HIGH-FREQUENCY ULTRASONIC VOCALIZATION INDUCED BY INTRACEREBRAL GLUTAMATE IN RATS

Direct injection of glutamate, a neuroexcitatory agent, into the anter ior hypothalamic-preoptic area of the rat brain induced ultrasonic voc alization. This vocalization was characterized by short-duration calls (below 60 ms) of high sound frequency (pitch), mostly above 40 kHz, a nd was similar to the known 50-kHz vocalization observed in natural si tuations. The glutamate-induced vocalization was dose dependent within the dose range of 16.9-67.6 mu g and was antagonized by local pretrea tment with MK-801, an NMDA antagonist. The increasing dosage of glutam ate induced more calls and had a significant influence on frequency an d intensity of emitted ultrasound. The average sound frequency increas ed whereas the mean sound intensity decreased with the dosage of gluta mate. On the other hand, the mean duration of a single call and the ba ndwidth did not significantly change with doses of glutamate. Injectio n of carbachol, a muscarinic cholinomimetic agent, into the same brain sites as glutamate, induced a different type of ultrasonic vocalizati on with low sound frequency and long call duration, known as 22-kHz ca lls. The results suggest that high sound frequency, short-duration cal ls (50 kHz) and low sound frequency, long-duration calls (22 kHz) have different neurophysiological and neurochemical mechanisms.