Fos expression in the brain induced by peripheral injection of CCK or leptin plus CCK in fasted lean mice

We previously reported a synergistic interaction between leptin and cholecystokinin (CCK) to reduce food intake through CCK-A receptors in lean mice fasted for 24 h. To identify the activated neuronal pathways, we investigated changes in Fos expression in brain nuclei 2 h after single or combined intraperitoneal (i.p.) injections of leptin (120 μg/kg) and sulfated CCK-8 (3.5 μg/kg) in male lean mice (C57BL/6) fasted for 24 h using immunohistochemistry for Fos, the protein product of the early gene, c-fos. Leptin did not increase Fos expression in the brain compared with vehicle-treated mice. CCK increased the numbers of Fos-positive neurons in the nucleus of the solitary tract (NTS)/area postrema (AP), central nucleus of the amygdala (CeA) and, to a smaller extent, in the paraventricular nucleus of the hypothalamus (PVN) (5.2-, 2.3- and 0.3-fold respectively). Injections of leptin–CCK further enhanced Fos expression by 40% in the PVN compared with that induced by CCK alone, but not in the other nuclei. Devazepide (a CCK-A receptor antagonist, 1 mg/kg, i.p.) prevented the increase in Fos expression induced by leptin–CCK in the PVN and by CCK alone in the PVN, CeA and NTS/AP. These results indicate that in fasted mice, i.p. injection of CCK increases Fos expression in specific brain nuclei through CCK-A receptors while leptin alone had no effect. Leptin in conjunction with CCK selectively enhanced Fos expression in the PVN. The PVN may be an important site mediating the synergistic effect of leptin–CCK to regulate food intake.     

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.     

Effect of fasting and immobilization stress on estrogen receptor immunoreactivity in the brain in ovariectomized female rats

The present study examined the effect of 48-h fasting and 1-h immobilization on estrogen receptor immunoreactivity in selected hypothalamic areas and the nucleus of the solitary tract (NTS) in ovariectomized rats. Fasting induced an increase in ER-immunoreactive cells in the paraventricular nucleus (PVN), paraventricular nucleus (PeVN) and NTS compared with the unfasted control group. Similarly, immobilization caused an increase in ER-positive cells in the same areas, PVN, PeVN and NTS, versus the non-immobilized group. There was no significant increase in the number of ER-immunoreactive cells in the preoptic area (POA), arcuate nucleus (ARC) or ventromedial hypothalamic nucleus (VMH) following fasting and immobilization. Our previous work in ovariectomized rats with estrogen microimplants in the brain revealed that the PVN and A2 region of the NTS are the feedback sites of estrogen in activating the neural pathway to suppress pulsatile LH secretion during 48-h fasting. The result in the food-deprived rats suggests that estrogen modulation of the suppression of LH secretion during fasting is partly due to the increase in estrogen receptors in the PVN and A2 region. The physiological significance of the increase in neural ER following immobilization remains to be elucidated.     

Change in the expression of NPY receptor subtypes Y1 and Y2 in central and peripheral neurons related to the control of blood pressure in rats following experimental hypertension

Neuropeptide Y (NPY) is known to participate in central mechanisms of blood pressure control. However, variations on the expression of its receptors in response to a hypertensive challenge are not well defined, specially when considering that Y1 and Y2 often mediate opposite responses. In this study we have employed in situ hybridization to analyze changes in mRNA expression of NPY receptor subtypes Y1 and Y2 in the nucleus tractus solitarii (NTS), paraventricular nucleus of the hypothalamus (PVN) and petrosal and nodose ganglions 2 h, 3 and 7 days after aortic coarctation induced hypertension. Quantification by image analysis showed significant differences between sham-operated and aortic-coarcted hypertensive rats. Y1 receptor mRNA expression was increased (39%) in petrosal ganglion, 3 days after surgery. Y2 receptor mRNA expression was increased (143%) in the NTS of hypertensive compared with sham rats 2 h after surgery. Y2 receptor mRNA was decreased (62%) in the nodose ganglion of hypertensive compared with sham rats 2 h after surgery. No change was seen in Y1 and Y2 mRNA expression in the PVN in any analyzed period. The data suggest that NPY Y1 and Y2 receptors might participate in the mechanisms involved in the establishment/maintenance of hypertension induced by aortic coarctation. Acute changes seem to be involved with the adaptation to the new hypertensive state.     

