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(A)ergic drug (agonist or antagonist) infusions into the SNR have age- specific and site-specific effects on flurothyl-induced seizures. Developme ntal and cell-specific regulation of GABA(A) receptor subunit expression ma y be responsible for these specific effects. To test this hypothesis, in si tu hybridization was used to examine regional expression of alpha 1 and gam ma 2L GABA(A) receptor subunit mRNAs in the SNR during development. Distinc t temporal and spatial patterns of expression were observed. In rats at pos tnatal days (PN) 21-60, fewer neurons were labeled with probes directed to al and gamma 2L subunits in SNRanterior compared with SNRposterior. In addi tion, neurons in SNRanterior contained higher amounts of hybridization grai ns than in SNRposterior. In PN 15 rats, the labeling of neurons was relativ ely diffuse throughout the anterior and posterior SNR regions with moderate amounts of hybridization grains for both subunits. The finding of age-rela ted differential distribution of al and gamma 2L subunit mRNAs in the SMR s uggests that GABA(A) receptor heterogeneity may play a role in the age-spec ific and site-specific effects of GABA(A)ergic agents on seizures in the SN R.