Anxiolytic effect of a CRH receptor antagonist in the dorsal periaqueductal gray

Corticotropin-releasing hormone (CRH) is anxiogenic when microinjected into the dorsal periaqueductal gray (DPAG). Microinjection of alpha-helical-CRH9-41 (0.5 microgram), a CRH receptor antagonist, however, failed to change anxiety levels. The objective of this study was to verify if this compound has any effect in the anxiogenic behavior of rats submitted to 4 hr of restraint stress 24 hr before the test in an elevated plus maze. Results showed that stressed rats had a decreased exploration of open arms without changing the number of enclosed arm entries. The stress effect was reversed by intra-DPAG injection of alpha-helical-CRH9-41 (0.5 microgram). These results suggest that the anxiogenic behavior of rats previously stressed by forced immobilization might involve facilitation of CRH-mediated neurotransmission in the DPAG.     

Corticotropin-releasing hormone and arginine vasopressin: mRNA and secretion are differentially regulated according to the pattern of exposure to noradrenaline in rat hypothalamic neurones

Hypothalamic corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) are secreted from the median eminence in a pulsatile manner and regulated by noradrenaline during stress. This study investigated the effect of pulsatile noraderanaline on CRH/AVP mRNAs and secretion. Foetal hypothalamic neurones were cultured on plastic coverslips, inserted into perifusion chambers and noraderanaline pulses given at various doses or pulse intervals for 24 h. CRH and AVP release rose in a dose dependant manner; however, maximal increases in mRNAs were seen with an intermediate noraderanaline pulse dose. The effect of noraderanaline pulse frequency was determined by giving noraderanaline pulses at intervals of 15-120 min vs continuous noraderanaline. Both pulsatile and continuous noraderanaline increased CRH and AVP release, but secretion was reduced after 22 h of treatment in the continuous noraderanaline and rapid pulse groups. CRH mRNA levels were maximally increased by medium interval pulses and AVP mRNA by rapid interval pulses. Neither CRH nor AVP mRNAs were stimulated by continuous noraderanaline. To determine noraderanaline specificity, pulses of veratridine (VER; 15-120 min intervals) vs continuous VER were examined. Only pulsatile VER increased CRH and AVP mRNAs, with maximal effects seen with the 60 min pulse interval for both. Thus, noraderanaline pulse pattern regulates CRH and AVP gene expression in both a coordinate and differential manner. Since noraderanaline plays an important role during stress, the pattern of noraderanaline signals may be critical to the observed changes in CRH and AVP expression.     

The CRH1 receptor antagonist R121919 attenuates stress-elicited sleep disturbances in rats,particularly in those with high innate anxiety

Excessive corticotropin-releasing hormone (CRH) secretion in limbic and prefrontal brain areas has been postulated to underly stress-related clinical conditions. Studies in mice with deleted or pharmacologically compromised CRH type 1 receptors (CRH-R1) point to a key role of the CRH/CRH-R1 signaling cascade as a potential drug target. Therefore, we compared the effect of a selective high affinity CRH-R1 antagonist (R121919) on sleep-wake behavior in two rat lines selectively bred for either high or low innate anxiety. We found that the subcutaneous injection of the solvent of R121919, a citrate buffer solution, transiently increased circulating levels of the stress hormones ACTH and corticosterone and reduced sleep, especially in high-anxiety animals. When R121919 was added to the solvent, hormone levels and sleep patterns returned to baseline and were indistinguishable between the rat lines. This finding is in accord with previous observations from a clinical trial in depressed patients and studies in rats with high innate anxiety that suggested major effects of CRH-R1 antagonism in the presence of a pathological (i.e. CRH hypersecretion) condition only.     

Imipramine reduces the local inflammatory response to carrageenin

Imipramine was administered chronically to LEW/N, outbred and F344/N rats which were then exposed to the aseptic irritant carrageenin in order to determine whether the decreased hypothalamic expression of CRH m-RNA previously shown to be associated with imipramine affects peripheral immune processes. Both LEW/N and outbred but not F344/N rats had vigorous inflammatory responses to carrageenin, and imipramine was associated with significant decreases in the local cellular inflammatory response to carrageenin. Imipramine was also associated with changes in the expression of peripheral blood cell MHC class II expression in LEW/N and outbred rats. These results suggest that at doses comparable to those used clinically imipramine has significant effects on response to an inflammatory stimulus.     

