Classical neurotransmitters in the ovijector of Ascaris suum: localizationand modulation of muscle activity

Ascaris suum possesses a well-developed nervous system which is regulated b y a number of classical neurotransmitters including acetylcholine (ACh), ga mma-aminobutyric acid (GABA), glutamate and serotonin. The vagina vera, the distal part of the ovijector, displays intrinsic, rhythmic activity which has been shown to be modulated by FMRFamide-related peptides (FaRPs) in vit ro. Confocal scanning laser microscopy coupled with immunocytochemistry, an d histochemical studies, revealed that the nerve plexus of the ovijector co ntains GABAergic and glutamatergic innervation. Although no distinctive cho linergic or serotoninergic innervation was apparent, cholinesterase activit y was localized to discrete areas of the musculature of the vagina vera. Th e effects of classical transmitters on the activity of the vagina vera in v itro were examined. ACh was excitatory, stimulating a brief but powerful co ntraction of the vagina vera with a threshold for activity of 1 mu M. Both GABA and glutamate were inhibitory, causing a cessation of contractile acti vity at high concentrations (> 10 mu M) Although less potent than glutamate , GABA had more profound effects and induced longer-lasting paralysis of th e tissue. The threshold concentrations for activity were 5 mu M for glutama te and 10 mu M for GABA. Serotonin had no consistent effect on the vagina v era. This study demonstrates that classical transmitters modulate the activ ity of the ovijector of A. suum.