Effects of Chemical Stimulation in the Periaqueductal Gray on Vocalization in the Squirrel Monkey

Twenty-nine agonists and 32 antagonists of more than 10 transmitters known to be present in the periaqueductal gray(PAG)have been injected into the squirrel monkey's PAG in order to test their effects on spontaneous vocalization at sites yielding vocalization with electrical stimulation. Vocalization could be elicited with the glutamate agonists sodium-L-glutamate,