Interferon-alpha and transforming growth factor-beta 1 regulate corticotropin-releasing factor release from the amygdala: comparison with the hypothalamic response.

Interferon-alpha (IFN-alpha) and transforming growth factor-beta 1 (TGF-beta 1) have been reported in different brain regions. The amygdala contains high levels of corticotropin releasing factor (CRF) and has been implicated as a central site for its stress-related autonomic and behavioral response. IFN-alpha will release arginine vasopressin (AVP) from both amygdala and hypothalamus, which further supports a role for the amygdala in neuroimmune interactions. In the present study, we compared the effects of these cytokines on the in vitro release of CRF from the amygdala and hypothalamus. In addition, we evaluated the possible involvement of guanylate cyclase-mediated signaling in CRF release. IFN-alpha stimulates CRF release from both amygdala and hypothalamus. The CRF release by IFN-alpha, Interleukin-2 (IL-2) and acetylcholine is blocked by guanylate cyclase inhibitors, indicating a role for cGMP accumulation in this CRF release. TGF-beta 1 had no effect on basal release of CRF, nor on the CRF-release induced by IL-2, but selectively blocked the acetylcholine-induced release in both amygdala and hypothalamus. Taken with a previous report that TGF-beta 1 specifically inhibits AVP release by acetylcholine, these results suggest that TGF-beta 1 may modulate HPA axis activation, by antagonizing (acetylcholine-evoked) CRF and AVP release. These data further support a role for the amygdala in the bidirectional communication between neuroendocrine and immune system.

Microglia-passaged simian immunodeficiency virus induces neurophysiological abnormalities in monkeys.

Four rhesus macaques were inoculated intravenously with a cryopreserved stock of microglia obtained from a simian immunodeficiency virus (SIV)-infected rhesus macaque. Before infection, three of the four monkeys were trained and tested daily on a computerized neuropsychological test battery. After SIV infection, behavioral testing continued to monitor deficits associated with disease progression. Five additional age-matched, behaviorally trained monkeys served as controls. Neurophysiological testing for visual and auditory evoked responses was accomplished 37-52 weeks after infection in all monkeys. Subsequently, all four SIV-infected monkeys and one control subject were sacrificed, and samples of brain tissue were taken for pathological analysis. SIV-infected monkeys demonstrated abnormal responses in both auditory and visual evoked responses. In addition, around the time of electrophysiological recording, all three SIV-infected, behaviorally trained monkeys exhibited significant decreases in progressive-ratio performance, reflecting a reduction in reinforcer efficacy. One subject also demonstrated impairments in shifting of attentional set and motor ability at that time. Neuropathological evaluation revealed that all four SIV-infected monkeys exhibited numerous perivascular and parenchymal infiltrating T cells. These findings document that SIV causes electrophysiological, behavioral, and neuropathological sequelae similar to what has been observed in the human neuroAIDS syndrome. Our observations further validate the simian model for the investigation of the pathogenesis of AIDS dementia and for the investigation of drugs with potential therapeutic benefits.

Mineralocorticoid and glucocorticoid receptor antagonists in animal models of anxiety.

The behavioral effects of intracerebroventricular (i.c.v.) administration of a specific mineralocorticoid receptor (MR) antagonist [RU28318 (10-50 ng/2 microliters)], a glucocorticoid receptor (GR) antagonist [RU38486 (1-50 ng/2 microliters)], or both antagonists (50 ng/2 microliters), were studied in two different animal models of fear and anxiety in rats. In the defensive burying paradigm simultaneous blockade of MR and GR increased immobility behavior, whereas a small decrease in defensive burying was seen. In the fear-potentiated startle test concurrent MR and GR blockade led to an increase in fear-potentiated startle at the highest loudness level (105 dB). In both tests the antagonists were not effective when given separately. The findings are discussed in terms of the involvement of GR and MR in neural mechanisms of fear and anxiety.

Interleukin-2 (IL-2) induces corticotropin-releasing factor (CRF) release from the amygdala and involves a nitric oxide-mediated signaling; comparison with the hypothalamic response.

