A hypothalamic endorphinic lesion attenuates acquisition of cocaine self-administration in the rat.

The present study explores the role of beta-endorphin-producing neurons of the arcuate nucleus in the behavioral effects of cocaine (i.e. acquisition of cocaine self-administration). Eight-week-old female rats were treated with a single estradiol valerate injection that causes a progressive lesion that is specific to beta-endorphin-producing neurons throughout the arcuate nucleus. Cocaine acquisition was suppressed following estradiol valerate pretreatment, while water reinforced behavior was similar to controls. Since estradiol valerate treated rats exhibit low estrogen plasma levels, estrogen replacement was performed but cocaine self-administration acquisition remained suppressed. In addition, analysis of beta-endorphin, dopamine, and DOPAC tissue levels confirmed the specificity of the endorphinic lesion resulting from estradiol valerate treatment. The suppression of cocaine self-administration acquisition following estradiol valerate treatment provides evidence for a significant role for beta-endorphin in cocaine reward.

A critical role for beta-endorphin in cocaine-seeking behavior.

Endogenous beta-endorphin levels in the brain are elevated in response to cocaine and are downstream of the mesolimbic dopaminergic system. However, beta-endorphin's direct involvement in cocaine reinforcement has not been demonstrated. In the present study, a single bilateral microinjection of anti-beta-endorphin antibodies (4 microg) to the nucleus accumbens during the maintenance phase of cocaine self-administration (1 mg/kg/infusion) significantly increased the number of active and inactive lever responses. The increase in lever responses is reminiscent of rat behavior during extinction of cocaine self-administration. Further, a cocaine dose-response demonstrates that the increased lever presses in anti-beta-endorphin antibody-injected rats was still present after substitution with a lower dose of cocaine. These findings support a critical role for beta-endorphin in the cocaine brain reward system.

Effect of experimenter-delivered and self-administered cocaine on extracellular beta-endorphin levels in the nucleus accumbens.

Beta-endorphin is an endogenous opioid peptide that has been hypothesized to be involved in the behavioral effects of drugs of abuse including psychostimulants. Using microdialysis, we studied the effect of cocaine on extracellular levels of beta-endorphin in the nucleus accumbens, a brain region involved in the reinforcing effects of psychostimulant drugs. Experimenter-delivered cocaine (2 mg/kg, i.v.) increased extracellular beta-endorphin immunoreactive levels in the nucleus accumbens, an effect attenuated by 6-hydroxy-dopamine lesions or systemic administration of the D1-like receptor antagonist, SCH-23390 (0.25 mg/kg, i.p.). The effect of cocaine on beta-endorphin release in the nucleus accumbens was mimicked by a local perfusion of dopamine (5 microm) and was blocked by coadministration of SCH-23390 (10 microm). Self-administered cocaine (1 mg/kg/infusion, i.v.) also increased extracellular beta-endorphin levels in the nucleus accumbens. In addition, using functional magnetic resonance imaging, we found that cocaine (1 mg/kg, i.v.) increases regional brain activity in the nucleus accumbens and arcuate nucleus. We demonstrate an increase in beta-endorphin release in the nucleus accumbens following experimenter-delivered and self-administered cocaine mediated by the local dopaminergic system. These findings suggest that activation of the beta-endorphin neurons within the arcuate nucleus-nucleus accumbens pathway may be important in the neurobiological mechanisms underlying the behavioral effects of cocaine.

Impaired release of beta-endorphin in response to serotonin in a rat model of depression.

Involvement of both the serotonergic and the endogenous opioid systems in the onset of depressive behavior has been suggested. Previously we showed that serotonin (5-hydroxytryptamine) facilitates beta-endorphin release in the nucleus accumbens (NAcc). Herein, the microdialysis method was used to assess in vivo the effects of serotonin on beta-endorphin release in a rat model of depressive behavior (the Flinders sensitive line, FSL), before and after antidepressant treatment. The basal extracellular level of beta-endorphin in the NAcc of FSL rats did not differ significantly from that in control rats. However, serotonin-induced beta-endorphin release was impaired in FSL rats. Chronic treatment (18 days) with desipramine or paroxetine did not significantly affect the extracellular levels of beta-endorphin in the NAcc of either the FSL or control rats. However, the chronic antidepressant treatment did normalize the serotonin-induced release of beta-endorphin in FSL rats, as well as their behavioral manifestation of depressive behavior. Our results show that depressive behavior may relate to an impaired effect of serotonin on beta-endorphin release in the NAcc in a rat model of depression, and suggest a possible new mode of action of antidepressant drugs.

Correlation of cytokine secretion by mononuclear cells of Alzheimer patients and their disease stage.

Cytokine secretion by human mononuclear cells (MNC) was investigated in age-matched controls and in patients with Alzheimer's disease (AD). AD patients were divided into two study groups: 'mild' and 'moderately severe'. A significant increase in interleukin-2 (IL-2) and gamma interferon (IFN-gamma) secretion was found in AD patients in the moderately severe stage of the disease, whereas in the mild stage of the disease there was a significant decrease in interleukin-3 activity (IL-3) and tumor necrosis factor (TNF) levels. No significant differences were found in the level of production of interleukin-1 (IL-1 beta). Our results demonstrate the existence of defective immune functions in AD patients which are correlated with the clinical condition of these patients.

Decreased IL-3 production by peripheral blood mononuclear cells in patients with multiple sclerosis.

The production of interleukin-3 by peripheral blood mononuclear cells (MNC) was assessed in patients with relapsing multiple sclerosis (MS) in both the active and the stable state, and in healthy controls. IL-3 levels were compared to levels of production of interleukin-2 (IL-2), tumor necrosis factor (TNF) and gamma-interferon (gamma-IFN). No significant differences in IL-3 levels were observed between stable-state patients and controls. When levels of cytokine production of patients in the inactive phase were compared to those of the same patients during relapse a significant decrease in IL-3 levels was observed, as opposed to significant increases in gamma-IFN and TNF levels, and an increase, though a non-significant, in IL-2 levels. The functional significance of lowered IL-3 production is unknown. However, the findings support the hypothesis of a highly complex interaction of overlapping regulatory influences within the cytokine network which parallels MS disease activity.