FUNCTIONAL-ROLE OF VENTRAL RESPIRATORY GROUP EXPIRATORY NEURONS DURING VOCALIZATION

The activities of expiratory neurons of the caudal ventral respiratory group (cVRG) (n = 31) were recorded extracellularly during vocalizati on in unanesthetized, decerebrate cats. Vocalization was induced by el ectrical stimulation (0.2 ms, 20-80 mu A, 100 Hz, lasting for 2-5 s) o f the periaqueductal gray (PAG). The firing rates of more than two-thi rds of the neurons (24/31) increased during periods of vocalization in duced by stimulation of the PAG, with an increase in abdominal muscle activities. The axons of most of these neurons (19/24) projected to th e contralateral lumbar spinal cord, and one-third of the bulbospinal n eurons (6/19) were orthodromically activated by stimulation of the PAG . Even after sectioning of the axons of bulbospinal cVRG neurons by mi dsagittal lesion between the obex and the C-1 spinal cord, stimulation of the PAG still induced adduction of the vocal cords and vocalizatio n. However, activities of abdominal muscles during vocalization were a bolished. These results indicate that the efferent signals for vocaliz ation from the PAG may be relayed at the cVRG neurons and converted in to adequate activation of these neurons, contributing to the activatio n of the abdominal muscles for vocalization.