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

A role of noradrenergic receptors in anxiolytic-like effect of high CRF in the rat frontal cortex

Corticotropin releasing factor (CRF) is a neuropeptide widely distributed in the brain as a hormonal modulator and neurotransmitter. The best known behavioral function of CRF is activation of stress and anxiety via the hypothalamus and limbic structures but the role of CRF in the cortex is still poorly understood. Our previous studies have shown anxiolytic-like effects of high doses of CRF injected into the Fr2 frontal cortex and involvement of CRF1 receptors (R) in that effect. These results seemed to be controversial as most other studies suggested anxiogenic and not anxiolytic effects of CRF1R stimulation. Since stress is associated with adrenergic system, in the present study, we focused on participation of alpha1 and alpha2 or beta adrenergic receptors in the anxiolytic-like effect of CRF. Moreover, we verified whether these effects of CRF in the Fr2 were really connected with CRF1R. Male Wistar rats were bilaterally microinjected with CRF in a dose of 0.2 μg/1 μl/site or with the specific agonist of CRF1R, stressin 1 (0.2-0.0125 μg/1 μl/site) into the Fr2 area. The elevated plus maze (EPM) test was performed 30 min later to assess the anxiolysis. An involvement of noradrenergic receptors in the CRF induced anxiolytic-like effect in the Fr2 was studied by pretreatment with the alpha1 antagonist prazosin, alpha2 agonist clonidine, alpha2 antagonist RS 79948 or beta antagonist propranolol, 20-30 min before CRF. The influence on anxiety was assessed in the EPM test. The results show that anxiolytic behavior after CRF microinjection into the Fr2 area seems to be mainly connected with the CRF1R activation because a similar effect was observed after stressin 1 administration and it was blocked by CRF1R antagonist. The results observed after administration of noradrenergic ligands indicated that anxiolytic effects of CRF in the Fr2 engaged the alpha1 and alpha2 adrenergic receptors but not beta receptors.

Neuroendocrine regulation of GnRH release and expression of GnRH and GnRH receptor genes in the hypothalamus-pituitary unit in different physiological states

This review is focused on the relationship between neuroendocrine regulation of GnRH/LH secretion and the expression of GnRH and GnRH receptor (GnRHR) genes in the hypothalamic-pituitary unit during different physiological states of animals and under stress. Moreover, the involvement of hypothalamic GABA-ergic, Beta-endorphinergic, CRH-ergic, noradrenergic, dopaminergic and GnRH-ergic systems in the regulation of expression of the GnRH and GnRHR genes as well as secretion of GnRH/LH is analyzed. It appears that the neural mechanisms controlling GnRH gene expression in different physiological states may be distinct from those regulating GnRH/LH release. The hypothalamic GnRHR gene is probably located in different neural systems and may act in a specific way on GnRH gene expression and GnRH release.

The role of corticotropin-releasing factor and noradrenaline in stress-related responses, and the inter-relationships between the two systems

Substantial evidence indicates that brain neurons containing and secreting noradrenaline and corticotropin-releasing factor (CRF) are activated during stress, and that physiological and behavioural responses observed during stress can be induced by exogenous administration of CRF and adrenoceptor agonists. This review focusses on the evidence for the involvement of these two factors in stress-related responses, and the inter-relationships between them. The possible abnormalities of these two systems in depressive illness are also discussed.

Maternal programming of defensive responses through sustained effects on gene expression

There are profound maternal effects on individual differences in defensive responses and reproductive strategies in species ranging literally from plants to insects to birds. Maternal effects commonly reflect the quality of the environment and are most likely mediated by the quality of the maternal provision (egg, propagule, etc.), which in turn determines growth rates and adult phenotype. In this paper we review data from the rat that suggest comparable forms of maternal effects on defensive responses stress, which are mediated by the effects of variations in maternal behavior on gene expression. Under conditions of environmental adversity maternal effects enhance the capacity for defensive responses in the offspring. In mammals, these effects appear to 'program' emotional, cognitive and endocrine systems towards increased sensitivity to adversity. In environments with an increased level of adversity, such effects can be considered adaptive, enhancing the probability of offspring survival to sexual maturity; the cost is that of an increased risk for multiple forms of pathology in later life.

