Extrahypothalamic Brain Research Articles

Effects of acute and chronic ketoconazole administration on hypothalamo–pituitary–adrenal axis activity and brain corticotropin-releasing hormone

We have been investigating the effects of ketoconazole on cocaine reward in rats for several years now. However, we recently confirmed that ketoconazole-induced changes in cocaine self-administration and reinstatement do not always correspond with decreases in plasma corticosterone, which suggests that other mechanisms must be underlying the behavioral effects that we observe. This experiment was therefore designed to determine the effects of acute, repeated and chronic ketoconazole administration on corticotropin-releasing hormone (CRH) content in hypothalamic and extra-hypothalamic brain sites in rats following the same dosing regimen that we use in our behavioral studies. Although ketoconazole significantly increased the concentration of ACTH in trunk blood, there were no significant effects on plasma cortisol, corticosterone or testosterone. There was also a significant increase in CRH content in the median eminence after the acute administration of ketoconazole that just failed to reach statistical significance following repeated or chronic administration. However, acute, repeated and chronic treatment with ketoconazole each significantly increased CRH content in the medial prefrontal cortex (MPC), but did not consistently affect the peptide in any other brain region studied. Since the MPC and CRH have been implicated in the neurobiology of cocaine, CRH-induced alterations in dopaminergic neurotransmission may play an important role in this peptide’s effects on cocaine responsiveness. Taken together with the results from previous studies, these data suggest that ketoconazole may affect cocaine reward, at least in part, through interactions with dopamine and CRH within the MPC.

Directional cues for arcuate NPY projections are present in the adult brain

Arcuate nucleus neuropeptide Y (NPY) neurons project within the hypothalamus and to several extrahypothalamic brain areas. Plasticity in the formation of arcuate NPY projections established postnatally may underlie the phenotypic characteristics of food intake and body weight. In this work we determined if directional cues for axonal outgrowth of NPY arcuate neurons exist in the adult brain. For this purpose, an embryonic (E15) arcuate nucleus of WT mice was grafted into the third ventricle of 2-week- and 2-month-old NPY knockout (KO) mice. One month after the transplantation, the distribution of NPY-positive terminals in the brains of NPY-KO mice was studied using immunohistochemistry. NPY-positive terminals were found inside of the grafted tissue as well as in the host hypothalamus, including the arcuate nucleus, the paraventricular and periventricular nuclei, the lateral hypothalamic and preoptic areas, and in extrahypothalamic areas such as the amygdala and the thalamic paraventricular nucleus. This pattern of distribution of NPY fibers was found in both groups of grafted mice. The brain areas reinnervated by NPY-positive terminals in the NPY-KO mice closely corresponded to the normal targets for the arcuate NPY neurons as revealed by the distribution of agouti gene-related protein immunoreactivity. Our data show that directional cues for NPY arcuate nucleus projections are present in the adult brain, suggesting their involvement in the formation of normal arcuate NPY connections and a possibility for their functional reconstruction.

Increased corticotropin-releasing hormone immunoreactivity in monoamine-containing pontine nuclei of depressed suicide men.

A number of clinical investigations and postmortem brain studies have provided evidence that excessive corticotropin-releasing hormone (CRH) secretion and neurotransmission is involved in the pathophysiology of depressive illness, and several studies have suggested that the hyperactivity in CRH neurotransmission extends beyond the hypothalamus involving several extra-hypothalamic brain regions. The present study was designed to test the hypothesis that CRH levels are increased in specific brainstem regions of suicide victims with a diagnosis of major depression. Frozen tissue sections of the pons containing the locus coeruleus and caudal raphe nuclei from 11 matched pairs of depressed suicide and control male subjects were processed for radioimmunocytochemistry using a primary antiserum to CRH and a ([125])I-IgG secondary antibody. The optical density corresponding to the level of CRH-immunoreactivity (IR) was quantified in specific pontine regions from the film autoradiographic images. The level of CRH-IR was increased by 30% in the locus coeruleus, 39% in the median raphe and 45% in the caudal dorsal raphe in the depressed suicide subjects compared to controls. No difference in CRH-IR was found in the dorsal tegmentum or medial parabrachial nucleus between the subject groups. These findings reveal that CRH-IR levels are specifically increased in norepinephrine- and serotonin-containing pontine nuclei of depressed suicide men, and thus they are consistent with the hypothesis that CRH neurotransmission is elevated in extra-hypothalamic brain regions of depressed subjects.

