Ventromedial and dorsomedial hypothalamic syndromes in the weanling rat: is the "center" concept really outmoded?

This report juxtaposes findings from weanling rats with precise lesions in the ventromedial (VMNL rats) to data of weanling rats with lesions in the dorsomedial (DMNL) hypothalamic nuclei. Despite the proximity of the two nuclei their destruction produces opposite effects in most cases but similar responses in other parameters. Absolute and relative food intake are normal in VMNL rats yet they become obese in the face of normal body weight gains. DMNL rats show both reduced absolute food intake and body weight but normal relative food intake and body composition. Both VMNL and DMNL cause reduced linear growth and running wheel activity. DMNL rats defend their lower body weight set point against various challenges and maintain normal body composition. Organ growth in both absolute and relative terms is reduced in VMNL rats. In DMNL rats relative organ growth is normal. Pancreatic growth, protein/pancreas and content and concentrations of several pancreatic enzymes are normal in DMNL but reduced in VMNL rats. Mean 24-hour plasma growth hormone (GH) and corticosterone (B) levels are reduced and insulin levels are greatly elevated in VMNL rats; prolactin (PRL) levels are normal. In DMNL rats, GH, B, insulin and somatomedin activity are normal but PRL is elevated. Circadian rhythms of GH, insulin and triiodothyronine are normal in DMNL rats but B levels are disrupted, as they are in VMNL rats. Glucose incorporation and oxidation in adipose tissue of VMNL rats are enhanced in VMNL rats but normal in DMNL rats. Gluconeogenesis in VMNL rats is enhanced as early as 4 hours post-operatively; in DMNL rats it is normal at this time and several weeks thereafter. Basal lipolysis in epididymal fat pads is elevated in both VMNL and DMNL rats but epinephrine-stimulated lipolysis is elevated in VMNL and decreased in DMNL rats. Both VMNL and DMNL rats show normal basal and epinephrine-stimulated lipolysis in interscapular brown adipose tissue. Several hepatic enzymes are normal in DMNL and depressed in VMNL rats. The above data suggest that the DMN and its circuitry are part of an "organismic" set point system with a "true" body weight and no fat set point, as seems to be the case in the VMNL rat.