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

Associations between prenatal exposure of serotonergic medications and biobehavioural stress regulation: Protocol for systematic review and meta-analysis (Preprint)

Background

Up to 20% of mothers experience antenatal depression and approximately 30% of these women are treated with serotonergic psychotropic pharmacological therapy during pregnancy. Serotonergic antidepressants readily cross the placenta and the fetal blood-brain barrier, altering central synaptic serotonin signaling and potentially altering serotonin levels in the developing fetal brain.

Objective

The aim of this study is to assess the impact of prenatal exposure to serotonergic antidepressants, accounting for maternal mood disturbances, on markers of stress regulation during childhood.

Methods

We will follow PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines and will search MEDLINE, Embase, CINAHL, PsycINFO, and ClinicalTrials.gov for full-length studies that assessed physiological (eg, cortisol level, heart rate variability, salivary amylase, pupillary size, C-reactive protein) indices of stress regulation in children of pregnant people who were treated with a serotonergic antidepressant at any point during pregnancy. We will assess the quality of observational studies using the Newcastle-Ottawa Scale and the quality of experimental studies using the Cochrane risk-of-bias tool. When possible, we will conduct a random-effects meta-analysis. If meta-analysis is not possible, we will conduct a narrative review. If a sufficient number of studies are found, we will perform subgroup analysis and assess outcomes measured by drug class, dose, trimester of exposure, and child’s age and gender.

Results

We registered our review protocol with PROSPERO (International Prospective Register of Systematic Reviews; CRD42021275750), completed the literature search, and initiated title and abstract review in August 2021. We expect to finalize this review by April 2022.

Conclusions

Findings should identify the impact of prenatal antidepressant effects on stress regulation and distinguish it from the impact of prenatal exposure to maternal mood disturbances. This review should inform decisions about serotonergic antidepressant use during pregnancy.

Trial Registration

PROSPERO CRD42021275750; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=275750

International Registered Report Identifier (IRRID)

PRR1-10.2196/33363

Dynorphins in Development and Disease: Implications for Cardiovascular Disease

It is well-established that cardiovascular disease continues to represent a growing health problem and significant effort has been made to elucidate the underlying mechanisms. In this review, we report on past and recent high impact publications in the field of intracrine network signaling, focusing specifically on opioids and their interrelation with key modulators of the cardiovascular system and the onset of related disease. We present an overview of studies outlining the scope of cardiovascular and cerebrovascular processes that are affected by opioids, including heart function, ischemia, reperfusion, and blood flow. Specific emphasis is placed on the importance of dynorphin molecules in cerebrovascular and cardiovascular regulation. Evidence suggests that excessive or insufficient dynorphin could make an important contribution to cardiovascular physiology, yet numerous paradoxical observations frequently impede a clear understanding of the role of dynorphin. Thus, we argue that dynorphin-mediated signaling events for which an immediate regulatory effect is disputed should not be dismissed as unimportant, as they may play a role in cross-talk with other signaling networks. Finally, we consider the most recent evidence on the role of dynorphin during cardiovascular-related inflammation and on the potential value of endogenous and exogenous inhibitors of kappa-opioid receptor, a major dynorphin A receptor, to limit or prevent cardiovascular disease and its related sequelae.

Stress and metabolism

Obesity, lipid disorders, type 2 diabetes, high blood pressure and coronary heart disease are frequently encountered in wealthy populations. All these disorders frequently occur as clusters, constituting the metabolic syndrome. It is currently admitted that insulin resistance plays a central role in the pathogenesis of this syndrome. Stress responses include activation of the sympathetic nervous system and stimulation of epinephrine and cortisol release. These hormones may over the long term reduce insulin sensitivity. Cortisol may also favour the development of central obesity. In healthy individuals, mental stress increases heart rate, but simultaneously decreases vascular resistance in skeletal muscle. This results in a moderate increase in blood pressure, and an acute increase in insulin-mediated glucose disposal. In obese patients, mental stress elicits responses which differ widely from those of healthy individuals. While mental stress enhances catecholamine-mediated energy expenditure in obese patients to the same extent as in lean subjects, it fails to decrease systemic vascular resistance due to endothelial dysfunction. This leads to enhanced blood pressure responses and the absence of stimulation of glucose disposal in obese subjects during mental stress. It can be hypothesized that repeated professional or social stress may activate the sympathoadrenal system, resulting in high cortisol levels, stimulation of the sympathetic nervous system, and epinephrine secretion. All these factors may eventually lead to the development of central obesity and insulin resistance. Furthermore, the blood pressure responses to mental stress may be enhanced in insulin-resistant individuals, favouring the development of vascular complications.

