Intracerebroventricular administration of corticotropin-releasing factor antagonist attenuates c-fos mRNA expression in the paraventricular nucleus after stress

Characterization and gonadal hormone regulation of a sexually dimorphic corticotropin-releasing factor receptor 1 cell group

Corticotropin-releasing factor binds with high affinity to CRF receptor 1 (CRFR1) and is implicated in stress-related mood disorders such as anxiety and depression. Using a validated CRFR1-green fluorescent protein (GFP) reporter mouse, our laboratory recently discovered a nucleus of CRFR1 expressing cells that is prominent in the female rostral anteroventral periventricular nucleus (AVPV/PeN), but largely absent in males. This sex difference is present in the early postnatal period and remains dimorphic into adulthood. The present investigation sought to characterize the chemical composition and gonadal hormone regulation of these sexually dimorphic CRFR1 cells using immunohistochemical procedures. We report that CRFR1-GFP-ir cells within the female AVPV/PeN are largely distinct from other dimorphic cell populations (kisspeptin, tyrosine hydroxylase). However, CRFR1-GFP-ir cells within the AVPV/PeN highly co-express estrogen receptor alpha as well as glucocorticoid receptor. A single injection of testosterone propionate or estradiol benzoate on the day of birth completely eliminates the AVPV/PeN sex difference, whereas adult gonadectomy has no effect on CRFR1-GFP cell number. These results indicate that the AVPV/PeN CRFR1 is regulated by perinatal but not adult gonadal hormones. Finally, female AVPV/PeN CRFR1-GFP-ir cells are activated following an acute 30-min restraint stress, as assessed by co-localization of CRFR1-GFP cells with phosphorylated (p) CREB. CRFR1-GFP/pCREB cells were largely absent in the male AVPV/PeN. Together, these data indicate a stress and gonadal hormone responsive nucleus that is unique to females and may contribute to sex-specific stress responses.

Chlordiazepoxide and lavender oil alter unconditioned anxiety-induced c-fos expression in the rat brain

Lavender oil has a long history of use for treating anxiety, but only recent research has examined its effects using standard behavioural methods used to test novel drugs. The aim of this study was to investigate the effects of inhaled lavender oil on anxiety related behaviour of rats in the open field and to compare them with the effects of chlordiazepoxide (CDP), a typical anxiolytic drug. Additionally c-fos immunochemistry was used to investigate whether lavender oil produced the same pattern of c-fos expression as CDP in eight different brain areas associated with anxiety. As previously found, lavender oil showed anxiolytic properties in the open field similar to but not as extensive as those of CDP. Immunochemistry results indicated that exposure to the open field increased c-fos expression, while CDP reversed the effects of this behavioural stressor on c-fos expression in all brain regions examined except the central nucleus of the amygdala, where c-fos expression increased. Lavender oil had similar effects to CDP on the paraventricular nucleus of the hypothalamus, the dorsomedial hypothalamic nucleus and the central nucleus of the amygdala. These results strengthen the suggestion that inhaling lavender oil has anxiolytic behavioural effects, but they are weaker than the effects of benzodiazepines, and there is limited evidence that they are mediated by the same neural processes.

Cyclooxygenase and nitric oxide synthase in the presympathetic neurons in the paraventricular hypothalamic nucleus are involved in restraint stress-induced sympathetic activation in rats

Stress is one of the important factors to activate the sympathetic nervous system. We recently reported that central administration of corticotropin-releasing factor (CRF), known as a stress-related neuropeptide, increases the expression of both cyclooxygenase (COX) and nitric oxide synthase (NOS) in presympathetic neurons in the paraventricular hypothalamic nucleus (PVN). In the present study, therefore, we investigated whether brain COX and NOS can also mediate restraint stress (RS)-induced sympathetic activation by assessing the plasma catecholamine levels and neuronal activation of presympathetic neurons in the PVN. In addition, we examined effects of RS on the expression of both COX and NOS isozymes in the presympathetic PVN neurons. Intraperitoneal administration of an inhibitor for COX-1, COX-2 or inducible NOS (iNOS), but not for neuronal NOS (nNOS), reduced RS-induced elevation of plasma catecholamine levels and Fos expression in the presympathetic PVN neurons. Moreover, RS increased the expression of COX-1, COX-2 and iNOS in the presympathetic PVN neurons, whereas nNOS expression did not change. These results suggest that COX-1, COX-2 and iNOS in the presympathetic PVN neurons mediate acute RS-induced sympathetic activation.

Corticotropin-releasing factor receptors and urocortins, links between the brain and the heart

Corticotropin-releasing factor (CRF), a 41 amino acid peptide, was discovered as a key signal in mediating neuroendocrine, autonomic, and behavioral responses to stress. It was revealed later that there exist additional CRF-like peptides, termed urocortins. The CRF receptor subtype 1 (CRF1 receptor) is predominant in the brain whereas subtype 2 (CRF2 receptor) is highly expressed in the brain and the heart. Both centrally and peripherally administered CRF and urocortins produce significant hemodynamic effects via activation of CRF receptors in the brain and the heart. CRF and urocortins are important neural and cardioactive hormones, and are potentially useful therapy for heart failure.

