Central nervous system actions of corticotropin-releasing factor on cardiovascular function in the absence of locomotor activity

Cardiovascular functions of central corticotropin-releasing factor related peptides system

The corticotropin-releasing factor (CRF) related peptides system has widespread distributions in central nervous system, to perform many physiological and pathophysiological functions, including cardiovascular functions. A complex connection exists between the central CRF related peptides system and cardiovascular system. There are multiple pathways and mechanisms through which the central CRF related peptides system influences cardiovascular functions. A dysfunction in the central CRF related peptides system may lead to a wide range of alterations in cardiovascular functions. Though there are difficulties or limitations in establishing exact modulatory roles of the central CRF related peptides system in cardiovascular functions. The central CRF related peptides system as target to prevent cardiovascular diseases is being pursued with increasing interest. In this review, we summarize recent understanding on cardiovascular functions of the CRF related peptides system in limbic forebrain, hypothalamus and brain stem structures, discuss mechanisms of the central CRF related peptides system in control of cardiovascular functions, and suggest that the central CRF related peptides system may be a potent candidate for prevention of cardiovascular diseases.

Distribution of corticotropin-releasing factor neurons in the mouse brain: a study using corticotropin-releasing factor-modified yellow fluorescent protein knock-in mouse

We examined the morphological features of corticotropin-releasing factor (CRF) neurons in a mouse line in which modified yellow fluorescent protein (Venus) was expressed under the CRF promoter. We previously generated the CRF-Venus knock-in mouse, in which Venus is inserted into the CRF gene locus by homologous recombination. In the present study, the neomycin phosphotransferase gene (Neo), driven by the pgk-1 promoter, was deleted from the CRF-Venus mouse genome, and a CRF-Venus∆Neo mouse was generated. Venus expression is much more prominent in the CRF-Venus∆Neo mouse when compared to the CRF-Venus mouse. In addition, most Venus-expressing neurons co-express CRF mRNA. Venus-expressing neurons constitute a discrete population of neuroendocrine neurons in the paraventricular nucleus of the hypothalamus (PVH) that project to the median eminence. Venus-expressing neurons were also found in brain regions outside the neuroendocrine PVH, including the olfactory bulb, the piriform cortex (Pir), the extended amygdala, the hippocampus, the neocortices, Barrington's nucleus, the midbrain/pontine dorsal tegmentum, the periaqueductal gray, and the inferior olivary nucleus (IO). Venus-expressing perikarya co-expressing CRF mRNA could be observed clearly even in regions where CRF-immunoreactive perikarya could hardly be identified. We demonstrated that the CRF neurons contain glutamate in the Pir and IO, while they contain gamma-aminobutyric acid in the neocortex, the bed nucleus of the stria terminalis, the hippocampus, and the amygdala. A population of CRF neurons was demonstrated to be cholinergic in the midbrain tegmentum. The CRF-Venus∆Neo mouse may be useful for studying the structural and functional properties of CRF neurons in the mouse brain.

Neuropeptidergic mediators of spontaneous physical activity and non-exercise activity thermogenesis

Lean individuals have high levels of spontaneous physical activity (SPA) and the energy expenditure derived from that activity, termed non-exercise activity thermogenesis or NEAT, appears to protect them from obesity. Conversely, obesity in different human populations is characterized by low levels of SPA and NEAT. Like in humans, elevated SPA in rats appears to protect against obesity: obesity-resistant rats have significantly greater SPA and NEAT than obesity-prone rats. We review the literature on brain mechanisms important in mediating SPA and NEAT. The focus is on neuropeptides, including cholecystokinin, corticotropin-releasing hormone (also known as corticotropin-releasing factor), neuromedin U, neuropeptide Y, leptin, agouti-related protein, orexin-A (also known as hypocretin-1), and ghrelin. We also review information regarding interactions between these neuropeptides and dopamine, a neurotransmitter important in mediating motor function. Finally, we present evidence that elevated signaling of pathways mediating SPA and NEAT may protect against weight gain and obesity.

