Stress-induced changes of circulating neuropeptide Y in the rat: comparison with catecholamines

Stress-induced changes in adrenal neuropeptide Y expression are regulated by a negative feedback loop

Neuropeptide Y is a co-transmitter that is synthesized by chromaffin cells in the adrenal medulla. During the fight-or-flight response these cells release NPY in addition to epinephrine and norepinephrine. Following the stress-induced reflex, the levels of NPY are increased as part of a homeostatic response that modulates catecholaminergic signaling. Here, we examined the control of NPY expression in mice after brief exposure to the cold water forced swim test. This treatment led to a shift in NPY expression between two populations of chromaffin cells that reversed over the course of 1 week. When NPY(GFP) BAC transgenic animals were exposed to stress, there was an increase in cytoplasmic, non-secretable GFP, indicating that stress increased NPY promoter activity. In vivo blockage of Y2 (but not Y1 or Y5) receptors increased basal adrenal NPY expression and so modulated the effects of stress. We conclude that release of NPY mediates a negative feedback loop that inhibits its own expression. Thus, the levels of NPY are determined by a balance between the potentiating effects of stress and the tonic inhibitory actions of Y2 receptors. This may be an efficient way to ensure the levels of this modulator do not decline following intense sympathetic activity.

A putative morphological substrate of the catecholamine-influenced neuropeptide Y (NPY) release in the human hypothalamus

Neuropeptide Y (NPY) is a 36 amino acid peptide, which among others, plays a pivotal role in stress response. Although previous studies confirmed that NPY release is increased by stress in several species, the exact mechanism of the stress-induced NPY release has not been elucidated yet. In the present study, we examined, with morphological means, the possibility that catecholamines directly influence NPY release in the human hypothalamus. Since the use of electron microscopic techniques is virtually impossible in immunostained human samples due to the long post mortem time, double-label immunohistochemistry was utilised in order to reveal the putative catecholaminergic-NPY associations. The present study is the first to demonstrate juxtapositions between the catecholaminergic, tyrosine hydroxylase (TH)/dopamine-beta hydroxylase (DBH)-immunoreactive (IR) and NPY-IR neural elements in the human hypothalamus. These en passant type associations are most numerous in the infundibular and periventricular areas of the human diencephalon. Here, NPY-IR neurons often form several contacts with catecholaminergic fibre varicosities, without any observable gaps between the contacting elements, suggesting that these juxtapositions may represent functional synapses. The lack of phenylethanolamine N-methyltransferase (PNMT)-NPY juxtapositions and the relatively few observed DBH-NPY associations suggest that the vast majority of the observed TH-NPY juxtapositions represent dopaminergic synapses. Since catecholamines are known to be the crucial components of the stress response, the presence of direct, catecholaminergic (primarily dopaminergic)-NPY-IR synapses may explain the increased NPY release during stress. The released NPY in turn is believed to play an active role in the responses that are directed to maintain the homeostasis during stressful conditions.

Neuropeptide Y, an orexigenic hormone, regulates phagocytic activity of lizard splenic phagocytes

Present in vitro study in the wall lizard Hemidactylus flaviviridis, for the first time in ectothermic vertebrates, demonstrated the immunoregulatory role of neuropeptide Y (NPY) and its receptor-coupled downstream signaling cascade. NPY inhibited the percentage phagocytosis and phagocytic index of splenic phagocytes. The inhibitory effect of NPY on phagocytosis was completely antagonized by Y(2) and Y(5) receptor antagonists. This suggests that NPY mediated its effect on phagocytosis through Y(2) and Y(5) receptors. Further, NPY receptor-coupled downstream signaling cascade for NPY effect on phagocytosis was explored using the inhibitors of adenylate cyclase (SQ 22536) and protein kinase A (H-89). The SQ 22536/H-89 in a concentration-related manner decreased the inhibitory effect of NPY on phagocytosis. Further, an increase in intracellular cAMP level was observed in response to NPY. Taken together, it can be concluded that NPY via Y(2) and Y(5) receptor-coupled AC-cAMP-PKA pathway downregulated the phagocytic activity of lizard splenic phagocytes.

Neuropeptide Y is a mediator of chronic vascular and metabolic maladaptations to stress and hypernutrition

Neuropeptide Y (NPY) is a central neuromodulator and peripheral sympathetic neurotransmitter that also has important regulatory roles in cardiovascular, neuroendocrine, immune and metabolic functions during stress. Focusing on the peripheral actions of the peptide in rodent models, we summarize recent studies from our laboratory demonstrating that stress-induced release of NPY mediates accelerated atherosclerosis/restenosis, obesity and metabolic-like syndrome, particularly when combined with a high fat, high sugar diet. In this review, we propose mechanisms of NPY's actions, its receptors and cellular substrates that increase the risk for cardiovascular and metabolic diseases when chronic stress is associated with pre-existing vascular injury and/or states of hypernutrition.

Chronic psychosocial stress alters NPY system: different effects in rat and tree shrew

The neuropeptide Y (NPY) system has been largely studied in relation to affective disorders, in particular for its role in the mechanisms regulating the pathophysiology of anxiety and depression and in the stress-related behaviours. Although NPY has been previously investigated in a variety of animal models of mood disorders, the receptor subtype mainly involved in the modulation of the stress response has not been identified. In the present study, the chronic psychosocial stress based on the resident-intruder protocol-an ethologically relevant paradigm known to induce behavioural and endocrine modifications which mimic depression-like symptoms-was used. Two different species were investigated: rat and tree shrew (Tupaia belangeri); the latter is regarded as an intermediate between insectivores and primates and it was chosen in this study for its pronounced territoriality. In these animals, the regulation of NPY and of Y(1), Y(2) and Y(5) receptors mRNA expression was evaluated after chronic stress and chronic antidepressant treatment by in situ hybridization in selected brain regions known to be involved in the pathophysiology of mood disorders. The animals were exposed to psychosocial stress for 35 days and concomitant daily fluoxetine treatment (10 mg/kg for rats and 15 mg/kg for tree shrews) after the first week of stress. The results confirmed a major role for hippocampal and hypothalamic NPY system in the pathophysiology of mood disorders. Although there were no evident differences between rat and tree shrew in the NPY system distribution, an opposite effect of chronic psychosocial stress was observed in the two species. Moreover, chronic antidepressant treatment was able to counteract the effects of stress and restored basal expression levels, suggesting the utility of these paradigms as preclinical models of stress-induced depression. Overall, although evident species differences were found in response to chronic psychosocial stress, the present study suggests a role for NPY receptors in the stress response and in the action of antidepressant drugs, providing further support for an involvement of this neuropeptidergic system in the pathophysiology of depression and anxiety.

