decreased in hypertensive rats; cells with decreased levels were scattered throughout each tissue. In contrast, levels of NPY mRNA were unchanged in hypertensive rats compared with controls. Changes in TH mRNA levels suggest that the developing phase of renal hypertension is associated with a decrease in sympathetic outflow to the periphery. In contrast, the failure of NPY mRNA levels to change suggests a different regulatory mechanism for NPY expression or a different role for NPY in sympathetic neurotransmission.

Parabrachial nucleus projection towards the hypothalamic supraoptic nucleus: electrophysiological and anatomical observations in the rat

It has been proposed that the pontine parabrachial nucleus (PBN) participates in the regulation of body fluid balance and the release of vasopressin from the neurohypophysis, although the pathways mediating the latter response are uncertain. This study in the rat, utilizing anatomical and electrophysiological methods, describes a projection from the lateral PBN towards the hypothalamic supraoptic nucleus (SON). Rats received iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L, 2% solution). After 14-17 days, rats were sacrificed and their brains prepared for immunofluorescent visualization of projections to the SON region. PHA-L-labelled terminals were found primarily in perinuclear regions immediately dorsal to the SON. In contrast, injections within the medial PBN and the nearby Kölliker-Fuse nucleus did not reveal labelling in or around the SON. Extracellular recordings from 86 of 118 antidromically identified neurons in anaesthetized rats revealed a set of complex synaptic responses after stimulation in the PBN. Excitatory responses (in 82 of 86 cells) of short (less than 100 msec, 39/82 cells) and long (greater than 100 msec, 43/82) duration were observed in both vasopressin- and oxytocin-secreting cells of the SON, while 4/86 cells displayed a depressant response to PBN stimulation. In the adjacent perinuclear zone, 22/39 nonneurosecretory cells responded with an increase in their excitability consequent to an identical stimulus. These data suggest a predominantly facilitatory influence of lateral PBN neurons on SON neurosecretory cells in the rat, and that the PBN-SON projection is an indirect one that utilizes an interneuronal network located in the perinuclear zone adjacent to the SON.

Effects of neonatal sympathectomy with 6-hydroxydopamine or guanethidine on survival of neurons in the intermediolateral cell column of rat spinal cord

The effects of removing target cells on survival of, and inputs to, sympathetic preganglionic neurons were studied in rats that were sympathectomized with 6-hydroxydopamine (6-OHDA) or guanethidine sulfate. Separate groups of neonatal and 1-week male rats were given injections of 6-OHDA for 10 days and of guanethidine for 3 weeks (5 days/week), respectively. Histofluorescence results suggest that catecholaminergic neurons in most ganglia are destroyed with treatment except for adrenal medulla, which is unaffected [14], and the pelvic ganglion where only partial destruction occurs. Cells in the intermediolateral cell column from representative spinal cord segments of treated and control adult rats were counted. In 6-OHDA-treated rats, cells decreased in number in all segments compared to controls. In guanethidine-treated rats, cells were also decreased in number; in some segments the decrease was significantly greater than with 6-OHDA. Sympathectomy had no effect on neurons in the intermediate gray of L5 or in the ventral horn of T3. The results of this study demonstrate that peripheral sympathectomy causes loss of sympathetic preganglionic neurons and that guanethidine is slightly more effective than 6-OHDA.

Alterations in brain hexokinase activity associated with streptozotocin-induced diabetes mellitus in the rat

The effects of streptozotocin-induced diabetes mellitus on the activity of discrete regions of the brain were studied with histochemical localization and photodensitometric quantification of the metabolic enzyme, hexokinase. Two weeks after a single injection of streptozotocin (65 mg/kg, i.p.), plasma glucose and osmolarity levels were elevated, and plasma sodium concentrations were depressed. These changes were reversed in diabetic rats treated with insulin. Accompanying these symptoms of diabetes were significant increases in hexokinase activity in the magnocellular division of the paraventricular nucleus of the hypothalamus (mPVH, 12.1%), the medial subdivision of the nucleus of the tractus solitarius (mNTS, 15.5%), and the commissural subdivision of the NTS (cNTS, 10.9%). An increase, though just below the level of significance, was also observed in the supraoptic nucleus of the hypothalamus (SON, 11.5%). The increases in hexokinase activity were completely reversed in the cNTS (and SON) and only partly reversed in the mPVH and mNTS of insulin-treated diabetic rats. No changes in hexokinase activity were seen in the subfornical organ, medial preoptic area, parvocellular division of the PVH, locus coeruleus, or dorsal motor nucleus of the vagus of diabetic rats. These results reinforce the idea that the brain is not exempt from changes associated with diabetes mellitus and suggest that metabolic alterations in the mPVH (and SON) and two divisions of the NTS are likely related to changes in vasopressin production and blood volume, respectively.

