Cholinergic modulation of the acoustic startle response in the caudal pontine reticular nucleus of the rat

The startle response is a useful behavioural model to assess drug effects o n sensorimotor information processing in the mammalian central nervous syst em. Prepulse inhibition of the acoustic startle response in rats is an oper ational measure for sensorimotor gating mechanisms which may be necessary f or attention and response selection. The caudal pontine reticular nucleus i s a key element of the pathway that mediates the acoustic startle response and receives an inhibitory cholinergic projection that might be important f or prepulse inhibition. The present study tested whether prepulse inhibitio n of acoustic startle is modulated by microinfusions of the muscarinic/nico tinic acetylcholine receptor agonist carbachol and of the muscarinic acetyl choline receptor antagonist scopolamine. Carbachol (0-40 nmol/0.5 mu l) dos e dependently attenuated startle and enhanced prepulse inhibition. Scopolam ine (0-40 nmol/0.5 mu l) dose-dependently enhanced startle and reduced prep ulse inhibition at a dose of 10 nmol. Scopolamine (40 nmol) also increased the spontaneous motor activity of the rats. These findings lend support to the hypothesis that muscarinic acetylcholine receptors in the caudal pontin e reticular nucleus inhibit the acoustic startle response and are involved in the mediation of prepulse inhibition of startle. (C) 1999 Elsevier Scien ce B.V. All rights reserved.