Acute stress differentially affects corticotropin-releasing hormone mRNA expression in the central amygdala of the "depressed" flinders sensitive line and the control flinders resistant line rats

Preclinical and clinical evidence suggests that neuropeptides play a role in the pathophysiology of mood disorders. In the present study, we investigated the involvement of the peptides corticotropin-releasing hormone (CRH), neuropeptide Y (NPY) and nociceptin/orphanin FQ (N/OFQ) and of their receptors in the regulation of emotional behaviours. In situ hybridization experiments were performed in order to evaluate the mRNA expression levels of these neuropeptidergic systems in limbic and limbic-related brain regions of the Flinders Sensitive Line (FSL) rats, a putative genetic animal model of depression. The FSL and their controls, the Flinders Resistant Line (FRL) rats, were subjected to one hour acute restraint and the effects of the stress exposure, including possible strain specific changes on these neuropeptidergic systems, were studied. In basal conditions, no significant differences between FSL and FRL rats in the CRH mRNA expression were found, however an upregulation of the CRH mRNA hybridization signal was detected in the central amygdala of the stressed FRL, compared to the non stressed FRL rats, but not in the FSL, suggesting a hypoactive mechanism of response to stressful stimuli in the "depressed" FSL rats. Baseline levels of NPY and N/OFQ mRNA were lower in the FSL rats compared to the FRL in the dentate gyrus of hippocampus and in the medial amygdala, respectively. However, the exposure to stress induced a significant upregulation of the N/OFQ mRNA levels in the paraventricular thalamic nucleus, while in the same nucleus the N/OFQ receptor mRNA expression was higher in the FSL rats. In conclusion, selective alterations of the NPY and N/OFQ mRNA in limbic and limbic-related regions of the FSL rats, a putative animal model of depression, provide further support for the involvement of these neuropeptides in depressive disorders. Moreover, the lack of CRH activation following stress in the "depressed" FSL rats suggests a form of allostatic load, that could alter their interpretation of environmental stimuli and influence their behavioural response to stressful situations.

Intracellular signaling mechanisms mediating catecholamine release upon activation of NPY Y1 receptors in mouse chromaffin cells

The adrenal chromaffin cells synthesize and release catecholamine (mostly epinephrine and norepinephrine) and different peptides, such as the neuropeptide Y (NPY). NPY stimulates catecholamine release through NPY Y1 receptor in mouse chromaffin cells. The aim of our study was to determine the intracellular signaling events coupled to NPY Y1 receptor activation that lead to stimulation of catecholamine release from mouse chromaffin cells. The stimulatory effect of NPY mediated by NPY Y1 receptor activation was lost in the absence of extracellular Ca2+. On the other hand, inhibition of nitric oxide synthase and guanylyl cyclase also decreased the stimulatory effect of NPY. Moreover, catecholamine release stimulated by NPY or by the nitric oxide donor (NOC-18) was inhibited by mitogen-activated protein kinase (MAPK) and protein kinase C inhibitors. In summary, in mouse chromaffin cells, NPY evokes catecholamine release by the activation the NPY Y1 receptor, in a Ca2+-dependent manner, by activating mitogen-activated protein kinase and promoting nitric oxide production, which in turn regulates protein kinase C and guanylyl cyclase activation.

Exposure to acute physical and psychological stress alters the response of rat macrophages to corticosterone, neuropeptide Y and beta-endorphin

The objective of the present study was to investigate the effect of acute exposure to electric tail shock stress (ES) and a stress witnessing procedure (SW), as models for physical and psychological stress paradigms, respectively on adherence, phagocytosis and hydrogen peroxide (H(2)O(2)) release from rat peritoneal macrophages. In addition, we studied the in vitro effects of corticosterone (CORT), neuropeptide Y (NPY) and beta-endorphin (BE) on adherence, phagocytosis and H(2)O(2) release from macrophages isolated from control rats and from rats that had been exposed to ES or SW procedures 24 h earlier. ES and SW comparably diminished phagocytosis and H(2)O(2) release, but did not influence macrophage adherence. In vitro treatment with CORT and NPY notably suppressed phagocytosis and potentiated H(2)O(2) release from macrophages. BE suppressed both phagocytosis and H(2)O(2) release from macrophages. Previous exposure to ES and SW altered the responsiveness of the isolated macrophages to their in vitro treatment with mediators of stress, making the cells less sensitive to the influence of CORT and NPY and to a lesser extent to BE. It could be concluded that changes in the local macrophage milieu induced by ES and SW 24 h earlier modify macrophage responses to subsequent in vitro exposure to the stress mimics, CORT, NPY and BE.

Prolactin response to formalin is related to the acute nociceptive response and it is attenuated by combined application of different stressors

Subcutaneous injection of diluted formalin (0.2 ml of 4% solution/100 g BW) can influence the increase of plasma epinephrine levels in rats exposed to exteroceptive (handling, immobilization), as well as to interoceptive stressors (insulin-induced hypoglycemia), without having any effect on norepinephrine release. In the present studies, the effect of the above-mentioned stressors has been investigated on formalin-induced prolactin (PRL) and corticosterone secretion. Administrations of formalin via chronically implanted subcutaneous cannula into the hind limb without handling induce an immediate increase in both plasma PRL and corticosterone levels. While PRL concentration reaches its peak value within 5 min then returns to the basal level by the end of the 30th min, corticosterone level also starts to rise immediately after formalin administration reaching its highest concentration within 15-30 min, but it remains at this high level during the next 60 min, then it declines and returns to the pre-injection level. Application of formalin to animals exposed to different heterotypic stressors (like handling or insulin-induced hypoglycemia) produces an attenuated PRL response, while plasma corticosterone levels induced by the same nociceptive component remained unchanged. Combinations of formalin injection with immobilization also show an attenuated PRL response. The present data indicate that plasma PRL response to formalin is related to its acute nociceptive phase, and application of different stressors prior to formalin injection significantly attenuate plasma PRL levels, while it does not influence corticosterone responses.

