Meal patterns of rats with dorsomedial hypothalamic nuclei lesions or sham operations

Abstract

Rats with bilateral dorsomedial hypothalamic electrolytic lesions (DMNL rats) are hypophagic, hypodipsic and have reduced linear and ponderal growth when compared to sham operated controls (SCON). Nevertheless, previous studies have shown that DMNL rats eat and drink adequate amounts for their size and have normal body composition. In the present study we investigated meal parameters: meal size, and frequency (both light and dark period), total intake and meal size per metabolic size (body weight 0.75). Compared to SCON, DMNL rats at twelve days post surgery weighed less, were shorter, but had a normal body composition as determined by the Lee Index, and were hypophagic (grams eaten/day). The animals were placed into individual, self-contained feeding modules and given powdered chow. After familiarization to the modules, meal parameters were recorded continuously by a computer for an eight day period. While dark phase meal frequency did not differ significantly between groups, the lesioned rats took more meals during the light period. Over the eight-day measurement period DMNL rats were hypophagic compared to SCON in absolute terms. However, when total intake and meal size were normalized to metabolic size, these two parameters did not differ significantly between groups. Upon refeeding, after a one-day fast, the initial meal size of the normally hypophagic DMNL rats exceeded that of SCON. Rats with DMNL have previously been shown to have deficits in some hypothesized short-term food intake control mechanism (e.g., cholecystokinin, glucose sensing). Thus overeating by the lesioned rats after a fast could possibly result from a specific short term control deficit. Nevertheless, under ad lib conditions, except for a slight diurnal disruption in meal frequency, meal parameters were normal in the DMNL rats.