Production of weanling rat ventromedial and dorsomedial hypothalamic syndromes by electrolytic lesions with platinum-iridium electrodes

Abstract

Weanling Sprague-Dawley rats received bilateral anodic electrolytic lesions with platinum-iridium (PtIr) electrodes in the ventromedial (VMN) and dorsomedial (DMN) hypothalamic areas. Sham-operated rats served as controls. The rats were maintained for 48 days (experiment 1) and 33 days (experiment 2) and food intake, body weight (b.w.), nose-tail length and obesity index were recorded. The data of both experiments indicate that all parameters change in the same direction, as they do when lesions are produced with anodic stainless steel electrodes: in the VMN-P-lesioned animals, b.w. gains and overall mean food intake were normal, carcass fat increased and linear growth was reduced. In experiment 2, however, there was a temporary hyperphagia during the 1st 2 weeks of the study. In the DMN-lesioned rats, both ponderal and linear growth and food intake were decreased but body composition was normal. Plasma obtained at sacrifice in experiment 2 showed slight but significant hyperinsulinemia in the VMN rats (p less than 0.02 vs control and p less than 0.05 vs DMN rats). Prolactin (PRL) levels, on the other hand, were higher in the DMN-lesioned rats (p less than 0.05 vs control and p less than 0.02 vs VMN rats). The data indicate that the changes characteristic of the weanling rat VMN and DMN syndrmes are due to 'true' tissue destruction rather than to artifactitious side effects of the lesions. They also suggest, therefore, than an 'irritative focus' hypothesis is not required to account for the observed alterations. They further suggest that the DMN may play role in the control of PRL release.