Influence of cold stress on neuropeptide Y and sympathetic neurotransmission

Chronic cold stress of rats (4 degrees C; 1-3 weeks) induced a marked increase in gene expression (adrenal medulla; superior cervical ganglia), tissue content (mesenteric arterial bed) and nerve stimulation-induced overflow of NPY-immunoreactivity (NPYir) from the perfused mesenteric arterial bed. In contrast increased NPY neurotransmission was offset by an apparent decrease in the evoked overflow of norepinephrine (NE) due to a presumed deactivation of NE by nitric oxide (NO), despite increased sympathetic nerve activity. The net effect of these offsetting system was no change in basal or the evoked increase in perfusion pressure (sympathetic tone). It is concluded that differences in NPY and NE transmission act as an important compensatory mechanism preventing dramatic changes in arterial pressure when sympathetic nerve activity is high during cold stress.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

NPY Y1 receptors are present in axonal processes of DRG neurons

Using a sensitive immunohistochemical method, the localization of the neuropeptide Y (NPY) Y1 receptor (Y1R) was studied in contralateral and ipsilateral dorsal root ganglion (DRG) neurons of rats subjected to different unilateral manipulations with focus on their axonal processes and projection areas. Y1R-like immunoreactivity (LI) was observed in the contralateral sciatic nerve and dorsal roots of lesioned rats, and double staining revealed colocalization with calcitonin gene-related peptide (CGRP). Y1R-LI was also seen in fibers close to and even within the epidermis. A fairly small number of nerve endings double-labeled for Y1R and CGRP were present in the dorsal horn. After unilateral crush of the sciatic nerve Y1R- and CGRP-LI accumulated in the same axons proximal to the lesion. After dorsal rhizotomy CGRP-LI was strongly reduced in the ipsilateral dorsal horn. No certain change was observed for Y1R- or NPY-LI, but Y1R/CGRP double-labeled nerve endings disappeared after the lesion. These results strongly suggest centrifugal transport of Y1Rs in DRG neurons, mainly to the peripheral sensory branches. To what extent these Y1Rs are functional has not been analyzed here, but a recent study on Y1R null mice provides evidence for involvement of prejunctional Y1Rs in peripheral sensory functions

Neuropeptide Y and the adrenal gland: a review

This paper sets out to review several aspects of NPY and adrenal function, starting with the localisation of NPY in the adrenal, then describing the regulation of NPY release and considering whether the adrenal is a significant source of circulating NPY. The review then describes the regulation of adrenal content of peptide, and finally covers the actions of NPY on the adrenal gland, and the receptor subtypes thought to mediate these effects. The regulation and actions of NPY are discussed with reference to both the adrenal cortex and the medulla.

Activity-wheel running blunts suppression of splenic natural killer cell cytotoxicity after sympathectomy and footshock

We used chemical sympathectomy by 6-hydroxydopamine (6-OHDA) to examine whether adaptation by the sympathetic nervous system (SNS) is a plausible explanation for our prior finding that activity-wheel running blunts the suppression of splenic natural killer cell cytotoxicity after footshock. Male Fischer rats were assigned to treatments using a group (activity wheel vs. sedentary)x treatment (6-OHDA vs. saline)x condition (footshock vs. no shock) design. After 5-6 weeks, rats were injected i.p. with saline or with 40, 80, and 80 mg/kg 6-OHDA on pre experimental days -5, -3, and -1. Half the rats received 6 min of random footshock during a 40-min period. Cytotoxicity was determined by standard 4-h 51Cr release assay. Sympathectomy reduced splenic [NE] by 72%. After 6-OHDA injection and footshock, percent lysis was 33% lower in sedentary rats compared with activity-wheel runners and home-cage controls, p=0.048. The results suggest that activity-wheel running leads to adaptations that offset an altered SNS modulation of splenic NK cell cytotoxicity in response to footshock.

Treadmill exercise training blunts suppression of splenic natural killer cell cytolysis after footshock

This study extended to treadmill exercise training our prior report (Dishman RK, Warren JM, Youngstedt SD, Yoo H, Bunnell BN, Mougey EH, Meyerhoff JL, Jaso-Friedmann L, and Evans DL. J Appl Physiol 78: 1547-1554, 1995) that activity wheel running abolished the suppression of footshock-induced natural killer (NK) cell cytolysis. Twenty-four male Fischer 344 rats were assigned to one of three groups (n = 8, all groups): 1) a home-cage control group, 2) a sedentary treatment group, or 3) a treadmill-running group (0 degrees incline, 25 m/min, 35 min/day, 6 days/wk). After 6 wk, the treadmill and sedentary groups received 2 days of footshock. Splenic NK cytotoxicity was determined by standard 4-h (51)Cr release assay. Percentages of lymphocytes were determined by flow cytometry. Plasma levels of ACTH, corticosterone, and prolactin concentration were measured by radioimmunoassay. After footshock, percentage of lysis relative to home-cage controls was 40% and 80% for sedentary and treadmill-trained animals, respectively (P < 0.05). Our results indicate that the protective effect of chronic exercise on innate cellular immunity in the Fischer 344 male rat is not restricted to activity wheel running, nor is it explained by elevations in basal NK activity, increased percentages of splenic NK and cytotoxic T cells, or increased plasma levels of ACTH, corticosterone, and prolactin.

Increased concentrations of plasma neuropeptide Y in patients with eclampsia and preeclampsia

OBJECTIVE

Epinephrine and norepinephrine are associated with the hyperstimulation of the sympathetic nervous system. Neuropeptide Y is a potent vasoconstrictive substance that is released in response to sympathetic nerve stimulation.

STUDY DESIGN

The concentrations of plasma neuropeptide Y in pregnant patients with eclampsia (n = 8), preeclampsia (n = 8), and normotension (n = 8) were measured by radioimmunoassay on admission and 6 days after delivery. Correlations between plasma concentration of neuropeptide Y and mean arterial blood pressure were also evaluated in these patients on admission and 6 days after delivery.

RESULTS

The plasma level of neuropeptide Y in women with eclampsia (P <.001) and preeclampsia (P <.003) was found to be significantly elevated with respect to that in normotensive pregnant women. At 6 days after delivery the concentration of plasma neuropeptide Y was significantly decreased in women with eclampsia, women with preeclampsia, and women with normotensive pregnancies compared with the value measured on admission (P <.0001, P <.0001, and P <.002, respectively). At admission the plasma neuropeptide Y level was positively correlated with mean arterial blood pressure in women with eclampsia and preeclampsia. However, no significant correlations were observed between plasma neuropeptide Y concentration and mean arterial blood pressure both at admission and 6 days after delivery in normotensive pregnant women and 6 days after delivery in women with eclampsia and preeclampsia.

CONCLUSION

We have concluded that the level of neuropeptide Y in plasma is increased in women with eclampsia and preeclampsia. Elevated plasma neuropeptide Y levels may play a key role in the development of eclampsia and preeclampsia.

Neuropeptide Y blocks anxiogenic-like behavioral action of corticotropin-releasing factor in an operant conflict test and elevated plus maze

Central administration of neuropeptide Y (NPY) produces anxiolytic-like behavioral effects in rat models of anxiety. Because previous evidence has suggested a relationship between NPY and corticotropin-releasing factor (CRF) in the brain, we have focused on the interaction of these neuropeptide systems in emotional responsiveness to stressful stimuli. Intracerebroventricular administration of CRF produced a marked response suppression in an operant incremental shock conflict paradigm. NPY [(1 microg, intracerebroventricularly (i.c.v.)] significantly antagonized the response-suppressing effects of CRF (0.75 microg, i.c.v.) on punished responding in the conflict test at doses that produced little or no behavioral effect when administered alone. Central administration of the CRF antagonist [D-Phe(12), Nle(21,38),C(alpha) MeLeu(37)]CRF (D-Phe CRF(12-41)) alone did not alter punished or unpunished responding in the conflict test. However, pretreatment with the CRF antagonist before a subthreshold dose of NPY (1 microg, i.c.v.) produced a significant potentiation of the release of punished responding relative to NPY alone and untreated controls. NPY also antagonized the "anxiogenic-like" behavioral effects of CRF in the elevated plus maze. These findings support the hypothesis that NPY and CRF may reciprocally modulate an animal's behavioral response to stressful stimuli.

