DAILY VARIATION IN THE CONTENT OF INDOLEAMINES, CATECHOLAMINES AND RELATED-COMPOUNDS IN THE PINEAL-GLAND OF SYRIAN-HAMSTERS KEPT UNDER LONGAND SHORT PHOTOPERIODS

This study examined the diurnal changes in the content of 5-hydroxytry ptophan (5-HTP), serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) , N-acetylserotonin (NAS), melatonin, 5-methoxytryptophol (5-ML), nora drenaline (NA), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOP AC) in the pineal gland of Syrian hamsters kept under long (14L:10D) a nd short (10L:14D) photoperiods. The nocturnal increase in NAS and mel atonin levels was dependent upon the prevailing photoperiod, with a pr olonged duration when the night lengthened. In both photoperiods, NAS and melatonin contents increased several hours after the onset of dark ness, and, in animals kept in short photoperiod, the levels of both co mpounds began to decrease before light onset. On the contrary, decreas es were noted in 5-HT, 5-HIAA, and 5-ML contents during the night, whi ch was directly proportional to the dark phase. 5-HTP levels did not s how a rhythmic variation. Correlations between the mean values of 5-HT -related compounds showing daily rhythms were very high when group mea ns were compared, but they decreased when values from individual anima ls were considered. In addition, when correlations were calculated on per-animal basis during the night phase, a weak negative correlation w as found for 5-HT vs NAS and 5-HT vs melatonin, although the correlati on of 5-HT with positively 5-HT-correlated compounds (5-HIAA and 5-ML) continued to be high. These results indicate that the nocturnal incre ase in the N-acetyl transferase activity is the major factor generatin g the rhythm of pineal 5-HT content, but that other photoperiod-depend ent mechanisms (i.e., 5-HT synthesis or release) seem to be also impli cated. On the other hand, this study shows that NA content in the Syri an hamster pineal gland does not exhibit daily variations, although ma rked nocturnal increases in the levels of DA and DOPAC were evident. T hese results suggest the existence of parallel daily alterations in pi neal catecholamine synthesis and release, and suggest a role for DA in the pineal activation at night.