Recurrent hypoglycemia alters hypothalamic expression of the regulatory proteins FosB and synaptophysin

A limiting factor to the clinical management of diabetes is iatrogenic hypoglycemia. With multiple hypoglycemic episodes, the collective neuroendocrine response that restores euglycemia is impaired. In our animal model of recurrent hypoglycemia (RH), neuroendocrine deficits are accompanied by a decrease in medial hypothalamic activation. Here we tested the hypothesis that the medial hypothalamus may exhibit unique changes in the expression of regulatory proteins in response to RH. We report that expression of the immediate early gene FosB is increased in medial hypothalamic nuclei, anterior hypothalamus, and posterior paraventricular nucleus of the thalamus (THPVN) of the thalamus following RH. We identified the hypothalamic PVN, a key autonomic output site, among the regions expressing FosB. To identify the subtype(s) of neuronal populations that express FosB, we screened candidate neuropeptides of the PVN for coexpression using dual fluorescence immunohistochemistry. Among the neuropeptides analyzed [including oxytocin, vasopressin, thyrotropin-releasing hormone, and corticotropin-releasing factor (CRF)], FosB was only identified in CRF-positive neurons. Inhibitory gamma-aminobutyric acid-positive processes appear to impinge on these FosB-expressing neurons. Finally, we observed a significant decrease in the presynaptic marker synaptophysin within the PVN of RH-treated vs. saline-treated rats, suggesting that rapid alterations of synaptic morphology may occur in association with RH. Collectively, these data suggest that RH stress triggers cellular changes that support synaptic plasticity, in specific neuroanatomical sites, which may contribute to the development of hypoglycemia-associated autonomic failure.

Role of brain nicotinic acetylcholine receptor in centrally administered corticotropin-releasing factor-induced elevation of plasma corticosterone in rats

The present study was undertaken to clarify the central mechanisms involved in the intracerebroventricularly administered corticotropin-releasing factor-induced elevation of plasma corticosterone in urethane- and alpha-chloralose-anesthetized rats using microdialysis and immunohistochemical techniques. When corticotropin-releasing factor was given at 0.5, 1.5, and 3.0 nmol/animal intracerebroventricularly, it dose-dependently increased noradrenaline release but not adrenaline release in the hypothalamic paraventricular nucleus. The 1.5 nmol/animal dose of corticotropin-releasing factor-induced noradrenaline release was attenuated by CP-154,526 (butyl-ethyl-{2,5-dimethyl-7-(2,4,6 trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl}amine), a selective corticotropin-releasing factor receptor 1 antagonist, at 1.3 micromol/animal, intracerebroventricularly, and was also abolished by phentolamine at 0.66 micromol/animal, intracerebroventricularly. In addition, the corticotropin-releasing factor-induced elevation of noradrenaline release in the hypothalamic paraventricular nucleus and plasma corticosterone were abolished by hexamethonium, a non-selective nicotinic acetylcholine receptor antagonist, at 1.8 micromol/animal, intracerebroventricularly, and alpha-conotoxin MII, a potent alpha(3)beta(2) nicotinic acetylcholine receptor antagonist, at 30 nmol/animal, i.c.v. Corticotropin-releasing factor at 1.5 nmol/animal, i.c.v. evoked a significant expression of Fos, an immediate-early transcription factor in neurons, on the dopamine-beta-hydroxylase-containing neurons and alpha(3) nicotinic acetylcholine receptor subunit-expressing neurons in the locus coeruleus, but not in the medullary A(1) and A(2) regions containing noradrenergic neurons. These results suggest that centrally administered corticotrophin-releasing factor elevates plasma corticosterone by the corticotropin-releasing factor 1 receptor and alpha(3) subunit-containing nicotinic acetylcholine receptor (probably alpha(3)beta(2) nicotinic acetylcholine receptor) mediated activation of the locus coeruleus noradrenergic neurons projecting to the paraventricular nucleus in rats.

