Effect of Delta-Opioid Receptor Over-Expression on Cortical Expression of GABAA Receptor α1-Subunit in Hypoxia

Recent studies show that both delta-opioid receptors (DOR) and GABA receptors play a neuroprotective role in the mature cortex. Since we have observed that DOR over-expression renders the cortex more tolerant to hypoxic stress, we asked whether DOR over-expression affects GABA receptors expression in the cortex under hypoxia. As the first step, we investigated the expression of GABA(A) receptor alpha 1-subunit (GABA(A) R alpha 1, the most abundant alpha-subunit of GABA receptors in the adult brain) in the mouse cortex with transgenic DOR over-expression after hypoxia. The results showed that GABA(A) R alpha 1 expression was lower in the transgenic than wild-type cortex, suggesting that DOR overexpression induces an inhibitory effect on GABA(A) receptor expression. Hypoxia for 1-3 days significantly increased GABA(A) R alpha 1 expression in the wild-type cortex, which may be an adaptive strategy for protecting the cortex against hypoxic stress. interestingly, such increase was not found in the transgenic cortex with DOR over-expression. This may represent an interactive regulation in the transgenic cortex to efficiently balance energy production and consumption for better adaptation to hypoxic environment. Since DOR over-expression increases cortical tolerance to hypoxia, an increase in GABA receptors expression (an energy-costing process) may not be necessary in the cortex with DOR over-expression.