Central alpha1-adrenergic system in behavioral activity and depression

Central alpha(1)-adrenoceptors are activated by norepinephrine (NE), epinephrine (EPI) and possibly dopamine (DA), and function in two fundamental and opposed types of behavior: (1) positively motivated exploratory and approach activities, and (2) stress reactions and behavioral inhibition. Brain microinjection studies have revealed that the positive-linked receptors are located in eight to nine brain regions spanning the neuraxis including the secondary motor cortex, piriform cortex, nucleus accumbens, preoptic area, lateral hypothalamic area, vermis cerebellum, locus coeruleus, dorsal raphe and possibly the C1 nucleus of the ventrolateral medulla, whereas the stress-linked receptors are present in at least three areas including the paraventricular nucleus of the hypothalamus, central nucleus of the amygdala and bed nucleus of the stria terminalis. Recent studies utilizing c-fos expression and mitogen-activated protein kinase activation have shown that various diverse models of depression in mice produce decreases in positive region-neural activity elicited by motivating stimuli along with increases in neural activity of stress areas. Both types of change are attenuated by various antidepressant agents. This has suggested that the balance of the two networks determines whether an animal displays depressive behavior. A central unresolved question concerns how the alpha(1)-receptors in the positive-activity and stress systems are differentially activated during the appropriate behavioral conditions and to what extent this is related to differences in endogenous ligands or receptor subtype distributions.     

Effects of clonidine injections into the bed nucleus of the stria terminalis on fear and anxiety behavior in rats

Emotions such as fear and anxiety are mediated by a neural network containing nuclei like the amygdala, the bed nucleus of the stria terminalis and the periaqueductal gray. Noradrenaline is a neurotransmitter closely connected with the processing of stimuli eliciting these emotions. The bed nucleus of the stria terminalis contains the highest density of noradrenaline within the brain. In the present study, we investigated effects of injections of the noradrenergic alpha2-adrenoceptor agonist clonidine into the bed nucleus of the stria terminalis on learned and unlearned fear (anxiety) in rats on different animal models of fear and anxiety: acquisition and expression of fear-potentiated startle, sensitization of the acoustic startle response by foot shocks and light-enhanced startle. Clonidine injections disrupted acquisition and expression of fear-potentiated startle, as well as light-enhanced startle, whereas sensitization was not affected. These results indicate that noradrenaline within the bed nucleus of the stria terminalis mediates both fear and anxiety. We suggest that there is rather a neurochemical than a neuroanatomical dissociation between learned fear and anxiety as hypothesized by Walker and Davis (Walker, D.L. and M. Davis, 1997b, Double dissociation between the involvement of the bed nucleus of the stria terminalis and the central nucleus of the amygdala in startle increases produced by conditioned versus unconditioned fear, J. Neurosci. 17, 9375-9383.).     

Role of the bed nucleus of the stria terminalis versus the amygdala in fear,stress, and anxiety

The bed nucleus of the stria terminalis is a limbic forebrain structure that receives heavy projections from, among other areas, the basolateral amygdala, and projects in turn to hypothalamic and brainstem target areas that mediate many of the autonomic and behavioral responses to aversive or threatening stimuli. Despite its strategic anatomical position, initial attempts to implicate the bed nucleus of the stria terminalis in conditioned fear were largely unsuccessful. Recent studies have shown, however, that the bed nucleus of the stria terminalis does participate in certain types of anxiety and stress responses. In this work, we review these findings and suggest from the emerging pattern of evidence that, although the bed nucleus of the stria terminalis may not be necessary for rapid-onset, short-duration behaviors which occur in response to specific threats, the bed nucleus of the stria terminalis may mediate slower-onset, longer-lasting responses that frequently accompany sustained threats, and that may persist even after threat termination.     

Acetaldehyde, a major constituent of tobacco smoke, enhances behavioral, endocrine, and neuronal responses to nicotine in adolescent and adult rats.