Corticotropin-releasing factor receptor-1: a therapeutic target for cardiac autonomic disturbances

Corticotropin-releasing factor (CRF), a neuropeptide involved in triggering a myriad of responses to fear and stress, is favourably positioned in the CNS to modulate the sympathetic and parasympathetic branches of the cardiac autonomic nervous system. In vivo studies suggest that central CRF inhibits vagal output and stimulates sympathetic activity. Therefore, CRF may function to inhibit exaggerated vagal activation that results in severe bradycardia or even vasovagal syncope. On the other hand, CRF receptor-1 (CRF(1)) antagonists increase cardiac vagal and decrease sympathetic activity, thereby also implicating CRF(1) as a therapeutic target for autonomic disturbances resulting in elevated sympathetic activity, such as hypertension and coronary heart disease. The central distribution of CRF(1) and the cardiovascular effects of CRF(1) agonists and antagonists, suggest it mediates CRF-induced autonomic changes. However, there is insufficient information regarding the autonomic effects of CRF(2)-selective compounds to rule out CRF(2) contribution. This review provides an update on the autonomic effects of CRF and the neuronal projections thought to mediate these cardiovascular responses.

Urocortins and corticotropin releasing factor type 2 receptors in the hypothalamus and the cardiovascular system

In addition to urocortin (Ucn I), Ucn II and Ucn III were identified as endogenous ligands for corticotropin-releasing factor type 2 receptor (CRF2 receptor). CRF2 receptor is abundantly located in central hypothalamic ventromedial nucleus (VMH) and in peripheral cardiovascular system. In this mini-review, we focused on the roles of these urocortins and CRF2 receptor in the hypothalamus and the cardiovascular system. Ucn II mRNA was increased in the parvocellular part or the magnocellular part of the hypothalamic paraventricular nucleus (PVN) following immobilization stress or 3 days of water deprivation, respectively. Therefore, it is thought that Ucn II may modulate CRF and vasopressin synthesis in the PVN in a paracrine or autocrine fashion through PVN CRF2 receptor. The early and later phases of Ucn I-mediated feeding suppression may be CRF1 and CRF2 receptor-mediated events, respectively. Ucn II decreases food intake at a later phase, beyond 4 h post injection. A large dose of corticosterone increased plasma leptin and insulin levels as well as the levels of CRF2 receptor mRNA. Adrenalectomy, starvation, and immobilization each lowered plasma leptin and insulin levels and were associated with decrements in CRF2 receptor mRNA levels in the VMH. Peripheral injection of leptin increased VMH CRF2 receptor mRNA, as can induce reductions of food intake and body weight, indicating that circulating leptin is involved in the regulation of VMH CRF2 receptor mRNA expression. Therefore, it is also plausible that VMH CRF2 receptor transduces the anorexogenic effects of leptin as well as those of urocortins. The systemic administration of Ucn II decreases mean arterial pressure (arterial vascular tone) and causes tachycardia via vascular CRF2 receptor in rats, similar to the effects of Ucn I. Thus, CRF2 receptor seems to mediate cardioprotective effects of urocortins.

Central alpha-adrenergic receptors and corticotropin releasing factor mediate hemodynamic responses to acute cold stress

Behavioral stress is likely to contribute to the development of hypertension in susceptible individuals. We reported that hemodynamic response patterns to acute startle vary and that those patterns predict the predisposition of rats to sustained stress-induced elevations in arterial pressure. Since considerable evidence suggests that central catecholamines and corticotropin releasing factor (CRF) contribute to the regulation of arterial pressure and the development of hypertension, we investigated the role of central alpha-adrenergic receptors and CRF in mediating different hemodynamic response patterns to acute cold water stress in conscious rats. Rats were instrumented for arterial pressure, heart rate and cardiac output determination and for intracerebroventricular (icv) administration of selective antagonists. After acclimation to a water tight cage, ice water (1 cm deep) was rapidly added then drained 1 min later. Although the early startle response to cold water stress elicited a pressor response in all rats, the hemodynamic response pattern varied between rats. Vascular responders (n=19) had an initial considerable increase in systemic vascular resistance and a decrease in cardiac output. In contrast, mixed responders (n=11) had a smaller increase in vascular resistance and an increase in cardiac output. Pretreatment with phentolamine (30 microgram/5 microliter, icv, n=8), prazosin (10 microgram/5 microliter, icv, n=12) or alpha-helical CRF(9-41) (10 microgram/5 microliter, icv, n=9) prevented the decrease in cardiac output elicited by acute cold water stress in vascular responders without affecting mixed responders. Yohimbine (3 microgram/5 microliter, icv, n=8) pretreatment did not alter hemodynamic responses. Therefore, we conclude that central alpha(1)-adrenoceptors and CRF mediate the specific hemodynamic response patterns to acute startle and may be responsible for the predisposition to develop hypertension in vascular responders.

