THE ENDOGENOUS OPIOID SYSTEM HAS A TONIC ACTIVATING ACTION ON THE LYMNAEA-STAGNALIS LOCOMOTOR NEURONS

Keeping specimens of the pond snail Lymnaea stagnalis in the aqueous s olution of the opiate antagonist naloxone (0.1 mM) or naltrexone (0.1 mM) resulted in a suppression of motor activity, and, particularly, in a decrease in the rate of ciliary locomotion, The activity of ciliomo tor serotonergic neurons of the Pedal A cluster was intracellularly re corded in preparations of isolated ganglia, Naloxone (0.1 mM) suppress ed, whereas the opiate agonists morphine (0.1 mM) and DAGO (0.05 mM) a ccelerated the synaptically driven firing of the Pedal A neurons both in preparations of the entire CNS and isolated pedal ganglia, The obta ined results testify to the occurrence of tonic activatory influence o f the endogenous opioids on the ciliomotor pedal neurons of snails and suggest that this influence is, at least partially, mediated by their synaptic input.