We have previously shown that acetaldehyde, a constituent of tobacco smoke, increases nicotine self-administration in adolescent, but not adult, rats. The aim of this study was to determine whether acetaldehyde influences other behavioral, endocrine, or neuronal responses to nicotine at either age. Juvenile (postnatal day (P) 27) and adult (P90) male Sprague-Dawley rats were treated with saline, acetaldehyde (16 microg/kg/injection x 2, i.v.), nicotine (30 microg/kg/injection x 2, i.v.) or a combination of acetaldehyde and nicotine. Locomotion and center time were evaluated for 30 min in a novel open field, before measurement of plasma corticosterone levels and brain c-fos mRNA. Nicotine increased locomotor activity in juveniles but decreased it in adults; in contrast, center time was increased at both ages. Acetaldehyde potentiated nicotine's locomotor effects, but not center time. Nicotine induced c-fos expression in the bed nucleus of the stria terminalis, the central nucleus of the amygdala (CeA), nucleus accumbens, and the superior colliculus (SC) at both ages, whereas it activated the hypothalamic paraventricular nucleus (PVN) and consequent corticosterone secretion only in adults. Acetaldehyde potentiated nicotine-induced c-fos in CeA and SC, and activation of PVN c-fos expression/plasma corticosterone release; however, this drug interaction was only observed in behaviorally tested animals, not those that were minimally stressed. Thus, acetaldehyde may modulate the interaction of nicotine and stress. Although pharmacokinetic studies showed that acetaldehyde did not change nicotine levels in either brain or serum, nicotine penetration into the brain was slower in juveniles as compared to adults.     

Brain pattern of histone H3 phosphorylation after acute amphetamine administration: its relationship to brain c-fos induction is strongly dependent on the particular brain area

Recent evidence strongly suggests a critical role of chromatin remodelling in the acute and chronic effects of addictive drugs. We reasoned that Immunohistochemical detection of certain histone modifications may be a more specific tool than induction of immediate early genes (i.e. c-fos) to detect brain areas and neurons that are critical for the action of addictive drugs. Thus, in the present work we studied in adult male rats the effects of a high dose of amphetamine on brain pattern of histone H3 phosphorylation in serine 10 (pH3S(10)) and c-fos expression. We firstly observed that amphetamine-induced an increase in the number of pH3S(10) positive neurons in a restricted number of brain areas, with maximum levels at 30 min after the drug administration that declined at 90 min in most areas. In a second experiment we studied colocalization of pH3S(10) immunoreactivity (pH3S(10)-IR) and c-fos expression. Amphetamine increased c-fos expression in medial prefrontal cortex (mPFC), dorsal striatum, nucleus accumbens (Acb), major Island of Calleja (ICjM), central amygdala (CeA), bed nucleus of stria terminalis lateral dorsal (BSTld) and paraventricular nucleus of the hypothalamus (PVN). Whereas no evidence for increase in pH3S(10) positive neurons was found in the mPFC and the PVN, in the striatum and the Acb basically all pH3S(10) positive neurons showed colocalization with c-fos. In ICjM, CeA and BSTld a notable degree of colocalization was found, but an important number of neurons expressing c-fos were negative for pH3S(10). The present results give support to the hypothesis that amphetamine-induced pH3S(10)-IR showed a more restricted pattern than brain c-fos induction, being this difference strongly dependent on the particular brain area studied. It is likely that those nuclei and neurons showing pH3S(10)-IR are more specifically associated to important effects of the drug, including neural plasticity. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.     

Autoradiographic localization of V1 vasopressin binding sites in rat brain and kidney

Monoiodination of the V1 vasopressin antagonist [Mca1,Sar7]AVP did not alter its high-affinity binding to liver plasma membranes. Monoradioiodinated [Mca1,125I-Tyr2,Sar7]AVP was therefore used to label V1-specific binding sites in the rat brain and kidney. The accumbens nucleus, the septal nucleus, the central amygdala, the bed nucleus of the stria terminalis, the stigmoid hypothalamic nucleus and the nucleus of the solitary tract exhibited specific labeling with both the radioiodinated V1 antagonist and tritiated AVP. Of the circumventricular structures only the choroid plexi and the area postrema showed V1-specific binding sites. The subfornical organ and hypothalamic loci of AVP synthesis such as the paraventricular nucleus, the supraoptic nucleus and the suprachiasmatic nucleus were not marked by the V1 antagonist while bearing [3H]AVP binding sites. As demonstrated by HPLC and binding to liver plasma membranes, the radiolabeled antagonist remained intact during tissue incubation. In addition to renal cortical and medullary [3H]AVP binding sites, medullary tubular and vascular structures could be labeled with the V1 antagonist, indicating the presence of both V1 and V2 AVP receptor subtypes in the rat kidney.     