Cortisol, prolactin, growth hormone and neurovegetative responses to emotions elicited during an hypnoidal state

The present study describes the responses of cortisol, prolactin and growth hormone (GH) to emotions elicited during sessions in which an hypnoidal state was induced. The purpose of the study was to provide answers for the following questions: 1) Do sessions with an emotional content have more hormonal surges than baseline, relaxation-only, sessions? 2) Does the induction of a fantasy of pregnancy and nursing elicit a prolactin response? 3) Are there any associations between surges of different hormones? 4) Are hormonal responses related to the intensity, type, or mode of expression of the emotions? For this purpose, thirteen volunteers and twelve patients with minor emotional difficulties were studied during sessions under hypnosis. The period of observation lasted for about three hours. Heart rate (HR), skin conductance (SC) and vagal tone (VT) were monitored. Serum cortisol, prolactin and growth hormone were sampled every 15 minutes. The volunteers had three types of sessions- "blank", consisting of relaxation only (12 sessions), "breast feeding", in which a fantasy of pregnancy and breast feeding was induced (12 sessions) and "free associations" in which the subjects were encouraged to evoke experiences or feelings (17 sessions). The patients had only sessions of free associations (38 sessions). Sessions of free associations had more hormonal surges than "blank" and "breast feeding" sessions. This was true for cortisol (8/17 v.3/24; p < 0.03), prolactin (7/17 v. 3/24; p < 0.05) and GH (9/17 v. 4/24; p < 0.02). During the 55 sessions of free associations (volunteers plus patients) there were 32 surges of cortisol, 18 of prolactin and 28 of GH. Cortisol and prolactin surges were negatively correlated (p < 0.03). GH had no significant association with either cortisol or prolactin. Visible emotions were positively associated with GH surges (p < 0.05). but not with cortisol or prolactin. Cortisol surges were correlated positively with evocations of real events (p < 0.01) and negatively with evocations containing defensive elements (p < 0.01). Cortisol correlated positively with shock and intimidation (p < 0.02) and negatively with rage (p < 0.04). The AUC of the cortisol peaks during shock and intimidation was significantly higher than that of the pool of all other cortisol peaks (12.4 micromol x min x l(-1) v. 7.1 micromol x min x l(-1); p < 0.005). Rage had a marginally significant positive association with prolactin surges (p=0.07). The distribution of GH surges did not show any significant association with types of emotions. The present study provides evidence that cortisol, prolactin and GH respond to psychological stress in humans. However, they are regulated differently from one another. Cortisol and prolactin surges appear to be alternative forms of response to specific emotions. GH surges depend on the intensity of the emotion, probably as a consequence of the associated muscular activity. The current paradigm of stress, implying corticotrophin-releasing hormone (CRH) as the initial step of a cascade of events, is insufficient to account for the diversity of hormonal changes observed in psychological stress in humans.

Blood pressure and heart rate are increased by AF-DX 116, a selective M2 antagonist, in autonomic imbalanced and hypotensive rats caused by repeated cold stress

