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BEHAVIORAL PHARMACOLOGY

Metabotropic Glutamate Subtype 5 Receptors Modulate Locomotor Activity and Sensorimotor Gating in Rodents

Department of Neuroscience, Merck Research Laboratories, West Point, Pennsylvania (G.G.K., M.B., P.J.C.); and Behavioral Pharmacology, San Diego, California (U.C.C., L.M.H., D.R., L.J.B.)

Use-dependent N-methyl-D-aspartate receptor (NMDAR) antagonists produce behaviors in human volunteers that resemble schizophrenia and exacerbate those behaviors in schizophrenic patients, suggesting that hypofunction of NMDAR-mediated neuronal circuitry may be involved in the etiology of clinical schizophrenia. Activation of the metabotropic glutamate receptor subtype 5 (mGluR5) enhances NMDAR-mediated currents in vitro. Thus, activation of mGluR5 could potentiate hypofunctional NMDARs in neuronal circuitry relevant to schizophrenia. To further elucidate the role of mGluR5, the present study examined the effects of mGluR5 antagonist administration, with and without coadministration of the use-dependent NMDAR antagonist phencyclidine (PCP), on locomotor activity and prepulse inhibition (PPI) of the acoustic startle response in rodents. We further examined PPI in mGluR5 knockout mice. Finally, we examined PPI after administration of the mGluR5 agonist 2-chloro-5-hydroxyphenylglycine (CHPG) alone and in combination with amphetamine. The data indicate that the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine has no effect on locomotor activity or PPI by itself but does potentiate both PCP-induced locomotor activity and disruption of PPI. We further found that mGluR5 knockout mice display consistent deficits in PPI relative to their wild-type controls. Finally, the data indicate that CHPG has no effect on PPI by itself, but ameliorates amphetamine-induced disruption of PPI. Collectively, these data suggest that mGlu5 receptors play a modulatory role on rodent PPI and locomotor behaviors and are consistent with the hypothesis that mGlu5 agonist/potentiators may represent a novel approach for antipsychotic drug development.

Address correspondence to: Dr. Gene G. Kinney, Department of Neuroscience, Merck and Co., Inc., P.O. Box 4, WP46–300, West Point, PA 19486. E-mail: gene_kinney{at}merck.com

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