Circannual somatostatin gene and somatostatin receptor gene expression in the early post-natal rat pineal gland

The origin of somatostatin in the pineal gland is controversial as a double origin - neural in pinealopetal nerve fibers and parenchymal corresponding to locally synthesized peptide - is suggested. We have investigated the ontogeny and possible circadian and circannual variations of somatostatin and somatostatin receptor gene expression in the rat pineal gland using RT-PCR. Somatostatin gene expression was observed in the pineal of animals up to 15 days of postnatal life in autumn and winter, but not in prepubertal or adult rats; no transcript was detected during spring and summer at any age and a circadian rhythm was only detected in 15-day-old rats, In situ hybridization confirmed these results. The transcript of the somatostatin receptor gene (SSTR2) was detected at all ages studied with no seasonal variations in its expression, indicating separate regulatory mechanisms. In conclusion, somatostatin and somatostatin receptor mRNAs are expressed in the neonatal rat pineal with circadian and seasonal variations.