Neuropeptide Y inhibits glutamate release and long-term potentiation in rat dentate gyrus

The effect of intracerebroventricular injection of neuropeptide Y (NPY) was assessed on LTP in dentate gyrus. We report that NPY attenuated LTP and inhibited KCl-induced glutamate release in synaptosomes prepared from dentate gyrus. Activity of the stress-activated kinase, c-Jun NH2-terminal kinase (JNK) in synaptosomes was increased by incubation with NPY or following intracerebroventricular injection. Activation of JNK might underlie the inhibitory effect of NPY on LTP.

The neuropeptides, VIP and NPY, that are present in the thyroid nerves are not released into the thyroid vein

In the present study, we tested the hypothesis that the neuropeptides, vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), which are present in the thyroid nerves, act as physiological neurotransmitters involved in the regulation of thyroid hormone secretion and thyroid blood flow. Specifically, we examined whether these neuropeptides can be released into thyroid blood vessels by electrical stimulation of the major thyroid nerves or whether their expression is altered by changes in iodine intake. Sprague-Dawley rats were used in this study. The cervical sympathetic trunk or the superior laryngeal nerve was stimulated by bipolar electrodes in anesthetized rats. During nerve stimulation, blood samples were withdrawn from the thyroid vein. Thyroid blood flow was monitored by laser Doppler blood flowmetry. Sympathetic stimulation caused a marked decrease in thyroid blood flow, which was associated with a significant increase in release of norepinephrine. However, these effects were not accompanied by any change in NPY release into the thyroid vein. Stimulation of the superior laryngeal nerve was not associated with changes in thyroid blood flow or VIP release into the thyroid vein. In a separate experiment, rats were fed a diet containing low-, high-, or normal iodine concentrations. Triiodothyronine (T3) and thyroxine (T4) levels in thyroid venous plasma were significantly reduced in rats fed a low-iodine diet but not in a separate group of rats fed a high iodine diet. However, these treatments had no effect on VIP or NPY concentrations in thyroid venous plasma or in thyroid ganglia. Thus, our results indicate that VIP and NPY, which are present in the thyroid nerves, may not be directly involved in the regulation of thyroid function.

Differential effects of high salt intake on neuropeptide Y and adrenergic markers in hearts of Dahl rats

Adrenergic markers and neuropeptide Y (NPY) were examined in Dahl NaCl-sensitive and -resistant outbred male rats, fed either 0.35% or 8% NaCl diets for 8 weeks. The high salt diet caused left ventricular hypertrophy in sensitive rats but not in the resistant strain. Norepinephrine stores were not affected by high salt intake, but tyrosine hydroxylase, and dopamine beta-hydroxylase were elevated in the salt-induced hypertrophied left ventricle in conjunction with increased levels of nerve growth factor and p75 neurotrophin receptor. In contrast, high salt intake reduced ventricular neuropeptide Y in both Dahl salt-resistant and -sensitive rats.

Role of neuropeptide Y in cold stress-induced hypertension

Chronic cold stress (4 degrees C) produced a sustained increase in mean arterial pressure in both normotensive and borderline hypertensive rats (BHR). The high blood pressure in BHRs was significantly reversed by a neuropeptide Y (NPY) Y1 receptor antagonist suggesting that NPY is involved in mediating stress-induced hypertension. Corresponding increases in adrenal NPY messenger RNA and NPY immunoreactivity were found during the stress; furthermore, chronic cold stress also potentiated the pressor response of rats to a subsequent acute stress test in which NPY has been shown to play a role. These results suggest that chronic cold stress-induced hypertension is mediated by elevated NPY release and vascular tone as a result of increased NPY gene expression and storage.

Modulation of immune cell function by the autonomic nervous system

This review discusses some of the major findings implicating the autonomic nervous system in the regulation of immune function. The sympathetic nervous system, the primary focus of this line of research, directly innervates the major lymphoid organs, and physiological release of sympathetic neurohormones at these sites has been documented. Leukocytes have been shown to express receptors for catecholamines, as well as neuropeptide Y, and studies in vitro and in vivo have indicated that occupation of these receptors by the appropriate ligands produces functional changes in immunological cells. Finally, altered sympathetic regulation may underlie some of the immunological abnormalities observed in chronic stress, clinical depression, and ageing.

The potentiality and practicality of a 'salt-free' diet for the prevention and amelioration of human disorders

The potential of a salt-free diet, which restricts sodium intake to 10 mmol/day, for the prevention and amelioration of human diseases and conditions, may be considerable. Several human disorders may be the result of dietary-salt-generated high-bodily-sodium motility and fluid retention, this being incompatible with the maintenance of bodily homeostasis whenever the body is subjected to stress. Equally importantly, the present-day impracticalities of adopting a 'salt-free' diet appear man-made, and therefore soluble once a sufficiency of purpose exists.

Inhibitory effect of cilnidipine on pressor response to acute cold stress in spontaneously hypertensive rats

We investigated the effect of cilnidipine on cardiovascular and neuroendocrine responses to acute cold stress in conscious and unrestrained or moderately restrained spontaneously hypertensive rats (SHRs). Acute cold stress significantly increased mean blood pressure without marked change in heart rate. The acute cold stress-induced elevation in blood pressure was almost abolished by 1 mg/kg, p.o. of prazosin. The cold stress also elevated plasma norepinephrine and epinephrine levels. Cilnidipine at 3 mg/kg, p.o. significantly inhibited the pressor response to acute cold stress. Although 3 mg/kg, p.o. of nifedipine, nicardipine or manidipine lowered mean blood pressure to a similar extent as cilnidipine, none of these three drugs affected the pressor response. Cilnidipine also reduced the cold stress-induced increment in plasma norepinephrine but not the epinephrine level. These findings suggest that acute cold stress may induce the elevation in blood pressure due to an enhanced activation of the sympathoadrenal system in SHRs and that cilnidipine may suppress the pressor response by inhibiting the sympathetic nerve activity.