Interleukin-2 (IL-2)-like immunoreactivity and IL-2 receptor immunoreactivity have been reported in different brain regions, under normal and pathophysiological conditions. IL-2 stimulates hypothalamic corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) release and that of pituitary adrenocorticotropin. The amygdala, known to contain high levels of CRF, is involved in stress-related reactions, including regulation of the hypothalamo-pituitary-adrenal axis. IL-2 will release AVP from both the hypothalamus and the amygdala, which further supports a role for cytokine effects in the amygdala in neuroimmune interactions. In the present study, we compared the effects of IL-2, acetylcholine and norepinephrine on the in vitro release of CRF from the amygdala or hypothalamus. In addition, we used these release systems to evaluate the possible involvement of nitric oxide (NO)-mediated signaling in CRF release. IL-2 stimulates CRF release in both regions, in a calcium- and dose-dependent manner. Nitroprusside, an NO generator, also induces CRF release. This IL-2-induced CRF release is antagonized by Ng-methyl-L-arginine and hemoglobin, known NO antagonists. Finally, norepinephrine and acetylcholine induce CRF release. The norepinephrine-induced CRF release is antagonized by phentolamine and propanolol and the acetylcholine-induced release by atropine and mecamylamine, which suggests the involvement of both alpha and beta adrenergic receptors and both muscarinic and nicotinic receptors. The acetylcholine-induced CRF release is antagonized by Ng-methyl-L-arginine, but the norepinephrine-induced response is not. These data support the suggestion that the amygdala may participate in communications between the neuroendocrine and immune systems.

IL-1 beta potentiates the acetylcholine-induced release of vasopressin from the hypothalamus in vitro, but not from the amygdala.

In addition to the magnocellular hypothalamic nuclei, arginine vasopressin (AVP)-containing neurons have also been identified in limbic structures, including the hippocampus and amygdala. In the present study, we compared the qualitative properties of the in vitro release of AVP from the dissected hypothalamus with the in vitro release from the dissected amygdala and used these release systems to evaluate the interactions with neurotransmitters and cytokines. The areas of the paraventricular nucleus and supraoptic nucleus that contain the AVP neurons and that receive cholinergic innervation are also interleukin (IL)-1 beta immunoreactive. Acetylcholine or high KCl (60 mM) induces AVP release in both regions, and the AVP release is calcium dependent. Acetylcholine-induced AVP release is antagonized by atropine or mecamylamine, indicating that both muscarinic and nicotinic receptors are mediating the cholinergic effect in these brain regions. IL-1 beta (100 U/ml) had no effect on the basal AVP release from the hypothalamus, but significantly potentiated the acetylcholine-induced AVP release, lowering the threshold from 500 to 100 nM. This effect was completely blocked in the presence of neutralizing antibodies to IL-1 beta, atropine (10 microM) or mecamylamine (10 microM). IL-6, like IL-1 beta, also potentiated acetylcholine-induced AVP release, but to a lesser extent. Neither tumor necrosis factor-alpha nor interferon-gamma had any effect on the basal or acetylcholine-induced AVP release from the hypothalamus. None of the cytokines tested had any effect on the basal or acetylcholine-induced AVP release from the amygdala. Our results suggest a hypothalamic site of action of IL-1 beta and IL-6 on the acetylcholine-induced AVP release. The stimulatory effects of IL-1 and IL-6 on adrenocorticotropin release have been ascribed to an increased release of corticotropin-releasing factor (CRF). These data further suggest that, in addition to CRF, AVP plays a role in the bidirectional communication between neuroendoc ine and immune systems. Understanding the mode of interaction between IL-1 beta and IL-6 with AVP could clarify pathophysiologic or toxic effects of high brain levels of these cytokines.

The role of limbic and hypothalamic corticotropin-releasing factor in behavioral responses to stress.