Environmental programming of stress responses through DNA methylation: life at the interface between a dynamic environment and a fixed genome

Early experience permanently alters behavior and physiology. These effects are, in part, mediated by sustained alterations in gene expression in selected brain regions. The critical question concerns the mechanism of these environmental “programming” effects. We examine this issue with an animal model that studies the consequences of variations in mother-infant interactions on the development of individual differences in behavioral and endocrine responses to stress in adulthood. Increased levels of pup licking/grooming by rat mothers in the first week of life alter DNA structure at a glucocorticoid receptor gene promoter in the hippocampus of the offspring. Differences in the DNA methylation pattern between the offspring of high- and low-lickinglgrooming mothers emerge over the first week of life; they are reversed with cross-fostering; they persist into adulthood; and they are associated with altered histone acetylation and transcription factor (nerve growth factor-induced clone A [NGFIA]) binding to the glucocorticoid receptor promoter. DNA methylation alters glucocorticoid receptor expression through modifications of chromatin structure. Pharmacological reversal of the effects on chromatin structure completely eliminates the effects of maternal care on glucocorticoid receptor expression and hypothalamic-pituitary-adrenal (HPA) responses to stress, thus suggesting a causal relation between the maternally induced, epigenetic modification of the glucocorticoid receptor gene and the effects on stress responses in the offspring. These findings demonstrate that the structural modifications of the DNA can be established through environmental programming and that, in spite of the inherent stability of this epigenomic marker, it is dynamic and potentially reversible.

Maternal programming of steroid receptor expression and phenotype through DNA methylation in the rat

Increased levels of pup licking/grooming and arched-back nursing by rat mothers over the first week of life alter the epigenome at a glucocorticoid receptor gene promoter in the hippocampus of the offspring. Differences in the DNA methylation pattern between the offspring of High and Low licking/grooming--arched-back mothers emerge over the first week of life, are reversed with cross-fostering, persist into adulthood and are associated with altered histone acetylation and transcription factor (NGFI-A) binding to the glucocorticoid receptor promoter. Central infusion of the adult offspring with the histone deacetylase inhibitor trichostatin A removes the previously defined epigenomic group differences in histone acetylation, DNA methylation, NGFI-A binding, glucocorticoid receptor expression, and hypothalamic-pituitary-adrenal responses to stress, thus suggesting a causal relation between the epigenomic state, glucocorticoid receptor expression and the effects of maternal care on stress responses in the offspring. These findings demonstrate that an epigenomic state of a gene can be established through a behavioral mode of programming and that in spite of the inherent stability of this epigenomic mark, it is dynamic and potentially reversible.

Comparison of the effects of diazepam, the CRF1 antagonist CP-154,526 and the group II mGlu receptor agonist LY379268 on stress-evoked extracellular norepinephrine levels

The present study used an elevated platform procedure to investigate the effects of diazepam, a CRF1 antagonist CP-154,526 and a group II mGlu2/3 receptor agonist LY379268 on stress-evoked increase in extracellular norepinephrine (NE). Pretreatment with either diazepam (1 mg/kg, i.p.), CP-154,526 (20 mg/kg, i.p.) or LY379268 (1, 3 and 10 mg/kg, p.o.) significantly reduced platform stress-evoked NE. Interestingly, at the highest dose tested (10 mg/kg) LY379268 caused a marked increase in baseline NE levels. We tested whether this effect would diminish after repeated dosing. In contrast to acute administration, a challenge injection of LY379268 after repeated dosing (10 mg/kg x days) did not alter basal NE. Importantly, although less effective, LY379268 still significantly reduced stress-evoked NE. We further show that this increase in basal NE may involve mGlu2/3 receptor regulation of the GABAergic system. To this end, administration of the GABAB agonist, baclofen (4 mg/kg, i.p.), 2 h after dosing with LY379268, reversed the increase in baseline NE. These data suggest that, like diazepam and CP-154,526, group II mGlu2/3 receptor agonists can attenuate stress-evoked increase in extracellular NE in the rat prefrontal cortex. In addition they reveal a 'stress-like' increase in NE after high doses of LY379268 which may reflect mGlu3 receptor modulation of GABAergic transmission.

The programming of individual differences in defensive responses and reproductive strategies in the rat through variations in maternal care

There are profound maternal effects on individual differences in defensive responses and reproductive strategies in species ranging literally from plants to insects to birds. Maternal effects commonly reflect the quality of the environment and are most likely mediated by the quality of the maternal provision (egg, propagule, etc.), which in turn determines growth rates and adult phenotype. In this paper, we review data from the rat that suggest comparable forms of maternal effects on both defensive responses to threat and reproductive behavior and which are mediated by variations in maternal behavior. Ultimately, we will need to contend with the reality that neural development, function and health are defined by social and economic influences.

Maternal Programming of Individual Differences in Defensive Responses in the Rat

This paper describes the results of a series of studies showing that variations in mother-pup interactions program the development of individual differences in behavioral and endocrine stress responses in the rat. These effects are associated with altered expression of genes in brain regions, such as the amygdala, hippocampus, and hypothalamus, that regulate the expression of stress responses. Studies from evolutionary biology suggest that such "maternal effects" are common and often associated with variations in the quality of the maternal environment. Together these findings suggest an epigenetic process whereby the experience of the mother alters the nature of the parent-offspring interactions and thus the phenotype of the offspring.