Effects of AVP V1a and CRH receptor antagonist on psychological stress responses to frustrating condition in sheep

Arginine vasopressin (AVP) and corticotropin-releasing hormone (CRH) are released in the brain to regulate behavioral and physiological stress responses. To elucidate the respective roles of these peptides under certain stressors, we examined the effects of intracerebroventricular infusions of either AVP V1a receptor antagonist, [Pmp(1), Tyr (Me)(2)]- Arg(8)-Vasopressin (Pmp, Tyr-AVP) or CRH receptor antagonist, alpha-helical CRF 9-41 (alphahCRF) on stress responses induced by frustrating condition in sheep. Four ovariectomized Corriedale ewes were assigned to the experiment. In a "frustrating" condition (FC), food was withheld for 60 minutes from only the experimental ewe while this ewe was in the presence of the other ewes that were given food. As "non-frustrating" control condition (C), food was withheld for 60 minutes from all ewes, thereby controlling for the nonspecific effects of lack of food. FC induced a significant rise in the plasma cortisol concentration (p < 0.05) and increased the pawing number and rectal temperature compared with that in C (p < 0.1). The effects of either Pmp, Tyr-AVP or alphahCRF on these stress responses were analyzed. The rise in cortisol restored nearly to the control level by infusion of Pmp, Tyr-AVP or alphahCRF. The pawing number restored nearly to the control level by alphahCRF. The hyperthermia restored nearly to the control level by Pmp, Tyr-AVP. These data suggest that both endogenous CRH and AVP might be concerned with inducing physiological and behavioral stress responses to frustrating condition in sheep.

Corticotropin-releasing factor (CRF) is involved in the acute anorexic effect of alpha-melanocyte-stimulating hormone: a study using CRF-deficient mice

Alpha-melanocyte-stimulating hormone (alpha-MSH) and its receptors are critical and indispensable for maintaining appropriate feeding behavior and energy homeostasis in both mice and humans. Corticotropin-releasing factor (CRF) is a candidate for mediating the anorexic effect of alpha-MSH. In the present study, we examined whether CRF and its receptors are involved in the anorexic effect of alpha-MSH, using CRF-deficient (CRFKO) mice and a CRF receptor antagonist. Intracerebroventricular administration of NDP-MSH, a synthetic alpha-MSH analogue, suppressed food intake in wild-type (WT) mice. This effect was abolished by pretreatment with a non-selective CRF receptor antagonist, astressin, suggesting that the effect of alpha-MSH-induced anorexia was mediated by a CRF receptor. In CRFKO mice, administration with NDP-MSH did not affect food intake at an early phase (0-4h). In addition, CRF mRNA levels in the hypothalamus were significantly increased in NDP-MSH-treated mice. Therefore, our findings, using CRFKO, strongly support evidence that CRF is involved in the acute anorexic effect of alpha-MSH. On the other hand, NDP-MSH administered to CRFKO mice led to suppressed food intake at the late phase (4-12h), similar to the effect in WT mice. Further, NDP-MSH similarly reduced food intake during the late phase in all types of mice, including WT, CRFKO, and CRFKO with corticosterone replacement. The results would suggest that alpha-MSH-induced suppression of food intake at late phase was independent of glucocorticoids and CRF.

Induction of Fos-immunoreactivity in the rat brain following disinhibition of the dorsomedial hypothalamus

Activation of neurons in the dorsomedial hypothalamus (DMH) appears to play an important role in signaling the excitation of brain regions responsible for experimental fever and for many of the physiological and behavioral changes seen in experimental stress or anxiety in rats. Here, we examined the effect of disinhibition of the DMH by unilateral microinjection of bicuculline methiodide (BMI) on Fos expression in selected regions of the brain that have been implicated in anxiety and responses to stress and fever in rats. Disinhibition of the DMH resulted in dramatic increases in local Fos expression and also increased the numbers of Fos-positive neurons in the lateral septal nucleus and in both the parvocellular and magnocellular subdivisions of the paraventricular nucleus, with greater increases ipsilateral to the injection site in the DMH. However, microinjection of BMI had no significant effect on Fos expression in the bed nucleus of the stria terminalis, another forebrain area implicated in stress and anxiety. In the brainstem, disinhibition of the DMH increased Fos expression in the nucleus tractus solitarius and the ventrolateral medulla bilaterally with greater increases again ipsilateral to the site of the microinjection, and also in the midline rostral raphe pallidus. Thus, disinhibition of neurons in the DMH in conscious rats results in increases in Fos expression in selected forebrain and brainstem regions that have been implicated in stress-induced physiological changes, anxiety, and experimental fever.