CRF in the central nervous system appears to have activating properties on behavior and to coordinate behavioral responses to stress. These behavioral effects of CRF appear to be independent of the pituitary-adrenal axis and can be reversed by a CRF antagonist, alpha-helical CRF9-41. The CRF antagonist reverses not only decreases in behavior associated with stress, but also increases in behavior associated with stress, thus suggesting that the role of CRF is stress dependent and not intrinsic to a given behavioral response. Further, microinjection of alpha-helical CRF9-41 and immunotargeting of CRF neurons in separate brain compartments reveal a link between the anatomical sites that contain CRF and the nature of the behavioral response to stress that can be modified by suppression of endogenous CRF activity therein. Hence, consistent with the dual role of other hypothalamic-releasing factors in integrating hormonal and neural mechanisms by acting both as secretagogues for anterior pituitary hormones and as extrapituitary peptide neurotransmitters, CRF may coordinate coping responses to stress at several bodily levels (Fig. 6). Moreover, dysfunction in such a fundamental homeostatic system may be the key to a variety of pathophysiological conditions including mental disorders.

Responding to acoustic startle during chronic ethanol intoxication and withdrawal.

Ethanol (EtOH) withdrawal is characterized by a hyperexcitable state that includes anxiety, tremor, muscle rigidity and seizures. The present three experiments examined the effects of EtOH dependence and withdrawal on the acoustic startle response, an easily quantifiable measure of behavioral reactivity to exteroceptive stimuli. Two intensities of startle stimuli, 105 and 120 dB pulses, were presented to rats during chronic EtOH exposure and during EtOH withdrawal. Prepulse inhibition, which is a sensitive measure of sensorimotor gating processes associated with filtering sensory stimulation, was also assessed during chronic EtOH exposure and withdrawal. Prepulse inhibition was induced by the presentation of a weak 80 dB acoustic stimulus 100 ms prior to a 120 dB stimulus pulse. After 14 days of EtOH liquid diet administration the magnitude of responses elicited by 105 and 120 dB startle stimuli was less in ethanol-treated subjects during continued EtOH access than in animals fed a control liquid diet. When EtOH liquid diet treatment was continued for an additional 3-day period and animals were tested 8 h after withdrawal from EtOH, withdrawn animals were more reactive to startle stimuli at both intensities than were animals maintained on the EtOH liquid diet. A time-course experiment with repeated startle testing at 4, 8, and 12 h post-EtOH exposure revealed significant increases in responding to the 105 dB startle intensity at 8 h post-EtOH exposure. The ability of animals to respond to a prepulse stimulus was not affected during chronic EtOH treatment, but was reduced during withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Construct validity of a self-stimulation threshold paradigm: effects of reward and performance manipulations.

A discrete-trial current-threshold intracranial self-stimulation (ICSS) paradigm has been used extensively to examine the effects of drugs on reward thresholds. However, there is little work to date validating that this specific procedure measures reward. The purpose of the present study was to establish the construct validity of this procedure by testing the procedure's ability to measure reward effects and to discriminate these reward effects from performance effects. The discrete-trial ICSS procedure provides four measures: current thresholds, response latency, extra responses and time-out responses. The effects of a performance manipulation (variations in the force required to operate the manipulandum) and of a reward manipulation (variations in the train duration of the electrical stimulation) were evaluated on the four measures. Reward effects were reflected primarily in changes in thresholds, with no effect on any of the other three measures. Conversely, performance effects were reflected primarily in changes in response latency, extra responses and time-out responses, with only a small effect on thresholds. Finally, the paradigm's potential as a useful tool in the elucidation of the neurobiological basis of reward was demonstrated by investigating the effects of two pharmacological agents, cocaine and curare, on the four measures derived from the discrete-trial current-threshold ICSS procedure. The results suggest that the discrete-trial current-threshold procedure can readily discriminate reward from performance treatments.

Potentiation of acoustic startle by corticotropin-releasing factor (CRF) and by fear are both reversed by alpha-helical CRF (9-41).