Central actions of corticotropin-releasing factor on autonomic nervous activity and cardiovascular functioning

The physiological role of corticotropin-releasing factor (CRF) in mediating stress-induced activation of the pituitary-adrenal axis, together with the neuroanatomical distribution of immunoreactive CRF and CRF receptors, provides a compelling rationale for investigating actions of CRF within the central nervous system (CNS) on autonomic nervous outflow and cardiovascular function. Evidence is reviewed showing that CRF acts within the CNS to elicit stress-like patterns of autonomic nervous outflow and cardiovascular changes in conscious animals. In addition, blockade of CRF-mediated neurotransmission is demonstrated to alter the expression of stress-induced autonomic nervous and cardiovascular responses. Together, the anatomical, pharmacological and physiological data support the hypothesis that the autonomic nervous and cardiovascular responses to selected stressful stimuli may be mediated in part by CRF-containing neuronal pathways.

The therapeutic potential of CRF1 antagonists for anxiety

Preclinical studies suggest that the brain corticotropin-releasing factor (CRF) systems mediate anxiety-like behavioural and somatic responses through actions at the CRF1 receptor. CRF1 antagonists block the anxiogenic-like effects of CRF and stress in animal models. Cerebrospinal fluid levels of CRF are elevated in some anxiety disorders and normalise with effective treatment, further implicating CRF systems as a therapeutic target. Prototypical CRF1 antagonists are highly lipophilic, non-competitive antagonists of peptide ligands. Modification of the chemotype and the identification of novel pharmacophores are yielding more drug-like structures with increased hydrophilicity at physiological pHs. Newer compounds exhibit improved solubility, pharmacokinetic properties, potency and efficacy. Several clinical candidates have entered Phase I/II trials. However, unmet challenges await resolution during further discovery, clinical development and therapeutic application of CRF1 antagonists.

Cardiovascular effects of long-term central and peripheral administration of urocortin, corticotropin-releasing factor, and adrenocorticotropin in sheep

The neuroendocrine hormones ACTH and corticotropin- releasing factor (CRF), which are involved in the stress response, have acute effects on arterial pressure. New evidence indicates that urocortin (UCN), the putative agonist for the CRF type 2 receptor, has selective cardiovascular actions. The responses to long-term infusions of these hormones, both peripherally and centrally, in conscious animals have not been studied. Knowledge of the long-term effects is important because they may differ considerably from their acute actions, and stress is frequently a chronic stimulus. The present experiments investigated the cardiovascular effects of CRF, UCN, and ACTH in conscious sheep. Infusions were made either into the lateral cerebral ventricles (i.c.v.) or i.v. over 4 d at 5 microg/h. UCN infused i.c.v. or i.v. caused a prolonged increase in heart rate (HR) (P < 0.01) and a small increase in mean arterial pressure (MAP) (P < 0.05). CRF infused i.c.v. or i.v. progressively increased MAP (P < 0.05) but had no effect on HR. Central administration of ACTH had no effect, whereas systemic infusion increased MAP and HR (P < 0.001). In conclusion, long-term administration of these three peptides associated with the stress response had prolonged, selective cardiovascular actions. The striking finding was the large and sustained increase in HR with i.c.v. and i.v. infusions of UCN. These responses are probably mediated by CRF type 2 receptors because they were not reproduced by infusions of CRF.

Fish oil prevents the adrenal activation elicited by mental stress in healthy men

OBJECTIVES

A diet rich in n-3 fatty acids (fish oils) is associated with reduced risks of cardiovascular and metabolic diseases, but the mechanisms remain incompletely understood. Sympathoadrenal activation is postulated to be involved in the pathogenesis of these diseases, and may be inhibited by n-3 fatty acids. We therefore evaluated the effects of a diet supplemented with n-3 fatty acids on the stimulation of the sympathetic nervous system and of stress hormones elicited by a mental stress.

METHODS

Seven human volunteers were studied on two occasions, before and after 3 weeks of supplementation with 7.2 g/day fish oil. On each occasion, the concentrations of plasma cortisol, and catecholamines, energy expenditure (indirect calorimetry), and adipose tissue lipolysis (plasma non esterified fatty acid concentrations) were monitored in basal conditions followed by a 30 min mental stress (mental arithmetics and Stroop's test) and a 30 min recovery period.

RESULTS

In control conditions, mental stress significantly increased heart rate, mean blood pressure, and energy expenditure. It increased plasma epinephrine from 60.9 +/- 6.2 to 89.3 +/- 16.1 pg/ml (p<0.05), plasma cortisol from 291 +/- 32 to 372 +/- 37 micromol/l (p<0.05) and plasma non esterified fatty acids from 409 +/- 113 to 544 +/- 89 micromol/l (p<0.05). After 3 weeks of a diet supplemented with n-3 fatty acids, the stimulation by mental stress of plasma epinephrine, cortisol, energy expenditure, and plasma non esterified fatty acids concentrations, were all significantly blunted.