Central type 2 corticotropin-releasing hormone receptor mediates hypothalamic-pituitary-adrenocortical axis activation in the rat

In an attempt to clarify the role of the type 2 corticotropin-releasing hormone (CRH) receptor (CRHR-2) in the brain in activation of the hypothalamic-pituitary-adrenocortical axis, we conducted experiments using male Wistar rats. First, an injection of urocortin-2 (7.5 microg) into the lateral ventricle resulted in transient increases in CRH heteronuclear RNA (hnRNA) in parvocellular paraventricular nucleus (PVN) and in plasma adrenocorticotropic hormone (ACTH), whereas sustained increases in arginine vasopressin (AVP) hnRNA and c-fos mRNA in the parvocellular PVN were observed as compared with vehicle treatment. Pretreatment with the selective CRHR-2 antagonist antisauvagine-30 (20 microg) into the lateral ventricle 15 min prior to agonist injection attenuated the stimulatory effects of urocortin-2 on the above-mentioned hypothalamic-pituitary-adrenal axis variables. These effects were similar or rather more potent than those induced by pretreatment with 50 microg of alpha-helical CRH. Second, we found longer-lasting increases in CRH and AVP hnRNA and c-fos mRNA in parvocellular PVN and in plasma ACTH following central administration of urocortin-3 (7.5 microg) than following urocortin-2. Pretreatment with antisauvagine-30 antagonized the effects of urocortin-3 on the above-mentioned variables. Finally, central administration of antisauvagine-30 as well as alpha-helical CRH profoundly attenuated restraint-stress-induced increases in AVP hnRNA. However, alpha-helical CRH, but not antisauvagine-30, attenuated restraint-stress-induced increases in CRH hnRNA in the PVN. Both antagonists transiently attenuated stress responses of c-fos mRNA in PVN and plasma ACTH. These results indicate that there is a CRHR-2-mediated mechanism in the brain that stimulates CRH- and AVP-producing neurons in the PVN which results in the promotion of plasma ACTH secretion.

Conditional CRF receptor 1 knockout mice show altered neuronal activation pattern to mild anxiogenic challenge

RATIONALE

Regional-specific corticotropin-releasing factor receptor 1 (CRF-R1) knockout mice have been generated recently as a tool to dissociate CNS functions modulated by this receptor. In these mice, CRF-R1 function is postnatally inactivated in the anterior forebrain including limbic brain structures but not in the pituitary leading to normal activity of the hypothalamic-pituitary-adrenocortical (HPA) axis under basal conditions and reduced anxiety-related behavior in the light-dark box and the elevated plus maze (EPM) as compared to wild-type (WT) mice (Müller et al., Nat Neurosci 6:1100-1107, 2003).

OBJECTIVE

To identify neurobiological correlates underlying this reduced anxiety-like behavior, the expression of c-Fos, an established marker for neuronal activation, which was examined in response to a mild anxiogenic challenge.

MATERIALS AND METHODS

Mice were placed for 10 min on the open arm (OA) of the EPM, and regional c-Fos expression was investigated by immunohistochemistry.

RESULTS

OA exposure enhanced c-Fos expression in both conditional CRF-R1 knockout and WT mice in a number of brain areas (39 of 55 quantified), including cortical, limbic, thalamic, hypothalamic, and hindbrain regions. The c-Fos response in conditional CRF-R1 knockout animals was reduced in a restricted subset of activated neurons (4 out of 39 regions) located in the medial amygdala, ventral lateral septum, prelimbic cortex, and dorsomedial hypothalamus.

CONCLUSIONS

These results underline the importance of limbic CRF-R1 in modulating anxiety-related behavior and suggest that reduced neuronal activation in the identified limbic and hypothalamic key structures of the anxiety circuitry may mediate or contribute to the anxiolytic-like phenotype observed in mice with region-specific deletion of forebrain CRF-R1.

Reduced hypothalamic vasopressin secretion underlies attenuated adrenocorticotropin stress responses in pregnant rats

We sought to explain decreased ACTH secretory responses to stress in pregnant rats by investigating hypothalamic CRH and vasopressin secretion and actions on anterior pituitary corticotrophs. In late pregnancy median eminence, CRH content was reduced (by 12%). Anterior pituitary proopiomelanocortin mRNA expression, measured by in situ hybridization but not radioimmunoassayed ACTH content, was also reduced (by 45% on d 21); CRH receptor (CRHR)1 mRNA expression was unaltered in pregnancy, but V1b receptor mRNA expression was reduced (by 19%). ACTH secretory responses, measured in jugular blood, to CRH (200 ng/kg iv) or vasopressin (1.7 microg/kg, iv) were reduced on d 21 vs. virgins (49% and 44%), but the response to combined CRH and vasopressin injection was intact. Either antalarmin (CRHR1 antagonist; 20 mg/kg ip) or dP(Tyr(Me)2),Arg-NH2(9))AVP (V1a/b antagonist; 10 microg/kg, iv) pretreatment reduced the ACTH secretory response to forced swimming (90 sec) in virgin rats (by 57% and 40%), but only antalarmin was effective in pregnant rats (53% decrease). In vitro, measuring ACTH secretion from acutely dispersed anterior pituitary cells showed increased corticotroph sensitivity in pregnancy to CRH and to CRH augmentation by vasopressin, attributable to increased intracellular cAMP action. Hence, in late pregnancy, reduced anterior pituitary CRHR1 or V1b receptor expression did not impair corticotroph responses to CRH or vasopressin. Rather, diminished secretagogue secretion in vivo accounts for reduced action of stress levels of exogenous CRH or vasopressin alone; the late pregnancy attenuated ACTH secretory response to swim stress is deduced to be due to reduced vasopressin release by parvocellular paraventricular nuclei neurones.

