Electrical stimulation of the ventromedial hypothalamus enhances both fat utilization and metabolic rate that precede and parallel the inhibition of feeding behavior

The effects of ventromedial hypothalamic (VMH) stimulation on various metab olic parameters in freely moving animals were measured using a specific ind irect calorimetric chamber associated with a quantitative measurement of lo comotor activity, which allows the separate measurement of locomotor energy expenditure from that of background metabolism, BM (free from expenses due to locomotion). To obtain circumscribed VMH stimulation, a slight-intensit y (20-25 mu A) bipolar, constant current was applied for 15 min at the begi nning of the dark phase on ad libitum fed rats. The VMH stimulation suppres sed feeding for 40 min, then animals progressively recovered within the sub sequent 60 min as shown by comparison with the control group. On different days, the same stimulation parameters were applied while food was unavailab le, and metabolic parameters were recorded. An increase in BM lasting 30 mi n was observed. This increase in metabolic rate was sustained by means of a recruitment of lipid stores as indicated by a concomitant drop in respirat ory quotient. These observations indicate that the VMH is part of the sympa thetic nervous system, capable of inducing lipolysis. The sequence of metab olic and feeding events may then in part be due to VMH-induced lipolysis th at provides more fuel to the metabolic economy, raising the BM, which in tu rn decreases hunger. (C) 1999 Elsevier Science B.V. All rights reserved.