A series of experiments were performed to investigate the effects of alpha-helical CRF [9-41] (AHCRF), a structural analogue and functional antagonist of corticotropin-releasing factor (CRF), on CRF- and fear-potentiated acoustic startle amplitude. Intracerebroventricular (ICV) administration of the CRF antagonist AHCRF reversed the potentiation of startle amplitude that was produced by ICV administration of CRF (1.0 micrograms). Doses of AHCRF that antagonized CRF-potentiated startle amplitude also reversed the potentiation of startle produced by conditioned "fear" but failed to lower startle baseline or antagonize strychnine-potentiated acoustic startle. These results suggest that CRF and "fear" may potentiate acoustic startle through overlapping neural substrates.

Cellular and molecular mechanisms of drug dependence.

The molecular and cellular actions of three classes of abused drugs--opiates, psychostimulants, and ethanol--are reviewed in the context of behavioral studies of drug dependence. The immediate effects of drugs are compared to those observed after long-term exposure. A neurobiological basis for drug dependence is proposed from the linkage between the cellular and behavioral effects of these drugs.

Lesions of the dorsomedial nucleus of the thalamus, medial prefrontal cortex and pedunculopontine nucleus: effects on locomotor activity mediated by nucleus accumbens-ventral pallidal circuitry.

A GABAergic nucleus accumbens-ventral pallidum projection is believed to serve as the critical first-order accumbens efferent pathway underlying the behavioral expression of mesolimbic dopamine (DA) activity in the rat. In a series of experiments, we studied the effects of lesions of several ventral pallidal efferent terminal regions on the rat locomotor response to apomorphine following 6-hydroxydopamine denervation of the nucleus accumbens. Lesions of the dorsomedial nucleus of the thalamus (DMT), but not the medial prefrontal cortex or the predunculopontine nucleus, significantly depressed the 'supersensitive' locomotor response to apomorphine. Lesions of the DMT did not depress baseline locomotion, but did diminish the locomotor activation produced by intracerebral injection of the gamma-aminobutyric acid antagonist picrotoxin into the ventral pallidum. These results suggest that accumbens-pallidothalamic circuitry plays a crucial role in translating the effects of mesolimbic DA activity to lower motor circuitry responsible for locomotor behavior in the rat.

Central dopamine hyperactivity in rats mimics abnormal acoustic startle response in schizophrenics.

Schizophrenic patients show loss of the normal inhibition of the acoustic startle response (ASR) when the startle stimulus is preceded by a weak prepulse stimulus. In rats experimentally induced to have locally supersensitive dopamine receptors within forebrain dopamine terminal regions, we find a similar deficit in "prepulse inhibition" of the ASR. Our results suggest that there are intriguing parallels between the aberrant sensory gating of the ASR demonstrated by schizophrenics and that demonstrated by rats during stimulation of supersensitive brain dopamine receptors. Thus, prepulse inhibition of the ASR provides a useful paradigm for investigating the bridge between mesolimbic dopamine overactivity and the specific time-dependent information processing-sensory gating disturbances that have been identified in schizophrenic patients.

Corticotropin-releasing factor potentiates acoustic startle in rats: blockade by chlordiazepoxide.

A series of experiments was performed to investigate the effects of corticotropin-releasing factor (CRF) on the amplitude of the acoustic startle response (ASR) in rats. Intracerebroventricular (ICV) administration of 1 microgram rat CRF significantly potentiated acoustic startle amplitude; these effects were reversed in a dose-dependent manner by pretreatment with the benzodiazepine chlordiazepoxide (CDP). Doses of CDP that antagonized CRF-potentiated ASR did not lower startle baseline or antagonize amphetamine- or strychnine-potentiated ASR. These results suggest that CRF has "anxiogenic" properties and may serve as a neuroendocrine modulator of stress-enhanced behaviors.

Stimulation of food intake in rats by centrally administered hypothalamic growth hormone-releasing factor.

