TOXICITY OF PYRETHROID, CYPERMETHRIN ON NEUROSECRETORY ACTIVITY IN FRESHWATER SNAIL, LYMNAEA ACUMINATA (L)

A detailed study on the morphology of nervous system, neurosecretory cells and the seasonal variations in the neuro secretory cells along with effect of sublethal concentration of cypermethrin in a freshwater snail, Lymnaea acuminata has been carried out. The nervous system consists of several paired as well as unpaired ganglia forming a ring, like a pair of cerebral, pleural, pedal, parietal ganglia and a single visceral ganglia. Two types of neurosecretory cells, A and B, were identified by using Mallory's triple staining method. A cells were found to be pyriform in shape with long axon while B cells were round without axon. Seasonal variations in neurosecretory cells were observed in cerebral ganglia along with the exposure to sublethal concentration of cypermethrin for 24 and 96 hours exposure span. It was found that the number of neurosecretory cells (A and B) decrease progressively after 24 and 96 hours exposure period.