CONCLUSION

Supplementation with n-3 fatty acids inhibits the adrenal activation elicited by a mental stress, presumably through effects exerted at the level of the central nervous system.

Effects of dexamethasone on the metabolic responses to mental stress in humans

The haemodynamic effects of the sympathetic nervous system (SNS) activations elicited by hypoglycaemia, acute alcohol administration, or insulin can be prevented by a pretreatment with dexamethasone in humans. This suggests a possible role of central corticotropin releasing hormone (GRIT) release. Mental stress activates the SNS, and decreases systemic vascular resistances though a beta-adrenergic-mediated vasodilation thought to involve vascular nitric oxide release. It also increases insulin-mediated glucose disposal, an effect presumably related to vasodilation. In order to evaluate whether activation of SNS by mental stress is glucocorticoid-sensitive, we monitored the haemodynamic and metabolic effects of mental stress during hyperinsulinaemia in healthy humans with and without a 2-day treatment with 8 mg day(-1) dexamethasone. Mental stress decreased systemic vascular resistances by 21.9% and increased insulin-mediated glucose disposal by 2 8.4% without dexamethasone pretreatment. After 2 days of dexamethasone treatment, whole body insulin-mediated glucose disposal was decreased by 40.8%. The haemodynainic effects of mental stress were however, not affected. Mental stress acutely increased insulin-mediated glucose disposal by 28.0%. This indicates that mental stress elicits a stimulation of SNS through dexamethasone-insensitive pathway, distinct of those activated by insulin, alcohol, or hyperglycaemia.

Participation of the hypothalamus-hypophysis axis in the sympathetic activation of human obesity

Previous studies have shown that hypothalamic and hypophyseal factors are involved in the acute sympathoexcitation induced by a variety of laboratory stimuli. Whether a chronic condition of sympathetic activation, such as that characterizing human obesity, is also dependent on these factors has never been investigated. In 40 normotensive obese subjects ([mean+/-SEM] age, 39.1+/-0.8 years) we measured blood pressure (Finapres), heart rate (ECG), and postganglionic muscle sympathetic nerve activity (MSNA) (microneurography). In 20 subjects measurements were repeated, according to a double-blind randomized sequence, after a midnight oral dose of dexamethasone (1 mg) (n=10) or placebo (n=10), while in the remaining subjects they were performed again after 1 week of a daily evening oral administration of 1 mg of dexamethasone (n=10) or placebo (n=10). The same protocol was performed in 16 age-matched lean normotensives. In both groups acute dexamethasone administration markedly reduced plasma cortisol (radioimmunoassay), without affecting hemodynamic and neural variables. In contrast to the acute administration, in obese subjects prolonged dexamethasone administration, although not affecting blood pressure and heart rate, significantly reduced both plasma cortisol (from 16.0+/-1.3 to 0.7+/-0.1 microg/dL; P<0.01) and MSNA (from 59.5+/-2.8 to 39.6+/-2.9 bursts per 100 heartbeats; P<0.02; -33.1+/-4.1%). This was not the case in lean subjects, in which the dexamethasone-induced reduction in plasma cortisol was associated with a slight and nonsignificant MSNA decrease. In both lean and obese subjects, placebo administration caused no change in any variable. Thus, prolonged dexamethasone administration exerts in obese subjects marked sympathoinhibitory effects that are not detectable in lean individuals. This suggests that hypothalamic and hypophyseal factors substantially contribute to the sympathoexcitation of obesity.

Central corticotropin releasing factor (CRF) and adrenergic receptors mediate hemodynamic responses to cocaine