Efficacy of the herbal medicine Unkei-to as an adjunctive treatment to hormone replacement therapy for postmenopausal women with depressive symptoms

OBJECTIVE

Although hormone replacement therapy (HRT) improves menopausal depressive symptoms, women unresponsive to HRT need an antidepressant drug as an effective adjunctive therapy. The aim of this study was to assess whether the herbal medicine Unkei-to has an impact on HRT-resistant menopausal depressive symptoms as an effective adjunctive therapy combined with HRT.

METHODS

Twenty-four HRT-resistant menopausal depressive women were randomly assigned to group 1 (n = 12) or group 2 (n = 12). Subjects in group 1 were accessioned into 6 months of open treatment with Unkei-to as an adjunctive therapy and changed to Toki-shakuyaku-san for 6 months following a 1-month washout period. Group 2 started with Toki-shakuyaku-san for 6 months and then changed to Unkei-to for 6 months following a 1-month washout period.

RESULTS

Three months' treatment with Unkei-to as an adjunctive therapy significantly improved Zung's Self-Rating Depression Scale (ZSDS) scores, State-Anxiety (STAI-1) scores, and Trait-Anxiety (STAI-2) scores noted before treatment, and this effect continued at 6 months. Treatment with Unkei-to was also significantly effective in reduction of ZSDS scores, STAI-1 scores, and STAI-2 scores at 3 months compared with Toki-shakuyaku-san treatment, and this effect continued at 6 months.

CONCLUSIONS

Unkei-to is another option as an adjunctive herbal therapy in HRT-resistant menopausal depressive women.

Brain Circuits Involved in Corticotropin-Releasing Factor-Norepinephrine Interactions during Stress

Corticotropin-releasing factor (CRF)- and norepinephrine (NE)-containing neurons in the brain are activated during stress, and both have been implicated in the behavioral responses. NE neurons in the brain stem can stimulate CRF neurons in the hypothalamic paraventricular nucleus (PVN) to activate the hypothalamic-pituitary-adrenocortical axis and may affect other CRF neurons. CRF-containing neurons in the PVN, the amygdala, and other brain areas project to the area of the locus coeruleus (LC), and CRF injected into the LC alters the electrophysiologic activity of LC-NE neurons. Neurochemical studies have indicated that CRF applied intracerebroventricularly or locally activates the LC-NE system, and microdialysis and chronoamperometric measurements indicate increased NE release in LC-NE terminal fields. However, chronoamperometric studies indicated a significant delay in the increase in NE release, suggesting that the CRF input to LC-NE neurons is indirect. The reciprocal interactions between cerebral NE and CRF systems have been proposed to create a "feed-forward" loop. It has been postulated that a sensitization of such a feed-forward loop may underlie clinical depression. However, in the majority of studies, repeated or chronic stress has been shown to decrease the behavioral and the neurochemical responsivity to acute stressors. Repeated stress also seems to decrease the responsivity of LC neurons to CRF. These results do not provide support for a feed-forward hypothesis. However, a few studies using certain tasks have indicated sensitization, and some other studies have suggested that the effect of CRF may be dose dependent. Further investigations are necessary to establish the validity or otherwise of the feed-forward hypothesis.

Corticotropin-releasing hormone receptor blockade fails to alter stress-evoked catecholamine release in prefrontal cortex of control or chronically stressed rats

Although it is well documented that stress can increase the activity of central dopamine and norepinephrine neurons, little is known about the role of other neurotransmitters in modulating this response. Previous studies have implicated corticotropin-releasing hormone in modulating stress-evoked changes in the activity of locus coeruleus neurons. The present study examines whether corticotropin-releasing hormone contributes to stress-evoked increases in extracellular norepinephrine and dopamine in rat medial prefrontal cortex, as monitored by in vivo microdialysis. As noted previously, 30 min of tail-shock increased extracellular levels of norepinephrine and dopamine in the medial prefrontal cortex of naïve rats, and this was enhanced in rats previously exposed to chronic cold ( approximately 5 degrees C for 2-3 weeks). Previous intraventricular administration of a corticotropin-releasing hormone antagonist (D-Phe-corticotropin-releasing hormone; 3 and 9 microg) did not alter the tail-shock evoked in increase in extracellular levels of norepinephrine and dopamine in either naïve or chronically cold-exposed rats. Intraventricular administration of 3 microg of D-Phe-corticotropin-releasing hormone attenuated the increase in extracellular norepinephrine induced by co-administration of 3 microg of corticotropin-releasing hormone, confirming the efficacy of this compound. Results of the present study suggest that endogenous corticotropin-releasing hormone does not play a role in modulating the release of norepinephrine and dopamine occurring in response to acute tail-shock or the expression of a potentiated response to tail-shock in rats exposed chronically to cold.