Rats exposed to SART (specific alternation of rhythm in temperature) stress, which are ideal animal models for vagotonia-type dysautonomia, show various changes in cardiac and circulatory systems. In this study, attention was directed to cholinergic function in the SART-stressed rat heart and the effects of AF-DX 116, a specific muscarinic M2 antagonist, on blood pressure and heart rate. The results were compared with those obtained for atropine and pirenzepine. In SART-stressed rats, systolic and diastolic blood pressures (SBP and DBP) were lower than in unstressed rats. Oral AF-DX 116 resulted in greater elevation of DBP than SBP in unstressed rats. In stressed rats, greater and more prolonged elevation of SBP than in unstressed rats was noted, particularly at higher doses. A dose-dependent SBP change in stressed rats, caused by intravenous AF-DX 116, was shifted upward in parallel with that in unstressed groups, unlike with oral administration. The positive chronotropic effect of this drug was smaller in stressed rats than in unstressed rats, in contrast to the pressor effect. SART-stressed rats may thus have an enhanced sympathetic tone in the heart, as well as changes in muscarinic M2 receptors at sympathetic nerve endings and at the heart muscle. The effects of AF-DX 116 on blood pressure and heart rate thus may arise from peripheral action and AF-DX 116 may be useful for treating hypotension related to autonomic imbalance of the vagotonia type.

Endogenous corticotropin-releasing hormone inhibits conditioned-fear-induced vagal activation in the rat

The role of the endogenous corticotropin-releasing hormone (CRH) system in the regulation of heart rate, PQ interval (a measure of vagal activity), gross activity and release of adrenocorticotropic hormone (ACTH), noradrenaline and adrenaline into the blood during conditioned fear was studied in freely moving rats. Intracerebroventricular (i.c.v.) infusion of alpha-helical CRH-(9-41) (10 microgram/3 microliter), a non-selective CRH receptor antagonist, under resting conditions had no significant effect on gross activity, heart rate and PQ interval, indicating that alpha-helical CRH at this dose was devoid of agonist effects. Conditioned fear was induced by 10 min forced exposure to a cage in which the rat had experienced footshocks (5x0.5 mAx3 s) 1 day before. Conditioned-fear rats showed freezing behaviour, associated with an increase in heart rate, PQ interval, noradrenaline and adrenaline, indicating that the conditioned-fear-induced cardiac effects were the result of coactivation of the sympathetic and parasympathetic nervous system. The i.c.v. pre-treatment of rats with alpha-helical CRH significantly reduced the conditioned-fear-induced tachycardiac and ACTH response, and enhanced the increase in PQ interval, without affecting the noradrenaline and adrenaline response. These results suggest that endogenous CRH reduces the vagal response to conditioned-fear stress in rats. To test this, rats were pre-treated with atropine methyl nitrate (0.3 mg/kg, subcutaneously; s.c.), a peripherally acting cholinergic receptor antagonist. This resulted in a complete blockade of the alpha-helical CRH-induced decrease in heart rate response and increase in PQ interval. From these findings, it is concluded that endogenous CRH in the brain inhibits vagal outflow induced by emotional stress.

5-HT(2A/2C) receptor agonist-induced increase in urinary isatin excretion in rats: reversal by both diazepam and dexamethasone

Isatin, a stress-related biological substance, increases in rat urine in association with elevated catecholamine biosynthesis during stress. The goal of this study was to unravel how the biosynthetic pathway of isatin is related to stress response. The importance of the serotonergic compounds in anxiety, which is the major emotional process of stress response, has emerged. m-Chlorophenylpiperazine (m-CPP), a 5-HT(1A/1B/2A/2C) receptor agonist, and (+/-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride [(+/-)-DOI], a 5-HT(2A/2C) agonist, both of which have anxiogenic properties, induced a marked increase in 24-hr urinary isatin excretion, whereas neither 1-(m-chlorophenyl)-biguanide (m-CPBG), a 5-HT3 agonist, nor 2-methyl-5-HT, a 5-HT(3,4) agonist, affected urinary isatin excretion. 5-HT(2A/2C) receptor antagonists such as ketanserin and ritanserin prevented the increase in urinary isatin excretion induced by the 5-HT(2A/2C) receptor agonist m-CPP. These findings are the first to provide evidence that pharmacological substances cause increases in urinary isatin excretion via specific 5-HT receptors, probably 5-HT(2A/2C) receptors. In addition, both the synthetic glucocorticoid dexamethasone and diazepam prevented the m-CPP-induced increase in urinary isatin excretion. These observations suggest that the mechanism by which m-CPP elicits enhancing effects on urinary isatin excretion has something in common with stress response involving activation of hypothalamic CRF cells and the sympathetic nervous system.