Central oxytocinergic neurotransmission: a drug target for the therapy of psychogenic erectile dysfunction.

A group of oxytocinergic neurons originating in the paraventricular nucleus of the hypothalamus and projecting to extrahypothalamic brain areas (e.g. hippocampus, medulla oblongata and spinal cord) control penile erection. Activation of these neurons by dopamine and dopamine agonists, excitatory amino acids (N-methyl-D-aspartic acid) or oxytocin itself, or by electrical stimulation leads to penile erection, while their inhibition by GABA and GABA agonists or by opioid peptides and opiate-like drugs inhibits this sexual response. The activation of oxytocinergic neurons in the paraventricular nucleus by dopamine, oxytocin and excitatory amino acids is apparently secondary to the activation of nitric oxide (NO) synthase. NO in turn activates, by a mechanism that is as yet unidentified, the release of oxytocin from oxytocinergic neurons in extrahypothalamic brain areas. Several peptide analogues of hexarelin, a growth hormone releasing peptide, also induce penile erection when injected into the paraventricular nucleus and, to a lesser extent, systemically, apparently by acting on a specific receptor to activate oxytocinergic neurons as shown for the above drugs and oxytocin. Paraventricular oxytocinergic neurons and mechanisms similar to those reported above are also involved in the expression of penile erection in physiological contexts, namely when penile erection is induced in the male by the presence of an inaccessible receptive female, which is considered a model for psychogenic impotence in man, as well as during copulation. These findings show that paraventricular oxytocinergic neurons projecting to extra-hypothalamic brain areas and to the spinal cord are a likely target for the treatment of erectile dysfunction of central origin.

Correlation of estrogen β-receptor messenger RNA with endogenous levels of plasma estradiol and progesterone in the female rat hypothalamus, the bed nucleus of stria terminalis and the medial amygdala

Estrogen receptor β (ERβ) has been previously mapped in the rat central nervous system. This study aims to explore the regulation of ERβ mRNA as it is expressed in the intact and cycling female rat brain. Young adult female rats (90+ day, N=20) were screened for estrous phases via vaginal cytology and sacrificed. Brains and blood were collected and processed for in situ hybridization and estradiol (E2) and progesterone (P4) hormone assays, respectively. ERβ mRNA levels exhibited significant correlations with ovarian steroid ratios (E2/P4) in various brain regions, including the bed nucleus of stria terminalis, the medial nucleus of amygdala, and the anteroventral periventricular nuclei but not the paraventricular and the supraoptic nuclei or the preoptic area of the hypothalamus. No regulatory changes were detected in the cortex. Specifically, in the affected regions, higher P4 levels were significantly correlated with higher ERβ mRNA expression. In contrast, there was a tendency for higher E2 levels to be correlated with lower ERβ mRNA expression, but this tendency reached significance only in the bed nucleus of stria terminalis. These results suggest that ERβ mRNA is regulated in the intact and cycling female rat hypothalamic as well as extrahypothalamic brain regions, and the circulating ovarian hormones play a critical role.

Sex differences in the regulation of tyrosine hydroxylase gene transcription by estrogen in the locus coeruleus of TH9-LacZ transgenic mice

Although estrogen is recognized increasingly as having an important role in modulating extrahypothalamic brain function, the mechanisms through which this occur are not well established. The norepinephrine (NE) neurons of the locus coeruleus provide an important neuromodulatory influence upon multiple neural networks throughout the brain and estrogen has been implicated in their regulation. Using a tyrosine hydroxylase (TH) promoter-LacZ transgenic mouse model, which enables rates of TH gene transcription to be examined in vivo, we have examined here whether estrogen regulates expression of the TH gene in the locus coeruleus of males and females. Optical area measurements of Xgal reaction product in the locus coeruleus revealed that gonadectomy exerted opposite effects on TH gene transcription in males and females; transgene expression was increased in males ( P<0.01) but reduced in females ( P<0.05). Estrogen reversed these effects in both sexes by suppressing gene expression in males ( P<0.05) but elevating it in the female ( P<0.05). These studies reveal a marked and unexpected sex difference in the regulation of TH gene activity in the mouse. While estrogen in the male, synthesized from circulating testosterone, suppresses TH gene transcription, estrogen in the female enhances TH promoter activity. The present results indicate that estrogen may exert very different sex-dependent effects upon the biosynthesis of NE within the locus coeruleus.

