The effects of l-Dopa,clonidine, and apomorphine on the acoustic startle reaction in rats

The present investigation provides evidence for noradrenergic involvement in the elaboration of the acoustic startle reaction.Within-subject experiments demonstrated that an amine-depleting dose of reserpine enhanced the level of the startle reaction and that this effect was reversed by the catecholamine precursor, l-Dopa. Chemical assays suggested a correlation between the accumulation of noradrenaline and reversal of reserpine effects. Administration of the noradrenaline receptor-stimulating agent, clonidine (0.125 or 0.250 mg/kg) produced marked reductions in startle amplitude reducing the response far below normal values in reserpinized subjects. By contrast, the dopamine receptor-stimulating agent, apomorphine (1.0 mg/kg) did not alter the response. None of the pharmacological agents used was found to alter the inhibition of the startle reaction which results from the presentation of neutral stimuli (prepulses) shortly before reflex elicitation.Taken together with an earlier report, the present data suggest that noradrenaline and serotonin have partially antagonistic control over the startle reaction.Submitted in partial fulfillment of the requirements for the Ph. D. degree from the University of Rochester. The thesis advisors, Dr. Carol Kellogg and Dr. James Ison, are warmly thanked for their advice, encouragement, guidance, and continuing support. The research was supported in part by NSF grant GB-14814, NIMH grant MH-10825, and ONR contact N00014-68-0091.