title: 5-HT modulation of auditory and visual sensorimotor gating: I. Effects of 5-HT releasers on sound and light prepulse inhibition in Wistar rats.
abstract: Increasing evidence suggests an important role for serotonin (5-HT) neurons in the etiology and treatment of schizophrenia. The prepulse inhibition paradigm is used as a model for sensorimotor gating processes that are disrupted in schizophrenia. The present study assessed the general role of 5-HT in modulating auditory and visual prepulse inhibition in Wistar rats. A general overactivation of central serotonerigic pathways was produced pharmacologically by four different agents which all shared the common property of releasing 5-HT, i.e., p-chloroamphetamine, 3,4-methylenedioxymethamphetamine, N-ethyl-3,4-methylenedioxymethamphetamine, or fenfluramine. Within each test session, both sound and light prepulses were used to obtain a cross-modal assessment of auditory and visual sensory gating processes. All four 5-HT releasing agents produced dose-related disruptions of auditory and visual prepulse inhibition, with p-chloroamphetamine being the most potent. The releasers depressed baseline to varying degrees. The alpha 2-adrenergic agonist clonidine decreased baseline startle without substantially disrupting prepulse inhibition, demonstrating that the two effects were dissociable. Using fenfluramine as the most selective 5-HT releaser, two approaches were used to demonstrate 5-HT mediation of its disruptive effect on prepulse inhibition. In the first approach, the selective 5-HT uptake blocker MDL 28,618A was used to prevent fenfluramine-induced 5-HT release. In the second approach, prior exposure to a neurotoxic dose of p-chloroamphetamine (10 mg/kg) was used to produce a substantial, sustained depletion of cortical 5-HT, presumably reflecting the loss of 5-HT terminals. Both approaches reduced the disruptive effect of fenfluramine on auditory and visual prepulse inhibition, thereby demonstrating 5-HT mediation of these effects. Neither manipulation significantly affected the depressant effect of fenfluramine on startle baseline, demonstrating that the baseline-reducing and prepulse inhibition-reducing effects of fenfluramine could be dissociated. MDL 28,618A alone did not affect prepulse inhibition or basal startle levels, demonstrating an important functional difference between pharmacologically induced 5-HT uptake blockade and 5-HT release. In summary, these data indicate that serotonergic overactivation can disrupt auditory and visual sensorimotor gating as measured using sound and light prepulse inhibition in rats. These data support a potential role of excessive 5-HT activity as a contributing factor to disrupted sensory gating processes seen in schizophrenia and possibly other neuropsychiatric disorders.
authors.affiliation: Hoechst Marion Roussel Inc., Cincinnati, OH 45215, USA.
authors.forename: J H
authors.initials: JH
authors.lastname: Kehne
authors.forename: R A
authors.initials: RA
authors.lastname: Padich
authors.forename: T C
authors.initials: TC
authors.lastname: McCloskey
authors.forename: V L
authors.initials: VL
authors.lastname: Taylor
authors.forename: C J
authors.initials: CJ
authors.lastname: Schmidt
mesh_terms: D015104:3,4-Methylenedioxyamphetamine / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005277:Fenfluramine / Q000494:pharmacology; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013216:Reflex, Startle / Q000187:drug effects*; D012701:Serotonin / Q000378:metabolism*; D018490:Serotonin Agents / Q000494:pharmacology*; D010133:p-Chloroamphetamine / Q000494:pharmacology
chemical_list: D018490:Serotonin Agents; D005277:Fenfluramine; D012701:Serotonin; D015104:3,4-Methylenedioxyamphetamine; D010133:p-Chloroamphetamine