BRAIN MECHANISMS OF VOCAL PRODUCTION IN SQUIRREL MONKEYS

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This project investigates the effect of neurological and pharmacological interventions on the incidence and structure of squirrel monkey vocalizations emitted during standardized conditions in the laboratory. A collaborative study has focused on the effect of various cerebral lesions on the production of the isolation call (IC). We tested whether ablation of midline frontal neocortex lying peripheral to a previously discovered critical band of limbic cortex would interfere with IC production. We found that in the absence of this neocortical tissue there was full recovery of spontaneously produced ICs. Other current work is directed at the chemical substrates mediating vocal production. The role of the adrenergic system in IC production was studied. We established dose-response relationships for the alpha-adrenergic agonist clonidine and alpha-2 antagonist yohimbine, using rate of IC production as the behavioral response measure. Both drugs exhibit dose-dependent effects on IC production, the agonist decreasing and the antagonist increasing calling rate. Since yohimbine reverses the clonidine-induced reduction of IC calling rate, we tested the specificity of an alpha-2 mechanism in mediating this behavior by substituting the alpha-1 antagonist prazosin for yohimbine. We found that this drug, in a dose of 0.25 mg/kg, was completely ineffective in reversing clonidine-induced vocal suppression. In another experiment, we established that adrenergic and opiatergic mechanisms can interact in mediating IC calling rate. Systemic administration of yohimbine concurrently with naloxone resulted in up to 7-fold increases in calling over rates following treatment with either drug alone. The role of cholinergic mechanisms in mediating alarm call production was investigated. We found that a centrally active cholinomimetic, physostigmine, was ineffective by itself, but it blocked the increased calling produced by the anticholinergic compound benactyzine. Cholinergic or anticholinergic compounds tested were without effect on IC production.