Developmental sex differences in glutamic acid decarboxylase (GAD 65) and the housekeeping gene, GAPDH

Previous work has demonstrated that the GABAergic system is involved in sexual differentiation of the rodent hypothalamus. The present study was designed to further examine this involvement by investigating developmental sex differences in GAD 65 protein levels in hypothalamic and extrahypothalamic brain regions known to be sexually dimorphic in adulthood. Brain nuclei were micro-dissected and GAD 65 protein levels were quantified using western immunoblotting. Sex differences in levels of GAD 65 were found in the dorsomedial nucleus and preoptic area of the hypothalamus and also the medial amygdaloid nucleus and CA1 subfield of the hippocampus. Unexpectedly, there were sex differences in protein levels of the housekeeping gene, GAPDH, cautioning against the use of GAPDH for standardizing protein samples during western immunoblotting.

Distribution of estrogen receptor β immunoreactivity in the rat central nervous system

The discovery of estrogen receptor beta (ER beta) and subsequent localization of its mRNA in the rat central nervous system (CNS) has provided new insights about estrogen action in brain. A critical step in understanding the role of ER beta is demonstrating that the mRNA is translated into functional protein. The present study used a new ER beta-specific polyclonal antiserum (Z8P) and immunocytochemistry (ICC) to investigate the distribution of ER beta in the rat CNS. Ovariectomized female rats were perfusion fixed, and free-floating sections were incubated with Z8P. After visualization with a standard ABC method, nuclear immunoreactivity was seen in neurons throughout the brain, including the olfactory nuclei, laminae IV-VI of the cerebral cortex, medial septum, preoptic area, bed nucleus of the stria terminalis, supraoptic nucleus, paraventricular nucleus, zona incerta, medial and cortical amygdaloid nuclei, cerebellum, nucleus of the solitary tract, ventral tegmental area, and spinal trigeminal nucleus. Moreover, the results of a double-label ICC/ in situ hybridization study revealed that ER beta mRNA and immunoreactivity were colocalized in neurons of the brain, thus confirming the specificity of the antiserum. Through the use of Western blot analysis, Z8P was shown to recognize in vitro translated ER beta, but not ER alpha, as well as a 60-kDa protein from rat granulosa cells and ovary extracts. The results of these studies have demonstrated that (1) ER beta mRNA is translated into immunoreactive protein throughout the rat brain, and (2) ER beta resides in the cell nucleus. Together, these data provide an anatomic foundation for future studies and advance our understanding of estrogen action in hypothalamic and extrahypothalamic brain regions.

Water deprivation upregulates the three calmodulin genes in exclusively the supraoptic nucleus of the rat brain

Calmodulin (CaM), the ubiquitous intracellular calcium-binding protein, is coded by three bona fide CaM genes (CaM I, CaM II and CaM III) in mammals. They code for the same protein and are transcribed at particularly high levels in the brain, where CaM plays an essential role in basic neuronal functions. In this study, the expression of the three CaM genes in response to osmotic stimuli by water deprivation was investigated in the rat brain, with particular interest as concerns the hypothalamic magnocellular nuclei. CaM mRNA levels were determined by quantitative in situ hybridization autoradiography with gene-specific [ 35 S ]cRNA probes. In response to osmotic challenge, it was found that upregulation of the three CaM genes participates in the activation of the hypothalamo-hypophyseal system in the supraoptic nucleus (SON) (126% to 169%), but not in the magnocellular part of the paraventricular hypothalamic nucleus (PVN) (−10%). CaM mRNA levels decreased by 10%–15% in the suprachiasmatic nucleus (SCh) and many other extrahypothalamic brain areas. The opposite responses of the CaM gene expression in the SON and the magnocellular part of the PVN suggest a functional difference between them. Moreover, the significantly different magnitudes of the changes in the CaM mRNA levels in the SON nucleus (138%, 126% and 169% for CaM I, CaM II and CaM III, respectively) exemplify the precise differential control of the CaM gene expression in the brain.

