Identifiable cerebral motoneurons mediating an anterior tentacular withdrawal reflex in Aplysia

Abstract

The mechanosensory and motor properties of a pair of identified clusters of neurons in the cerebral ganglion of Aplysia were examined. Tactile stimulation of either anterior tentacle produces EPSP [excitatory postsynaptic potential] and spikes in the cerebral B neurons. This is followed by contraction of both tentacles. This reflex is centrally mediated. Bathing the CNS in high Mg2+ seawater totally blocks the reflex, whereas bathing the anterior tentacle blocks the tentacular contraction but not the synaptic response in the B neurons. If these neurons are stimulated intracellularly there is a contraction of the ipsilateral tentacle. Bathing the CNS in high Mg2+ seawater does not block the intracellularly evoked contraction indicating that there are no interposed central neurons. The B neurons are motor neurons mediating an anterior tentacular withdrawal reflex.