Hypothalamic growth hormone-releasing factors (GRFs) have been purified recently from human pancreatic (hp) tumours and from rat hypothalamus (rh). GRF peptides have strong homology with peptides of the glucagon, vasoactive intestinal polypeptide and PHI-27 family. Aside from their potent actions on release of somatotropin, no other biological actions of GRFs have been reported. GRF has been localized in neurones bordering the ventromedial hypothalamic nucleus, a region associated frequently with experimental analysis of feeding behaviour. We now report that intracerebroventricularly (i.c.v.)-administered rhGRF and hpGRF(1-40) in doses of 0.2, 2.0 and 20.0 pmol, produced an increase in food intake in hungry rats. This effect seemed to be specific to GRF as i.c.v. injections of a structurally related but physiologically inactive peptide in the same doses had no effect on feeding. In addition, peripheral injections of rhGRF or growth hormone had no effect on food intake, suggesting that the present effects may be mediated centrally. Injections (i.c.v.) of rhGRF (0.2, 2.0 and 20.0 pmol) had no effect on general activity, suggesting that GRF does not produce nonspecific arousal.

Neuroleptic-like disruption of the conditioned avoidance response requires destruction of both the mesolimbic and nigrostriatal dopamine systems.

An examination of the ability to learn an active avoidance response was made in rats subjected to 6-hydroxydopamine (6-OHDA) lesions of the individual terminal areas of the midbrain dopamine (DA) system or a lesion to all these terminal regions in one group. Lesions were made by infusing 8 micrograms (base) of 6-OHDA in 2 microliter of vehicle into the following forebrain regions (each region representing a separate group of rats); frontal cortex, nucleus accumbens, corpus striatum and a double lesion of nucleus accumbens and corpus striatum. A separate group of rats received a smaller 6-OHDA lesion of the ventral substantia nigra. Only those rats with the combined double lesion of both the nucleus accumbens and corpus striatum (90% total depletion of dopamine) showed a severe deficit in acquisition of active avoidance. However, the rats with the separate 6-OHDA lesions to the mesolimbic or nigrostriatal DA systems did show the appropriate blockade of the amphetamine-induced locomotion or stereotyped behavior, respectively. In contrast, the rats with the double lesion showed no response to a low or high dose of amphetamine, remained cataleptic for the duration of the experiment but rapidly recovered from transient aphagia and adipsia (less than 10 days post lesion). Results suggest that a severe deficit in acquisition of an active avoidance response, similar to that observed with high doses of neuroleptics, requires destruction of all of the dopamine innervation of nucleus accumbens and corpus striatum. Results also suggest that both the mesolimbic and nigrostriatal dopamine systems act in concert to produce response enabling to important environmental events, and that the severe response enabling deficits observed in Parkinson's disease involves not only degeneration of the nigrostriatal dopamine system, but of the mesolimbic dopamine system as well.

Different effects of cholecystokinin and satiety on lateral hypothalamic self-stimulation.

The effects of cholecystokinin (CCK) and satiety were compared in animals lever-pressing for rewarding electrical stimulation of the lateral hypothalamus. For some rats, conditions of food deprivation and satiation, respectively, increased or decreased responding whereas the self-stimulation behavior of other rats was unresponsive to these feeding manipulations. CCK, at doses thought to signal satiety, reduced the responding of all rats independent of whether they were, or were not, responsive to real satiety. This same result was obtained with the aversive agent lithium chloride. These data suggest that the reduced feeding observed following CCK administration is due to aversive consequences and not satiety.

Self-stimulation at the lateral hypothalamus and locus coeruleus after specific unilateral lesions of the dopamine system.

A group of rats was trained to press levers for electrical stimulation from bipolar electrodes aimed at the lateral hypothalamus (LH), and another group was trained to self-stimulate from electrodes in the locus coeruleus (LC). All rats in both groups were subjected to unilateral injections of 6-hydroxydopamine into the substantia nigra and midbrain ventral tegmentum. The lesions produced profound depletions of dopamine from the ipsilateral frontal cortex, nucleus accumbens/olfactory tubercle, and corpus striatum. Pretreatment with desmethylimipramine prevented loss of noradrenaline in excess of that caused by electrode implantation. The destruction of the dopamine projections produced a persistent and pronounced deficit in intracranial self-stimulation from ipsilateral electrodes in both the LH and LC groups, but only transient effects on self-stimulation from contralateral electrodes at these sites. These results suggest that an intact dopamine system is required for the expression of self-stimulation behaviour.