Brain thyrotropin-releasing hormone content varies through amygdaloid kindling development according to afterdischarge frequency and propagation.

Thyrotropin-releasing hormone (TRH), present in extra hypothalamic brain areas, has been proposed to have neuromodulatory functions and to be susceptible to change by electrical stimulation paradigms. We measured TRH concentrations of several brain areas during kindling development before its establishment and determined whether the changes detected in TRH levels were related to the behavioral stages of kindling, the number of stimulations required to reach these stages and, with the electrophysiological parameters characteristic of this paradigm (amygdaloid afterdischarge (AD) frequency, duration, and propagation). Male Wistar rats were implanted stereotaxically with indwelling bipolar electrodes in the basolateral nucleus of the amygdala and with two stainless-steel electrodes epidurally in frontal cortex. Amygdaloid kindling was induced by daily electrical stimulation; AD frequency and duration were recorded and analyzed throughout the development of kindling. TRH was extracted from several regions and quantified by radioimmunoassay (RIA). Modifications in TRH concentrations were detected, depending on the region assayed, from stage II of kindling. A positive correlation was noted between the levels of TRH and the frequency and propagation of AD, but not with the number of stimulations. The rate of change in TRH concentration in relation to AD frequency or duration was highest in frontal cortex followed by hippocampus and amygdala. A graded response was noted in the increase in TRH concentration dependent on the increase of AD frequency and propagation. The rate of response correlated with the region's epileptogenic susceptibility.

The neuropharmacology of yawning.

Yawning is a phylogenetically old, stereotyped event that occurs alone or associated with stretching and/or penile erection in humans and in animals from reptiles to birds and mammals under different conditions. Although its physiological function is still unknown, yawning is under the control of several neurotransmitters and neuropeptides at the central level as this short overview of the literature on the neurochemistry of yawning shows. Among these substances, the best known are dopamine, excitatory amino acids, acetylcholine, serotonin, nitric oxide, adrenocorticotropic hormone-related peptides and oxytocin, that facilitate yawning and opioid peptides that inhibit this behavioral response. Some of the above compounds interact in the paraventricular nucleus of the hypothalamus to control yawning. This hypothalamic nucleus contains the cell bodies of oxytocinergic neurons projecting to extra-hypothalamic brain areas that play a key role in the expression of this behavioral event. When activated by dopamine, excitatory amino acids and oxytocin itself, these neurons facilitate yawning by releasing oxytocin at sites distant form the paraventricular nucleus, i.e. the hippocampus, the pons and/or the medulla oblongata. Conversely, activation of these neurons by dopamine, oxytocin or excitatory amino acids, is antagonized by opioid peptides, that, in turn, prevent the yawning response. The activation and inhibition, respectively of these oxytocinergic neurons is related to a concomitant increase and decrease, respectively, of paraventricular nitric oxide synthase activity. However, other neuronal systems in addition to the central paraventricular oxytocinergic neurons are involved in the control of yawning, since they do not seem to be involved in the expression of yawning induced by the stimulation of acetylcholine or serotoninergic receptors, nor by adrenocorticotropic hormone (ACTH) and related peptides. Nitric oxide is also involved in the induction of yawning by the latter compounds and neuronal links, for instance between dopamine and acetylcholine and dopamine and serotonin, seem to be involved in the yawning response. Finally, other neurotransmitters, i.e. gamma-aminobutyric acid (GABA) and noradrenaline, and neuropeptides, i.e. neurotensin and luteinizing hormone-releasing hormone (LH-RH), influence this behavioral response. In conclusion, in spite of some recent progress, little is known of, and more has to be done to identify, the neurochemical mechanisms underlying yawning at the central level.

