Vasopressin increases the central nervous system suppressive control over gill reflex behaviours and associated neural activity in Aplysia.

Exposure of the abdominal ganglion of Aplysia to arginine vasopressin (10(-12) M) reduces the amplitude of the gill withdrawal reflex, accelerates its rate of habituation, and causes a concomitant decrease in the number of action potentials evoked in gill motor neuron L7. The effects of vasopressin on both the reflex and the concomitant neural activity evoked in L7 were completely reversible. Vasopressin did not affect the passive membrane properties of L7. The results indicate that a vertebrate neurohypophyseal hormone can affect behavioural responses as well as modify the synaptic efficacy of the reflex pathway.