Cytokine-purine interactions in behavioral depression in rats

This paper reviews recent findings from our laboratories concerning metabolic and immune mediators of behavioral depression in rats. Specifically, a single injection of 6 mg/kg of reserpine substantially increases behavioral depression, as evidenced by an increase in the amount of time spent floating by independent groups of rats tested for swim performance at various times during the next week. The behavioral impairment consists of two components. An early component emerges one hour after reserpine treatment and persists for about 24 hours. The deficit is not reversed by intracranial ventricular infusion of the receptor antagonist for interleukin-1β (IL-1β). A second, late-component deficit appears approximately 48 hours after reserpine treatment and recovers within a week. Late-component depression is reversed by central infusion of the IL-1β receptor antagonist, and is mimicked by central infusion of the proinflammatory cytokine. Importantly, both early and late components of reserpine-induced depression and IL-1β induced depression are reversed by a systemic injection of the highly selective A_2A adenosine receptor antagonist 8-(3-Chlorostyryl) caffeine. These data are discussed in terms of the overlap in the conservation-withdrawal reaction during sickness, traumatic stress, and major depression and the regional contribution of purines and cytokines to the organization of this reaction in the brain.