GABA Improved Visual Cortical Function In Chronic Morphine Exposed Cats

Drug abuse is a major social and medical problem around the world. Chronic opiates exposure can not only create a physical and psychological dependence, but also led to maladaptive changes in brain function, including the visual cortical function. Previous results suggest that chronic morphine exposure led to degradation of response modulation of the primary visual cortex (area17) cells in cats, such as higher spontaneous activity, lower signal-to-noise ratios, weaker orientation and direction selectivity, weaker response modulation and a longer time course of response. On the other hand, other results show that chronic morphine exposure can also cause damage to GABAergic system.GABAergic system is one of the most important inhibitory systems in the cortex. Some previous results suggest that GABAergic inhibition plays an important role in visual function regulation. They also support that complement inhibition to neurons which lack of inhibition can improve their function. There is strong possibility that the degradation of response modulation of visual cortical cells in chronic morphine-treated cats is caused by the declining of inhibition of GABAergic system. So we consider whether complement of inhibition could recover the damage caused by chronic opiates exposure in cells of area17. If it could, we can confirm this hypothesis that the degradation of visual function is indeed caused by the declining of inhibition of GABAergic system.To test this hypothesis, we used multibarreled microelectrodes to study the effects of electrophoretic application of GABA and the GABAA receptor antagonist bicuculline, respectively, on the properties of individual area17cells in morphine-treated cats (MCs) and saline-treated cats (SCs) as control. We tested spontaneous activity, signal-to-noise ratios, orientation selectivity, and direction selectivity in cells of area17of both group, before and after drug administration.The results of this study show that the administration of GABA improved visual function in MCs. GABA decreased spontaneous activity, increased ability to signal visual stimuli, and improved orientation and direction selectivity. After GABA application, some area17cells in MCs even displayed responses similar to cells in SCs. On the other hand, administration of bicuculline shows degradation of response modulation to cells in SCs. Bicuculline exerted a much weaker effect on neuronal responses in MCs than in SCs. In contrast, GABA exerted a much stronger effect on neuronal responses in MCs than in SCs. In addition, to the cells which already show strongly selectivity, GABA even can also improve there orientation and direction selectivity in MCs, but shows no effect in SCs.These results confirm the degradation of GABA-mediated inhibition in chronic morphine exposed cats, and also suggest that the degradation of response modulation of visual cortical cells in chronic morphine-treated cats is caused by the degradation of inhibition of GABAergic system. Complement of GABA could improve visual cortical function in cells of area17, and recover the damage caused by chronic opiates exposure. Thus, the fact can contribute to important implications in treatment to declines in sensory, motor, and cognitive happened on drug users.