TIME-COURSE OF VMN LESION EFFECTS ON LORDOSIS AND ULTRASOUND PRODUCTION IN HAMSTERS

Lesions of the ventromedial hypothalamus (VMN) depress lordosis but in crease ultrasonic vocalization in female hamsters. These changes are c onsistent with the behavioral incompatibility of lordosis and ultrasou nd production and suggest that the VMN coordinates short-term changes in these behaviors. In keeping with past results, unilateral lesions d isrupted lordosis responses to contralateral flank stimulation. The ch ange appeared within 15 min after the lesion and was much more rapid t han the corresponding effect in rats. For hamsters, these findings sup port other evidence suggesting VMN mediation of somatosensory, not jus t hormonal, influences on lordosis. In a companion study, ultrasound r ates became depressed within 15 min of bilateral lesion of the VMN, su ggesting a role for the VMN in the short-term control of ultrasound pr oduction. Calling at later time intervals was facilitated by the lesio ns. The direction and time course of the lesion effects on lordosis an d ultrasound production suggest that the VMN cannot easily account for the behavioral incompatibility of these 2 responses.