Evidence against differential release of noradrenaline, neuropeptide Y, and dopamine-beta-hydroxylase from adrenergic nerves in the isolated perfused sheep spleen

The subcellular storage and release of noradrenaline (NA), dopamine-beta-hydroxylase (D beta H), and neuropeptide Y (NPY) was studied in the isolated perfused sheep spleen. Subcellular distribution studies showed a bimodal distribution for NA which was well reflected by D beta H and indicated the occurrence of two types of NA storage vesicles. The most dense, presumably large dense-cored vesicles (LDV), contain both membrane-bound and soluble D beta H; the less dense presumably corresponds to small dense-cored vesicles (SDV) and at least does not contain soluble D beta H. The distribution of NPY is extended but shows a peak only at the position of LDV, indicating that LDV contain NPY. Continuous electrical stimulation of the splenic nerve at 2 Hz, 5 Hz, 10 Hz, and 20 Hz or at 20 hz with bursts induced the release of NA, NPY, and D beta H. The ratio among these components was constant. The fractional release of D beta H and NA was comparable at all frequencies used; that of NPY was 10-20 times lower, suggesting the occurrence of a large nonreleasable NPY pool. The present data argue against a high frequency stimulation or intermittent stimulation-induced preferential release of NPY from adrenergic neurons and question the concept of frequency-dependent chemical coding of sympathetic transmission in general. The simplest interpretation of our data is that NA and NPY are released at all frequencies from a single pool. The present finding might signify that only large dense-cored vesicles are involved in the sympathetic stimulation-evoked secretion of catecholamines from adrenergic nerve terminals of the isolated sheep spleen.

Localization of neuropeptide Y Y1 receptors in the rat nervous system with special reference to somatic receptors on small dorsal root ganglion neurons

Immunohistochemical staining with an antiserum against the neuropeptide Y (NPY)-Y1 receptor (Y1-R) protein was shown in rat small dorsal root ganglion (DRG) neurons, which also were Y1-R mRNA-positive and calcitonin gene-related peptide (CGRP)-positive. The Y1-R-like immunoreactivity was almost exclusively located in the somatic plasmalemma and in the perinuclear region. Intracellular recording showed that the Y1 agonist [Leu31,Pro34]NPY evoked an outward current in small DRG neurons, suggesting a functional somatic Y1-R. No evidence for axonal transport of Y1-R protein was obtained after analysis of the dorsal horn for double staining with CGRP, after dorsal rhizotomy, or after compression of dorsal roots and the sciatic nerve. It is proposed that blood-borne NPY released from sympathetic nerves and adrenal medulla is the endogenous ligand for the Y1 receptors on the small DRG neurons. Y1-R-positive neurons were also seen in the dorsal horn of spinal cord, the hypothalamic arcuate nucleus, pyramidal cells in the cerebral cortex, Purkinje and basket cells in the cerebellar cortex, and in many other brain regions.

Neuropeptide Y is an inducible gene in the human immune system

This study reports on neuropeptide Y (NPY) mRNA expression in human peripheral blood mononuclear cells (PBMC) and lymphoid tissues. By reverse transcription polymerase chain reaction (RT-PCR) it is shown that activated human PBMC of normal blood donors expressed the NPY gene. The PCR products had the expected size and Northern blotting demonstrated the presence of the 0.8-kb NPY mRNA. To define the subpopulations of mononuclear cells expressing this neuropeptide, purified monocytes, B cells and T cells were stimulated with specific activators. Monocytes and in vitro matured macrophages expressed NPY mRNA in response to phorbol myristate acetate (PMA). B lymphocytes expressed NPY mRNA following stimulation with antibody to surface immunoglobulin and PMA. In order to analyze whether these cell types express NPY under physiological conditions in vivo, human bone marrow, tonsil and thymus were analyzed. In situ hybridization of bone marrow revealed a small number of cells containing high levels of NPY mRNA which was also detected in RNA extracts of human thymus and tonsil. In summary, NPY is an inducible gene in human lymphocytes and monocytes and it is expressed at sites where these cells are activated in vivo.

Multiple neuropeptide Y receptors are involved in cardiovascular regulation. Peripheral and central mechanisms

1. Neuropeptide Y (NPY) occurs in both the central and peripheral nervous system. In the periphery, NPY coexists with noradrenaline (NA) in perivascular sympathetic fibers. 2. NPY has a vasopressor effect, reflecting direct vasoconstriction of blood vessels and potentiation of the NA-evoked response. NPY also suppresses the release of NA from sympathetic fibers. 3. The post- and pre-junctional NPY receptors are referred to as Y1 and Y2, respectively. They recognize not only NPY but also the homologous gut hormone peptide YY (PYY). 4. The Y1 and Y2 receptors have been characterized in numerous test systems using analogs of NPY/PYY. Already the deletion of the first N-terminal amino acid (NPY 2-36) results in a marked loss of potency at the Y1 receptor. The Y2 receptor is much less dependent upon an intact N-terminus, and a wide range of C-terminal NPY fragments retain quite high potency. 5. Recently, yet another NPY receptor, Y3, that is distinct from Y1 and Y2 in that it recognizes PYY poorly, has been demonstrated in the brainstem and in the periphery. 6. Further attempts to characterize the various receptor types have relied on truncated and substituted analogs of NPY/PYY. Although such studies suggest the existence of at least three types of NPY receptors, the lack of antagonists has represented a problem. 7. Since NPY may regulate cardiovascular functions via peripheral and central receptors its physiological and possibly pathophysiological significance has attracted much attention. 8. The responsiveness to NPY seems to be altered in animal models of hypertension and elevated plasma levels of NPY have been found in patients under various conditions of stress and in primary hypertension. A number of studies have suggested that NPY may be a pathogenetic factor behind primary hypertension. 9. Antagonists for the various NPY receptors would be useful for an analysis of which effects of these peptides are physiologically relevant. It is tempting to predict that both agonists and antagonists of the NPY receptors could be useful as drugs, for instance, in the treatment of primary hypertension.

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

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

Cholinergic stimulation of neuropeptide Y secretion from the isolated perfused rat stomach

Neuropeptide Y (NPY) is present in both extrinsic sympathetic adrenergic nerve terminals and intrinsic nerves of the gastrointestinal (GI) tract. Based on this localization a number of functions have been attributed to GI NPY including regulation of blood flow, intestinal fluid and electrolyte transport, and motility. There is nothing currently known, however, about the regulation of its secretion from GI nerves. The effect of cholinergic agonists and antagonists on secretion of NPY immunoreactivity (NPY-IR) from the isolated perfused rat stomach was investigated in the present study. Perfusate samples were extracted and concentrated on SepPak cartridges. Basal levels of NPY-IR varied between 98 and 147 fmol/min. Release was stimulated by high potassium concentrations (50 mM) and acetylcholine (ACh; 1 microM). ACh-induced secretion was unaffected by atropine, but inhibited by hexamethonium. Further evidence for a nicotinic component in the regulation of NPY-IR secretion was obtained by the finding of hexamethonium-induced reduction in basal secretion and stimulation of secretion by 1,1-dimethyl-4-phenyl-piperazinium (DMPP). In conclusion, cholinergic agonists and antagonists can modulate gastric NPY-IR secretion, and the cholinergic stimulatory effects are probably mediated via nicotinic receptor stimulation at the level of the intrinsic ganglia.