Metabolic alterations in discrete regions of the rat brain during development of spontaneous hypertension

Hexokinase histochemistry was used to identify brain regions that undergo metabolic changes during the development of hypertension in the spontaneously hypertensive rat (SHR). Photodensitometric measurements of reaction product were made in the commissural subdivision of the nucleus of the tractus solitarius, medial subfornical organ, supraoptic nucleus, magnocellular division of the parvocellular division of the paraventricular nucleus, anterior hypothalamic area, and posterior hypothalamus of prehypertensive SHR (4 weeks) and SHR with developing hypertension (8 weeks). These values were compared with those obtained from age-matched Sprague-Dawley and Wistar-Kyoto rats. At 4 weeks, significantly lower levels of hexokinase were observed in the commissural subdivision of the nucleus of the tractus solitarius and the magnocellular division of the paraventricular nucleus of SHR; a higher level was seen in the posterior hypothalamus. At 8 weeks, significantly higher levels of hexokinase were observed in the anterior hypothalamic area and the posterior hypothalamus. These results can be compared to those from adult SHR where lower levels of activity were found in the parvo- and magnocellular divisions of the paraventricular nucleus. Together these results suggest that, while the role of the magnocellular division of the paraventricular nucleus remains unclear, the commissural subdivision of the nucleus of the tractus solitarius and posterior hypothalamus may participate in the initial events leading to hypertension whereas the parvocellular division of the paraventricular nucleus does not.

Effects of colchicine on hexokinase activity in the paraventricular and supraoptic nuclei of spontaneously hypertensive and normotensive rats

The effects of intracerebroventricular (ICV) colchicine (70 micrograms per rat) on systolic pressures and levels of hexokinase activity in the hypothalamic paraventricular (PVH) and supraoptic (SON) nuclei were investigated in adult normotensive and spontaneously hypertensive rats (SHR). One day after colchicine injection, systolic pressures had dropped significantly in Sprague-Dawley (SD) rats, Wistar-Kyoto (WKY) rats, and SHR; the largest decrease was seen in SHR. Postinjection pressures in SHR were within the normotensive range. No further decreases were observed two days after injections. Quantitative analysis of hexokinase activity in control animals verified that the parvo- and magnocellular PVH (but not SON) of SHR contained significantly lower levels of hexokinase than in WKY or SD rats. Two days after colchicine injection, hexokinase activities in pPVH and mPVH were similar in all three strains. Activity had decreased significantly in SD and WKY rats. In SHR, no differences between control and postinjection values were found. Hexokinase activity in SON was significantly decreased to the same extent in all strains. As metabolic activity in the pPVH, mPVH, and SON decreased after colchicine injection in normotensive rats whereas no such decreases occurred in the pPVH and mPVH of SHR, the findings suggest that colchicine may have differential effects on the metabolic activity of specific cell groups in brain depending on the physiological state of the animal.

Regional alterations in hexokinase activity within rat brain during dehydration and rehydration

Histochemical localization and photodensitometric quantification of the metabolic enzyme, hexokinase (HK), were used to study changes in brain metabolic activity that occur during the development of (5 days) and recovery from (7 days) dehydration. In water-deprived (WD) rats, HK activity increased after 2 days in the subfornical organ (SFO, 22%), nucleus circularis (NC, 36%), parvo- and magnocellular divisions of the paraventricular nucleus (pPVH, 17%; mPVH, 46%) and supraoptic nucleus (SON, 46%). Activity in SFO declined to control levels at 3 days but increased again thereafter. In pPVH, mPVH, and SON, activity was elevated until the end of the experiment. In NC, activity returned to control levels within 2 days of drinking by the rats. In salt-loaded (2% NaCl in water) rats, changes were similar to those of WD rats up to 2 days of dehydration (SFO, 25%; NC, 20%; pPVH, 16%; mPVH, 38%; SON, 50%). Activity in SFO and pPVH returned to control levels after 3 days and remained unchanged. In mPVH, SON, and NC, activity remained elevated and declined to control levels when salt-free water was provided. Results confirm that water deprivation is a stronger dehydrating stimulus than salt loading. In addition, metabolic activity, as measured by HK activity, varies daily during periods of dehydration and rehydration. These changes cannot always be predicted from results obtained only at the end of a period of dehydration. It is concluded that it is necessary to study dehydration-induced changes in brain metabolism on a daily basis to more fully understand the roles of discrete brain regions in the regulation of body fluids.

Decreased hexokinase activity in paraventricular nucleus of adult SHR and renal hypertensive rats

Metabolic activity was assessed in the brains of spontaneously hypertensive rats (SHR) using the histochemical hexokinase (HK) technique and photodensitometric analysis. Of eight regions known to play a role in cardiovascular regulation, only the paraventricular nucleus of the hypothalamus (PVH) exhibited alterations in HK activity. Significantly lower levels of HK activity in SHR than in control Sprague-Dawley and Wistar-Kyoto rats were measured in both the parvo- and magnocellular divisions of the PVH. No differences in HK activity were found in the anterior hypothalamic nucleus, posterior hypothalamic nucleus, supraoptic nucleus, subfornical organ, central nucleus of the amygdala, or the medial nucleus of the tractus solitarius of SHR. Similar results were obtained in renal hypertensive rats; furthermore, a positive correlation was found between levels of arterial pressure and densitometric readings. These latter results strongly suggest that metabolic alterations in the PVH of SHR are directly related to the increases in arterial pressure and are not due to the genetic makeup of SHR. In light of studies by others, the data from the present study have been interpreted to suggest that the decreases in metabolic activity in the PVH of the adult SHR are the result of a central attempt to bring the level of the arterial pressure down to normal levels and not to the altered activity of a region that might be acting to keep arterial pressure elevated.