Cocaine administration evokes cardiovascular responses that are variable in rats such that the pressor response is attributable to either a large increase in systemic vascular resistance and a decrease in cardiac output (vascular responders) or a smaller increase in systemic vascular resistance and no change or an increase in cardiac output (mixed responders). This study was designed to determine the role of central corticotropin releasing factor (CRF) and adrenergic receptors in mediating specific hemodynamic response patterns. Rats were instrumented for ascending aortic blood flow determination (cardiac output) using a pulsed Doppler system, arterial pressure measurement and for intravenous and intracerebroventricular (icv) administration of drugs. After characterizing the hemodynamic response pattern in individual rats to cocaine (5 mg/kg, i.v., 4-6 trials), selective receptor antagonists were administered icv 10 min before cocaine (5 mg/kg, i.v.). Pretreatment with the CRF antagonist alpha-helical CRF(9-41) (10 microg/5 microl, icv) prevented the decrease in cardiac output in vascular responders without altering hemodynamic responses to cocaine in mixed responders. Astressin (5 microg/5 microl, icv) exerted a similar effect in vascular responders. The alpha(2) receptor antagonist, yohimbine (3 microg/microl, icv) also prevented the decrease in cardiac output in vascular responders. Lower doses of alpha-helical CRF(9-41) (1 and 3 microg) were ineffective whereas higher doses of either CRF antagonist were lethal within 24 h. In contrast, propranolol (3 or 30 microg, icv) pretreatment enhanced the cocaine-induced decrease in cardiac output and increase in systemic vascular resistance noted in vascular responders and resulted in a decrease in cardiac output in mixed responders. We conclude that CRF and adrenoceptors in the CNS play an important role in determining the hemodynamic response pattern to cocaine. Furthermore, central beta-adrenoceptors may be responsible for the reported effects of intravenous propranolol on cocaine-induced responses.

Suppression of alcohol-induced hypertension by dexamethasone

BACKGROUND

Alcohol consumption is associated with an increased incidence of hypertension and stroke, but the triggering mechanisms are unclear. In animals, alcohol causes activation of the sympathetic nervous system and also stimulates the release of corticotropin-releasing hormone (CRH), which has sympatho-excitatory effects when administered centrally.

METHODS

To determine whether alcohol evokes sympathetic activation and whether such activation is attenuated by the inhibition of CRH release, we measured blood pressure, heart rate, and sympathetic-nerve action potentials (using intraneural microelectrodes) in nine normal subjects before and during an intravenous infusion of alcohol (0.5 g per kilogram of body weight over a period of 45 minutes) and for 75 minutes after the infusion. Each subject received two infusions, one after the administration of dexamethasone (2 mg per day) and one after the administration of a placebo for 48 hours.

RESULTS

The infusion of alcohol alone evoked a marked (P < 0.001) and progressive increase in the mean (+/- SD) rate of sympathetic discharge, from 16 +/- 3 bursts per minute at base line to 30 +/- 8 bursts per minute at the end of the two-hour period. This sympathetic activation was accompanied during the second hour by an increase in mean arterial pressure of 10 +/- 5 mm Hg (P < 0.001). After the administration of dexamethasone, the alcohol infusion had no detectable sympathetic effect. The dexamethasone-induced suppression of sympathetic activation was associated with a decrease in mean arterial pressure of 7 +/- 6 mm Hg (P < 0.001) during the alcohol infusion and with suppression of the pressor effect during the second hour.

CONCLUSIONS

Alcohol induces pressor effects by sympathetic activation that appear to be centrally mediated. It is possible that these alcohol-induced hemodynamic and sympathetic actions could participate in triggering cardiovascular events.

Predicted primary and antigenic structure of canine corticotropin releasing hormone

Although the dog has been recognized as a useful model for the study of the cerebrospinal and peripheral actions of corticotropin releasing hormone (CRH) the exact amino acid composition of canine CRH is still unknown. In the present study the structure of canine CRH was predicted from the partial sequence of the gene encoding canine CRH. The CRH gene was amplified from genomic DNA obtained from white blood cells by a polymerase chain reaction and subsequently sequenced using the dideoxy method. The likely structure of canine CRH is: SEEPPISLDLTFHLLREVLEMARAEQLAQQAHSNRKLMEII-NH2, which is identical to the structure of human, rat and equine CRH. PEPSCAN analysis of 3 different CRH antisera predicted an antiserum raised against a conjugate of human CRH and CNBr -activated thyroglobulin to be the antiserum of choice for the measurement of CRH in the dog. Preliminary data confirmed the existence of the highest cross-reactivity of a canine hypothalamus extract, known to have a high content of CRH, with antisera directed against human, rat CRH. As a result of the present study immunological tools for CRH estimations are characterized. Also, a homologous DNA probe for in situ hybridizations has become available for further investigations.