Physiological roles of urocortins, human homologues of fish urotensin I, and their receptors

Urocortin 1, a human homologue of fish urotensin I, together with its related-compounds (urocortins 2 and 3), comprises a distinct family of stress peptides. Urocortin 1 has a high affinity for both corticotropin-releasing factor (CRF) type 1 receptor (CRF1) and CRF type 2 receptor (CRF2), and urocortins 2 and 3 have a high affinity for CRF2, while CRF has a low affinity for CRF2 and a high affinity for CRF1. These differences of the binding affinity with receptors make the biological actions of these peptides. Besides the binding affinity with receptors, the limited overlap of the distribution of CRF and urocortins may also contribute to the differences of physiological roles of each peptide. Urocortins show 'stress-coping' responses such as anxiolysis and dearousal in the brain. In the periphery, recent studies show the potent effects of urocortins on the cardiovascular and immune systems. In this review article, we take a look over the series of peptides included in this family, especially in terms of the versatility of biological actions, along with the various characters of the receptors.

Single administration of interleukin-1 increased corticotropin releasing hormone and corticotropin releasing hormone-receptor mRNA in the hypothalamic paraventricular nucleus which paralleled long-lasting (weeks) sensitization to emotional stressors

Single exposure to the proinflammatory cytokine interleukin-1 induces sensitization of the adrenocorticotropin hormone and corticosterone responses to stressors weeks later (hypothalamus-pituitary-adrenal sensitization). Hypothalamus-pituitary-adrenal responses are controlled by corticotropin-releasing hormone and arginine-vasopressin secreted from parvocellular corticotropin-releasing hormone neurons of the hypothalamic paraventricular nucleus and may involve autoexcitatory feedback mechanisms. Therefore, we studied the temporal relationship between resting levels of corticotropin-releasing hormone, corticotropin-releasing hormone-R1 and arginine-vasopressin receptor (V1a, V1b) mRNAs in the paraventricular nucleus and the development of hypothalamus-pituitary-adrenal sensitization to an emotional stressor (novelty). The adrenocorticotropin hormone precursor molecule proopiomelanocortin hnRNA in the pituitary gland served as an index for acute activation. Single administration of interleukin-1 induced sensitization of the hypothalamus-pituitary-adrenal to novelty from 3 to 22 days later, but not after 42 days. Single administration of interleukin-1 induced biphasic increases in corticotropin-releasing hormone and corticotropin-releasing hormone-R1 mRNAs in the paraventricular nucleus: an early peak within 24 h, followed by a delayed (>7 days) increase that peaked after 22 days. Hypothalamic V1a and V1b mRNA levels were unaffected. In contrast, in the pituitary gland, there was an early decrease in corticotropin-releasing hormone-R1 mRNA (from 10.5 to 3 h after interleukin-1) and V1b receptor mRNA (3 to 6 h), which returned to control levels from 24 h onwards. Thus, interleukin-1-induced long-lasting hypothalamus-pituitary-adrenal sensitizations associated with prolonged activation of corticotropin-releasing hormone and corticotropin-releasing hormone-R1 mRNA expression in the paraventricular nucleus, but not with changes in the expression of proopiomelanocortin hnRNA or V1b receptor or corticotropin-releasing hormone R1 mRNAs in the pituitary gland. We propose that transient exposure to immune events can induce long-lasting hypothalamus-pituitary-adrenal sensitization, which at least in part involves long-term hypothalamic adaptations that enhance central corticotropin-releasing hormone signaling.

Regulation of corticotropin-releasing factor (CRF) type-1 receptor gene expression by CRF in the hypothalamus

We reported previously that acute stress and intracerebroventricular (i.c.v.) injection of corticotropin-releasing factor (CRF) increased neuronal activation and CRF type-1 receptor (CRFR-1) mRNA expression in the CRF-producing neurons of the parvocellular paraventricular nucleus (PVN) of the hypothalamus. In this study, to determine whether CRF can act directly on hypothalamic CRF neurons, thereby increasing CRFR-1 expression, microinjection of CRF into PVN neurons in vivo and primary cultures of dispersed rat fetal hypothalami in vitro were performed. Microinjection of 0.1 microg of CRF into the PVN significantly increased c-fos and CRFR-1 mRNA expression in the CRF-producing parvocellular PVN, 30 min or 180 min after injection, respectively. This effect was blocked by a CRF antagonist, alpha-helical CRF. CRF, when injected into the lateral ventricle at the same dose, increased neither CRFR-1 nor c-fos mRNA levels in the PVN. Primary culture of hypothalamic neurons revealed that CRFR-1 like immunoreactivity was located in CRF-containing neurons, and that the CRFR-1 mRNA level was significantly increased 4 h after incubation with 10(-8) M CRF. These results demonstrate that CRF directly affects hypothalamic neurons to increase CRFR-1 mRNA expression, providing evidence of a direct role for CRF in the regulation of CRFR-1 expression of hypothalamic neurons.

