Gene expressions of opioid receptors and G-proteins in pineal glands.

In our previous studies, the opioid receptors located on pinealocytes have been identified and characterized, and these receptors have been found to play a stimulatory role in melatonin synthesis by activating the rate limiting enzyme, N-acetyltransferase (NAT). In the present study, by using reverse transcriptase polymerase chain reaction (RT-PCR) followed by nested-PCR, segments of delta and mu opioid receptors have been amplified from mRNA of rat pineal gland and cerebral cortex. In addition, segments of delta and mu opioid receptors have also been amplified from mRNA of human pineal gland. Furthermore, G(alphai/o)- and G(beta)-protein-coupled receptor mRNAs have been amplified and identified from rat pineal gland. The regulatory effects of morphine on G(alphai/o) and G(beta) mRNA levels have been semiquantitatively analyzed. Acute morphine administration caused significant increase in G(alphai/o), and G(beta), mRNA levels in rat pineal gland, but not in other brain regions. Further studies are needed in order to elaborate the mechanisms of these opioid receptors in regulating G-protein expression in pineal gland.