Brainstem mechanisms of vocalization analyzed by electrical stimulation and chemical stimulation of sodium glutamate in cats

Abstract

The functional connection between the midbrain and the lower brain structures which organize vocalization was investigated in cats. To induce vocalization, repetitive electrical stimulation (0.2ms, 10-300 microA, 100Hz, lasting for 5 to 10s) was delivered to the caudal part of the ventrolateral periaqueductal gray (PAG), adjacent reticular formation (RF) or the pontine call site (PCS) which is located in the ventrolateral pontine RF. In Ketamine-anesthetized cats (n = 12), the stimulus threshold was the lowest in the ventrolateral PAG, and the stimulus threshold within the RF near the PAG tended to be higher than that in the PAG. In the effective RF area, the stimulus threshold was lower in the ventral area than that in the dorsal area. The effective area extended from the PAG through the RF to the PCS. The stimulus threshold around the PCS was the lowest in all animals. The size of the effective area was about 1 to 1.5mm in diameter within the PAG and the RF, and was wider than that in the PCS, which was about 0.5 to 1.0mm in diameter. There was a tendency for a wider effective area to correlate with a higher stimulus threshold. These results suggest that axons from the PAG area pass through the nearby RF and then compose a narrower fiber bundle in the PCS. In unanesthetized decerebrate cats (n = 5), a microinjection of glutamate, (2M sodium glutamate dissolved in 0.1M phosphate buffer (pH = 7.4)), was made with a glass micropipette (tip outer diameter: 200 microns) attached to a microsyringe with a polyethylene tube.(ABSTRACT TRUNCATED AT 250 WORDS)