Neurochemical properties of the prolactin releasing peptide (PrRP) receptor expressing neurons: evidence for a role of PrRP as a regulator of stress and nociception

In addition to its stimulatory effect on prolactin release, the neuropeptide prolactin releasing peptide (PrRP) has been shown to be a mediator of the stress response. To analyze the neurochemical properties of the cells responsive to PrRP and involved in stress modulation, we examined PrRP receptor co-expression with two neuropeptides involved in stress, corticotropin releasing hormone (CRH) and enkephalin (ENK). We find that although PrRP receptor is highly expressed in the parvocellular division of the paraventricular nucleus of hypothalamus (PVN), the majority of the cells expressing PrRP receptor are neither CRH- nor ENK-positive. The only region where the PrRP receptor co-expresses extensively with CRH is the bed nucleus of the stria terminalis (BST). There is also a small number of cells positive for CRH and PrRP receptor in the central nucleus of amygdala (CEA), while the remaining PrRP receptor-positive cells co-express ENK. Furthermore we find that the PrRP receptor-expressing neurons in the brainstem parabrachial nucleus (PB) largely express ENK rather than CRH. From these results we propose a model in which PrRP modulates the hypothalamic-pituitary-adrenal axis through trans-synaptic modulation of hypothalamic CRH release rather than through direct activation of PVN neurons. We also suggest that PrRP may modulate nociception by virtue of its receptor's co-expression with ENK in PB. Our results provide a theoretical framework by which future studies examining the role of PrRP in brain could be elucidated.

Isolation rearing in the rat disrupts the hippocampal response to stress

Both human schizophrenia and the effects of isolation rearing in rats produce deficits in hippocampal and cortical functioning. This study was concerned with identifying changes associated with altered neuronal function in the rat hippocampus following isolation rearing. Rats were isolated from weaning at 21 days postnatal for 6 weeks and the hippocampal sensitivity to isolation rearing and stress were studied using c-fos immunohistochemistry and in vivo microdialysis. Isolation rearing altered neuronal activity measured by Fos-like immunoreactivity in the specific brain areas as measured by either increased or reduced expression. Basal neuronal activity in the ventral CA1 hippocampus in isolation-reared rats was notably higher compared to group-reared rats but markedly lower Fos-like immunoreactivity was found in the central and basolateral nuclei of the amygdala. Exposure to stress produced differential effects on neuronal activity in isolation-reared rats between the dorsal and ventral hippocampus, with increased Fos-like immunoreactivity in the dorsal hippocampus but lower Fos-like immunoreactivity in the ventral hippocampus compared to group-reared rats. These results indicate that isolation rearing may alter the relationship between hippocampal neuronal function in the dorsal and ventral hippocampus. An in vivo microdialysis study showed that systemically administered parachloroamphetamine (2.5 mg/kg, i.p.) enhanced extracellular 5-hydroxytryptamine (5-HT) in the dorsal hippocampus in group-reared but not in isolation-reared rats. Restraint stress had no effect on hippocampal extracellular 5-HT in group-reared rats but reduced levels in isolation-reared rats during the period of restraint. Inescapable mild footshock produced a marked increase in extracellular hippocampal 5-HT in group-reared but not isolation-reared rats. Overall the results provide extensive evidence that isolation rearing alters presynaptic 5-HT hippocampal function and that the neuronal response to stress is altered by isolation. Isolation rearing in the rat alters hippocampal function, including the serotonergic system, leading to changes in neurotransmitter systems in other brain areas. These changes may model aspects of human neurodevelopmental disorders such as schizophrenia.

Role of corticotropin-releasing factor, vasopressin and the autonomic nervous system in learning and memory

Learning and memory are essential requirements for every living organism in order to cope with environmental demands, which enables it to adapt to changes in the conditions of life. Research on the effects of hormones on memory has focused on hormones such as adrenocorticotropic hormone (ACTH), glucocorticoids, vasopressin, oxytocin, epinephrine, corticotropin-releasing factor (CRF) that are released into the blood and brain following arousing or stressful experiences. Most of the information have been derived from studies on conditioned behavior, in particular, avoidance behavior in rats. In these tasks, an aversive situation was used as a stimulus for learning. Aversive stimuli are associated with the release of stress hormones and neuropeptides. Many factors play a role in different aspects of learning and memory processes. Neuropeptides not only affect attention, motivation, concentration and arousal or vigilance, but also anxiety and fear. In this way, they participate in learning and memory processes. Furthermore, neuropeptides such as CRF and vasopressin modulate the release of stress hormones such as epinephrine. In turn, systemic catecholamines enhance memory consolidation. CRF and vasopressin are colocalized in neurons from the nucleus paraventricularis, which project to nuclei in the brainstem involved in autonomic regulation. The objective of this paper is to discuss the role of CRF, vasopressin, and the autonomic nervous system (ANS) in learning and memory processes. Both CRF and vasopressin have effects in the same direction on behavior, learning and memory processes and stress responses (release of catecholamines and ACTH). These neuropeptides may act synergistically or in a concerted action aimed to learn to adapt to environmental demands.