The interaction of bombesin and corticotropin-releasing hormone on ingestive behavior in the domestic fowl

An experiment was conducted to investigate if bombesin (BM) elicits its effects on feeding through the release of corticotropin-releasing factor (CRF). Single Comb White Leghorn (SCWL) and broiler cockerels were stereotaxically implanted with a 23-gauge stainless steel cannula in the right lateral ventricle. Birds were infused with 0 or 0.5 microg BM, 5 microg alphaCRF (a CRF antagonist), or a combination of both. Food and water consumption were monitored at 15-min intervals through 3 h postinjection. Food and water consumption were both significantly decreased by BM in both SCWL and broilers. In SCWL, alphaCRF had no effect on food intake by itself, but attenuated the effects of BM. In broilers, alphaCRF caused a slight, but significant, decrease in food intake, but also attenuated the effects of BM. Water consumption was not affected by alphaCRF in either broilers or SCWL. We conclude that BM may mediate its central effects on food intake in chickens through the release of CRF.

Metyrapone-induced glucocorticoid depletion modulates tyrosine hydroxylase and phenylethanolamine N-methyltransferase gene expression in the rat adrenal gland by a noncholinergic transsynaptic activation

The hypothalamic corticotropin-releasing hormone system and the sympathetic nervous system are anatomically and functionally interconnected and hormones of the hypothalamic-pituitary-adrenocortical axis contribute to the regulation of catecholaminergic systems. To investigate the role of glucocorticoids on activity of the adrenal gland, we analysed plasma and adrenal catecholamines, tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) mRNA expression in rats injected with metyrapone or dexamethasone. Metyrapone-treated rats had significantly lower epinephrine and higher norepinephrine production than control rats. Metyrapone increased TH protein synthesis and TH mRNA expression whereas its administration did not affect PNMT mRNA expression. Dexamethasone restored plasma and adrenal epinephrine concentrations and increased PNMT mRNA levels, which is consistent with an absolute requirement of glucocorticoids for PNMT expression. Adrenal denervation completely abolished the metyrapone-induced TH mRNA expression. Blockage of cholinergic neurotransmission by nicotinic or muscarinic receptor antagonists did not prevent the metyrapone-induced rise in TH mRNA. Finally, pituitary adenylate cyclase activating polypeptide (PACAP) adrenal content was not affected by metyrapone. These results provide evidence that metyrapone-induced corticosterone depletion elicits transsynaptic TH activation, implying noncholinergic neurotransmission. This may involve neuropeptides other than PACAP.

Hippocampal noradrenergic responses to CRF injected into the locus coeruleus of unanesthetized rats

Intracerebral administration of corticotropin-releasing factor (CRF) activates cerebral noradrenergic neurons. Direct infusion of CRF into the locus coeruleus (LC) increases norepinephrine (NE) release in the cortex and hippocampus as assessed by in vivo microdialysis. In a recent study using in vivo chronoamperometry in anesthetized rats, CRF injected into the LC increased apparent NE release in the hippocampus, but did so after a significant delay, much longer than observed following infusion of glutamate into the same site. Because this delay may have been an artifact of the urethane anesthesia, we developed a method for chronoamperometric recording from the hippocampus of unanesthetized rats. CRF infusion into the LC of such animals induced an increase in the apparent release of hippocampal NE after a mean delay of about 7 min, reached a peak around 16 min after CRF, and dissipated within 30 min. Thus the response closely resembled that previously reported in urethane-anesthetized rats. As in anesthetized rats, glutamate infused into the same site resulted in a much more rapid response (starting within 1 min and with a peak around 7 min). These results suggest that the urethane anesthesia does not substantially alter hippocampal NE release following infusion of CRF into the LC, and that the relatively long delay in the response is not an artifact of the anesthesia. The large differences in the responses to glutamate and CRF suggest that the effects of CRF are not exerted directly on receptors on LC neurons, and more likely reflect indirect actions on other cells in this region.

An inhibitory effect of cytokine-induced neutrophil chemoattractant on corticotropin-releasing factor-induced increase in locomotor activity

To investigate whether cytokine-induced neutrophil chemoattractant (CINC) has an influence on corticotropin-releasing factor (CRF) in the central nervous system, the effects of intracerebroventricular (i.c.v.) injection of CINC on CRF-induced behavior were examined. Intracerebroventricular CRF injection produced an increase in locomotor activity, which was significantly reduced by i.c.v. injection of CINC. The intravenous injection of CINC did not alter CRF-induced locomotor hyperactivity. These results suggested that CINC has a functional antagonistic action on the response to CRF and may attenuate stress responses.