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.     

NOS isoenzyme content in brain nuclei as related to food intake in experimental cancer cachexia

Evidence implies that nitric oxide (NO) in the central nervous systems mediates anorexia in tumor-bearing hosts. We have therefore evaluated, by immunohistochemical image analyses, net alterations of nitric oxide synthases (nNOS, eNOS, iNOS) in brain nuclei [paraventricular hypothalamic nucleus (PVN), medial habenular nucleus (MHB), lateral habenular nucleus (LHB), paraventricular thalamic nucleus (PV), lateral hypothalamic area (LHA), ventromedial hypothalamic nucleus (VMH), nucleus of the solitary tract (NTS)] of tumor-bearing mice (TB) with prostanoid-related anorexia. Pair-fed (PF) and freely fed (FF) non-tumor-bearing mice were used as controls. c-fos was analyzed as indicator of neuronal activation. nNOS was significantly increased in VMH and PVN from TB mice, while eNOS was significantly increased in LHB and LHA. iNOS was significantly increased in LHA and PVN nuclei, but decreased in MHB, LHB and VMH from tumor-bearers. However, several of these alterations were similarly observed in brain nuclei from pair-fed controls. Provision of unspecific NOS-antagonists to TB mice increased nNOS, eNOS and iNOS in several brain nuclei (PVN, LHA, VMH), but left tumor-induced anorexia unchanged. c-fos was significantly increased in all brain nuclei in PF mice except for NTS, LHA and PVN compared to controls, while tumor-bearing mice had increased c-fos in LHA and PVN only compared to controls. Our results demonstrate a complex picture of NOS expression in brain areas of relevance for appetite in tumor-bearing hosts, where most changes seemed to be secondary to stress during negative energy balance. By contrast, NOS content in PVN and LHA nuclei remains candidate behind anorexia in tumor disease. However, nitric oxide does not seem to be a primary mediator behind tumor-induced anorexia. NO may rather secondarily support energy intake in conditions with negative energy balance.     

Hypothalamic-pituitary-adrenocortical responses to single vs. repeated endotoxin lipopolysaccharide administration in the rat

Lipopolysaccharide (LPS) is a potent stimulator of the hypothalamic-pituitary-adrenal (HPA) axis. However, the alteration in the HPA axis responsiveness and brain corticosteroid receptor levels during long-term administration of LPS has not been studied well. The present study was designed to examine the effect of single vs. repeated intraperitoneal (i.p.) LPS injection on the HPA axis and brain corticosteroid receptor levels in male Wistar rats. In addition, c-fos mRNA expression was examined in the hypothalamic paraventricular nucleus (PVN) and brainstem catecholaminergic nuclei such as the locus coeruleus (LC) and nucleus tractus solitarius (NTS), the sites known to be involved in LPS-induced HPA axis stimulation. Rats that had received i.p. LPS injection for 6 consecutive days (6-LPS group) had similar levels of plasma adrenocorticotropin (ACTH) and corticosterone (CORT) compared to animals that had received i.p. saline (6-saline group). A single injection of LPS to the 6-saline group (6-saline+challenge) resulted in a substantial increase in plasma ACTH and CORT at 2 h, whereas an additional injection of LPS to the 6-LPS group (6-LPS+challenge) showed less of an increase. As determined by in situ hybridization histochemistry, proopiomelanocortin (POMC) mRNA levels in the anterior pituitary (AP) and corticotropin-releasing hormone (CRH) mRNA levels in the PVN were higher in the 6-LPS than in the 6-saline group. A single injection of LPS to the 6-saline group resulted in a significant increase in AP POMC mRNA and PVN CRH mRNA at 2 h, while injection of LPS to the 6-LPS group showed no additional increase in these levels. C-fos mRNA expression was prominent in the PVN, LC, and NTS following a single injection of LPS, but not following repeated LPS injection. These results suggest that stimulatory input into the PVN decreased following repeated LPS injection. Furthermore, type II glucocorticoid receptor (GR) mRNA levels in the 6-LPS and 6-LPS+challenge groups were decreased in the hippocampus, but not in the PVN or AP. Adrenalectomy with 40% CORT pellet replacement restored ACTH responses following repeated LPS injections to levels similar to those following a single LPS injection. Decreased hippocampal GR mRNA may contribute to the elevated PVN CRH mRNA levels in the 6-LPS group. Nevertheless, inhibition of the pituitary ACTH response by glucocorticoids and reduced hypothalamic drive are partly responsible for decreased pituitary-adrenal responsiveness following repeated LPS injection.     