Local circuit regulation of paraventricular nucleus stress integration: glutamate-GABA connections

Limbic neurocircuits play a central role in regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis. Limbic influences on adrenocortical hormone secretion are mediated by transynaptic activation or inhibition of hypophysiotrophic neurons in the medial parvocellular paraventricular nucleus (PVN). Projections from the ventral subiculum, prefrontal cortex, medial amygdala, lateral septum, paraventricular thalamus and suprachiasmatic nucleus (SN) terminate in the immediate surround of the PVN, an area heavily populated by GABAergic interneurons. As such, these regions are positioned to modulate paraventricular output via excitation or inhibition of interneuronal projections into the PVN. In addition, the same limbic and diencephalic regions have projections to local PVN-projecting hypothalamic and basal telencephalic nuclei, including the dorsomedial and medial preoptic nuclei and the bed nucleus of the stria terminalis. These regions are involved in both inhibitory and excitatory regulation of the stress axis, indicating that they contain heterogeneous neuronal populations whose relative impact on the PVN is determined by the nature of afferent stimuli. Thus, limbic modulation of the pituitary-adrenocortical system appears to be a multisynaptic process integrated at the level of local PVN-projecting neurocircuits. Local circuits are likely the primary integrators of anticipatory stress responses, and may indeed be the focus of HPA dysfunction seen with aging or affective disease.     

Noradrenaline in the bed nucleus of the stria terminalis is critical for stress-induced reactivation of morphine-conditioned place preference in rats.

The effect of noradrenaline in the bed nucleus of the stria terminalis and locus coeruleus on maintenance and reactivation of morphine-conditioned place preference induced by footshock stress was investigated in rats. After receiving alternate injection of morphine (10 mg/kg) and saline for 6 consecutive days, the rats spent more time in the drug-paired compartment (morphine-conditioned place preference) on day 7. These animals did not show morphine-conditioned place preference on day 37 following sham-footshock once every 3 days from days 8 to 36 (28 days drug-free). However, 15 min of intermittent footshock once every 3 days could induce the maintenance of morphine-conditioned place preference on day 37 with significantly more time spent in the drug-paired compartment than on day 0. Microinjection of the alpha(2)-adrenoceptor agonist, clonidine (0.1 or 1 microg), into the locus coeruleus 30 min before footshock did not affect stress-induced maintenance of conditioned place preference. However, infusions of clonidine (1 microg) into the bed nucleus of the stria terminalis significantly attenuated the maintenance of conditioned place preference induced by footshock stress. In another experiment, after a 21-day extinction of morphine-conditioned place preference, a single footshock could reactivate the morphine place preference that was significantly blocked by pretreatment with infusion of clonidine (0.1 or 1 microg) into the bed nucleus of the stria terminalis but not the locus coeruleus. Reactivation of morphine-conditioned place preference elicited by footshock stress was significantly inhibited by 6-hydroxydopamine-induced lesions in the ventral noradrenergic bundle, most of the norepinephrine input to the bed nucleus of the stria terminalis arising from caudal brain stem noradrenergic cell groups. In contrast, chemical lesions of the dorsal noradrenergic bundle that arises from the locus coeruleus had no such effects. These findings suggest that noradrenergic neurons in locus coeruleus are not involved in stress-induced reinstatement of drug-seeking and further clearly demonstrate that noradrenaline in the bed nucleus of the stria terminalis plays a critical role in mediating this effect. Comprehension of the neurochemical events underlying the stress-induced and the bed nucleus of the stria terminalis-mediated reinstatement of drug-seeking may, therefore, throw more light on the biological bases of drug dependence and addictive behavior     

