Localization of interleukin-2 immunoreactivity and interleukin-2 receptors in the rat brain: interaction with the cholinergic system.

The present work characterizes the presence of interleukin-2 (IL-2)-like immunoreactive material and IL-2 binding sites in the adult rat brain. The results show that there are detectable levels of IL-2-like material in extracts of rat hippocampus, striatum, and frontal cortex. However, specific [125I]IL-2 binding sites were observed only in the hippocampus, using both homogenate-binding and autoradiographic techniques. In this region of the rat brain, specific [125I]IL-2 binding was inhibited by 100 nM non-radioactive recombinant human IL-2. In kainate-lesioned hippocampi, the density of [125I]IL-2 sites was apparently increased, suggesting their localization to extrinsic innervation and/or glial cells. In slices of hippocampus, which contain both IL-2-like immunoreactive material and specific IL-2 sites, exogenous IL-2 significantly decreased the potassium (25 mM)-evoked, but not the basal, release of acetylcholine. This IL-2-induced effect was concentration-dependent, and was apparent at a relatively low concentration (1 nM). This IL-2 effect was also region-specific, such that acetylcholine release from other tissue slices (striatal, frontal cortical) was not affected. In slices from kainate-lesioned hippocampi, the IL-2-induced reduction of acetylcholine release was only modestly enhanced, suggesting that the extra IL-2 sites that appear post-lesion may not be localized to cholinergic terminals.