Maternal care, gene expression, and the transmission of individual differences in stress reactivity across generations

Naturally occurring variations in maternal care alter the expression of genes that regulate behavioral and endocrine responses to stress, as well as hippocampal synaptic development. These effects form the basis for the development of stable, individual differences in stress reactivity and certain forms of cognition. Maternal care also influences the maternal behavior of female offspring, an effect that appears to be related to oxytocin receptor gene expression, and which forms the basis for the intergenerational transmission of individual differences in stress reactivity. Patterns of maternal care that increase stress reactivity in offspring are enhanced by stressors imposed on the mother. These findings provide evidence for the importance of parental care as a mediator of the effects of environmental adversity on neural development.

NPY Y1 receptors exert opposite effects on corticotropin releasing factor and noradrenaline overflow from the rat hypothalamus in vitro

Neuropeptide Y (NPY), corticotropin releasing factor (CRF) and noradrenaline play important roles in the regulation of a number of endocrine and autonomic functions. NPY is co-localised with noradrenaline in the central nervous system and has been observed to modulate noradrenaline release. Recent morphological and physiological studies also support co-modulatory interactions between NPY and CRF. Earlier in vivo studies in our laboratory showed a potentiation of K(+)-stimulated noradrenaline release following NPY administration, possibly due to an NPY Y1 receptor mechanism. In this study, in vitro superfusion techniques were established to simultaneously monitor the release of endogenous noradrenaline and CRF from the hypothalamus of adult rats and to examine the direct neuromodulatory action of NPY on the overflow of CRF and noradrenaline. Administration of 0.10 microM NPY significantly increased CRF overflow to 395% basal levels and reduced hypothalamic noradrenaline overflow to 61% of basal levels. These effects were blocked by prior administration of the NPY Y1 receptor antagonist GR231118. Thus, this study suggests that NPY, working through a Y1 receptor, has dual and opposing effects on CRF and noradrenaline overflow in vitro.

Noradrenaline systems in the hypothalamus, amygdala and locus coeruleus are involved in the provocation of anxiety: basic studies

A variety of stressful events, including emotional stress, cause a marked increase in noradrenaline release in several brain regions, and especially in the hypothalamus, amygdala and locus coeruleus, in the rat brain. These findings suggest that an increased noradrenaline release could be closely related to the provocation of negative emotions such as anxiety and/or fear. In order to confirm this hypothesis, we carried out several studies. Diazepam, a typical benzodiazepine anxiolytic, significantly attenuated not only the immobilization stress-induced increase in noradrenaline release in the three rat brain regions but also the emotional changes of these animals, and these effects were antagonized by flumazenil, a benzodiazepine antagonist. Naloxone and opioid agents, such as morphine, beta-endorphin and [Met(5)]-enkephalin, significantly enhanced and attenuated the stress-induced increase in noradrenaline release in these regions and the stress-induced emotional change, respectively. Two stressful events which predominantly involve emotional factors, i.e., psychological stress and conditioned fear, caused significant increases in noradrenaline release selectively in these three brain regions and these increases were also significantly attenuated by pretreatment with diazepam in a flumazenil reversible manner. Yohimbine, an alpha(2)-adrenoceptor antagonist which caused a marked increase in noradrenaline release in the several brain regions, had an anxiolytic action in the two behavioral tests involving anxiety, i.e., the conditioned defensive burying test and the modified forced swim test. beta-Carbolines, which possess anxiogenic properties, significantly increased noradrenaline release in the hypothalamus, amygdala and locus coeruleus. Taken together, these findings suggest that the increased release of noradrenaline in the hypothalamus, amygdala and locus coeruleus is, in part, involved in the provocation of anxiety and/or fear in animals exposed to stress, and that the attenuation of this increase by benzodiazepine anxiolytics acting via the benzodiazepine receptor/GABAA receptor/chloride ionophore supramolecular complex may be the basic mechanism of action of these anxiolytic drugs.

Footshock-induced changes in brain catecholamines and indoleamines are not mediated by CRF or ACTH

