Hormonal control of sleep-appetitive behaviour and diurnal activity rhythms in the cleaner wrasse Labroides...

In its natural environment the cleaner wrasse, Labroides dimidiatus, possesses a hiding place in the reef, where it disappears every night. In my experiments, the Labroides was offered a specific sleeping cave in tanks. Photocells at the entrance to each cave, connected to a printer, counted the sleep-appetitive behaviour (SAB), viz. the investigation of the sleeping-place. Untreated animals visited the cave 45.6 times within 90 min prior to darkness. The swimming activity, which was measured 3 times daily, declined in the course of the light period. During the night the animals are totally motionless. Four substances which are involved in the sleep-influencing processes in mammals were tested. Injection of the neurotransmitter serotonin (0.05-0.5 micrograms/g b.wt. 5-HT) resulted in a decrease of swimming activity and SAB; the 5-HT blocking substance p-chlorophenylalanine (1-8 micrograms/g b.wt. PCPA) intensified this activity and suppressed SAB only in a concentration-range of 10 and 12 micrograms/g b.wt. In addition, the neuromodulatory properties of vasoactive intestinal polypeptide (VIP) and arginine vasotocin (AVT) were investigated. It is noteworthy to mention that VIP (1-1.5 micrograms/g b.wt.) lead to an remarkable increase, and AVT (0.5-4 micrograms/g b.wt.) to a significant reduction of the SAB.