| Summary: | 碩士 === 國立中山大學 === 生物科學系研究所 === 100 === Cocaine (CA) exposure during pregnancy causes long-lasting negative effects on fetal brain development and eventually results in motor dysfunction or changes in learning and memory performance. γ-amino-butyric acid (GABA) is the primary inhibitory neurotransmitter in the adult brain and undergo a switch from excitatory to inhibitory during early postnatal period. The excitatory/inhibitory switch is resulted in the relative temporal expression of K+-Cl- cotransporter 2 (KCC2). GABA is the neurotransmitter in the rat was born from excitement to inhibition and until the growth of thirty days have completely inhibitory. Here we test the effect of CA prenatal exposure on the expression of KCC2 in prefrontal cortex (recognition), hippocampus (memory), VTA (reward) and nucleus accumbens (reward). Protein expression profile of control or prenatal CA treated groups were evaluated by western blot in 2 days interval from postnatal day (PND) 8 to 30. The expression of KCC2 was time-dependently enhanced from PND 8 and reaches its maximal expression around PND 18 in prenatal CA exposure groups. The time-dependent profile of KCC2 expression in prefrontal cortex and NAc was significantly delayed in prenatal CA exposure group. We then correlate the KCC2 expression and the cocaine sensitivity by locomotor activity assay. We found group A shows a higher sensitivity to cocaine than group B in control rats. Surprisingly, group A of prenatal cocaine reduce the sensitive to cocaine to a similar extend like group B in control rats, suggesting prenatal exposure of cocaine might enhance the KCC2 expression. Furthermore, age range of A group (PND 22~27) and B group (PND 29~34) to repeated cocaine exposure resulted in up-regulation of KCC2 expression in B group earlier than A group. We found that the KCC2 expressions of repeated cocaine exposure in B group were higher than A group. In other words, in the B group, the inhibitory effect of GABA was significant and the locomotor activity was relatively slow. Therefore, the A group was more easy be cocaine addiction than B group. We next explore the signaling mechanism underlying cocaine exposure-induced KCC2 expression inhibition. Brain slices were incubated with cocaine with or without dopamine receptor antagonists and KCC2 expression was evaluated by western blot. Either SCH23390 (dopamine D1-receptor inhibitor) or eticlopride (dopamine D2-receptor inhibitor) significantly hamper the inhibition of KCC2 expression by cocaine in normal slices. However, only D2 antagonist eticlopride but not SCH23390 is effective reverse cocaine-induced KCC2 expression inhibition. Overall, results from our current studies provide a further insight into the molecular mechanism of cocaine-induced synaptic modification.
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