THE EFFECTS OF EXCITOTOXIN LESIONS OF THE LATERAL HYPOTHALAMUS ON SELF-STIMULATION REWARD

Unilateral microinjection into rat lateral hypothalamus (LH) of the excitotoxins ibotenic acid (IBO) and N-methyl-D-aspartic acid (NMDA) produced a local zone of neuronal death but also produced a zone of demyelination. The size of this demyelination zone was related to excitotoxin dose and was smaller than the zone of neuron killing. In behavioral testing, MFB self-stimulation reward and performance were measured with a rate-frequency curve-shift method before and after IBO or NMDA lesions of the LH. Excitotoxin lesions were made anterior or posterior to the LH electrode so that the zone of neuronal death, but not demyelination, extended to the electrode tip. These lesions produced small, temporary LH stimulation reward deficits, leading to the conclusion that intrinsic LH neurons are not a major substrate of MFB stimulation reward.