AGE-RELATED DECREASE IN GABA(B) RECEPTOR-BINDING IN THE FISCHER-344 RAT INFERIOR COLLICULUS

Quantitative receptor autoradiography was used to assess GABA(B) recep tor binding in three primary subdivisions of the inferior colliculus ( IC): dorsal cortex (DCIC), external cortex (ECIC), and the central nuc leus (CIC) of 3-, 18-20-, and 26-month-old Fischer 344 rats. GABA(B) b inding sites were localized using [H-3]GABA in the presence of a satur ating concentration of isoguvacine, a selective GABA(A) receptor agoni st, to displace [H-3]GABA bound to GABA(A) receptor sites. In the thre e IC subdivisions examined, GABA(B) receptor binding was significantly reduced in 26-month-old rats when compared to 3-month-old rats (DCIC, -44%; ECIC, -36%; CIC, -32%; p < 0.05). For comparison, GABA(B) bindi ng was determined in the portion of cerebellum located in the recess o f the IC. In the molecular layer of this region, there were no statist ically significant differences in receptor binding between 3, 18-20-, and 26-month-old rats. In addition, there was not a significant age-re lated change in the cross-sectional area of the IC. These findings pro vide additional evidence to support the existence of selective age-rel ated changes in GABA neurotransmitter function in the rat IC.