Glutamate-induced vocalization in the squirrel monkey.

In the squirrel monkey, 164 brain sites yielding vocalization when electrically stimulated were tested for their capability to produce vocalization when injected with mono-sodium-L-glutamate. The sites were located in the anterior limbic cortex, n. accumbens, substantia innominata, amygdala, n. striae terminalis, hypothalamus, midline thalamus, field H of Forel, substantia nigra, periventricular and periaqueductal gray, inferior colliculus, reticular formation of midbrain, pons and medulla, inferior olive, lateral reticular nucleus and nucleus of solitary tract. Of the 164 sites tested, 31 were positive. These were located in the substantia innominata, caudal periventricular and periaqueductal gray, lateral pontine and medullary reticular formation. While all the calls obtained from the forebrain and midbrain had a normal acoustic structure, most pontine and all medullary vocalizations had an artificial character. It is concluded that: the substantia innominata, caudal periventricular and periaqueductal gray, lateral pontine and medullary reticular formation represent relay stations of vocalization-controlling pathways; the periaqueductal gray represents the lowest relay station above the level of motor coordination; neurons responsible for motor coordination of vocalization lie in the reticular formation around the caudal brachium conjunctivum, the superior olive, n. facialis, n. ambiguus and below the n. solitarius; not all areas from which vocalization can be obtained by electrical stimulation of nerve cell bodies, dendrites and nerve endings (in contrast to fibers en passage) also yield vocalization when stimulated with glutamate.