The expression of GABA_A receptor subunits in the substantia nigra is developmentally regulated and region-specific

The substantia nigra pars reticulata (SNR) controls the spread of seizures. GABA_Aergic drug (agonist or antagonist) infusions into the SNR have age-specific and site-specific effects on flurothyl-induced seizures. Developmental and cell-specific regulation of GABA_A receptor subunit expression may be responsible for these specific effects. To test this hypothesis, in situ hybridization was used to examine regional expression of α1 and γ2L GABA_A receptor subunit mRNAs in the SNR during development. Distinct temporal and spatial patterns of expression were observed. In rats at postnatal days (PN) 21-60, fewer neurons were labeled with probes directed to α1 and γ2L subunits in SNR_anterior compared with SNR_posterior. In addition, neurons in SNR_anterior contained higher amounts of hybridization grains than in SNR_posterior. In PN 15 rats, the labeling of neurons was relatively diffuse throughout the anterior and posterior SNR regions with moderate amounts of hybridization grains for both subunits. The finding of age-related differential distribution of α1 and γ2L subunit mRNAs in the SNR suggests that GABA_A receptor heterogeneity may play a role in the age-specific and site-specific effects of GABA_Aergic agents on seizures in the SNR.