Stressful treatments have long been associated with increased activity of brain catecholaminergic and serotonergic neurons. An intracerebroventricular (icv) injection of the corticotropin-releasing factor (CRF) also activates brain catecholaminergic neurons. Because brain CRF-containing neurons appear to be activated during stress, it is possible that CRF mediates the catecholaminergic activation. This hypothesis has been tested by assessing the responses in brain catecholamines and indoleamines to footshock in mice pretreated icv with a CRF receptor antagonist, and in mice lacking the gene for CRF (CRFko mice). Consistent with earlier results, icv administration of CRF increased catabolites of dopamine and norepinephrine, but failed to alter tryptophan concentrations or serotonin catabolism. A brief period of footshock increased plasma corticosterone and the concentrations of tryptophan and the catabolites of dopamine, norepinephrine and serotonin in several brain regions. Mice injected icv with 25 microg alpha-helical CRF(9-41) prior to footshock had neurochemical responses that were indistinguishable from controls injected with vehicle, while the increase in plasma corticosterone was slightly attenuated in some experiments. CRFko mice exhibited neurochemical responses to footshock that were indistinguishable from wild-type mice. However, whereas wild-type mice showed the expected increase in plasma corticosterone, there was no such increase in CRFko mice. Similarly, hypophysectomized mice also showed normal neurochemical responses to footshock, but no increase in plasma corticosterone. Hypophysectomy itself elevated brain tryptophan and catecholamine and serotonin metabolism. Treatment with ACTH icv or peripherally failed to induce any changes in cerebral catecholamines and indoleamines. These results suggest that CRF and its receptors, and ACTH and other pituitary hormones, are not involved in the catecholamine and serotonin responses to a brief period of footshock.

Hippocampal norepinephrine-like voltammetric responses following infusion of corticotropin-releasing factor into the locus coeruleus

Intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) increases the activity of noradrenergic neurons in the locus coeruleus (LC) assessed by electrophysiological and neurochemical studies. It has been suggested that this effect of i.c.v. CRF is exerted directly on LC noradrenergic (LC-NE) neurons. Infusion of CRF directly into the LC increases cortical and hippocampal release of norepinephrine (NE) as indicated by in vivo microdialysis studies, but the electrophysiological studies have shown both increases and decreases. The present study used in vivo voltammetry to study changes in the extracellular concentrations of NE in the rat hippocampus in response to infusion of CRF (100 ng) into the LC. When the infusion cannula was located in or very close to the LC, the immediate response to CRF was a small decrease in the NE-like oxidation current, followed by a robust increase after about 6-7 min. The oxidation current reached a peak around 13 min and returned to baseline by about 30 min after CRF infusion. By contrast with CRF, infusion of glutamate into the LC increased the oxidation current with a delay of around 30 s and a peak within 90 s. The responses to LC infusion of CRF in rats treated with DSP-4 to deplete hippocampal NE were substantially smaller than those in untreated rats, suggesting that the oxidation signals in untreated rats reflected changes in concentrations of NE. The response to glutamate was markedly augmented by pretreatment with the NE reuptake inhibitor, desmethylimipramine, suggesting that the observed responses reflected changes in NE. Infusion of the same dose of CRF into brain structures outside the LC did not elicit consistent changes in oxidation current in the hippocampus. The time course of the responses to CRF is compatible with previously reported electrophysiological responses of LC-NE neurons to CRF and with neurochemical evidence indicating that CRF can affect the activity of LC-NE neurons. The results indicate that CRF may act in or close to the LC to induce release of hippocampal NE, but the delayed response to CRF compared with that to glutamate, suggests that CRF does not directly activate LC-NE neurons.

Influence of neonatal rearing conditions on stress-induced adrenocorticotropin responses and norepinepherine release in the hypothalamic paraventricular nucleus

Postnatal rearing conditions influence the development of hypothalamic-pituitary-adrenal (HPA) responses to stress in the rat. Thus, postnatal handling dampens HPA responsivity to stress, while prolonged periods of maternal separation have the opposite effect. HPA responses to stress are initiated by the release of corticotropin-releasing factor and/or arginine vasopressin from the neurones of the paraventricular nucleus of the hypothalamus (PVNh). A major source of input to the PVNh arises from brainstem noradrenergic neurones with signalling occurring via alpha1 adrenoreceptors. We examined the noradrenergic response to stress in the PVNh in adult animals exposed to daily periods of handling or maternal separation over the first 2 weeks of life using microdialysis in conscious animals. Maternal separation increased, while handling greatly decreased and norepinepherine responses to restraint stress in the PVNh as compared to non-handled controls; the same pattern was observed for plasma adrenocorticotropic hormone (ACTH) responses to stress. Rearing condition did not affect either alpha1 or alpha2 receptor levels in the PVNh. However, alpha2 receptor binding levels in the noradrenergic cell body regions of the locus coeruleus and the n. tractus solitarius were significantly increased in handled animals. These alpha2 receptors are principally located on noradrenergic neurones (i.e. autoreceptors) and inhibit noradrenaline release at terminal sites. The effects on alpha2 receptor levels could serve as a mechanism for the differences in stress-induced noradrenaline levels in the PVNh and in HPA activity among handled vs non-handled and maternal separation animals. Thus, early life events may serve to influence the differentiation of noradrenergic neurones and thus alter HPA responses stress in adulthood.