Connections of Barrington's nucleus to the sympathetic nervous system in rats

Barrington's nucleus (BN) has been considered a pontine center related exclusively to the control of pelvic parasympathetic activity. The present study demonstrates an anatomical linkage between BN and autonomic outflow to visceral targets innervated exclusively by the sympathetic division of the autonomic nervous system. Temporal analysis of infection after injection of pseudorabies virus (PRV), a retrograde transynaptic tracer, into two sympathetically innervated organs, the spleen and the kidney, revealed the presence of infected neurons in BN at early post-inoculation survival intervals. Immunohistochemical localization of PRV after spleen injections showed that a small subpopulation of BN neurons became labeled in a time frame coincident with the appearance of infected neurons in other brain regions known to project to sympathetic preganglionic neurons (SPNs) in the thoracic spinal cord; a larger number of infected neurons appeared in BN at intermediate intervals after PRV injections into the spleen or kidney. Coinjection of the retrograde tracer Fluoro-Gold i.p. and PRV into the spleen demonstrated that parasympathetic preganglionic neurons in the caudal medulla or lumbo-sacral spinal cord were not infected, indicating that infected BN neurons were not infected via a parasympathetic route. Thus, BN neurons become infected after PRV injections into the spleen or kidney either directly through BN projections to SPNs, or secondarily via BN projections to infected pre-preganglionic neurons. These results demonstrate an anatomical linkage, either direct or indirect, between BN and sympathetic activity. Because BN receives numerous inputs from diverse brain regions, the relation of BN with both branches of the autonomic nervous system suggests that this nucleus might play a role in the integration of supraspinal inputs relevant to the central coordination of sympathetic and parasympathetic activity.

Stress-induced C-fos expression in the rat locus coeruleus is dependent on neurokinin 1 receptor activation

These experiments examined the role of substance P-selective neurokinin 1 receptors in the restraint-induced activation of the rat locus coeruleus. Immunohistochemistry revealed high levels of neurokinin 1 receptor expression in the plasma membrane of tyrosine hydroxylase-positive locus coeruleus neurons. The selective neurokinin 1 receptor antagonists, RP 67580 (5 nmol) and L-760,735 (3.4 nmol), were administered intracerebroventricularly prior to restraint stress, and c-fos protein was measured as an index of locus coeruleus activation. Both antagonists attenuated the restraint-induced increase in locus coeruleus c-fos expression, whereas their inactive enantiomers were ineffective. These results suggest that neurokinin 1 receptors may mediate activation of locus coeruleus neurons during stress. Neurokinin 1 receptor antagonists may prove to be novel therapeutic compounds in the treatment of anxiety and depression.

Do centrally administered neuropeptides access cognate receptors?: an analysis in the central corticotropin-releasing factor system

To determine the extent to which centrally administered corticotropin-releasing factor (CRF) activates neurons that express CRF receptors (CRF-Rs), we followed the kinetics and distribution (relative to those of CRF-Rs) of Fos induction seen in response to intracerebroventricular (icv) injection of the peptide (1-10 microg). CRF provoked widespread Fos expression: its strength was dose-related, it peaked at 2 hr after injection, and it was antagonized in a dose-dependent manner by coinjection of CRF-R antagonists. The activation pattern closely mimicked the distribution of CRF-R1 mRNA, in including widespread Fos induction throughout the cortical mantle, in cell groups involved in sensory information processing, and in the cerebellum and several of its major afferents and targets. Dual labeling revealed extensive correspondence of CRF-stimulated Fos-immunoreactivity (Fos-ir) and CRF-R1 mRNA at these and other loci. Unique sites of CRF-R2 expression were relatively unresponsive to CRF but were more so after icv administration of urocortin (UCN), a new mammalian CRF-related peptide. Both CRF and UCN elicited activational responses in cell groups that are involved in central autonomic control but that express neither CRF-R, including the central amygdaloid and paraventricular hypothalamic nuclei, and brainstem catecholaminergic cell groups. The results support an ability of CRF-related peptides in the ventricular system to access receptor-expressing cells directly but leave open questions as to the basis for the recruitment of central autonomic structures, many of which have been identified as stress-related sites of CRF action.

Neuroendocrine and behavioral effects of CRH blockade and stress in male rats

Our previous data have shown that restraint (RT), a mild nonpainful stressor, acutely impairs nonsocial and social behavior in male rats. Corticotropin-releasing hormone (CRH) is a regulator of these behavioral responses. To evaluate whether CRH mediates the neuroendocrine and behavioral alterations present 24 h after restraint stress, we administered the CRH antagonist alpha-helical CRH(9-41) (alpha-hCRH) intracerebroventricularly to male rats and we compared its effects with those of saline. Twenty-four hours after treatment, nonsocial behaviors were significantly decreased by alpha-hCRH, this effect being independent of RT. Among social behaviors, only introductory activity showed significant differences as a result of both RT and alpha-hCRH. The concentrations of ACTH in the plasma and those of beta-endorphin in the anterior and neurointermediate lobes of the pituitary were affected by alpha-hCRH treatment. The effect on ACTH was simply related to the administration of the alpha-hCRH, while for beta-endorphin, significant interactions between alpha-hCRH and RT were found. On the whole, these results point to the role played by CRH in the control of neuronal mechanisms involved in the stress-induced effects.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Alcohol increases the expression of type 1, but not type 2 alpha corticotropin-releasing factor (CRF) receptor messenger ribonucleic acid in the rat hypothalamus

