Pineal and 5-methoxyindoles in the regulation of seasonal testicular cycle in Indian palm squirrel, Funambulus pennanti.

Effects of late afternoon injections of different doses of melatonin (aMT) and 5-methoxytryptamine (MT) were studied on the testes in sham operated (SO) and pinealectomized (Px) F. pennanti during various reproductive phases. 5-methoxyindoles (MI) in doses 10 and 50 micrograms given for 60 continuous days reduced the weight and activity of the testes in SO and Px animals during the active and regressive phases. During the inactive phase MI administration caused an inhibitory influence on the testes of Px animals. However, during the recrudescence phase no significant effect of MI injections was visible. Both aMT and MT injected for 20 and 40 days respectively failed to influence the testes significantly. Also 1 microgram of the MI had no effect. The results suggest a reproductive phase dependent effect of aMT and MT on the testes of this tropical rodent. The dose and duration of administration are critical and their effects are independent of the pineal gland.