Levels of ionotropic glutamate (Glu) N-methyl-D-aspartic acid (NMDA), 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propionic acid (AMPA), and kainic acid (KA) receptors in forebrain regions of juvenile rats (age 42 days) were quantified after 3 weeks of treatment with three different doses of risperidone (0.3, 1.0 and 3.0 mg/kg) and compared findings to those in adult rats treated with risperidone (3.0 mg/kg/day) previously. Risperidone (at 0.3 mg/kg/day) did not alter levels of three ionotropic Glu receptors in all brain regions examined. Risperidone (at 1.0 and 3.0 mg/kg/day) significantly decreased NMDA binding in caudate-putamen of juvenile and adult animals. In contrast, the same two doses of risperidone decreased NMDA receptors in nucleus accumbens of juveniles and not adults. Risperidone (at 1.0 and 3.0 mg/kg/day) increased AMPA receptors in medial prefrontal cortex and caudate-putamen of juvenile animals, whereas risperidone (at 3.0 mg/kg) increased AMPA receptors in caudate-putamen and hippocampus of adults. Kainate receptors were not altered by any dose of risperidone in any brain region examined in developing and mature animals. The findings indicate that risperidone exerts dose-dependent effects on Glu receptor subtypes in developing animals, and that Glu receptor responses to repeated administration of risperidone are different in juvenile animals than adults.
Keywords: Autoradiography, Caudate-putamen, Childhood-onset schizophrenia, Frontal cortex, Glutmate receptors, Risperidone