HARDERIAN-GLAND FUNCTION OF INDIAN TROPICAL PALM SQUIRREL, FUNAMBULUS-PENNANTI

The Harderian gland (HG) of the Indian palm squirrel, F. pennanti, is composed of acini of a single type of simple columnar cells with unifo rm-sized lipid droplets and porphyrin (P) in the lumen. Morphologicall y it presented no sexual dimorphism except for the HG weight which rev ealed that males are acyclic. Circadian study of Harderian gland porph yrin (HG-P), plasma melatonin, (aMT) and testosterone showed a charact eristic two peak cyclicity. In females, HG, HG-P and pineal gland weig ht, and plasma aMT presented an annual inverse relation. Circadian stu dy in females only exhibited a two peak cyclicity of HG-P, plasma aMT, and estradiol. Pinealectomy (PX) and harderianectomy (HGX) revealed i ncreased HG weight and gonad weight in males. Gonadectomy (GX), on the other hand, had no effect on HG in males. PX in females brought almos t a similar effect as noted for males, but HGX had no effect on ovaria n weight. GX, interestingly, reduced HG weight and P concentration. Da ily evening (4:30-5:00) administration of aMT and 5-methoxytryptamine (5-MT) in males reduced HG weight and HG-P content only in aMT-treated male and female squirrels, thereby suggesting that HG-P is perhaps ne gatively regulated by pineal gland production and vice versa. Injectio ns of gonadotropin and steroids during the sexually inactive phase sho wed no effect on HG-P content in both sexes. Short photoperiod (SP) in both sexes stimulated pineal weight without affecting HG weight, whil e long photoperiod (LP) increased HG-P but reduced the plasma aMT leve l again without affecting HG-P content. Continuous dark (CD) decreased HG-P, whereas continuous light was ineffective without effecting HG w eight in both sexes. In conclusion, HG in this rodent is functionally an important gland having diverse physiological effect in both sexes s ometimes with a very clear HG-pineal-gonad relationship. (C) 1996 Wile y-Liss, Inc.