Differential effects of haloperidol and clozapine on ionotropic glutamate receptors in rats

Despite multiple lines of investigation the effect of neuroleptics on glutamate‐mediated neurotransmission remains controversial. To study the effects of typical and atypical neuroleptics on selected parameters of glutamate‐mediated neurotransmission, male Sprague‐Dawley rats were randomly assigned to a 21‐day oral treatment course with vehicle, haloperidol (HDL), or clozapine (CLZ). Coronal slices of rat brain were then incubated with tritiated ligands to measure NMDA, AMPA, and kainate receptor, and glutamate reuptake site density. Regions of interest included the frontal cortex, anterior cingulate cortex, dorsal striatum, ventral striatum, and the nucleus accumbens. CLZ increased the density of AMPA receptors significantly in the frontal and anterior cingulate cortices compared with normal controls. In the dorsal and ventral striatum, and nucleus accumbens as a whole, CLZ‐treated rats had a higher AMPA receptor density compared with both the HDL‐ and vehicle‐treated controls. Additionally, within the nucleus accumbens, CLZ‐treated rats had a higher density of AMPA receptors compared with the HDL group in the core, and at trend level in the shell. There was a group by region interaction for NMDA receptor density, primarily reflecting the tendency of HDL treated rats to have high receptor densities in the frontal and anterior cingulate cortices. Kainate receptors and glutamate reuptake site densities did not differ significantly across groups. These results suggest a critical role for glutamate in the mediation of atypical antipsychotic drug action in anatomically‐specific regions, and further encourage the investigation of glutamate neurotransmitter systems in schizophrenia. Synapse 34:266–276, 1999. Published 1999 Wiley‐Liss, Inc.