Chronic administration of pineal peptides change the circadian locomotor activity and time-course of forced swimming in rats.

After chronic administration of epithalamin (a pineal peptide drug), an increase in the amplitude and shifts in the acrophase of rat's circadian locomotor activity to late hours were observed. These results were obtained only in rats with low initial amplitude of their circadian rhythm. Epithalamin also changed the time-course of forced swimming and decreased the rhythmic index of depression. These observations suggest that the pineal gland of the rat, via its peptides, may prevent the development of depressive-like events.