Circumventricular Organs: Gateways to the BrainLeptin Receptors In Hypothalamus And Circumventricular Organs

1. The adipose tissue‐derived hormone leptin reduces food intake and bodyweight via leptin receptors (Ob‐R) in the hypothalamus. 2. Leptin receptor immunoreactivity, demonstrated with an antiserum recognizing all Ob‐R isoforms, is present in hypothalamic neurons of the medial and lateral preoptic area, organum vasculosum lamina terminalis, subfornical organ, periventricular, suprachiasmatic, supraoptic (SON), paraventricular (PVN), arcuate (ARC), dorsomedial, ventromedial hypothalamic and tuberomammillary nuclei and lateral hypothalamic area. In the brainstem, Ob‐R immunoreactivity is present in the area postrema, nucleus tractus solitarius, hypoglossal nucleus and dorsal motor nucleus of the vagus nerve. 3. Leptin receptor immunoreactivity is present in magnocellular vasopressin and oxytocin neurons of the SON and PVN, in parvocellular corticotropin‐releasing hormone neurons of the PVN, neuropeptide Y and pro‐opiomelanocortin neurons of the ARC and in melanin‐concentrating hormone neurons of the lateral hypothalamic area. 4. The passage of leptin across the blood–brain barrier and the chemical mediators of the action of leptin in the hypothalamus are discussed.     

The neurotoxicity of homodimaprit (SKF-91488): Sites of action assessed by the [14C]2-deoxyglucose technique

Homodimaprit (SKF-91488) when injected into the lateral ventricle of the rat resulted in a delayed behavioral syndrome characterized by motor incoordination, hyperexcitability, and aggressive behavior, which occurred 18 hr after injection and ultimately caused death 24–72 hr after injection. In order to determine where the neural effects were occurring, the [¹⁴C]2-deoxyglucose technique was utilized to identify possible sites of brain neural activation. Histological examination revealed that homodimaprit produced periventricular lesions at 18 hr. Autoradiographic analysis demonstrated increased ipsilateral activation in the nucleus accumbens, lateral septal nucleus, bed nucleus of the stria terminalis, caudato-putamen, and the rostral half of the dorsal hippocampus. Bilateral activation was observed in the medial preoptico-hypothalamus, midline thalamic nuclei including the mediodorsal nucleus, and the periventricular central gray. These findings suggest that the delayed behavioral effects of homodimaprit are probably the result of the activation of these specific areas of the brain and the resulting periventricular lesions. The mechanism by which homodimaprit produces these effects, however, remains unknown.     

Induction of c-Fos and DeltaFosB immunoreactivity in rat brain by Vagal nerve stimulation.

Vagus nerve stimulation (VNS) is used as therapy for treatment-resistant depression or epilepsy. This study used immunohistochemistry for biomarkers of short-term (c-Fos) and long-term (DeltaFosB) neuronal activation to map regions in brain that are activated by acute (2 h) or chronic (3 weeks) VNS in conscious Sprague-Dawley rats. Electrodes (Cyberonics Inc.) were implanted on the left vagus nerve and 1 week after surgery, stimulation began using parameters employed clinically (one burst of 20 Hz, 250 micros pulse width, 0.25 mA stimulation for 30 s every 5 min). Radio telemetry transmitters were used for monitoring blood pressure, heart rate, activity, and respiratory rate during VNS; neither acute nor chronic VNS significantly affected these parameters. Acute VNS significantly increased c-Fos staining in the nucleus of the solitary tract, paraventricular nucleus of the hypothalamus, parabrachial nucleus, ventral bed nucleus of the stria terminalis, and locus coeruleus but not in the cingulate cortex or dorsal raphe nucleus (DRN). Acute VNS did not affect DeltaFosB staining in any region. Chronic VNS significantly increased DeltaFosB and c-Fos staining bilaterally in each region affected by acute VNS as well as in the cingulate cortex and DRN. Using these stimulation parameters, VNS was tested for antidepressant-like activity using the forced swim test (FST). Both VNS and desipramine significantly decreased immobility in the FST; whereas desipramine decreased immobility by increasing climbing behavior, VNS did so by increasing swimming behavior. This study, then, identified potential sites in brain where VNS may produce its clinical effects.     