Effects of neurotransmitters on the release of corticotropin releasing hormone (CRH) by rat hypothalamic tissue in vitro

Summary Effects of neurotransmitters on in vitro release of CRH from rat hypothalamic tissue were investigated. Three whole hypothalami or three mediobasal hypothalami from male rats, adrenalectomized 7 days before, were incubated for 10 min in a medium similar to cerebrospinal fluid at 37 ° C under 95% O₂, 5% CO₂. CRH activity was assayed by radioimmunological measurement of ACTH released by isolated pituitary cells from adrenalectomized rats.Norepinephrine (NE) at a concentration of 0.02×10^–6 M to 2×10^–6 M stimulated dose-related CRH release. At larger concentrations the response decreased again (bell-shaped dose-response relationship). The action of norepinephrine was completely blocked by coincubation with phentolamine. Similar results were obtained whether whole hypothalami or mediobasal hypothalami were incubated with norepinephrine. This suggests that the site of action of NE was within the mediobasal hypothalamus. The possibility that the observed effects were due to the CRH-like activity of vasopressin released from the hypothalamic tissue was excluded by simultaneous measurements of CRH activity and arginine-vasopressin concentrations in the medium. Dopamine at very large concentrations (17.6×10^–6 M) also stimulated CRH release. Acetylcholine, serotonin, histamine and GABA did not influence the basal CRH release at any of the concentrations tested.These results suggest that in the rat, norepinephrine may have a physiological role as stimulator of CRH-release at the level of the mediobasal hypothalamus. However, in view of the conflicting results obtained with similar and other methods, no definite conclusions should yet be drawn.This work was supported by Deutsche Forschungsgemeinschaft. Bonn-Bad Godesberg. SFB 87/B2. K.H. V. is a recipient of a Heisenberg Stipendium     

The neuroprotective actions of corticotropin releasing hormone

Corticotropin-releasing hormone (CRH) modulates the activity of the hypothalamic-pituitary-adrenal (HPA) axis, and has a key role in mediating neuroendocrine effects that occur in response to stressful stimuli. Disruption of the CRH system however has been shown to be closely associated with the progression of Alzheimer's disease (AD), and these observations prompted an investigation into the potential neuroprotective effects of the hormone. In addition to its regulatory affects on the molecular processes that underlie AD i.e., amyloid precursor protein (APP) processing and potentially tau phosphorylation, evidence is provided that the neuroprotective effects of CRH are mediated by a number of diverse mechanisms. These stem from activation of its high affinity receptor, the CRH type 1 receptor, and involve the induction of protective intracellular pathways including PKA-CREB that eventually lead to expression of neurotrophic factors. Conversely, inhibition of harmful events, such as caspase activation during apoptosis may also occur. Taken together, an impressive amount of evidence has accumulated recently, highlighting this new and potentially important function of CRH.     

Fetal undernutrition induces overexpression of CRH mRNA and CRH protein in hypothalamus and increases CRH and corticosterone in plasma during postnatal life in the rat

Prenatal undernutrition induces a variety of cardiovascular alterations in mammals when adults, including hypertension and hypercortisolism, which are thought to be caused by decreased glucocorticoid feedback control of the hypothalamus–pituitary–adrenal (HPA) axis programmed during fetal life. Hypothalamic CRH seems to be involved in blood pressure elevation of spontaneously hypertensive rats and in primary hypertension of humans, but the influence of prenatal undernutrition on CRH expression has deserved little attention. Here, we studied the expression of both CRH mRNA and CRH protein in the hypothalamus of neonatal and juvenile offspring of rats undernourished during fetal life, as well as the plasma levels of CRH and corticosterone. Prenatal undernutrition of pups was induced by submitting pregnant rats to diet restriction (10 g daily of 21% protein standard laboratory diet). Pups born from dams with free access to the standard laboratory diet served as controls. At day 2 of postnatal age, undernourished pups showed lower body and brain weights, but higher plasma CRH and corticosterone than normal pups. At day 40 of age, brain weight was significantly decreased in the undernourished rats, while plasma corticosterone, plasma CRH and systolic pressure were significantly increased in these animals. At days 2 and 40 of postnatal age, increased CRH mRNA expression and CRH concentration were found in the hypothalamus of undernourished rats. Results indicate that, in the rat, prenatal undernutrition led to fetal programming of CRH overexpression, a neuropeptide serving as activating signal to the HPA axis and/or to extrahypothalamic brain regions concerned with cardiovascular regulation.     

