CHOLINOMIMETIC DRUGS MAY AFFECT GROWTH AND METAMORPHOSIS OF THE SEA-URCHIN LARVA

Cell-to-cell and cell-environment interactions are known to play a rol e during the first events of sea urchin development. Larval metamorpho sis in benthic invertebrates is induced by environmental signals (cues ), received by membrane receptors. The activity of such cues may be di sturbed by the presence of toxic agents from pollution. We consider th e possibility that neurotransmitter receptor-like molecules may have a role in the regulation of larval development and metamorphosis. To in vestigate the effects exerted on these processes by neuroactive pollut ants, such as neurotoxic insecticides, we tested the function of acety lcholine receptors (muscarinic acetylcholine receptors mAChR and nicot inic acetylcholine receptors nAChR) in larvae of Paracentrotus lividus in the presence of four neuroactive drugs: carbamylcholine, an agonis t of mAChR; atropine, an antagonist of the same; nicotine, an agonist of nAChR; and eserine (physostigmine), which mimics an excess of ACh i n the receptorial sites. Under the conditions of our experiments, the effect of these neuroactive drugs on larval development was mainly a g rowth delay in comparison with the development of controls. At metamor phosis, the neurotransmission system, which is predominantly cholinerg ic in larvae, shifts to a biogenic-amine system in the rudiment. At th is stage, the weaker effects of the tested drugs show that their actio n was not exerted on transcription but rather on the regulation of mot ility in the ciliary bands.