Increased corticotropin-releasing factor immunoreactivity in select brain sites following kainate-elicited seizures

The literature has focused on the localization, regulation and function of corticotropin-releasing factor (CRF)-expressing neurons localized in the paraventricular nucleus (PVN) of hypothalamus. However, less information is available on the expression, regulation, and function of CRF at extrahypothalamic sites. The current study examined the induction of CRF in extrahypothalamic brain sites following generalized clonic seizures induced by kainic acid. At 24 h post seizure onset, there was a marked increase of CRF immunolabeled perikarya in select brain areas, which contained little, if any, CRF in control brains. This CRF-like labeling was observed in olfactory structures such as the main olfactory bulb (internal granular layer), anterior olfactory nucleus, and deep layers of piriform cortex. Other sites of increased CRF-like immunoreactivity included the tenia tecta, inner layers of cingulate cortex, lateral septum, dorsal endopiriform nucleus, fundus striatum, and nucleus of the lateral olfactory tract. Additionally, CRF-like labeling was atypically increased in the amygdala (lateral and basolateral amygdaloid nuclei) and hippocampal formation (pyramidal cells of regions CA1/CA3 and polymorph cells within the dentate hilus). An association between the increased CRF immunoreactivity and neuropathological processes, characteristic of this seizure model, is hypothesized and discussed.

Physiological and neurochemical aspects of corticotropin-releasing factor actions in the brain: the role of the locus coeruleus.

Corticotropin-releasing factor (CRF) is both a major regulator of the hypothalamo-pituitary-adrenal (HPA) axis and the activity of the autonomic nervous system. Besides, it exerts numerous effects on other physiological functions such as appetite control, motor and cognitive behavior and immune function. The basis for these effects is constituted by its distribution in hypothalamic and extra-hypothalamic brain areas, the latter being represented by limbic structures such as the central nucleus of the amygdala or by brain stem neurons such as the locus coeruleus (LC) or nucleus of the solitary tract (NTS). The effects of CRF are mediated through recently described CRF-receptor subtypes, whose molecular biology, biochemistry and pharmacological regulation are discussed in detail. In the second part of this review, we will focus on the physiology of CRF-systems in the brain, with a particular emphasis on cardiovascular regulation, respiration, appetite control and stress-related behavior. Finally, the role of the locus coeruleus in the control of CRF-mediated behavioral activities is discussed. The interaction of noradrenergic and CRF-neurons clearly implies that CRF appears to directly activate LC neurons in a stressful situation, thus ultimately coordinating the bodily response to a stressful stimulus.

N-Methyl- d-aspartic acid-induced penile erection and yawning: role of hypothalamic paraventricular nitric oxide

A dose of N-methyl- d-aspartic acid (NMDA, 50 ng) that induces penile erection and yawning when injected into the paraventricular nucleus of the hypothalamus, increased the concentration of NO 2 − from 1.10±0.28 μM to 7.32±1.12 μM and of NO 3 − from 4.96±0.69 μM to 10.5±1.61 μM in the paraventricular dialysate obtained from male rats by in vivo microdialysis. NO 2 − concentration was not increased by (±)-α-(amino)-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA, 100 ng) or by trans-(±)-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD) (100 ng), which were unable to induce these behavioral responses. N-Methyl- d-aspartic acid effect on NO 2 − concentration, penile erection and yawning was prevented by dizolcipine (MK-801) (10–100 ng) or by the nitric oxide synthase inhibitor N G-nitro- l-arginine methyl ester (20 μg), but not by the oxytocin receptor antagonist [d(CH 2) 5,Tyr(Me) 2,Orn 8]vasotocin (100 ng), or by the guanylate cyclase inhibitor methylene blue (20 μg) given in the paraventricular nucleus 15 min before N-methyl- d-aspartic acid or by the dopamine receptor antagonist haloperidol (0.5 mg/kg) given intraperitoneally 30 min before N-methyl- d-aspartic acid. In contrast, the nitric oxide scavenger hemoglobin (20 μg) given in the paraventricular nucleus prevented N-methyl- d-aspartic acid-induced NO 2 − concentration increase, but was unable to prevent penile erection and yawning. The results suggest that N-methyl- d-aspartic acid induces penile erection and yawning by increasing nitric oxide synthase activity in the paraventricular nucleus of the hypothalamus, possibly in the cell bodies of oxytocinergic neurons projecting to extra-hypothalamic brain areas and mediating these behavioral responses.

