Pharmacological receptors of nematoda as target points for action of antiparasitic drugs

Cholinergic receptors of parasitic nematodes are one of the most important possible sites of action of antiparasitic drugs. This paper presents some of our own results of electrophysiological and pharamcological examinations of nicotinic and muscarinic receptors of nematodes, as well as data from literature on a new class of anthelmintics that act precisely on cholinergic receptors. The nicotinic acetylcholine receptor (nAChR) is located on somatic muscle cells of nematodes and it is responsible for the coordination of parasite movement. Cholinomimetic anthelmintics act on this receptor, as well as acetylcholine, an endogenic neurotransmitter, but they are not sensitive to enzyme acetylcholineesterase which dissolves acetylcholine. As opposed to the nicotinic receptor of vertebra, whose structure has been examined thoroughly, the stoichiometry of the nicotinic receptor of nematodes is not completely known. However, on the grounds of knowledge acquired so far, a model has been constructed recently of the potential composition of a type of nematodes nicotinic receptor, as the site of action of anthelmintics. Based on earlier investigations, it is supposed that a conventional muscarinic receptor exists in nematodes as well, so that it can also be a new pharamocological target for the development of antinematode drugs. The latest class of synthesized anthelmintics, named aminoacetonitriles (AAD), act via the nicotinic receptor. Monepantel is the first drug from the AAD group as a most significant candidate for registration in veterinary medicine. Even though several groups of cholinomimetic anthelmintics (imiodazothiazoles, tetrahydropyrimidines, organophosphat anthelmintics) have been in use in veterinary practice for many years now, it is evident that cholinergic receptors of nematodes still present an attractive place in the examinations and development of new antinematode drugs.