Peripheral withdrawal recruits distinct central nuclei in morphine-dependent rats

This study examined if brain pathways in morphine-dependent rats are activated by opioid withdrawal precipitated outside the central nervous system. Withdrawal precipitated with a peripherally acting quaternary opioid antagonist (naloxone methiodide) increased Fos expression but caused a more restricted pattern of neuronal activation than systemic withdrawal (precipitated with naloxone which enters the brain). There was no effect on locus coeruleus and significantly smaller increases in Fos neurons were produced in most other areas. However in the ventrolateral medulla (A1/C1 catecholamine neurons), nucleus of the solitary tract (A2/C2 catecholamine neurons), lateral parabrachial nucleus, supramamillary nucleus, bed nucleus of the stria terminalis, accumbens core and medial prefrontal cortex no differences in the withdrawal treatments were detected. We have shown that peripheral opioid withdrawal can affect central nervous system pathways.     

Regional differences in naloxone modulation of Delta(9)-THC induced Fos expression in rat brain

Recent behavioral and pharmacological research shows extensive interplay between cannabinoid and opioid neurochemical systems. Here we examined the neuroanatomical basis of this interaction using c-fos immunohistochemistry. We compared Fos immunoreactivity in groups of male albino Wistar rats treated with vehicle, Delta(9)-tetrahydrocannabinol (THC, 10 mg/kg, i.p.), naloxone (10 mg/kg, i.p.) or THC and naloxone in combination. Locomotor activity was depressed in both THC treatment groups and moderately inhibited in rats given naloxone alone. Results showed that naloxone inhibited THC-induced Fos immunoreactivity in several key brain regions including the ventral tegmental area, ventromedial and dorsomedial hypothalamus, central caudate-putamen and ventrolateral periaqueductal grey. Conversely, naloxone and THC had an additive effect on Fos immunoreactivity in the central nucleus of the amygdala, the bed nucleus of the stria terminalis (lateral division), the insular cortex, and the paraventricular nucleus of the thalamus. These findings complement earlier pharmacological results showing potent modulation of cannabinoid-induced analgesia, appetite and reward by opioids. The inhibitory effects of naloxone on THC-induced ventral tegmentum, hypothalamic and periaqueductal grey Fos expression point to these structures as key sites involved in cannabinoid-opioid interactions.     

Increase of dialysate dopamine in the bed nucleus of stria terminalis by clozapine and related neuroleptics.

Neuroleptics are known to stimulate dopamine release in neostriatal terminal areas. In the present study, we have investigated by brain microdialysis in freely moving rats the effect of typical and atypical neuroleptics on dopamine transmission in the bed nucleus of stria terminalis, a dopamine terminal area belonging to the limbic system and recently assigned the so-called extended amygdala. Mean basal dialysate dopamine values were 14.3 f moles/20 microliters sample. Dopamine output in dialysates was increased dose-dependently by clozapine (max + 158%, 298%, and 461% of basal at 5, 10, and 20 mg/kg i.p., respectively), risperidone (max + 115% and 221% of basal at 1 and 3 mg/kg i.p., respectively), olanzapine (max + 138% and 235% of basal at 3 and 6 mg/kg i.p., respectively), BIMG 80 (max + 64% and 164% of basal at 3 and 5 mg/kg i.p., respectively), amperozide (max + 110% and 194% of basal at 3 and 6 mg/kg i.p., respectively). The selective dopamine D4 antagonist L-745,870 increased dialysate dopamine but at rather high doses and not as effectively as clozapine (max + 32%, 89%, and 130% of basal at 2.7, 5.4, and 10.8 mg/kg i.p., respectively). The typical neuroleptic haloperidol (0.1 and 0.5 mg/kg s.c.) and the selective D2 antagonist raclopride (0.14, 0.56, and 2.1 mg/kg s.c.), the serotonergic 5-HT2 antagonist ritanserin (0.5 and 1.5 mg/kg i.p.), and the adrenergic alpha 1 antagonist prazosin (0.91 and 2.73 mg/kg i.p.) did not affect dialysate dopamine in the bed nucleus of stria terminalis. Saline (1 ml/kg s.c. or 3 ml/kg i.p.) did not modify dialysate dopamine. Therefore, atypical neuroleptics share the ability of stimulating dopamine transmission in the bed nucleus of stria terminalis, but this property is not mimicked by any of the drug tested that selectively act on individual receptors among those that are affected by atypical neuroleptics. These observations raise the possibility that the property of increasing dopamine transmission in the bed nucleus of stria terminalis is the result of combined blockade of dopamine, serotonin, and noradrenaline receptors and that might be predictive of an atypical neuroleptic profile.     