Suppression of insulin-induced sympathetic activation and vasodilation by dexamethasone in humans

BACKGROUND

Physiological hyperinsulinemia in lean human subjects stimulates sympathetic nerve activity and blood flow in skeletal muscle, but the underlying mechanism is unknown. Potential mechanisms include central neural or peripheral actions of insulin. Glucocorticoids may potentially interfere with both such actions and thereby may attenuate sympathoexcitatory and vasodilatory effects of insulin in skeletal muscle.

METHODS AND RESULTS

To determine whether insulin-induced sympathetic activation and vasodilation are attenuated by dexamethasone, we measured muscle sympathetic nerve activity and muscle blood flow during euglycemic hyperinsulinemia before and after short-term administration of this pharmacological agent. Insulin concentrations, which normally doubled sympathetic activity and markedly increased blood flow, had no such stimulatory effect after short-term dexamethasone administration. In contrast, responses to two noninsulin sympathetic stimuli, the Valsalva maneuver and immersion of the hand in ice water, and the vasodilatory response to calf vascular occlusion were not altered by dexamethasone.

CONCLUSIONS

These results demonstrate a dramatic impairment of insulin-induced sympathetic activation and vasodilation by dexamethasone in lean, healthy humans. This study suggests that dexamethasone administration to lean subjects may offer an experimental model to examine underlying mechanisms that regulate the interplay between cardiovascular, sympathetic, and metabolic effects of insulin.

Relaxing actions of corticotropin-releasing factor on rat resistance arteries

1. Although it well established that corticotropin-releasing factor (CRF) injected i.v. can cause hypotension and vasodilatation, there is no in vitro evidence that CRF acts as a vasodilator. We have therefore tested the hypothesis that the hypotensive effect of i.v. CRF is due to a direct vasodilator action by carrying out experiments in vitro on rat resistance arteries (i.d. 150-300 microns). 2. Initial in vivo experiments confirmed that CRF (1.5 nmol.kg-1) injected i.v. caused hypotension in rats, this being partially antagonized by the CRF analogue CRF9-41. 3. For the in vitro experiments, vessels were taken from the mesenteric, cerebral and femoral vascular beds, and mounted as ring preparations in an isometric myograph. The vessels were pre-contracted with one of 3 agonists (prostaglandin F2 alpha, arginine vasopressin or noradrenaline) or with a high-potassium solution (K+). 4. With maximal concentrations of the agonists, CRF caused relaxation of mesenteric and cerebral vessels with 10 nM, and near complete relaxation with 100 nM. Femoral vessels pre-constricted with agonists and all vessels pre-constricted with K+ were less affected by CRF. In the mesenteric vessels, with sub-maximal levels of pre-constriction, CRF caused substantial relaxation at 1 nM and could cause complete relaxation at 10 nM. 5. The relaxant effect of CRF on contractions of mesenteric vessels was antagonized by 100 nM CRF9-41. Neither tetraethyl ammonium (30 mM) nor glibenclamide (3 microM) antagonized the relaxant effect of CRF. 6. The relaxant effect of CRF on mesenteric small arteries was found to be unaffected by removal of the endothelium. 7. The results indicate that CRF causes an endothelial-independent vasodilatation of rat resistance arteries under in vitro conditions at concentrations which are consistent with this being an important cause of the hypotension observed with i.v. injection of CRF.

Expression of c-fos in regions of the basal limbic forebrain following intracerebroventricular corticotropin-releasing factor in unstressed or stressed male rats