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. J. Comp. Neurol. 385:285–296, 1997. © 1997 Wiley-Liss, Inc.     

Adrenomedullin acts in the rat paraventricular nucleus to decrease blood pressure

Adrenomedullin is a recently discovered peptide involved in the control of fluid and electrolyte homeostasis and cardiovascular function through peripheral and central nervous system actions. The present study was undertaken to examine the cardiovascular effects of adrenomedullin microinjection directly into the paraventricular nucleus (PVN). Microinjection of adrenomedullin into the PVN of urethane anaesthetized male Sprague-Dawley rats resulted in site-specific, repeatable decreases in blood pressure. These hypotensive effects were found to be dose related, and were not mediated by activation of calcitonin gene-related peptide receptors. These data suggest that adrenomedullin influences cardiovascular regulation through receptor mediated actions at the PVN of the hypothalamus.     

Ascending mechanisms of stress integration: Implications for brainstem regulation of neuroendocrine and behavioral stress responses

In response to stress, defined as a real or perceived threat to homeostasis or well-being, brain systems initiate divergent physiological and behavioral processes that mobilize energy and promote adaptation. The brainstem contains multiple nuclei that engage in autonomic control and reflexive responses to systemic stressors. However, brainstem nuclei also play an important role in neuroendocrine responses to psychogenic stressors mediated by the hypothalamic-pituitary-adrenocortical axis. Further, these nuclei integrate neuroendocrine responses with stress-related behaviors, significantly impacting mood and anxiety. The current review focuses on the prominent brainstem monosynaptic inputs to the endocrine paraventricular hypothalamic nucleus (PVN), including the periaqueductal gray, raphe nuclei, parabrachial nuclei, locus coeruleus, and nucleus of the solitary tract (NTS). The NTS is a particularly intriguing area, as the region contains multiple cell groups that provide neurochemically-distinct inputs to the PVN. Furthermore, the NTS, under regulatory control by glucocorticoid-mediated feedback, integrates affective processes with physiological status to regulate stress responding. Collectively, these brainstem circuits represent an important avenue for delineating interactions between stress and health.     

迷走神经参与胃伤害性信息向下丘脑的传递

目的　 研究迷走神经是否参与胃伤害性信息向下丘脑室旁核的传递。 方法　 检测下列条件下c Fos蛋白在孤束核及下丘脑室旁核的表达 :①胃内注入福尔马林引起伤害性刺激 ;②福尔马林刺激结合双侧膈下迷走神经切断术。结果　胃内注入福尔马林引起的伤害性刺激可以诱导c Fos蛋白在孤束核和下丘脑室旁核等脑区的表达 ,但在胸段脊髓的I,V ,VII和X层无明显表达。胃内注入生理盐水的对照组则仅有极少量的表达 ,双侧膈下迷走神经切断术可以减少c Fos蛋白在这些部位的表达。 结论　 该研究结果表明 ,迷走神经参与了胃内脏伤害性信息向孤束核及下丘脑室旁核的传递     