Release of neuropeptide Y and noradrenaline during afferent nerve stimulation

The present study was carried out to investigate the possibility that noradrenaline (NA) and neuropeptide Y (NPY) are co-released after afferent vagal or saphenous stimulation (1, 5, 10 and 20 Hz) in chloralose-anaesthetized dogs. Electrical stimulation of the vagus elicited an increase in plasma NA levels for the 5, 10 and 20 (but not 1) Hz frequencies. Blood pressure only increased after a 20-Hz stimulation. In contrast, no change in plasma NPY levels was observed whatever the frequency of stimulation. Electrical stimulation of the saphenous nerve failed to change plasma NA and NPY levels. The present data suggest that (1) the release of NA varies according to the frequency of stimulation of nociceptive fibres, (2) NPY release does not seem to be involved in the pressor effect elicited by the stimulation of nociceptive-sensitive fibres, and (3) NPY and NA release are not necessarily linked.

Attenuation of corticotropin releasing factor-induced hypotension in anesthetized rats with the CRF antagonist, alpha-helical CRF9-41; comparison with effect on ACTH release

The effect of pretreatment with the corticotropin releasing factor (CRF-41) antagonist, alpha-helical CRF(9-41), on the hypotensive response obtained on peripheral administration of CRF-41 has been assessed in anesthetized Wistar rats. A single IV bolus dose of rat CRF-41 (2 nmol, at 0 min) produced a hypotensive effect which was rapid in onset (-52 mmHg at +1 min) and sustained throughout the 60-min study period (-42, -40, -26 and -16 mmHg at +3, +10, +30 and +60 min, respectively). The antagonist [alpha CRF(9-41)] was administered in consecutive bolus doses of 12.5, 25 and 50 nmol at -15, -10 and -5 min, respectively. This had no effect on mean arterial blood pressure (MABP) or heart rate, nor did it change significantly the magnitude of the initial rapid fall in MABP when CRF-41 was administered (-45 mmHg at +1 min). However, following pretreatment with alpha CRF(9-41), MABP returned to control values within 3 min and the sustained period of hypotension was completely blocked. Administration of CRF-41 resulted in 44% and 142% increases in norepinephrine and epinephrine measured at +60 min. Pretreatment with the antagonist attenuated the rise in circulating catecholamine levels observed after CRF-41 administration. In comparison, pretreatment with the antagonist did not alter the ACTH response to CRF-41 at +1 and +3 min and only reduced ACTH levels by 28% (p less than 0.05), 43% (p less than 0.001) and 41% (p less than 0.01) at 10, 30 and 60 min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in plasma catecholamine and neuropeptide Y levels after sympathetic activation in dogs

1. Plasma levels of noradrenaline (NA) and neuropeptide Y (NPY) were evaluated in two experimental models associated with an increase in sympathetic tone: conscious dogs which were subject to either sinoaortic denervation or acute administration of the alpha 2-adrenoceptor antagonist yohimbine. 2. Dogs that had undergone sinoaortic denervation exhibited a two fold increase in plasma NA without any change in NPY levels. 3. Yohimbine (0.05 mg kg-1 i.v. as a bolus) produced similar effects. A higher dose of yohimbine (0.5 mg kg-1 i.v.) increased both plasma NA (7 fold) and NPY (6.5 fold) levels. 4. The present results indicate that changes in plasma catecholamines and NPY are not always concomitant. They suggest that the simultaneous release of NA and NPY is only observed under in vivo conditions for a marked increase in sympathetic tone.

Neuropeptide Y radio-immunoassay: characterization and application

1. A sensitive and specific neuropeptide Y (NPY) radio-immunoassay has been developed. This radio-immunoassay does not detect the NPY-related peptides pancreatic polypeptide or peptide YY. NPY extracted from rat plasma using sequential C18 sorbent and affinity chromatography co-eluted with synthetic rat NPY when applied to high pressure liquid chromatography. 2. The procedure of stabilization of platelets followed by high speed centrifugation reduced basal values of NPY by 60%, and this may be consistent with removal of platelets that release NPY. Administration of the cholinesterase inhibitor physostigmine (0.3 mg/kg), intravenously, produced a small but significant increase (39%) from basal concentrations of NPY. 3. NPY concentrations in young (2-3-month-old) Sprague-Dawley and Fisher 944 rats were similar; however, NPY concentrations were significantly increased (55%) in 2-year-old Fisher 944 rats. Similar to plasma concentrations of noradrenaline, NPY levels increase with age.

Neuropeptide-Y innervation of the rat spleen: another potential immunomodulatory neuropeptide

Neuropeptide-Y (NPY) is a 36 amino acid peptide that acts as a chemical messenger in the central and peripheral nervous systems. NPY often is found colocalized with the classical neurotransmitter norepinephrine (NE) and can potentiate the effects of this neurotransmitter postsynaptically in many systems. Using immunocytochemistry for NPY and specific lymphoid cell markers, we mapped the distribution of NPY-positive nerve fibers in the rat spleen. NPY-positive nerve fibers were present along the vasculature, trabeculae, and capsule, and also were found associated with specific lymphoid parenchymal compartments of the spleen, in close contact with lymphocytes and macrophages. These contacts were investigated further at the electron microscopic level. NPY-positive nerve terminals were found in close apposition with lymphocytes in the periarteriolar lymphatic sheath, and with lymphocytes and macrophages in the marginal zone. Previous studies have reported that postganglionic noradrenergic nerve fibers innervate specific lymphoid compartments of the rat spleen, with nerve terminals forming direct appositions with cells of the immune system. The possible colocalization of NPY and NE in these nerve fibers was investigated by chemical sympathectomy with 6-hydroxydopamine, followed by immunocytochemical labeling of NPY and tyrosine hydroxylase (TH), the rate-limiting enzyme in norepinephrine synthesis. Colocalization also was investigated by labeling for NPY with a fluorescent label, eluting the NPY, and staining for TH with diaminobenzidine as the label. These studies demonstrate that norepinephrine and NPY are colocalized in the postganglionic sympathetic nerve fibers of the rat spleen.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of 6-OHDA lesion of central noradrenergic systems on corticosteroid receptors and neuroendocrine responses to stress

