ELECTROMYOGRAPHIC DIFFERENTIATION OF THE COMPONENTS OF PERIORAL MOVEMENTS INDUCED BY SKF-38393 AND PHYSOSTIGMINE IN THE RAT

Facial electromyography (EMG) coupled with visual observation was used to investigate spontaneous and drug induced perioral movements in freely moving rats. Four separate perioral behaviours were identified; facial tremor, purposeless chewing, gaping and yawning. Facial tremor, yawning and gaping but not purposeless chewing produced characteristic EMG signals. Normal rats displayed a low level of purposeless chewing, occasional bursts of facial tremor but not gaping or yawning. Each burst of facial tremor was accompanied by a transient increase in purposeless chewing. Administration of the D-1 agonist SKF 38393 induced a dose related increase in bursts of facial tremors and consequently an increase in the total number of purposeless chews. Gaping and yawning were not induced by SKF 38393 administration. Administration of the cholinesterase inhibitor physostigmine (0.1-0.4 mg/kg) induced a dose related increase in the total number of purposeless chews, but primarily these were not associated with facial tremor. Administration of physostigmine also increased gaping and yawning. Administration of the D-1 antagonist SCH 23390 almost abolished facial tremor in normal treated rats but only partially reduced that induced by SKF 38393 and physostigmine. SCH 23390 reduced purposeless chewing in SKF 38393 treated rats but not in normal or physostigmine treated animals. Administration of the cholinergic antagonist atropine almost abolished facial tremor in normal and physostigmine treated rats, but only reduced by 46% that induced by SKF 38393. Atropine reduced purposeless chewing in normal, physostigmine and SKF 38393 treated animals. Physostigmine induced gaping and yawning were abolished by atropine administration. Combined administration of SKF 38393 and physostigmine did not alter the total number of facial tremor bursts and purposeless chews compared to those observed in rats treated with physostigmine alone. Administration of SKF 38393 with physostigmine reduced physostigmine-induced yawning. The EMG technique described allows assessment of the different profiles of perioral movement induced by SKF 38393 and physostigmine, and the relationship that exists between the different components. The results suggest that it is necessary to individually assess each individual perioral behaviour. Assessment of only one component in isolation, or of an amalgamation of several behaviours will add to the confusion that exists over the origins of perioral movement.