ISOLATED retinal pacemaker neurons of Aplysia devoid of any morphologi
cally specialized photoreceptive processes responded to illumination.
Neurons were dissociated from other retinal cells and maintained in pr
imary culture for whole cell recording. The membrane potential was dep
olarized and action potentials were evoked by illumination. Light adap
tation diminished the response and prolonged the latency. Under voltag
e clamp neurons responded with increased inward current. Responses wer
e slower and smaller than specialized photoreceptor responses. Pairs a
nd small clusters of monopolar neurons also responded to light. These
photoresponsive monopolar neurons are likely to be the output neurons
of the ocular circadian clock. Although photoresponsive central neuron
s have been described in Aplysia, this is the first report of photores
ponses from isolated retinal neurons.