Relationship of glutamic acid and gamma-aminobutyric acid receptor to the auditory spatial response areas of the inferior collicular neurons in monaural plugged gerbil

Aim. To study the effects of gamma-aminobutyric acid (GABA), bicuculline, NMDA and DL-2-amino-5-phosphonovaleric acid (APV) on the auditory spatial response areas of the contralateral inferior collicular (IC) neurons in monaural plugged gerbils (Meriones unguicul). Methods. 4 weeks after plugging one side ear at the different postnatal ages (21 dpn, 42 dpn and 70 dpn), gerbils were treated with GABA, bicuculline, NMDA and APV respectively by iontrphoretic technique and the changes of auditory spatial response areas of the contralateral IC were recorded by electrophysiological method. Results. The auditory spatial response areas of 3 week, 6 week, adult plugging groups were 0.270 ± 0.579, 0.145 ± 0.096 and 0.067 ± 0.049 (m²) respectively and there was no significantly difference between the former two groups (t = 0.7569, P = 0.4508). After treatment the areas were reduced by GABA, APV and enlarged by bicuculline, NMDA. Except the APV effect on 3 week-plugging group (P = 0.1538, t = 5.8408), there were significantly different among the other groups before and after treatment. Comparing the variety rate of auditory spatial response areas by drug in three groups, there was a significant difference between the 3 week-plugging and adult-plugging groups by GABA, and between the 6 week-plugging and adult-plugging groups by bicuculline or APV (P = 0.0208, t = 2.4065; P = 0.0448, t = 2.0665; P = 0.0037, t = 3.1751). But there was no significant difference among the other groups. Conclusion. During the auditory development course of gerbil, the critical period of GABA inhibitive mechanism foundation is continued to the sixth week postnatal, the NMDA excitative mechanism foundation is at the sixth week prenatal and there is a phase to adjust and match with each other.