We investigated the ability of a moderately intoxicating dose of alcohol (3 g/kg, injected i.p. 3 h earlier) to up-regulate the genetic expression of CRF receptor type 1 (CRF-R1) and 2 (CRF-R2alpha) in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus as well as in the amygdala. The mRNA encoding CRF-R1 was not constitutively expressed in the PVN or the SON but was present in the amygdala. Alcohol selectively up-regulated CRF-R1 transcripts in the PVN. Basal levels of CRF-R2alpha transcripts were present in the limbic system and the ventromedial hypothalamic nucleus but were not altered by alcohol. We then determined whether the up-regulation of hypothalamic CRF-R1 mRNA levels was functionally connected to CRF-dependent pathways. We first showed that the i.c.v. injection of CRF significantly (P < 0.01) increased CRF-R1 but not CRF-R2alpha mRNA levels. We then injected the CRF antagonist, astressin, i.c.v. 30 min prior to alcohol, at a dose previously shown to completely block many CRF-dependent events in the brain, and found that it did not significantly interfere with-alcohol-induced gene expression of PVN CRF-R1. These results indicate that acute alcohol treatment selectively activates CRF-R1 in the endocrine hypothalamus and that this response does not appear to depend on the stimulation of CRF receptors. In contrast, no up-regulation of CRF-R1 or CRF-R2alpha gene expression was observed in extrahypothalamic regions thought to participate in the behavioral influence of alcohol.

Stress-induced expression of immediate early genes in the brain and peripheral organs of the rat

Stress causes rapid and transient expression of immediate early genes (IEGs) in the brain, and the monitoring of IEGs has enabled the visualization of the neurocircuitry of stress. Previous studies have postulated that stressors can be divided into two categories; processive and systemic. The neural circuits of brain activation differ between the two kinds of stressors. For example, processive stressors, such as immobilization (IMO), induce c-fos mRNA first in the cortical and limbic areas and then in the paraventricular hypothalamic nucleus (PVH), while c-fos expression in the PVH precedes that in other areas in animals subjected to systemic stressors. We further show that prior exposure to IMO stress for 6 days, or implantation of corticosterone pellets suppresses the induction of c-fos, fos B, jun B and NGFI-B, but not that of NGFI-A in the rat PVH. Plasma glucocorticoid may be an important factor regulating stress-induced IEG expression. It is well known that AP-1 and glucocorticoid receptors (GR) interact and suppress each other. Thus, decreased AP-1 levels in chronically stressed animals may help enhance the negative feedback effects of GR and prevent hypersecretion of glucocorticoid, which is implicated in the pathogenesis of stress-related diseases. IMO stress induces rapid expression of c-fos, c-jun and NGFI-A mRNAs in the heart and stomach. These were observed in the ventricular myocardium and coronary arteries, and in the epithelium, smooth muscles and arteries of the stomach after 30 min of IMO. IEG expression in the peripheral organs may provide a molecular basis for stress-induced psychosomatic disorders.

Region-specific immediate-early gene expression following the administration of corticotropin-releasing hormone in virgin and lactating rats

Central administration of corticotropin-releasing hormone (CRH) induces immediate-early gene (IEG) expression (c-fos and NGFI-B) in forebrain structures in a pattern similar to that observed following restraint stress. Lactating rats display modified neuroendocrine and behavioural responses to stress which have been hypothesized to be at least partially mediated through changes within the circuitry converging on the PVN, including CRH activated pathways. Quantitative measures of regional expression of c-fos and NGFI-B mRNA representative of two classical intracellular pathways, were used to define modification of the circuitry involved in the altered response to central CRH in the lactating female. Compared to saline controls, virgin female rats injected with 5 micrograms CRH i.c.v. displayed significantly increased immediate-early gene expression in the hypothalamic paraventricular nucleus (PVN), arcuate nucleus, lateral septum, bed nucleus of the stria terminalis, central, medial and cortical nuclei of the amygdala, and all subfields of the hippocampal formation. In lactating rats treated with CRH there was a significant increase in c-fos gene expression in the CeA and in the hippocampal subfields CA1, CA4 and dentate gyrus but not in the other areas examined. The i.c.v. administration of CRH significantly increased NGFI-B expression in the PVN, arcuate nucleus, medial amygdala and all hippocampal subfields of virgin rats. Lactating rats treated with CRH failed to show a significant increase in NGFI-B expression in the PVN, median eminence, arcuate nucleus, medial amygdala, CA2 and CA3 subfields of the hippocampus. These results further suggest that changes in specific neural circuits might at least partially underlie the modified responses to CRH and perhaps to stress in the lactating female.