Two types of receptor for adrenocortical hormones (type I or mineralocorticoid and type II or glucocorticoid) in the hippocampus and hypothalamus mediate the effects of corticosteroids on various brain functions including the negative feedback control of hypothalamo-pituitary-adrenal (HPA) axis activity. These brain regions are also densely innervated by noradrenergic terminals which may play a role in the regulation of HPA axis activity and the feedback action of corticosteroids. However, direct evidence for a noradrenergic control of corticosterone receptors is lacking. The present experiments tested the effects of 6-hydroxydopamine lesion of noradrenergic ascending pathways at the level of the pedunculus cerebellaris superior (PCS) on the status of type I and type II corticosteroid receptors. Binding of [3H]corticosterone was evaluated in cytosolic fractions of 24-h adrenalectomized animals 3 weeks after surgery. The PCS lesion produced an up-regulation of type I corticosteroid receptors in the hippocampus and of the type II receptor in the hypothalamus. The number of these receptors (Bmax) increased without any change in their affinity for corticosterone (Kd). Furthermore, in a functional study, we tested the effects of the lesion on the neuroendocrine responses to stress. Plasma corticosterone levels were lower in lesioned rats both under basal conditions and in response to the stress of gentle handling or exposure to footshock, indicating reduced activity of the HPA axis. These results are in line with recent studies indicating a facilitatory function of noradrenergic pathways on the HPA axis and suggest that this action could be mediated via a modulation of corticosteroid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Hydroxydopamine Lesion of Ventral Tegmental Area Dopaminergic Cell Bodies does not Impair Neuroendocrine Responses to Environmental Stimuli

Abstract To evaluate the influence of dopamine neurons in neuroendocrine responses to environmental stimulations, rats received bilateral injections of the neurotoxin 6-hydroxydopamine in the ventral tegmental area. Six weeks after the lesion, forebrain areas lost up to 88% of their dopamine content, and the areas innervated by the noradrenergic bundle, which passes through the ventral tegmental area, were also depleted of noradrenaline. Despite these profound changes of catecholamine content, we show that the responses of major neuroendocrine systems to environmental stimuli were not modified. Basal levels of circulating adrenocorticotropin, corticosterone, prolactin and catecholamines, as well as their increase by novel environment exposure, handling and/or electric footshock, were not modified by the lesion. These results favor the hypothesis that the effect of dopamine depletion is more on behavioral response initiation and/or performance than on the cognitive functions or emotional processes. They also question the importance of the ventral noradrenergic bundle in the activation of the hypothalamo-pituitary-adrenal axis by stressful stimuli.

Hormonal regulation of adult sympathetic neurons: the effects of castration on neuropeptide Y, norepinephrine, and tyrosine hydroxylase activity

Previous studies utilizing the hypogastric ganglia (HG) have indicated that gonadal steroids exert organizational and activational effects on noradrenergic biochemistry. Bilateral castration of male rodents at birth prevents the normal maturation of tyrosine hydroxylase (T-OH) activity in the HG; castration during adulthood results in a progressive decline in T-OH activity. Testosterone replacement corrects both the ontogenetic and adult functional alterations in the neurotransmitter-synthesizing enzyme. The present studies in adult male rats extend these previous observations and asked the question whether gonadal steroids regulate the neurotransmitters neuropeptide Y (NPY) and norepinephrine (NE) in the HG. Adult rodents were castrated and ganglia T-OH, NPY, and NE were examined at various time points after surgery. All three indices of sympathetic neuron biochemistry declined following castration, but they exhibited different profiles. It appears that hormones may affect enzyme activity and neurotransmitter pools differently within neurons. Testosterone replacement therapy fully restored T-OH activity, and NPY and NE levels in the HG. These studies extend the activational role of testosterone in regulating sympathetic neuron neurotransmitter and neuropeptide levels as well as neurotransmitter-synthesizing enzymes.

Alpha 2-adrenoceptor modulation of catecholamine and neuropeptide Y responses during haemorrhagic hypotension in anaesthetized dogs

The acute effects of oxymetazoline, an alpha 2-adrenoceptor agonist, and idazoxan, an alpha 2-adrenoceptor antagonist, on the release of neuropeptide Y were evaluated during haemorrhage in pentobarbital-anaesthetized dogs. Plasma concentrations of neuropeptide Y and catecholamines (adrenaline, noradrenaline, and dopamine) were determined in samples simultaneously collected from aorta, portal vein, and adrenal veins. In control dogs, adrenal catecholamine output, aortic concentrations neuropeptide Y and catecholamines markedly increased during the hypotension period. However, adrenal neuropeptide Y output decreased significantly during this period. Portal venous noradrenaline and neuropeptide Y concentrations increased significantly. In dogs treated with idazoxan, catecholamine output from the adrenals increased to an extent similar to that observed in control dogs. However, the increase in noradrenaline and neuropeptide Y in aortic or portal venous blood during haemorrhage was significantly potentiated in the presence of idazoxan. Administration of oxymetazoline abolished this increase, but did not alter adrenal catecholamine or neuropeptide Y output. The present study demonstrates that neuropeptide Y is co-released with noradrenaline from sympathetic nerve fibers during haemorrhage. Since the release of neuropeptide Y appeared to follow a similar time course to that of noradrenaline release, the present observations suggest that haemorrhagic hypotension enhances both neuropeptide Y and noradrenaline release presumably through a common releasing mechanism. These results also indicate that, in peripheral sympathetic nerves but not in the adrenal gland, neuropeptide Y release is also modulated presynaptically by the inhibitory alpha 2-adrenoceptors in conjunction with the noradrenaline release.

Are NPY and enkephalins costored in the same noradrenergic neurons and vesicles?

Separate studies show that NPY and enkephalins are widely distributed in peripheral noradrenergic neurons. In the present study, the subcellular costorage and release in response to intense sympathetic stimulation and reserpine at near therapeutic doses (0.05 mg/kg every other day) were examined. In young pig arteries and vas deferens, enkephalin and D beta H immunofluorescence show consistent but not total overlap. Also NPY is colocalized with D beta H in many fibers but with VIP (nonnoradrenergic) in others. Ultrastructural immunogold labeling indicates that individual terminals contain large dense cored vesicles (LDVs) which store either NPY or enkephalins, even though costorage of both peptides occurs. Some LDVs costore NPY and VIP, especially in the middle cerebral artery and in the lamina propria of vas deferens. Acute CNS ischemia depletes enkephalins and norepinephrine in all tissues analyzed without parallel loss of NPY. Reserpine depletes norepinephrine 70-85% but does not deplete NPY or enkephalins. The latter is in contrast to commonly used high doses known to produce nonspecific, detergent-like effects. In fact, low doses of reserpine induce a time-dependent new synthesis and processing of NPY precursor peptides in vas deferns. Contrasting effects of reserpine on NPY and enkephalin contents, new synthesis and apparent processing, and a differential response to acute CNS ischemia were found in every tissue studied. Activation of precursor neuropeptide processing occurred immediately upon intense sympathetic stimulation in most tissues. Dual localization of NPY in noradrenergic and nonnoradrenergic fibers and differences in subcellular LDV storage help explain why enkephalin correlates better than NPY with norepinephrine loss in response to acute CNS ischemia. Furthermore, the costorage of NPY and enkephalins in distinct subpopulations of noradrenergic fibers, which varies according to tissue, is likely to be under separate CNS control.

