Cholinergic molecules and sperm functions

Molecules acting on neurotransmitter systems are known to be present in sperms of several species: their presence was correlated to the regulation of sperm propulsion. To understand their function, a study was carried out on sperm activation, in the presence of cholinergic drugs (acetylcholine and drugs competitive at cholinergic receptors, agonist and antagonist, both muscarinic and nicotinic ones). The in vivo effects were also studied by demonstrating membrane depolarization with merocyanine, a potentiometric dye. Concentrated acetylcholine, up to 100 muM, inhibited both activation and membrane depolarization, while diluted to 10 muM, ACh enhanced it. The competitive drugs exerted on activation more or less the same effects as those on movement, reported in literature. 100 muM atropine reversibly prevented activation, while, more diluted, only delayed it. 1 muM nicotine and carbachol enhanced, and curare delayed activation and merocyanine staining. The results show the possibility that both nicotinic and muscarinic AChRs are involved in the mechanism of sperm activation. Further, the possibility that an ACh-like substance concentrated in the sperm liquid may be involved in maintaining the sperms in the quiescent state is discussed.