Experimental aggression and bruxism in rats

Aggression has been suggested as one of the etiologic factors in bruxism. Experimental bruxism, audible, nonfunctional grinding or clenching of the teeth, was provoked in aggressive animals by drugs affecting central dopaminergic systems. Electric foot-stimulation was used to induce aggression, evident as the threatening or fighting position, in paired male Wistar rats. After initial stimulation, shocks were given only to maintain the characteristic fighting pose. Apomorphine facilitated induction of aggressive behaviour by electric shocks, and the rats receiving both treatments showed bruxism more frequently than controls subjected to shocks alone: up to 95 bruxism periods registered by a tape recorder during 30 min, as opposed to a few sporadic periods in the controls. Without shocks, apomorphine-treated rats displayed stereotypy with locomotion and biting of various objects. Aggression and bruxism were not equally successfully induced after L-dopa given with a peripheral inhibitor of aromatic amino acid decarboxylase (benserazide) or when L-dopa treatment was modified with the inhibitor of dopamine-beta-hydroxylase (diethyldithiocarbamate) or monoamine oxidase inhibitor (iproniazid). However, all the present drug combinations known to enhance central dopaminergic function seemed to increase irritability and disposition to experimental oral dyskinesias. This was observed especially when a sensory stimulus was applied at the same time or the drug had an amine-releasing effect (pheniprazine).