Concomitant infusion of ovine corticotropin-releasing hormone does not prevent suppression of the hypothalamus-pituitary-adrenal axis by dexamethasone in male rats.

Glucocorticoids (GCs) suppress the hypothalamus-pituitary-adrenal (HPA) axis at various sites including hypothalamus, pituitary and extrahypothalamic brain. Previous studies have shown that corticotropin-releasing hormone (CRH) and vasopressin facilitate the recovery of HPA axis suppressed by GCs. In this study, we investigate whether the concomitant continuous infusion of CRH may prevent the suppression of HPA axis by GCs. Groups of male Wistar rats weighing 140 to 160 g were implanted subcutaneously with Alzet osmotic pump for delivery of dexamethasone (DEX), 2 micrograms/h and/or CRH, 0.66 microgram/h. Control rats were implanted with sialistic tube of similar size. Rats were decapitated 3 or 7 days after osmotic pump implantation. In spite of the suppression of plasma corticosterone, the body weight (BW), adrenal weight (AW), plasma corticotropin (ACTH) and pituitary ACTH content of rats treated with DEX for 3 days were not significantly different from those of control rats. Concomitant infusion of ovine CRH (oCRH) and DEX for 3 days caused impaired BW gain, adrenal atrophy in addition to further reduction of plasma corticosterone. Treatment with DEX and/or oCRH for 7 days caused further suppression of HPA axis as shown by reduced pituitary ACTH content. In conclusion, simultaneous infusion of oCRH and DEX does not prevent and may even worsen HPA axis suppression by DEX.

Estrogen inhibits hypothalamic pro-opiomelanocortin gene expression in hypothalamic neuronal cultures.

Many in vitro studies show estrogen regulation of the hypothalamic pro-opiomelanocortin (POMC) system, including a decrease in hypothalamic POMC mRNA after estradiol treatment. Because such in vivo experiments do not allow one to determine whether peripheral, interacting systems or extra-hypothalamic brain regions are involved in this regulation, we sought to establish whether estrogen acts directly in hypothalamus to decrease POMC mRNA. Using an in vitro approach, we studied effects of estradiol (E2) on POMC/cyclophilin mRNA concentrations (RNAse protection assays) in neuronal cultures derived from day 17 fetal rat hypothalamus. Chemically defined medium was deprived of progesterone for 2 days prior to E2 treatment and for the duration of the study. E2 (10(-13)-10(-9) M) dose-dependently decreased POMC mRNA concentrations during a 2-day treatment. Whereas the lowest dose (10(-13) M) of E2 resulted in a statistically significant 44% decrease in POMC mRNA concentrations relative to control cultures, this inhibitory effect was lost because higher doses (10(-11) and 10(-9) M) did not produce statistically significant decrements (22 and 16%, respectively) in POMC mRNA concentrations. Additional time course studies revealed that this decrease in POMC mRNA can be seen as early as 4 h after E2 (10(-13) M) treatment. We conclude that E2 inhibition of POMC mRNA concentrations in hypothalamic neuronal cultures indicates that this inhibition can occur directly in hypothalamus.

The effects of brain and C-type natriuretic peptides on corticotropin-releasing factor in brain of rats

The central corticotropin-releasing factor (CRF)-ergic system plays a critical role in anxiety and other behavioral stress responses. It has been shown that atrial (ANP), brain (BNP) and C-type (CNP) natriuretic peptides exert anxiolytic-like effects in behavioral studies. Our previous findings demonstrated that various doses of centrally administered ANP selectively altered the CRF content in different brain areas. In the present study, CRF immunoreactivity was determined in hypothalamic and extrahypothalamic brain regions after central injection of BNP or CNP in rats. A high dose (400 ng) of BNP significantly increased the CRF-like immunoreactivity (CRF-LI) in the hypothalamus and amygdala, while only a tendency towards an increase was found in the hippocampus. In the hypothalamus, the CRF-LI decreased after a high dose (400 ng) of CNP. The CRF-LI increased in the basal forebrain after a low dose (100 ng) of CNP. These results suggest that CRF may be involved in the mediation of some neuroendocrine and behavioral responses to BNP and CNP.