Intracerebroventricular infusion of CRF increases extracellular concentrations of norepinephrine in the hippocampus and cortex as determined by in vivo voltammetry

Previous studies have indicated that intracerebroventricular (i.c.v.) infusions of corticotropin-releasing factor (CRF) activate locus coeruleus (LC) noradrenergic neurons and increase the metabolism and extracellular concentrations of norepinephrine (NE) in several brain regions, suggesting increased release. To examine the temporal aspects and mechanism of the presumed release of NE, CRF was infused i.c.v. and the oxidation current was recorded using carbon fiber voltammetric electrodes placed in rat hippocampus or cortex. The CRF (1 microg, i.c.v.) caused a significant increase of oxidation current with a delay of approximately 5 min, and a peak at approximately 35 min. Similar responses were observed in the medial prefrontal cortex. The hippocampal response was markedly attenuated when CRF was infused into rats pretreated with DSP-4 to deplete NE, suggesting that the observed changes in current resulted from oxidation of NE. The increase of NE-like current did not occur when 25 microg alpha-helical CRF9-41 (ahCRF) was injected immediately before 1 microg CRF, suggesting that the response was mediated by cerebral CRF-receptors. Subcutaneous pretreatment with the ganglionic blocker, chlorisondamine, at a dose of 3 mg/kg had no effect on the voltammetric response to CRF, but a 6 mg/kg dose completely prevented the response. The beta-adrenoceptor antagonists, S-propranolol (5 mg/kg), nadolol (5 and 10 mg/kg), and timolol (5 mg/kg) attenuated the NE response to i.c.v. CRF to varying degrees. When chlorisondamine (3 microg) or nadolol (5 microg) were given i.c.v. before the CRF, the hippocampal responses were not blocked. These results suggest peripheral actions of ganglionic and beta-adrenergic blockers. We conclude that peripheral autonomic mechanisms, and probably both central and peripheral beta-adrenoceptors, contribute to the increased secretion of hippocampal NE in response to i.c.v. CRF.

KAT45, a noradrenergic human pheochromocytoma cell line producing corticotropin-releasing hormone

KAT45 cells were derived from a human pheochromocytoma, which also caused ectopic Cushing's syndrome, and developed into a cell line spontaneously after the continuous primary culture of the tumor cells. These human pheochromocytoma cells were compared with the extensively characterized PC12 rat pheochromocytoma cell line. KAT45 cells resembled PC12 cells in morphology, proliferation rate, response to cholinergic stimuli, and the development of dendrite-like projections after exposure to nerve growth factor. They produced norepinephrine and epinephrine in a ratio of 50:1, as opposed to production of dopamine by PC12 cells, in amounts 1 order of magnitude higher compared with PC12. Because of the ectopic Cushing's syndrome in our patient, her normal ACTH level, and the knowledge that PC12 cells and even normal rat chromaffin cells appear to produce CRH, we examined whether KAT45 cells also produced this neuropeptide. Indeed, KAT45 cells released authentic CRH and contained an apparently intact CRH transcript. Nicotine and KCl depolarization stimulated the secretion of CRH, whereas interleukin-1beta, glucocorticoids, and nerve growth factor stimulated its synthesis. In addition to the potential systemic effects of CRH, which in our patient produced ectopic Cushing's syndrome, CRH can exert paracrine effects within normal or tumoral adrenals. We used KAT45 cells as a model for the study of the local role of CRH. CRH affected several parameters of KAT45 cell metabolism, including their proliferation rate, synthesis of catecholamines, and production of POMC-derived peptides. KAT45 cells, in addition to the data they provided regarding the in vitro profile of a human CRH-producing pheochromocytoma, may prove to be a valuable auxiliary to the PC12 cell line.

Comparative study between normal rat chromaffin and PC12 rat pheochromocytoma cells: production and effects of corticotropin-releasing hormone

The adrenal medulla of several species and some human pheochromocytomas contain CRH. The first aim of the present work was to find out whether normal rat adrenal chromaffin cells and the PC12 rat pheochromocytoma cell line produce CRH in vitro and what regulates its production. CRH was measured and characterized in the media of both types of chromaffin cells under basal conditions and after exposure to K+, nicotine, interleukin-1 beta, and nerve growth factor (NGF). The second aim was to examine the biological effect of exogenous CRH (and of its antagonist) on the production of catecholamines from these two types of cells. Our results are as follows: 1) Both types of chromaffin cells contained and secreted comparable amounts of immunoreactive-CRH under basal conditions and after K(+)-induced depolarization, nicotine, and interleukin-1 beta; 2) the physicochemical characteristics of the immunoreactive-CRH in the cells and the media were identical to the putative CRH peptide on both sieve chromatography and RP-HPLC; 3) synthetic CRH induced the production of catecholamines from both cell types in a dose- and time-dependent manner; this effect was abolished by the antagonist, alpha helical CRH; 4) exposure of PC12 cells to NGF (for 1 week) resulted in their neuronal differentiation and the stimulation of their production of CRH by 30 times and of dopamine by 10 times, compared with parallel controls; this effect of NGF was abolished by alpha helical CRH. In conclusion, our data suggest that the production of CRH by PC12 cells represents the preservation of a normal chromaffin cell characteristic rather than a tumor-induced ectopic phenomenon.

