Photoresponsive pacemaker neurons from the dissociated retina of Aplysia.

Isolated retinal pacemaker neurons of Aplysia devoid of any morphologically specialized photoreceptive processes responded to illumination. Neurons were dissociated from other retinal cells and maintained in primary culture for whole cell recording. The membrane potential was depolarized and action potentials were evoked by illumination. Light adaptation diminished the response and prolonged the latency. Under voltage clamp neurons responded with increased inward current. Responses were slower and smaller than specialized photoreceptor responses. Pairs and 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 neurons have been described in Aplysia, this is the first report of photoresponses from isolated retinal neurons.