Observations on the function of the dopaminergic nerves innervating the pituitary gland

Analysis of the distribution of catecholamines in the pituitary glands of six mammalian species showed that the highest concentrations occur in the combined neural and intermediate lobes. Dopamine was the major catecholamine; its concentration varied between 6ng/mg protein (guinea-pig) and 38 ng/mg protein (domestic pig). Catecholamines were hardly detectable in the anterior lobes.Possible roles for the dopaminergic innervation of the posterior and intermediate lobes of the pituitary gland have been investigated. Firstly, turnover of the dopamine present in the combined neural and intermediate lobes has been demonstrated in the rat by a fall in the dopamine concentrations after inhibiting dopamine synthesis with α-methyl-ρ-tyrosine methyl ester and by the presence of 3,4-dihydroxyphenylacetic acid in the gland. Secondly, the dopamine concentrations in the neuro-intermediate lobes of the rat hypophysis were measured under some conditions in which an increased release of pituitary hormones is known to occur. During lactation, when increased amounts of oxytocin, melanophore stimulating hormone, prolactin and other pituitary hormones are released over a prolonged period of time, a decrease in pituitary dopamine content and an increase in its turnover has been observed. Water deprivation and intake of large amounts of NaCl is known to lead to a prolonged increased release of vasopressin and oxytocin; this was found to be accompanied by a rise in pituitary dopamine content. A decrease in the pituitary dopamine content was found in rats 8 days after adrenalectomy. Acute release of large quantities of vasopressin, oxytocin or corticotrophin did not cause measurable change in pituitary dopamine contents.The results suggest that the dopaminergic innervation of the pituitary gland may modulate the release of oxytocin and vasopressin from the neural lobe under conditions in which the secretion of these hormones is increased over a prolonged period and may exert a direct inhibitory control over the secretion of polypeptides from the intermediate lobe.     

Mediation of dehydration-induced peptidergic gene expression in the rat lateral hypothalamic area by forebrain afferent projections

We have previously shown in dehydrated rats that cellular levels of the mRNAs encoding the precursor peptides for corticotropin-releasing hormone and neurotensin/neuromedin N significantly increase in a restricted region of the lateral hypothalamic area (Watts, 1992, Brain Res. 581:208–216). The experiments reported here address the role that forebrain osmosensitive cell groups or regions associated with autonomic regulation play in developing this mRNA response. The first experiment showed that unilateral knife cuts placed between the rostral forebrain and the lateral hypothalamic area (LHA) will unilaterally attenuate the mRNA response in the LHA to dehydration. In a second experiment, small injections of the retrograde tracer Fluorogold into the region of the LHA containing these mRNAs revealed a direct input from the osmosensitive median preoptic nucleus and subfornical organ and from the fusiform nucleus of the bed nuclei of the stria terminalis, which is part of a complex of cell groups associated with autonomic regulation. We found that at least 30% of the neurons in the median preoptic nucleus and subfornical organ and 14% of the neurons in the fusiform nucleus of the bed nuclei of the stria terminalis that project to the LHA responded to a rapid increase in plasma osmolality with increased c-fos mRNA levels. In the final experiment, injections of Fluorogold into the LHA were made simultaneously with ipsilateral rostral knife cuts. Here the numbers of neurons accumulating Fluorogold in the median preoptic nucleus, subfornical organ, and the fusiform nucleus were all significantly decreased concomitantly with attenuated mRNA responses in the LHA to dehydration. We conclude that the LHA receives direct and functional projections from the median preoptic nucleus, subfornical organ, and the fusiform nucleus. These projections appear capable of mediating a substantial part of the response of peptidergic mRNAs in the LHA to dehydration. © 1996 Wiley-Liss, Inc.     

Brain-derived neurotrophic factor Val66Met polymorphism and dexamethasone/CRH test results in depressed patients

Data suggest that both neurotrophic and hypothalamic-pituitary-adrenocortical (HPA) systems are involved in the pathophysiology of depression. The aim of the present study was to investigate whether the non-conservative brain-derived neurotrophic factor (BDNF) Val66Met polymorphism has an impact on HPA axis activity in depressed patients. At admission, the dexamethasone/CRH (DEX/CRH) test was performed in 187 drug-free in-patients suffering from major depression or depressed state of bipolar disorder (DSM-IV criteria). Moreover, genotyping of BDNF Val66Met polymorphism was carried out using the fluorescence resonance energy transfer method (FRET). Homozygous carriers of the Met/Met genotype showed a significantly higher HPA axis activity during the DEX/CRH test than patients carrying the Val/Val or Val/Met genotype (ACTH, cortisol). Our results further contribute to the hypothesized association between HPA axis dysregulation and reduced neuroplasticity in depression and are consistent with the assumption that BDNF is a stress-responsive intercellular messenger modifying HPA axis activity.