Corticotropin-releasing factor has an integrative role on the behavioral, endocrine and autonomic responses to stress. Immediate-early gene (c-fos) expression was used to determine patterns of neural activity in the limbic system following i.c.v. infusion of corticotropin-releasing factor. Either 250 or 1000 pmol corticotropin-releasing factor infused into the lateral ventricle of precannulated and handled male rats resulted in marked c-fos expression 60 or 120 min later in localized regions of the basal forebrain, including the ventrolateral septum, the dorsal and medial parvicellular divisions of the paraventricular nucleus, the central nucleus of the amygdala, and dorsal bed nucleus of the stria terminalis. Pre-infusion of alpha-helical corticotropin-releasing factor (2500 pmol), a competitive corticotropin-releasing factor antagonist of corticotropin-releasing factor, had no effect on immediate-early gene expression alone but reduced that elicited by exogenous i.c.v. corticotropin-releasing factor (250 pmol)--in some areas to control levels. Fifteen minutes of restraint stress, a situation in which corticotropin-releasing factor is released endogenously, also activated c-fos expression in a pattern that resembled corticotropin-releasing factor infusions but was not identical. There was enhanced expression in the dorsal and medial areas of the paraventricular nucleus, but not its magnocellular region, and increased expression in the ventrolateral septum; however, there was no detectable response on the central amygdala. Preinfusion of alpha-helical corticotropin-releasing factor (2500 pmol) had no significant effect on stress-induced c-fos expression in the ventrolateral septum or paraventricular nucleus. This suggests that corticotropin-releasing factor release may form only a part of the central neurochemical response to restraint stress. Rats given i.c.v. corticotropin-releasing factor (250 pmol) before restraint stress showed additive effects on c-fos in the ventrolateral septum but not in the paraventricular nucleus; the central nucleus of the amygdala reacted as if corticotropin-releasing factor alone had been infused. Corticosterone levels were raised by both stress and corticotropin-releasing factor, but pretreatment with alpha-helical corticotropin-releasing factor reduced them after either procedure, which correlates with c-fos expression in the paraventricular nucleus and ventrolateral septum. These results show that corticotropin-releasing factor induces a specific pattern of c-fos expression in localized regions of the amygdala, hypothalamus and septum, which may indicate a corresponding pattern of neural activation. Restraint, one form of stress, activates c-fos in a similar but not identical manner, suggesting that corticotropin-releasing factor may not be the only neuropeptide involved in the response to this stressor.(ABSTRACT TRUNCATED AT 400 WORDS)

Differentiated hemodynamic responses to central versus peripheral administration of corticotropin-releasing factor in conscious rats

Corticotropin-releasing factor (CRF) modifies cardiovascular function and hemodynamic status after administration into the central nervous system and into the peripheral circulation. The mechanisms by which CRF alters arterial pressure and heart rate have been examined in detail whereas little information exists regarding the processes mediating CRF-induced changes in regional blood flow. Therefore, studies were performed in conscious, unrestrained Sprague-Dawley rats to examine potential mechanisms underlying the regional hemodynamic effects of intracerebroventricular versus intravenous administration of CRF. Intracerebroventricular administration of CRF increased arterial pressure, heart rate, and mesenteric vascular resistance while decreasing iliac vascular resistance. Intravenous pretreatment with the CRF receptor antagonist, alpha-helical CRF9-41, did not alter the cardiovascular and hemodynamic responses to central administration of CRF. In contrast, prior ganglionic blockade prevented CRF-induced responses except for the reduction in iliac vascular resistance. Intravenous administration of CRF reduced arterial pressure and mesenteric vascular resistance, elevated heart rate, and transiently increased iliac vascular resistance. Intravenous pretreatment with alpha-helical CRF9-41 completely abolished the cardiovascular and hemodynamic responses to peripheral administration of CRF. Ganglionic blockade prior to intravenous administration of CRF augmented the reductions in arterial blood pressure and mesenteric vascular resistance, prevented the increase in heart rate, and unmasked a decrease in iliac vascular resistance. The divergent actions and mechanisms of action of CRF on regional hemodynamics when administered peripherally, as opposed to centrally, indicate that this peptide produces different hemodynamic effects that are specific to its site of action.

Central regulation of stress responses: regulation of the autonomic nervous system and visceral function by corticotrophin releasing factor-41

Our understanding of the role of CRF in mediating integrated endocrine, autonomic and visceral stress responses is rudimentary at best. Delineating the large number of neurochemical factors that influence the activity of CRF-containing hypophyseotrophic neurones offers one direction for future research in this area. Another approach might be to examine the neuropharmacological actions of transmitters which are co-localized within CRF-containing neurones. For example, CRF and dynorphin-related peptides coexist within a subpopulation of paraventricular neurones (Roth et al, 1983), suggesting the potential for their simultaneous release and possible functional interactions between them. Interestingly, CRF and dynorphin-related peptides exhibit reciprocal actions on the release of each other in vitro and in vivo. CRF stimulates the release of immunoreactive dynorphin from rat hypothalamic slices (Nikolarakis et al, 1986) while dynorphin A1-17 inhibits the basal secretion of immunoreactive CRF from rat hypothalami (Yajima et al, 1986). In vivo experiments demonstrate that i.c.v. administration of dynorphin A1-13 reduces basal and hypotension-induced secretion of CRF into hypophyseal portal blood (Plotsky, 1986). Recent studies suggest that, in addition to their interactions at the level of release, these peptides may also modify the CNS actions of each other on autonomic and cardiovascular function (Overton and Fisher, 1989b). Thus, CRF-induced elevations of arterial pressure, heart rate and plasma catecholamine levels are attenuated by co-administration of low doses of dynorphin A1-17. The reciprocal release actions and neuropharmacological interactions between CRF and dynorphin A1-17 suggest that local integration or perhaps feedback regulation of stress-induced autonomic and cardiovascular responses may be achieved by the co-release of multiple neurotransmitters from a single source. In summary, the combined anatomical, pharmacological and physiological data provide support for the involvement of CRF neuronal systems in mediating the integration of endocrine, autonomic, and visceral functions, particularly in response to stress. Future research in this area may contribute to our understanding of the neurobiology of CRF as well as the CNS mechanisms governing homeostasis.