Leptin effects on the expression of type-2 CRH receptor mRNA in the ventromedial hypothalamus in the rat

The product of the ob gene, leptin, is thought to act in the hypothalamus to reduce food intake and body weight (b.w.) in rats and mice; however, the mechanisms of leptin action in the brain have not been fully elucidated. Corticotropin-releasing hormone (CRH) is a potent anorectic neuropeptide, and its type-2 receptor (CRHR-2) in the ventromedial hypothalamus (VMH) appears to play an important role in the expression of this anorectic effect. We explored here the impact of systemic leptin administration on CRH mRNA expression in the hypothalamic paraventricular nucleus (PVN) and CRHR-2 mRNA expression in the VMH in male rats, using in-situ hybridization histochemistry. The expression of CRH mRNA in the PVN and CRHR-2 mRNA in the VMH were increased at 2 h and 6 h, respectively, after a single intraperitoneal injection of leptin (1.0 mg/kg). Continuous subcutaneous infusion of leptin (1.2 mg/kg/day) via an osmotic minipump for 5 days increased the expression of CRHR-2 mRNA in the VMH, but not the expression of CRH mRNA in the PVN, compared with vehicle treatment. The rats that received the single or continuous administration of leptin showed reductions of food intake and b.w. compared with vehicle-treated rats. These results are consistent with our previous findings that the expression of CRHR-2 mRNA in the VMH is positively correlated with plasma leptin concentrations under various conditions, and highlight the importance of circulating leptin for the regulation of VMH CRHR-2 mRNA. The present results also raise the possibility that leptin reduces food intake and b.w. at least partially due to the enhancement of the anorectic effect of CRH via increased PVN CRH expression and/or VMH CRHR-2 expression.

Stress-induced increase in urinary isatin excretion in rats: reversal by both dexamethasone and alpha-methyl-P-tyrosine

The effects of acute food deprivation and acute cold exposure on 24-hr urinary isatin excretion in rats and a mechanism responsible for changes in urinary isatin excretion during stress were investigated. This is the first study to demonstrate by HPLC that urinary isatin excretion is increased by stress. Both types of stress induced a marked increase in urinary isatin excretion during the 24 hr following the initiation of stress. Dexamethasone administration prevented the increase in urinary isatin excretion induced by both of the different types of stress. Furthermore, administration of either the benzodiazepine receptor agonist diazepam or the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine prevented the increase in urinary isatin excretion induced by acute food deprivation, whereas the dopamine-beta-hydroxylase inhibitor diethyldithiocarbamate proved ineffective. These observations suggest that during stress, activated catecholamine-synthesizing cells and corticotropin-releasing factor cells, both of which play central roles in stress responses, may be involved in total isatin production. Isatin may serve as an endogenously generated marker for some types of stress.

Altered expression of type 2 CRH receptor mRNA in the VMH by glucocorticoids and starvation

In the rat, high-dose corticosterone (Cort) administration, the hypercortisolism of starvation, and adrenalectomy are all associated with decreased food intake and weight loss. We report here a study of the effects of high-dose Cort administration, starvation, and adrenalectomy on two peripheral hormones known to influence food intake and energy use, insulin and leptin. We also studied the impact of these interventions on the levels of type 2 corticotropin-releasing hormone receptor (CRHR-2) mRNA in the hypothalamic paraventricular nucleus (PVN) and ventromedial hypothalamus (VMH). The VMH is classically referred to as the satiety center because electrical stimulation of the VMH leads to inhibition of food intake, whereas CRHR-2 are thought to transduce the profound anorexogenic effects of CRH or its related peptide urocortin. Starvation and adrenalectomy each lowered plasma insulin and leptin levels and were associated with decrements in CRHR-2 mRNA levels in the VMH. Cort administration increased plasma leptin levels profoundly, as well as plasma insulin levels and the levels of VMH CRHR-2 mRNA. Under all experimental conditions, a positive correlation was seen between plasma leptin levels and VMH CRHR-2 mRNA. These data suggest that decreased food intake and weight loss after high-dose Cort administration at least partially depend on the profound impact of Cort on plasma leptin secretion in the rat; they suggest, moreover, an additional mechanism for the satiety-inducing effects of leptin, namely increasing CRHR-2 in the VMH. The concordance of a fall in plasma insulin and leptin levels with the fall in VMH CRHR-2 mRNA levels further supports the idea that compensatory responses during starvation and adrenalectomy include not only the disinhibiting effects of reduced insulin and leptin levels on appetite through already-described mechanisms but also via an effect of leptin on VMH CRHR-2. Neither Cort administration, starvation, nor adrenalectomy influenced the levels of CRHR-2 mRNA in the PVN, suggesting that these receptors are differentially regulated in different hypothalamic regions.

