Microdialysis reveals dynamics of coupling between noradrenaline release and melatonin secretion in conscious rats

The coupling between noradrenergic innervation of the pineal gland and melatonin production was investigated. Previously, the development of a microdialysis; technique was described which made it possible to study the noradrenaline (NA) input as well as the melatonin output with high time resolution. In the present study, we studied the effects of short-term changes in NA-release on melatonin secretion. A 1 min light pulse was applied around midnight and resulted in an immediate decrease of both NA and melatonin. While NA returned to basal levels in 40 min, melatonin did not reach the baseline within 2.5 h. This discrepancy in correlation between NA and melatonin indicates a rapid inactivation of N-acetyl-transferase (NAT), followed by a slow reactivation, possibly by de novo synthesis of NAT. During daytime, a perfusion with 60 mM potassium for 30 min, resulted in a rapid and short stimulation of NA release, which was not followed by an increase in melatonin production. This indicates that 30 min stimulation of NAT activation is not enough to increase the amount of melatonin produced. The combination of measuring NA input and melatonin output appears to be a valuable tool in studying the characteristics of pineal activity in great detail.