Age-related decrease in GABAB receptor binding in the Fischer 344 rat i inferior colliculus

Quantitative receptor autoradiography was used to asses GABA_B receptor binding in three primary subdivisions of the inferior colliculus (IC): dorsal cortex (DCIC), external cortex (ECIC), and the central nucleus (CIC) of 3-, 18–20- and 26-month-old Fischer 344 rats. GABA_B binding sites were localized using [³H]GABA in the presence of a saturating concentration of isoguvacine, a selective GABA_A receptor agonist, to displace [³H]GABA bound to GABA_A receptor sites. In the three 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.05 For comparison, GABA_B binding was determined in the portion of cerebellum located in the recess of the IC. In the molecular layer of this region, there were no statistically significant differences in receptor binding between 3, 18–20- and 26-month-old rats. In addition, there was not a significant age-related change in the cross-sectional area of the IC. These findings provide additional evidence to support the existence of selective age-related changes in GABA neurotransmitter function in the rat IC.