In our previous studies, the opioid receptors located on pinealocytes have
been identified and characterized, and these receptors have been found to p
lay a stimulatory role in melatonin synthesis by activating the rate limiti
ng enzyme, N-acetyltransferase (NAT). In the present study, by using revers
e 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(alpha i/o)- and G(beta)-protein-coupled receptor mRNAs have
been amplified and identified from rat pineal gland, The regulatory effect
s of morphine on G(alpha i/o) and G(beta) mRNA levels have been semiquantit
atively analyzed. Acute morphine administration caused significant increase
in G(alpha i/o) and G(beta), mRNA levels in rat pineal gland, but not in o
ther brain regions, Further studies are needed in order to elaborate the me
chanisms of these opioid receptors in regulating G-protein expression in pi
neal gland. (C) 1999 Academic Press.