Oxytocin increases nitric oxide production in the paraventricular nucleus of the hypothalamus of male rats: correlation with penile erection and yawning

A dose of oxytocin (50 ng i.c.v.) that induces penile erection and yawning, increased the concentration of NO2− from 0.98±0.29 to 4.2±0.79 μM and of NO3− from 5.6±0.33 to 12.03±0.99 μM in the dialysate from the paraventricular nucleus of the hypothalamus of male rats, as measured by in vivo microdialysis. NO2− concentration was also increased by [Thr4,Gly7]-oxytocin (100 ng i.c.v.) and oxytocin(1–8) (1 μg i.c.v.), which also induced penile erection and yawning, but not by oxytocin(1–6) (1 μg i.c.v.) or oxytocin(7–9) (1 μg i.c.v.), which were unable to induce these behavioral responses. The oxytocin effect on NO2− concentration, penile erection and yawning was prevented by the oxytocin receptor antagonist, d(CH2)5Tyr(Me)-Orn8-vasotocin (1 μg i.c.v.), or by the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (200 μg i.c.v.), but not by the dopamine receptor antagonist, haloperidol (0.5 mg/kg i.p.). The nitric oxide scavenger, hemoglobin (200 μg i.c.v.), prevented oxytocin-induced NO2− concentration increase, but was unable to prevent penile erection and yawning. Methylene blue (300 μg i.c.v.), an inhibitor of guanylate cyclase, was ineffective on oxytocin-induced NO2− concentration increase, but prevented the behavioral responses. The results suggest that oxytocin induces penile erection and yawning by increasing nitric oxide synthase activity in the cell bodies of oxytocinergic neurons projecting to extra-hypothalamic brain areas and mediating the behavioral responses.

Time-dependent alterations in corticotropin-releasing factor-like immunoreactivity in different brain regions after acute cocaine administration to rats.

Recent data from various laboratories suggest that the activation of endogenous corticotropin-releasing factor (CRF) may contribute to the behavioral and neuroendocrine effects of cocaine. In the present study, the time-dependent variations in CRF-like immunoreactivity (CRF-LI) in the hypothalamus and several extrahypothalamic brain regions were determined after acute cocaine administration to handled rats. The intraperitoneal injection of 7.5 mg/kg cocaine led to a significantly decreased CRF-LI level in the basal forebrain and to a significantly increased CRF-LI level in the amygdala 60 min after administration, while the CRF-LI content was decreased in the hypothalamus and in the hippocampus 180 min after cocaine treatment. These results suggest that the durations of the effects of cocaine on CRF-LI are in the brain region-specific, which might contribute to the mediation of the diverse behavioral and neuroendocrine effects of cocaine.

Regulation of ingestion by CRF and bombesin-like peptides: distinct meal-related peptide level changes.

Bombesin (BN) and corticotropin-releasing factor (CRF) have both been shown to induce satiety in rats when injected centrally. The present study assessed temporal changes in the utilization of BN- and CRF-like peptides in relationship to feeding status, fluctuations that may indicate the physiological participation of these peptides in the regulation of feeding. Alterations in the endogenous levels of CRF- and BN-like peptides associated with the initial spontaneous meal of the nocturnal cycle were determined in 15 hypothalamic and extrahypothalamic brain nuclei in the following three groups of rats: 1) a preprandial group consisting of rats killed before feeding, 2) a prandial group consisting of rats killed during the meal, and 3) a postprandial group consisting of rats killed 8-12 min after the meal. Findings revealed site-specific changes in BN and CRF content during the course of a meal. During ingestion, levels of BN were significantly elevated at the paraventricular, arcuate, and dorsomedial nuclei of the hypothalamus and reduced at the nucleus accumbens. In the case of CRF, feeding-related alterations were observed at the lateral (LH) and ventromedial (VMH) hypothalamic nuclei and at the central nucleus of the amygdala (Ce). At the LH, CRF content decreased after feeding compared with preprandial levels. At the VMH, CRF levels were significantly elevated both before and after food intake compared with prandial levels. In contrast, at the Ce marked increases in CRF concentrations were observed during ingestion. These data demonstrate, for the first time, site-specific fluctuations of BN and CRF in relationship to the animal's feeding status and suggest that these peptides may play a role in the regulation of food intake.