Influence of methyl parathion on gametogenic and acetylcholinesterase activity in the testis of whitethroated munia (Lonchura malabarica).

Adult male whitethroated munias, Lonchura malabarica (Aves; Passeriformes), were orally administered with methyl parathion (O, O-dimethyl O-(4-nitrophenyl) phosphorothioate), an extensively used organophosphate pesticide, in graded sublethal dose (5 micro g-, or 10 micro g-, or 20 micro g/100 g body wt/day) for variable durations (1-, 5-, or 10 day/s) during their peak reproductive activities in an annual gonadal cycle. No subtle changes in the feeding behavior, mobility, and body weight were noted between the control and different groups of pesticide-fed birds. As a result of the treatment, the paired testicular weight became reduced significantly only after 10 days at 10 micro g and 20 micro g dose levels, but significant decrease in the number of tubules containing healthy germ cells occurred even after single administration of methyl parathion (MP) at the lowest dose (5 micro g/100 g). With the increase in dose and progress of treatment, the number of tubules with healthy germ cells became gradually decreased. The activity of acetylcholinesterase (AChE) in both the brain and testes of MP-treated birds was inhibited in a dose and duration dependent manner. A significant negative correlation was observed between the number of tubules containing degenerated germ cells in the testis and the AChE activity in both the brain and testes of MP-administered birds. However, no remarkable changes in the cytomorphological features, including the nuclear diameter of Leydig cells, were noted in any testis of the pesticide-treated munias. The results of the present investigation suggest that methyl parathion ingestion is harmful to male gametogenic functions in the studied passeriform bird, and the given pesticide may exert its antigonadal effect by impairing cholinergic functions of the brain and/or testes.