Maintenance of enriched environment-induced changes of auditory spatial sensitivity and expression of GABA_A, NMDA, and AMPA receptor subunits in rat auditory cortex

Enriched environment (EE) has an important role in the development and plasticity of the brain. In this study, we investigated the maintenance of early EE exposure-induced changes of spatial sensitivity, and the possible underlying mechanisms of this maintenance. We found that, compared with the age-matched control, the spatial sensitivity of A1 neurons was still enhanced after EE rats had been returned to the normal condition for 2months. The enhancement was expressed by a sharper frequency tuning curve, smaller spatial receptive field, and a more selective directional curve of the early EE-exposed rats. Simultaneously, we detected significant increases in GABA_A receptor α1, β3 subunits; NMDA receptor NR2A, NR2B subunits; AMPA receptor GluR2 subunit protein expression; and in the ratios of GABA_Aα1/GABA_Aα3 and NR2A/NR2B. In particular, the expression ratio change of the GABA_Aα1/GABA_Aα3 was significant greater than that of NR2A/NR2B in early EE-exposed rats. These observations indicate that the persistent higher expression levels of the GABAergic and glutamatergic receptors expression induced by early EE exposure, especially enhancement of GABAergic inhibition in the auditory cortex, might be responsible for the maintenance of improved effects in auditory spatial sensitivity after the rats had been returned to the normal condition.