Differential Fos expression in the paraventricular nucleus of the hypothalamus, sacral parasympathetic nucleus and colonic motor response to water avoidance stress in Fischer and Lewis rats

The responsiveness of hypothalamic CRF to various stressors is reduced in the young female Lewis relative to the histocompatible Fischer rat. Whether such a difference impacts the brain-gut response to water avoidance stress was investigated by monitoring Fos immunoreactivity in the brain and sacral spinal cord and fecal pellet output. Exposure for 60 min to water avoidance stress increased the number of Fos positive cells in the paraventricular nucleus of the hypothalamus (PVN), nucleus tractus solitarius (NTS), and the parasympathetic nucleus of the lumbo-sacral spinal cord (L6-S1) in both Lewis and Fischer rats compared with non stress groups. The Fos response was lower by 32.0% in the PVN, and 63% in sacral parasympathetic nucleus in Lewis compared with Fischer rats while similar Fos expression was observed in the NTS. Stress-induced defecation was reduced by 52% in Lewis compared with Fischer rats while colonic motor response to CRF injected intracisternally resulted in a similar pattern and magnitude of defecation in both strains. The CRF receptor antagonist [ -Phe12,Nle^21,38C^aMeLeu³⁷]-CRF_12–41 injected intracisternally antagonized partly the defecation response in Lewis and Fischer rats. These data indicate that a lower activation of PVN and sacral parasympathetic nuclei in Lewis compared with Fisher rats may contribute to the differential colonic motor response and that the blunted CRF hypothalamic response to stress, unlike responsiveness to central CRF plays a role.     

Opposite regulation of body temperature by cholinergic input to the paraventricular nucleus and supraoptic nucleus in rats

Hypothalamic cholinergic system plays an important role in the regulation of body temperature and fluid balance. We have previously shown that cholinergic stimulation of the anterior hypothalamus and preoptic area was accompanied by a fall in body temperature, increased water intake, and increased Fos protein in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). In the present study, to estimate the role played by cholinergic input to the PVN and SON in thermoregulation and water intake, we used microdialysis for cholinergic stimulation with neostigmine and analysis of the nucleus, and also investigated immunoreactivity for c-Fos protein in the brain. This stimulation increased extracellular concentration of acetylcholine in these nuclei. Stimulation of the PVN decreased body temperature and increased water intake. On the other hand, stimulation of the SON increased body temperature. Both in PVN-stimulated and SON-stimulated rats, c-Fos-like immunoreactivity (Fos-IR) was evident in the PVN, SON and certain regions including locus coeruleus (LC), area postrema and nucleus of the solitary tract (NTS). Addition of atropine to the dialysis medium attenuated the increase of Fos-IR and suppressed the cholinergic stimulation-induced responses in body temperature and water intake. These results suggest that cholinergic muscarinic mechanisms in PVN and SON play an opposite function in the regulation of body temperature. The same neuronal pathway including LC and NTS may participate in an advance both in hypothermia and in hyperthermia.     

Connections of neurons in the region of the nucleus tractus solitarius with the hypothalamic paraventricular nucleus: Their possible involvement in neural control of the cardiovascular system in rats

Extracellular recordings were made from 607 spontaneously firing neurons within the nucleus tractus solitarius (NTS) and its vicinity in urethane-anesthetized male rats. Following electrical stimulation of the hypothalamic paraventricular nucleus (PVN) area, 21% of the neurons were orthodromically excited, 6% were inhibited and 2.5% were antidromically activated. The antidromic spike latencies were 22-64 ms. Among those orthodromically responding neurons, 81 neurons were tested by pressure pulse stimulation of the isolated carotid sinus. The pressure stimulation produced excitation in 7 and inhibition in 13 neurons. Of the 8 tested neurons which were antidromically activated, one neuron was excited and another neuron inhibited by the pressure pulse stimulation. These results provide electrophysiological evidence for reciprocal connections between neurons in the NTS region and the PVN, and give support to the hypothesis that the PVN is involved in the neural control of the cardiovascular system.     