Effects of exercise training on responses to central injection of CRF and noise stress

The purpose of this study was to test the hypothesis that the cardiovascular and sympathoadrenal responses to acute environmental stress are attenuated by exercise training. Furthermore, we tested the hypothesis that the cardiovascular and sympathoadrenal responses to intracerebroventricular (ICV) administration of corticotropin-releasing factor (CRF) would be attenuated by training. Conscious, unrestrained, male Sprague-Dawley rats assigned to either a treadmill trained (16-26 m/min, 30-60 min/day, 5 days/week) or nontrained (16-26 m/min, 10 min/day, 1 day/week) group were studied. After 8-10 weeks of training, maximal oxygen uptake was significantly higher in the trained (108 +/- 3 ml/kg/min) vs. the nontrained (94 +/- 4 ml/min/kg) group. There were no significant differences in baseline mean arterial pressure, heart rate and plasma catecholamine levels associated with training. Trained rats exhibited significantly attenuated elevations in arterial pressure (20 +/- 3 vs. 36 +/- 2 mmHg for nontrained) and heart rate (-3 +/- 3 vs. 12 +/- 5 beats/min for nontrained) in response to acute noise stress. Twenty minutes after ICV administration of CRF, blood pressure (trained = 119 +/- 2 mmHg, nontrained = 127 +/- 2 mmHg), heart rate (trained = 408 +/- 8 beats/min, nontrained = 424 +/- 10 beats/min), plasma norepinephrine levels (trained = 757 +/- 54 pg/ml, nontrained = 775 +/- 100 pg/ml) and plasma epinephrine levels (trained = 266 +/- 29 pg/ml, nontrained = 225 +/- 42 pg/ml) were significantly elevated in both trained and nontrained groups. CRF-induced elevations of blood pressure, but not heart rate or plasma catecholamine levels, were significantly attenuated in the trained group.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of separate or combined infusions of corticotrophin-releasing factor and vasopressin either intraventricularly or into the amygdala on aggressive and investigative behaviour in the rat

These experiments show that combined infusions of corticotrophin-releasing factor (CRF) and arginine vasopressin (AVP) into either the lateral ventricle or the amygdalae have synergistic effects on aggressive, investigative and other behaviours occurring during social interaction between male rats. They suggest, therefore, that the two peptides interact at intracerebral sites to control behaviour much as they do on the anterior pituitary to regulate ACTH release. CRF or AVP, alone or in combination, were infused into either the lateral ventricle (dose range: 10-250 pmol) or bilaterally into the amygdalae (dose range: 1-150 pmol) of male rats in two experiments. The rat was then paired with another, strange, male for 10 min. There was a U-shaped effect on aggressive behaviour after intra-amygdala infusions of CRF, lower doses increasing agonistic behaviour, higher ones decreasing it. This was not seen after icv infusions. AVP had no effect by either route; however, given together with CRF it potentiated the latter's effect on aggressive behaviour. Investigative behaviour was decreased by icv CRF but the effects of amygdala infusions were small. AVP had no consistent effect by either route. Combined infusions of both peptides given either icv or into the amygdala decreased investigative behaviour. Self-grooming increased, though in an irregular fashion, after incremental doses of either CRF or AVP given by either route. Both peptides given together showed additive effects on self-grooming. Climbing behaviour was lowered by CRF more prominently than by AVP and, again, the two peptides together profoundly reduced this behaviour. These experiments show that the behavioural effects of CRF and AVP on social interaction have different profiles, and that the effects of each peptide differ when it is given into the ventricles or directly into the amygdala. There is also clear evidence for synergistic effects of the two peptides on behavior after infusion by either route.