INCREASED IPSILATERAL EXPRESSION OF FOS FOLLOWING LATERAL HYPOTHALAMIC SELF-STIMULATION

Immunohistochemical labeling of Fos protein was used to visualize neur ons activated by rewarding stimulation of the lateral hypothalamic lev el of the medial forebrain bundle (MFB). Following training and stabil ization of performance, seven rats were allowed to self-stimulate for 1 h prior to anesthesia and perfusion. Brains were then processed for immunohistochemistry. Two control subjects were trained and tested in an identical manner except that the stimulator was disconnected during the final 1 h test. Among the structures showing a greater density of labeled neurons on the stimulated side of the brains of the experimen tal subjects were the septum, lateral preoptic area (LPO), medial preo ptic area, bed nucleus of the stria terminalis, substantia innominata (SI), and the lateral hypothalamus (LH). Several of these structures, the LPO, SI, and LH, have been implicated in MFB self-stimulation by t he results of psychophysical, electrophysiological, and lesion studies .