Nuclei and subnuclei gene expression profiling in mammalian brain

Information on the neuroanatomical expression of a given gene is critical to understanding its function in the central nervous system. The integration of laser capture microdissection (LCM), T7-based RNA amplification and cDNA microarrays allows for this information to be simultaneously generated for thousands of genes. To validate this integrative approach, we catalogued the gene expression profiles of seven rat brain nuclei or subnuclei. A hundred cells from the following seven brain nuclei were analyzed: locus coeruleus (LC), dorsal raphe nucleus (DR), parvocellular division (PA) and magnocellular division (MG) of the hypothalamic paraventricular nucleus (PVN) and CA1, CA3 and dentate gyrus (DG) divisions of the hippocampal formation. Of the 2145 genes investigated, 1402 genes (65%) gave a hybridization signal statistically different from the background level that was defined by non-specific hybridizations to 15 different plant genes. Validation of our microarray data on four arbitrarily selected genes was confirmed by Real-Time PCR. Previous research showing expression patterns of 'signature' genes (n=17) for specific brain nuclei are consistent with our findings. For example, as previously shown, enriched mRNA expression encoding the serotonin transporter or tyrosine hydroxylase was found in DR and LC cells, respectively. Interestingly, expression of the serotonin 5-HT(2B) receptor mRNA was also found in DR cells. We confirmed this new finding by in-situ hybridization. The hierarchical clustering analysis of gene expression shows that the two divisions of the PVN (PA and MG) are closely related to each other, as well as the three regions of the hippocampal formation (CA1, CA3 and DG), which also showed similar gene expression profiles. This study demonstrates the importance, feasibility and utility of cellular brain nuclei profiling.     

Microglia are Selectively Activated in Endocrine and Cardiovascular Control Centres in Streptozotocin‐Induced Diabetic Rats

Type 1 and 2 diabetes are associated with dysfunction in multiple hormone systems, as well as increased sympathetic nerve activity, which may contribute to the development of diabetic complications. In other pathologies, such as myocardial infarction, increased sympathetic drive is associated with neuroinflammation and microglial activation in the hypothalamic paraventricular nucleus (PVN), a brain region that regulates sympathetic drive and multiple endocrine responses. In the present study, we used immunohistochemistry to study microglial and neuronal activation in the PVN and related brain regions in streptozotocin (STZ)‐induced diabetic rats. As expected, STZ treatment was associated with elevated blood glucose within 1 week. STZ injections also caused neuronal activation in the PVN and superoptic nucleus (SON) but not in the nucleus tractus solitarius (NTS), which was evident by 6 weeks. STZ‐treated rats showed increased plasma osmolarity, which would be expected to activate PVN and SON neurones. There was no apparent increase in histochemical markers of microglial activation, including phospho‐p38, phospho‐extracellular signal regulated kinase, P2X4 receptor or interleukin 1‐β even at 10 weeks after STZ‐treatment. However, we did see a significant increase in the percentage of microglia with an activated morphology in the PVN, SON and NTS, although not in surrounding hypothalamic, brainstem or cortical regions. These morphological changes included a significant reduction in microglial process length and were evident by 8 weeks but not 6 weeks. The delayed onset of microglial changes compared to neuronal activation in the PVN and SON suggests the over‐excitation of neurones as a mechanism of microglial activation. This delayed microglial activation may, in turn, contribute to the endocrine dysregulation and the elevated sympathetic nerve activity reported in STZ‐treated rats.     