Maternal stress induces synaptic loss and developmental disabilities of offspring

Mild prenatal stress affects the serotonergic system in the hippocampus of rat offspring. Pregnant rats were daily exposed to mild stress treatments (consisting of crowding and saline injection) during days 15 to 21 of pregnancy. Their offspring were assessed by a series of biochemical, histological and behavioral tests. On 35 days after birth, 5-hydroxytryptamine (5-HT) level was decreased by 17% (P < 0.05), whereas 5-hydroxyindolacetic acid (5-HIAA) level was increased by 18% (P < 0.05) in the offspring of prenatally stressed rats. The metabolic rate (5-HIAA/5-HT) was increased by 49% (P < 0.01). Synaptic density in the hippocampus of prenatally stressed offspring was also decreased by 32% (P < 0.0001) on postnatal day 35. There was no significant group difference in the spatial learning acquisition test of the Morris water maze; however, in the reversal task, prenatally stressed 5-week old rats spent more time than control animals searching for the platform of the pool. Escape latency in the cued test showed no significant difference. Together with data in our previous studies, that have shown 5-HT to facilitate synapse formation and maintenance in the central nervous system, synaptic loss is suggested to occur in relation to changes of 5-HT system in the hippocampus of prenatally stressed offspring. This may be associated with reported changes in behavior and learning ability in prenatally stressed offspring.

Differential effects of CRH infusion into the central nucleus of the amygdala in the Roman high-avoidance and low-avoidance rats

Roman-high (RHA/Verh) and low (RLA/Verh) avoidance rats are selected and bred for rapid learning versus non-acquisition of two-way, active avoidance behavior in a shuttle box. RHA/Verh rats generally show a more active coping style than do their RLA/Verh counterparts when exposed to various environmental challenges. The central nucleus of the amygdala (CeA) is known to be involved in the regulation of autonomic, neuroendocrine and behavioural responses to stress and stress-free conditions, and it is considered in relation to coping strategies. Corticotropin-releasing hormone (CRH) seems to be a key factor in the control of the CeA output. Neuroanatomical studies have revealed that the majority of CRH fibers from the CeA have direct connections with autonomic regulatory nuclei in the brainstem, e.g. lateral parabrachial nucleus (lPB), ventrolateral periaquaductal gray (vlPAG). The modulating effects of CRH (30 ng) on CeA activity were studied by infusion of CRH into the CeA in freely moving male RHA/Verh and RLA/Verh rats under stress-free conditions. Heart-rate and behavioural activities were repeatedly measured before, during and after local administration of CRH or vehicle, after which early gene product FOS immunocytochemistry and CRH-mRNA in situ hybridisation were carried out in selected brain areas. CRH infusion into the CeA caused a long lasting increase in heart-rate and behavioural activation in the RHA/Verh rats, leaving the RLA/Verh rats unaffected. As a result of CRH infusion, the number of FOS positive cells in the CeA and lPB of RLA/Verh rats was increased whereas an opposite response was found in the RHA/Verh rats. However, CRH into the CeA of the Roman rat lines induced no pronounced effects on FOS staining in the vlPAG and CRH mRNA levels in the CeA. These results indicate that the CRH system of the CeA, connected with the output brainstem areas, is differentially involved in cardiovascular and behavioural responses.

Does prenatal stress impair coping and regulation of hypothalamic-pituitary-adrenal axis?

Prenatally stressed (PS) human infants and experimental animals show attentional deficits, hyperanxiety and disturbed social behavior. Impaired coping in stressful situations in adult PS monkeys and rodents is associated with dysregulation of the HPA axis, characterized by decreased feedback inhibition of corticotropin-releasing hormone (CRH) and prolonged elevation of plasma glucocorticoids in response to stress. PS rats have higher levels of CRH in the amygdala, fewer hippocampal glucocorticoid receptors and less endogenous opioid and GABA/BDZ (benzodiazepine) inhibitory activity. The mechanisms by which maternal stress induce these long-lasting changes in the developing fetal neuroaxis remain to be elucidated. It is suggested that impaired coping in stressful situations and dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, result from the action of maternal hormones released during stress on the developing fetus. The similarities in coping behavior and dysregulation of the HPA axis in PS animals to those in humans with depression, suggest that gestational stress, at a critical time during fetal development, may increase the propensity to develop this condition.

