The Role Of GABA_B Receptor In Ocular Dominance Plasticity

The connection of neurons in visual system can be precisely adjusted according to external environment and experience, which is called visual plasticity. The dramatic modification occurs in the critical period, a restricted time window after the birth during which the visual cortex is sensitive to experience. Visual plasticity weakens even disappears at adulthood after the critical period. Previous results suggest that GABA_A receptor-mediated inhibitory system plays an important role in the onset and closure of the critical period. However, the role of GABAergic inhibitory system during the critical period is unclear. The metabotropic GABA_B receptor, another important member of the inhibitory system, regulates inhibition via the potassium ion channel directly and regulation of the GABA release to the GABA_A receptors indirectly. The GABA_B receptor also regulates the concentration of cAMP through its linked G protein. The cAMP-PKA pathway has been shown to be important to visual plasticity. So far, the role of GABA_B receptor in ocular dominance plasticity has not been studied.First, we administrated the GABA_B receptor agonist baclofen or antagonist sch50911 into the visual cortex of monocularly deprived kittens during their critical period. The ocular dominance shift was impaired by sch50911 and was promoted by baclofen, suggesting that GABA_B receptors bidirectionally regulate the visual cortical plasticity during the critical period. We further addressed whether GABA_B receptors mediate the closure of the critical period. Neither the GABA_B receptors agonist baclofen nor antagonist sch50911 could restore ocular dominance plasticity at adult cats. Considering previous finding that the antagonist of the GABA_A receptors picrotoxin could restore plasticity in adult rats, we come up with two hypotheses: 1) GABA_B receptors have nothing to do with the closure of the critical period. 2) The mechanisms of ocular dominance plasticity between cat and rat are different. To validate these hypotheses, we infused GABA_A receptors inhibitor picrotoxin into the visual cortex of monocularly deprived adult cats. In contrary to the results in rats, no ocular dominance shift was detected in the adult cats. These results suggest different mechanisms are responsible for the closure of the critical period between cat and rat.