Corticotropin-releasing factor administered into the locus coeruleus, but not the parabrachial nucleus, stimulates norepinephrine release in the prefrontal cortex

Previous studies have indicated that intracerebroventricular application of corticotropin-releasing factor (CRF) activates noradrenergic neurons in the brain stem locus coeruleus (LC) and norepinephrine (NE) metabolism in several brain regions. To assess whether CRF has direct effects on LC noradrenergic neurons, CRF was infused into the LC and concentrations of NE and its metabolites were measured in microdialysates collected from the medial prefrontal cortex (PFM). Infusion of 100 ng of CRF into the LC significantly increased dialysate concentrations of NE and of its catabolite MHPG in the ipsilateral PFM, whereas no significant changes were observed following infusion of artificial CSF. No response was observed when the infusions of CRF occurred outside of the LC, including those in the parabrachial nucleus. Although CRF administered into the LC slightly increased dialysate concentrations of NE in the contralateral PFM, this effect was not statistically significant. The effect of CRF injected into the LC on dialysate NE was prevented by combination with a 10-fold excess of the CRF antagonist alpha-helical CRF9-41, indicating some specificity in the response. These results are consistent with anatomical and electrophysiological evidence suggesting that CRF may directly activate noradrenergic neurons in or close to the LC.

Corticotropin releasing factor mRNA and peptide levels are differentially regulated in the developing ovine brain

The regulation of CRF mRNA and protein in the developing ovine brain has been studied to assess the hypothesis that CRF is differentially regulated in the hypothalamus (Hypo), hippocampal-amygdala complex (H & A), frontal cerebral cortex (FCC) and brainstem (BS). We used a quantitative RNase protection assay and radioimmunoassay to determine mRNA and peptide concentrations, respectively, from the last third of gestation until term (i.e., from 95 to 142 days gestation (dg); term approximately 145 days). The major findings from this study are: (1) Hypothalamic CRF mRNA was increased by 2-fold in 140-142 dg fetuses compared to 128-138 and 95-123 dg fetuses; P = 0.016. (2) In the hypothalamus of 140-142 dg fetuses, there was a 2.5-fold increase in CRF mRNA derived from polyadenylation at poly(A) sites 2, 3 or 4; P = 0.005. (3) In 128-138 dg fetuses, CRF mRNA in the frontal cortex was 2-fold higher than in the other brain regions during this time period; P = 0.008. (4) CRF peptide concentrations in the Hypo were 2.5-fold higher in 140-142 dg fetuses compared to 95-106 and 128-138 dg fetuses; P = 0.007. (5) CRF peptide concentrations in the frontal cortex were 5.5-fold higher in 140-142 dg fetuses compared to fetuses at 95-106 dg; P = 0.004. (6) CRF peptide concentrations in the H & A were 5-fold higher in 140-142 dg fetuses compared to 95-106 dg fetuses; P = 0.029. The results from the present study demonstrate for the first time that CRF mRNA and peptide are differentially regulated in a region-specific manner during development.

CRF receptor antagonist attenuates stress-induced noradrenaline release in the medial prefrontal cortex of rats

Noradrenaline release in rat medial prefrontal cortex (PFC) was measured using a brain microdialysis technique. Immobilization stress increased noradrenaline release to a maximum level of 248.7 +/- 12.8% of the basal release, which was significantly attenuated by preinjection of alpha-helical CRF9-41 (50 micrograms/rat) into the lateral cerebroventricle. Intracerebroventricular injection of CRF also increased noradrenaline release in the medial PFC. These results suggest that immobilization-stress facilitates noradrenaline release in the medial PFC through activation of the CRF system in the brain.

Pentobarbital sodium inhibits the release of noradrenaline in the medial preoptic area in the rat

The effect of pentobarbital sodium (PB) on noradrenaline (NA) release in the medial preoptic area was studied in ovariectomized rats by a microdialysis method coupled to HPLC. Dialyzates were collected at 6-min intervals before and after the injection in freely moving rats. PB injected i.p. at a dose of 35 mg/kg caused a marked, approximately 40-50% decrease in NA release, which became evident 50 min after the injection and lasted for another 60 min during which the observation was performed. The results suggest that the anesthetic effect of barbiturates is related to the reduction in NA release in the brain.

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.

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.