AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 6 917-R924, Copyright © 1988 by American Physiological Society
Radio-frequency vs. electrolytic VMH lesions: differential effects on plasma hormones
B. M. King, M. F. Dallman, K. R. Esquerre and L. A. Frohman
Department of Psychology, University of New Orleans, Louisiana 70148.
Electrolytic lesions of the ventromedial hypothalamus (VMH) result in
marked hyperphagia and obesity, but several studies have found the excess
food intake and weight gain to be greatly reduced when lesions are produced
by electrocauterization with radio-frequency current. Unlike electrolytic
lesions, radio-frequency lesions leave few or no deposits of metallic ions
that can potentially stimulate adjacent tissue. In the present experiment,
weight gain and several endocrine responses previously associated with the
VMH syndrome were compared in female rats given either electrolytic,
radio-frequency, or sham VMH lesions. Both groups with VMH lesions became
obese, but rats with radio-frequency lesions displayed only 63.2% of the
weight gain of animals with irritative lesions (120.0 vs. 189.8 g in 20
days). Only rats with electrolytic lesions displayed elevated plasma
insulin levels during an initial period of food restriction, but both
groups with lesions were hyperinsulinemic when allowed to overeat. Plasma
growth hormone levels were decreased by electrolytic lesions but unaffected
by radio-frequency lesions. Morning corticosterone levels were elevated in
both VMH groups, but only the rats with electrolytic lesions were found to
have elevations in plasma adrenocorticotropin. It is concluded that some of
the endocrine dysfunctions resulting from electrolytic VMH lesions are due
to irritative stimulation rather than to tissue ablation.