The integrity of the ventral noradrenergic bundle (VNAB) is not necessary for a normal neuroendocrine stress response

The paraventricular nucleus of the hypothalamus (PVN) receives a dense noradrenergic innervation originating in the caudal brainstem and conveyed by the ventral noradrenergic bundle (VNAB). To evaluate the importance of this pathway, rats were bilaterally injected with 6-hydroxydopamine (6-OHDA) into the VNAB, posterior to the locus coeruleus to avoid the lesion of the dorsal noradrenergic system. These lesions reduced noradrenaline (NA) levels in the PVN by 60% without any significant change of NA levels in the cortex or of dopamine or serotonin in any part of the brain, indicating the specificity of the lesion. After one or three weeks, the neuroendocrine responses to stress were monitored. The secretion of adrenocorticotropic hormone (ACTH), corticosterone and prolactin were studied under basal conditions and after exposure to a novel environment. The activity of the sympathetic nervous system (SNS) was studied in catheterized rats. Plasma catecholamines were measured in basal conditions, and in response to gentle handling or exposure to footshocks. Apart from a transient increase of the adrenocortical axis activity which disappeared 3 weeks after surgery, the lesion did not change either basal levels of the hormones measured or their response to stress, indicating that the noradrenergic input to the PVN conveyed by the VNAB is not necessary for a normal neuroendocrine stress response to occur.

Involvement of neuropeptide Y in neuroendocrine stress responses. Central and peripheral studies

Neuropeptide Y (NPY) is closely associated to stress-reactive structures in the central and peripheral nervous system. In the periphery, the peptide is colocalized with catecholamines in postganglionic sympathetic fibres and the adrenal medulla. In the brain, the paraventricular nucleus of the hypothalamus receives a dense innervation of NPYergic neurons, some of which also contain monoamines. With the use of a specific immunoradiometric assay, we have demonstrated that NPY is released into the peripheral circulation during psychological stress together with catecholamines. The postganglionic origin of the peptide was demonstrated by the activity of the nicotinic antagonist hexamethonium to attenuate the response. Adrenalectomy or insulin-induced hypoglycemia did not alter basal or stimulated NPY plasma levels, showing that the adrenal is not a major source of circulating NPY in the rat. Although NPY and noradrenaline are frequently released in parallel in various experimental conditions, a clear dissociation can be found in several cases, such as cold stress or the response to phentolamine, where no change can be seen in plasma NPY despite a large activation of noradrenergic terminals. Furthermore, the neuropeptide may play a role in stress-induced pathological states such as hypertension, since its release is greater in animals previously submitted to chronic stress and high-sodium diet. On the other hand, its role in the central nervous system control mechanisms of the stress response is far from being clear, but to understand the interaction of NPY we need a better knowledge of the role of noradrenergic neurons in the central control of the adrenocortical axis or sympathetic nervous system activity.

Effects of neuropeptide Y on the renal, mesenteric and hindlimb vascular beds of the conscious rabbit

The effects of neuropeptide Y (NPY, 10 micrograms/kg bolus i.v.) on renal, mesenteric and hindlimb blood flow were determined in intact conscious rabbits with chronically implanted Doppler ultrasonic flow transducers. The role of sympathetic neuro-effectors was assessed using inhibition of peripheral alpha-adrenoceptors with phentolamine in each group, and in the renal flow group following chemical sympathectomy with 6-hydroxydopamine. In controls, NPY caused markedly non-uniform peak responses. Renal blood flow fell from 2.16 +/- 0.12 kHz to a minimum of 0.26 +/- 0.07 kHz following NPY administration (P less than 0.05). Mesenteric blood flow was reduced from 2.04 +/- 1.17 to 1.54 +/- 0.11 kHz (P less than 0.05). blood flow increased transiently from 2.33 +/- 0.15 to a peak of 3.33 +/- 0.19 kHz (P less than 0.05). Renal vascular resistance rose by 1189 +/- 309% and mesenteric resistance by 54 +/- 9% (P less than 0.05), while hindlimb resistance fell by 24 +/- 3% (P less than 0.05). Pretreatment with phentolamine accentuated the peak pressor response and the reduction in heart rate induced by NPY administration but had little effect on the local haemodynamic changes in each vascular bed. There was no change in the renal vascular response to NPY following sympathectomy. Indeed, the peak NPY-induced reduction in renal blood flow seen in control animals (87 +/- 4%) was unaffected by either alpha-adrenoceptor inhibition (90 +/- 5%) or by sympathectomy (86 +/- 5%). In conscious rabbits with intact cardiovascular reflexes, pharmacological doses of NPY cause profound renal vasoconstriction with smaller changes in mesenteric and hindlimb flow.(ABSTRACT TRUNCATED AT 400 WORDS)

Schedule-induced polydipsia experience decreases plasma corticosterone levels but increases plasma prolactin levels

To determine the neuroendocrine pattern of response to excessive drinking induced by exposure of rats to an intermittent distribution of food (schedule-induced polydipsia, SIP), the present experiment investigated changes in plasma corticosterone, prolactin and catecholamines in chronically catheterized rats that had developed or not this form of adjunctive behaviour. It was found that rats that engage in excessive drinking displayed decreased plasma levels of corticosterone and increased levels of prolactin during the course of a SIP session. There was, however, no differences between groups in plasma catecholamine levels. The difference observed between SIP-pos and SIP-neg rats were entirely condition-specific, since they disappeared in the absence of access to water.

Influence of stressor predictability and behavioral control on lymphocyte reactivity, antibody responses and neuroendocrine activation in rats

The present experiments were designed to study the influence of prediction and control of electric shocks on various aspects of immune function, and the possible intermediate role of glucocorticoid hormones. After two sessions of inescapable footshocks, the reactivity of splenocytes to concanavalin A was reduced by one third. This effect was completely reversed when each shock was preceded by a warning stimulus, even though the adrenocortical response was the same in both conditions. In another experiment, rats were submitted to ten sessions of continuous avoidance in a shuttle-box and a group of yoked animals received the same footshocks without any relationship to their shuttling behavior. Although yoked rats displayed a reduced reactivity of splenocytes to lectins, animals of the avoidance group had a reduced antibody response to sheep erythrocytes. In contrast, no difference was observed in the corticosterone or prolactin response. These data further support the importance of psychological factors on stress-induced changes in immune functions. Furthermore, they demonstrate that various aspects of the immune system are differentially affected by behavioral factors and the results argue against a major role for the adrenocortical system in mediating these changes.