Corticotropin-releasing factor and systemic capsaicin-sensitive afferents are involved in abdominal surgery-induced Fos expression in the paraventricular nucleus of the hypothalamus

We previously reported that abdominal surgery induces Fos expression in specific hypothalamic and medullary nuclei and also causes gastric stasis. The gastric ileus is reduced by systemic capsaicin and abolished by central injection of corticotropin-releasing factor (CRF) antagonist. We studied the influence of systemic capsaicin and intracerebroventricular (i.c.v.) injection of the CRF antagonist, α-helical CRF_9–41, on Fos expression in the brain 1 h after abdominal surgery in conscious rats using immunocytochemical detection. In control groups (vehicle s.c. or i.c.v.), abdominal surgery (laparotomy with cecal manipulation) performed under 7–8 min of enflurane anesthesia induced Fos staining in neurons of the spinal trigeminal, C1/A1 group, ventrolateral medulla, central amygdala, parabrachial nucleus, cuneate nucleus, nucleus tractus solitarii (NTS), paraventricular nucleus of the hypothalamus (PVN) and supraoptic nucleus (SON). Capsaicin (125 mg/kg s.c., 2 weeks before) or α-helical CRF_9–41 (50 μg i.c.v., before surgery) reduced the number of Fos-positive cells by 50% in the PVN while not modifying the number of Fos-labelled cells in the other nuclei. These results indicate that capsaicin-sensitive primary afferents and brain CRF receptors are part of the pathways and biochemical coding through which abdominal surgery activates PVN neurons 1 h post surgery.     

Identification of central sites involved in butorphanol-induced feeding in rats

Butorphanol (BT), a mixed kappa- and mu-opioid receptor agonist, induces vigorous food intake in rats. Peripheral injection of BT seems to increase food intake more effectively than intracerebroventricular administration. To further elucidate the nature of BT's influence on consummatory behavior, we examined which feeding-related brain areas exhibit increased c-Fos immunoreactivity (IR) following subcutaneous injection of 4 mg/kg body weight BT, a dose known to induce a maximal orexigenic response. We also evaluated whether direct administration of BT into the forebrain regions activated by peripheral BT injection affects food intake. Peripheral BT administration induced c-Fos-IR in the hypothalamic paraventricular nucleus (PVN), central nucleus of the amygdala (CeA), and nucleus of the solitary tract (NTS). However, 0.1-30 microg BT infused into the CeA, failed to increase food intake 1, 2, and 4 h after injection. Only the highest dose of BT (30 microg) injected into the PVN increased feeding. These results suggest that the PVN, CeA, and NTS mediate the effects of peripherally-injected BT. The PVN or CeA are probably not the main target sites of immediate BT action.     

Mu receptors at discrete hypothalamic and brainstem sites mediate opioid peptide-induced increases in central sympathetic outflow

Synthetic human beta-endorphin, 7.25 nmol intracisternally, in conscious, freely moving, cannulated adult male rats increased plasma concentrations of the 3 catecholamines, epinephrine, norepinephrine and dopamine. Similarly administered equimolar morphine increased only plasma epinephrine concentration significantly. A 10-fold greater intracisternal dose of morphine significantly increased plasma concentrations of all 3 catecholamines. This effect was inhibited by prior intra-arterial naloxone administration. Intracisternal administration of the selective mu receptor agonist [D-Ala2,NMe-Phe4,Gly-ol5]enkephalin (DAGO), 2.9 nmol, also increased plasma concentrations of the 3 catecholamines and, furthermore, these effects were significantly greater than those noted in response to equimolar beta-endorphin. The greater potency of DAGO than beta-endorphin to increase catecholamine secretion suggests that this opioid peptide-induced effect is mediated at mu receptors. Administration of DAGO, 0.1 nmol, directly into either the hypothalamic paraventricular nucleus (PVN) or brainstem nucleus of the solitary tract (NTS) significantly increased plasma concentrations of all 3 catecholamines when compared with either saline-infused controls or animals administered DAGO into other brain areas. These catecholamine-stimulating effects of DAGO administered into either PVN or NTS were prevented by prior intra-arterial naloxone administration. Heart rate, but not mean arterial blood pressure, increased in response to DAGO administration into the NTS while no significant cardiovascular changes were noted among the experimental groups in response to DAGO administered into the PVN. These data support a hypothesis that mu receptors at discrete and anatomically distant brain sites mediate opioid peptide-induced catecholamine secretion through activation of the central sympathetic outflow to the adrenal medulla and sympathetic nerve terminals.     

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.