Differential effects of the strychnine-insensitive glycine site antagonist (+)-HA-966 on the hyperactivity and the disruption of prepulse inhibition induced by phencyclidine in rats

A developmental influence of the N-methyl-D-aspartate receptor NR3A subunit on prepulse inhibition of startle

BACKGROUND

The N-methyl-D-aspartate (NMDA) receptor is composed of various conformations of multiple subunits (including NR1, NR2A-D, and NR3A-B). Peak expression of the NR3A subunit occurs approximately 2-3 weeks postnatal, with low levels in adulthood. In the brain, the NR3A subunit is localized primarily in the amygdala, hippocampus, striatum, and cortex. These regions are involved in the modulation of prepulse inhibition of startle (PPI), an operational measure of sensorimotor gating that is modulated by NMDA receptors. NR3A reduces NMDA current in native neurons expressing NR1 and NR2 subunits and forms glycine receptors when expressed with NR1 in the absence of NR2 in both oocyte and mammalian expression systems.

METHODS

To examine the role of NR3A in vivo, NR3A knockout (KO), and overexpressing transgenic mice were generated. Adult NR3A overexpressing mice exhibited normal PPI; PPI in NR3A KO mice was tested repeatedly from weaning through adulthood.

RESULTS

Male NR3A KO mice exhibited an increase in PPI at 3 and 4 weeks postnatal, whereas female NR3A KO mice did not differ from their WT counterparts at any age tested.

CONCLUSIONS

This sex-specific increase in PPI is consistent with the antagonistic role of the NR3A subunit in NMDA receptor function and with the observation that estrogen modulates NMDA receptor function.

Interactions of the mGluR5 gene with breeding and maternal factors on startle and prepulse inhibition in mice

Sensorimotor gating, measured by prepulse inhibition (PPI), is a fundamental form of information processing that is deficient in schizophrenia patients and mice lacking the gene for metabotropic glutamate receptor 5 (mGluR5). Both breeding strategies and mothering behaviors are capable of influencing the behavioral phenotype of knockout (KO) mice. Previous studies found a PPI deficit and increased startle magnitudes in mGluR5 KO mice derived from homozygous matings. Here we compared the PPI of mGluR5 wildtype (WT) and KO mice derived from heterozygous matings to that seen in mice derived from homozygous matings. Possible influences of postnatal mothering behaviors were examined using two different methods of cross-fostering. The potential developmental nature of the PPI deficit of the mGluR5 KO mice was also addressed via acute administration of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) to C57BL/6J mice. The mGluR5 KO mice exhibited reduced PPI independently of breeding strategy or postnatal mothering behavior. Startle magnitude, however, varied with breeding strategy. The PPI deficit seen in the mGluR5 KO mice is not mimicked by acute administration of an mGluR5 antagonist, and is therefore most likely due to compensatory alterations in neuronal circuitry occurring during development independent of maternal behaviors in the postnatal environment.

Phencyclidine in the social interaction test: an animal model of schizophrenia with face and predictive validity

Phencyclidine (PCP) is a hallucinogenic drug that can mimic several aspects of the schizophrenic symptomatology in healthy volunteers. In a series of studies PCP was administered to rats to determine whether it was possible to develop an animal model of the positive and negative symptoms of schizophrenia. The rats were tested in the social interaction test and it was found that PCP dose-dependently induces stereotyped behaviour and social withdrawal, which may correspond to certain aspects of the positive and negative symptoms, respectively. The effects of PCP could be reduced selectively by antipsychotic drug treatment, whereas drugs lacking antipsychotic effects did not alleviate the PCP-induced behaviours. Together these findings indicate that PCP effects in the rat social interaction test may be a model of the positive and negative symptoms of schizophrenia with face and predictive validity and that it may be useful for the evaluation of novel antipsychotic compounds.

Competitive NMDA receptor antagonists disrupt prepulse inhibition without reduction of startle amplitude in a dopamine receptor-independent manner in mice

Prepulse inhibition is thought to reflect the operation of the sensorimotor gating system in the brain, and is reduced in schizophrenic patients and in animals treated with non-competitive NMDA receptor antagonists such as phencyclidine and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine ((+)-MK-801). Previously, we reported that a competitive NMDA receptor antagonist, cis-4-phosphonomethyl-2-piperidine-carboxylate hydrochloride (CGS 19755), also disrupts prepulse inhibition concomitantly with a marked reduction of startle amplitude elicited by pulse alone in rats. In the present study, the effect of NMDA receptor antagonists on prepulse inhibition was tested in mice. In addition, involvement of the dopaminergic system in CGS 19755-induced disruption of prepulse inhibition was examined. When CGS 19755 was subcutaneously administered at 40 and 80 mg/kg, prepulse inhibition was disrupted without any change in the startle amplitude elicited by pulse alone. Intracerebroventricularly administered CGS 19755 disrupted prepulse inhibition at dosages of 0.1 and 0.2 microg/mouse. The same dosages of R-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (R-CPP), another competitive NMDA receptor antagonist, also decreased prepulse inhibition, while its less active enantiomer, S-CPP, did not affect prepulse inhibition at 0.2 microg/mouse (i.c.v.). A typical neuroleptic, haloperidol, did not significantly improve CGS 19755 (40 mg/kg s.c.)-induced disruption of prepulse inhibition. These results suggest that the disruption of prepulse inhibition by CGS 19755 and R-CPP is NMDA receptor-mediated and dopamine receptor-independent.