Hypothalamic obesity: comparison of radio-frequency and electrolytic lesions in male and female rats

Obesity-inducing lesions of the ventromedial hypothalamus (VMH) have generally been produced by passing anodal electrolytic current through a stainless steel electrode, which in addition to tissue ablation leaves deposits of metallic ions that might chronically irritate surrounding tissue. Although a few early investigators reported that nonirritative lesions (i.e., those that do not leave deposits) resulted in little or no obesity, their results were largely ignored when others observed substantial weight gain in animals after using the same techniques. The results of the present experiment suggest that these discrepancies were the result of a sex difference (the former group of studies all used male rats, while the latter group all used females). Male rats in the present study gained less than 80% of the weight gained by female rats regardless of lesion type, while rats with nonirritative radio-frequency lesions gained about 60% of the weight gained by rats with electrolytic lesions regardless of sex. Thus, female rats with radio-frequency lesions displayed substantial (albeit suppressed) weight gain, whereas male rats with identical lesions gained only slightly more weight than sham-lesioned controls. It is concluded that obesity resulting from electrolytic lesions of the VMH is due in part to tissue ablation and in part to chronic irritation (possibly of parasympathetic efferents mediating insulin release).