Psychotropic analgesic nitrous oxide and neurotransmitter mechanisms involved in the alcohol withdrawal state

We relate the extremely rapid and lasting beneficial effects of psychotropic analgesic nitrous oxide (PAN) on the alcohol withdrawal state (AWS) to the underlying neurotransmitter system disturbances and clinical findings. PAN is an opioid and its main therapeutic effects are produced by stimulating the underactive endogenous opioid system (EOS) found in the AWS. In common with other opioids, PAN also acts on other neurotransmitter systems. While controlling the cholinergic and adrenergic overactivity and the concomitant stress state, through its opioid agonism, it simultaneously stimulates the underactive serotonergic and GABA-ergic systems found in the AWS. PAN also ameliorates disturbances in corticotropin-releasing factor (CRF) dopaminergic, glutaminergic and second messenger function. This unique combination of stimulation and inhibition enables a single 20 minute administration of PAN to rapidly restore the patients' homeostatic balance with lasting effect, and almost no other medication requirements during the entire detoxification period. Unlike other currently available therapies this is achieved without sedation.

A CRF antagonist attenuates stress-induced increases in NA turnover in extended brain regions in rats

We investigated the effects of intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) antagonist, alpha-helical CRF9-41 (ahCRF), on increases in noradrenaline (NA) turnover caused by immobilization stress in rat brain regions. Pretreatment with ahCRF (50 or 100 micrograms) significantly attenuated increases in levels of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), the major metabolite of NA in rat brain, in the locus coeruleus (LC) region, and attenuated the MHPG-SO4/NA ratio after immobilization stress for 50 min in the cerebral cortex, hippocampus, amygdala, midbrain and hypothalamus. However, stress-induced increases in plasma corticosterone levels were not decreased significantly by pretreatment with ahCRF. These results suggest that CRF, released during stress, causes increases in NA release in extended brain regions of stressed rats.

Central and autonomic nervous system links to the APUD system (and their APUDomas)

The concept of the APUD system and the APUDomas associated with it has evolved significantly since Pearse's description in the 1960s. Part of this evolution has been an understanding of the relationships between the APUD system and the central and autonomic nervous systems. The APUD system now referred to as the diffuse neuroendocrine system, can be linked to the central nervous system and autonomic nervous system by genetics, embryology, cellular characteristics, anatomy, interaction of the systems, and the immune system. Awareness of these relationships may enable clinicians to better understand APUDomas and lead to better methods of detection of these tumours and their treatment.

Corticotropin-releasing factor activates the noradrenergic neuron system in the rat brain

The effect of corticotropin-releasing factor (CRF) on central noradrenaline (NA) metabolism was examined by measuring levels of the major metabolite of NA, 3-methoxy-4-hydroxy-phenylethyleneglycol sulfate (MHPG-SO4) in several rat brain regions. Various doses of CRF ranging from 0.5-10 micrograms injected ICV significantly increased MHPG-SO4 levels in several brain regions including the hypothalamus, amygdala, midbrain, locus coeruleus (LC) region, and pons + medulla oblongata excluding the LC region. Plasma corticosterone levels were also significantly increased after ICV CRF administration up to 0.5 micrograms. The present results that CRF not only elevates plasma corticosterone levels but also increases NA metabolism in many brain regions suggest its neurotransmitter and/or neuromodulator role exerting the excitatory action on central NA neurons.

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.

Corticotropin-releasing factor enhances noradrenaline release in the rat hypothalamus assessed by intracerebral microdialysis

Corticotropin-releasing factor (CRF) at a dose of 3 micrograms administered intracerebroventricularly (i.c.v.) elicited increases in noradrenaline (NA) release, which was assessed by intracerebral microdialysis in the anterior hypothalamus of conscious rats. These increases persisted until 140 min after infusion of CRF. These results indicate that CRF enhances NA release in the hypothalamus, an effect which may underlie the 'stress-like' properties of CRF.