RHYTHMIC ACTIVITIES OF ISOLATED AND CLUSTERED PACEMAKER NEURONS AND PHOTORECEPTORS OF APLYSIA RETINA IN CULTURE

Each eye of Aplysia contains a circadian clock that products a robust rhythm of optic nerve impulse activity, To isolate the pacemaker neuro ns and photoreceptors of the eye and determine their participation In the circadian clock and its generation of rhythmic autoactivity, the r etina was dissociated and its cells wee placed in primary cell culture , The isolated neurons and photoreceptors survived and vigorously exte nded neurites tipped with growth cones, Many of the photoreceptors pre viously described from histological sections of the intact retina were identified in culture, including the large R-type photoreceptor, whic h gave robust photoresponses, and the smaller tufted, whorled, and fla red photoreceptors. The pacemaker neuron responsible for the rhythmic impulse activity generated by the eff were identified by their distinc tive monopolar morphology. and recordings were made of their activity, Isolated pacemaker neurons produced spontaneous action potentials in darkness, and pacemaker neurons attached to fragments of retina or in an isolated cluster interacted to produce robust spontaneous activity, This study establishes that isolated retinal pacemaker neurons retain their innate autoactivity and ability to produce action potentials in culture and that clusters of coupled pacemaker neurons are capable of generating robust autoactivity comparable to pacemaker neuron rhythmi c activity recorded in the intact retina, which was previously shown t o correspond to 1:1 with the optic nerve compound action potential act ivity. (C) 1996 John Wiley & Sons, Inc.