Pharmacological approaches to habituation of the acoustic startle response in rats

Abstract

In a series of six experiments, the effects of pharmacological manipulations of the cholinergic (DFP, physostigmine, atropine, pilocarpine), the noradrenergic and dopaminergic (d-amphetamine), and the serotonergic (p-chlorophenylalanine and p-chloroamphetamine) systems on habituation of the acoustic startle response in rats (to a 1000-Hz, 110-dB tone) were examined. Only acute administration of DFP was found to significantly reduce the rate of habituation. There was a tendency of physostigmine and pilocarpine to depress the startle response and for atropine to facilitate it, suggesting that the cholinergic system may modulate the startle response level. Manipulations of the noradrenergic, dopaminergic, and serotonergic systems did not alter either the startle response level or the rate of habituation. However, recent literature from other laboratories was reviewed, and it was concluded that the doses and/or other conditions used in the present experiments were not appropriate for observing significant changes in the startle response. It was further concluded that either the neurotransmitter systems examined in the present study were not involved in the processes underlying habituation or that the pharmacological manipulations used were not appropriate for differentiating among the mechanisms that may underlie habituation.