Autoradiographic localization of kappa opiate receptors in CNS taste and feeding areas

Recent evidence suggests that kappa opiate receptors may play a key role in the regulation of appetite. Such evidence implies that kappa receptors might be localized within specific brain areas known to regulate ingestive behaviors. On the basis of this implication we employed an in vitro film autoradiographic technique using 3H-ethylketocyclazozine as ligand to identify putative kappa receptors within CNS "taste" nuclei and surrounding areas. Coronal cryostat sections of rat brain were incubated with ligand in the presence of D-Ala2, D-Leu5-enkephalin (DADLE) and morphine, apposed to LKB Ultrofilm for 60 days, processed and kappa receptor densities evaluated with the aid of a hand held photometer and video image analyzer. Highest kappa receptor densities were found within various gustatory and feeding sites including the rostral pole of the nucleus of the solitary tract, parabrachial nuclei, ventral posterior and medial portions of the thalamus, medial hypothalamus, medial nuclei of the amygdala and bed nucleus of the stria terminalis. Various other midline and medial limbic areas also showed significant kappa densities.     

Receptor-selective agonists induce emesis and Fos expression in the brain and enteric nervous system of the least shrew (Cryptotis parva)

Research on the mechanisms of emesis has implicated multiple neurotransmitters via both central (dorsal vagal complex) and peripheral (enteric neurons and enterochromaffin cells) anatomical substrates. Taking advantage of advances in receptor-specific agonists, and utilizing Fos expression as a functional activity marker, this study demonstrates a strong, but incomplete, overlap in anatomical substrates for a variety of emetogens. We used cisplatin and specific agonists to 5-HT₃ serotonergic, D₂/D₃ dopaminergic, and NK₁ tachykininergic receptors to induce vomiting in the least shrew (Cryptotis parva), and quantified the resulting Fos expression. The least shrew is a small mammal whose responses to emetic challenges are very similar to its human counterparts. In all cases, the enteric nervous system, nucleus of the solitary tract, and dorsal motor nucleus of the vagus demonstrated significantly increased Fos immunoreactivity (Fos-IR). However, Fos-IR induction was notably absent from the area postrema following the dopaminergic and NK₁ receptor-specific agents. Two brain nuclei not usually discussed regarding emesis, the dorsal raphe nucleus and paraventricular thalamic nucleus, also demonstrated increased emesis-related Fos-IR. Taken together, these data suggest the dorsal vagal complex is part of a common pathway for a variety of distinct emetogens, but there are central emetic substrates, both medullary and diencephalic, that can be accessed without directly stimulating the area postrema.     

Brain areas involved in production of morphine-induced locomotor hyperactivity of the C57B1/6J mouse

Previous studies reveal a dose-dependent increase in locomotor activity of the C57B1/6J mouse after administration of morphine or amphetamine. Concurrent partial lesions of both the dorsomedial caudate and lateral septal nuclei resulted in a significant decrease in morphine-induced, but not amphetamine-induced, hyperactivity. Concurrent partial lesions of the nucleus accumbens and stria terminalis produced only a nonsignificant decrease in the morphine-induced hyperactivity. Lesions of the individual brain structures did not significantly affect the morphine-induced locomotor hyperactivity. Microinjections of the opiate antagonist naloxone into discrete portions of the caudate and septal nuclei produced suppression of the morphine-induced hyperactivity response without affecting the hyperactivity caused by amphetamine injections. Only a slight suppression of morphine-induced locomotion was produced when naloxone was injected into the nucleus accumbens and stria terminalis. These data suggest that portions of the caudate and septum may be involved in the mediation of morphine-induced hyperactivity in the C57B1/6J mouse.     