Antisense oligonucleotides in neuroendocrinology: enthusiasm and frustration

Antisense oligodeoxynucleotides (ODN) offer the potential advantage to manipulate neuropeptide or neuropeptide receptor expression within the brain transiently and site-specifically, thus providing a tool for neuroendocrinological research into the physiological function of a particular neuropeptide system. In this study, various approaches are introduced which reveal that antisense ODN may exert acute, short-term effects on neuronal responsiveness to afferent stimuli, as well as long-term effects on neuropeptide/receptor protein availability in a given system depending on the duration of treatment. Short-term effects were seen in that oxytocin (OXT) and vasopressin (AVP) antisense ODN affected electrophysiological and secretory parameters of oxytocinergic and vasopressinergic neurons, respectively, as well as their ability to express the Fos protein in response to afferent stimulation a few hours after a single infusion into the hypothalamic supraoptic nucleus. In this study, two methodological approaches to study long-term effects of the antisense ODN are exemplified, in which antisense ODN directed against the mRNA coding for the neuropeptide itself or its receptor were used. The repeated infusion of corticotropin releasing hormone (CRH) antisense ODN into the paraventricular nucleus resulted in reduced immunoreactive CRH, but not AVP, in the external zone of the median eminence. Furthermore, in order to evaluate the receptor-mediated effects of CRH and AVP released locally within the paraventricular nucleus on adrenocorticotropin (ACTH) release from the pituitary, CRH receptor (and also AVP receptor) antisense ODN were repeatedly infused into the hypothalamic nuclei; this treatment resulted in an elevation of stimulated, but not basal, ACTH release into the blood. However, in addition to these obvious antisense effects, results are discussed which demonstrate sequence-unspecific effects of phosphorothioated ODN, suggesting that some of their mechanisms of action are not yet understood.

Activation of corticotropin-releasing factor in the limbic system during cannabinoid withdrawal

Corticotropin-releasing factor (CRF) has been implicated in the mediation of the stress-like and negative affective consequences of withdrawal from drugs of abuse, such as alcohol, cocaine, and opiates. This study sought to determine whether brain CRF systems also have a role in cannabinoid dependence. Rats were treated daily for 2 weeks with the potent synthetic cannabinoid HU-210. Withdrawal, induced by the cannabinoid antagonist SR 141716A, was accompanied by a marked elevation in extracellular CRF concentration and a distinct pattern of Fos activation in the central nucleus of the amygdala. Maximal increases in CRF corresponded to the time when behavioral signs resulting from cannabinoid withdrawal were at a maximum. These data suggest that long-term cannabinoid administration alters CRF function in the limbic system of the brain, in a manner similar to that observed with other drugs of abuse, and also induces neuroadaptive processes that may result in future vulnerability to drug dependence.

Corticotropin-releasing factor and systemic capsaicin-sensitive afferents are involved in abdominal surgery-induced Fos expression in the paraventricular nucleus of the hypothalamus

We previously reported that abdominal surgery induces Fos expression in specific hypothalamic and medullary nuclei and also causes gastric stasis. The gastric ileus is reduced by systemic capsaicin and abolished by central injection of corticotropin-releasing factor (CRF) antagonist. We studied the influence of systemic capsaicin and intracerebroventricular (i.c.v.) injection of the CRF antagonist, alpha-helical CRF9-41, on Fos expression in the brain 1 h after abdominal surgery in conscious rats using immunocytochemical detection. In control groups (vehicle s.c. or i.c.v.), abdominal surgery (laparotomy with cecal manipulation) performed under 7-8 min of enflurane anesthesia induced Fos staining in neurons of the spinal trigeminal, C1/A1 group, ventrolateral medulla, central amygdala, parabrachial nucleus, cuneate nucleus, nucleus tractus solitarii (NTS), paraventricular nucleus of the hypothalamus (PVN) and supraoptic nucleus (SON). Capsaicin (125 mg/kg s.c., 2 weeks before) or alpha-helical CRF9-41 (50 microg i.c.v., before surgery) reduced the number of Fos-positive cells by 50% in the PVN while not modifying the number of Fos-labelled cells in the other nuclei. These results indicate that capsaicin-sensitive primary afferents and brain CRF receptors are part of the pathways and biochemical coding through which abdominal surgery activates PVN neurons 1 h post surgery.

Permissive role of corticotropin-releasing factor in the acute stress-induced prolactin release in female rats

The present study examined the role of corticotropin-releasing factor (CRF) in the acute stress-induced release of prolactin (PRL) in ovariectomized estrogen-primed female rats. Acute immobilization stress induced a marked increase in serum PRL levels in animals treated with saline intraventricularly (i.c.v.). However, a prior icv injection of alpha-helical CRF(9-41), a CRF antagonist, completely eliminated the immobilization-induced PRL release in the majority of animals, providing evidence for involvement of CRF in the acute stress-induced PRL release. On the other hand, an i.c.v. injection of CRF did not affect basal PRL release at any dose in non-stressed animals, suggesting that the peptide plays a permissive role which enables other undefined stress mediator(s) to stimulate PRL release.