Overlapping and distinct brain regions associated with the anxiolytic effects of chlordiazepoxide and chronic fluoxetine.

Little is known about the sites of action for the behavioral effects of chronic antidepressants. The novelty-induced hypophagia (NIH) test is one of few animal behavioral tests sensitive to acute benzodiazepines and chronic antidepressants. The goals of these experiments were to examine patterns of brain activation associated with the behavioral response to novelty and identify regions that could regulate the anxiolytic effects of acute benzodiazepine and chronic antidepressant treatments, measured using the NIH test. In the first experiment, rats were treated acutely with the anxiolytic, chlordiazepoxide (2.5 or 5 mg/kg, i.p.). In separate experiments, animals were implanted with osmotic minipumps delivering vehicle or fluoxetine (5 or 20 mg/kg per day s.c.) for 3 or 28 days. NIH was assessed by giving animals access to a familiar palatable food in a novel environment. Associated brain areas were identified using c-fos immunohistochemistry. NIH was mitigated by acute chlordiazepoxide and chronic fluoxetine. Both drugs reversed novelty-induced changes in c-fos expression in the lateral division of the posterolateral part of the bed nucleus of the stria terminalis (STLP), cingulate cortex (Cg), and dorsal field CA2 of the hippocampus (dCA2). Chronic fluoxetine additionally increased c-fos expression in the anterior nucleus accumbens (aAcb) and the piriform cortex (Pir). The effects of the drugs on c-fos expression in many regions correlated with anxiolytic efficacy. These findings identified brain regions where the effects of chronic antidepressants and benzodiazepines may converge to produce anxiolytic activity, as well as distinct sites of action for the two classes of drugs.     

Dissection of peripheral and central endogenous opioid modulation of systemic interleukin-1beta responses using c-fos expression in the rat brain

In opiate addicts or patients receiving morphine treatment, it has been reported that the immune system is often compromised. The mechanisms responsible for the adverse effects of opioids on responses to infection are not clear but it is possible that central and/or peripheral opioid receptors may be important. We have utilised an experimental immune challenge model in rats, the systemic administration of the human pro-inflammatory cytokine interleukin-1beta (IL-1beta) to study the effects of selectively blocking peripheral opioid receptors only (using naloxone methiodide) or after blocking both central and peripheral opioid receptors (using naloxone). Pre-treatment with naloxone methiodide decreased (15%) IL-1beta-induced Fos-immunoreactivity (Fos-IR) in medial parvocellular paraventricular nucleus (mPVN) corticotropin-releasing hormone (CRH) neurons but increased responses in the ventrolateral medulla (VLM) C1 (65%) and nucleus tractus solitarius (NTS) A2 (110%) catecholamine cell groups and area postrema (136%). However no effect of blocking peripheral opioid receptors was detected in the central nucleus of the amygdala (CeA) or dorsal bed nucleus of the stria terminalis (BNST). We next determined the effect of blocking both central and peripheral opioid receptors with naloxone and, when compared to the naloxone methiodide pre-treated group, a further 60% decrease in Fos-IR mPVN CRH neurons induced by IL-1beta was detected, which was attributed to block of central opioid receptors. Similar comparisons also detected decreases in Fos-IR neurons induced by IL-1beta in the VLM A1, VLM C1 and NTS A2 catecholamine cell groups, area postrema, and parabrachial nucleus. In contrast, pre-treatment with naloxone increased Fos-IR neurons in CeA (98%) and dorsal BNST (72%). These results provide novel evidence that endogenous opioids can influence central neural responses to systemic IL-1beta and also suggest that the differential patterns of activation may arise because of actions at central and/or peripheral opioid receptors that might be important in regulating behavioural, hypothalamic-pituitary-adrenal axis and sympathetic nervous system responses during an immune challenge.