title: The circadian rhythm and photosensitivity of small impulses of the Bulla eye.
abstract: The eye of the mollusk Bulla gouldiana contains a pacemaker that generates a circadian rhythm in compound action potentials (CAPs) in the optic nerve. In this paper, we present evidence of a second circadian rhythm in the optic nerve of the eye maintained in darkness at 15 degrees C. This is a rhythm in the frequency of small (10-40 microV) neural impulses that occurs about 12 h out-of-phase with the rhythm in CAPs. Typically, the small-spike frequency is at a minimum within an hour of the peak in CAP frequency and is maximal during the subjective night. Like the CAP rhythm, the phase of the small-spike rhythm is determined by the prior light/dark cycle. A rebound in small-spike activity following the end of a light pulse and the presence of photoinhibited impulses in surgically reduced eyes suggests that the cells that generate the small-spikes may be photoreceptors that are inhibited by light. In addition, by using isolated nervous system preparations, we have found that small-spikes occur in the two optic nerves in a one-for-one relationship immediately following a light-to-dark transition. This inter-eye communication may be involved in the coupling of the ocular pacemakers.
authors.affiliation: Department of Biology, Vanderbilt University, Nashville, TN 37235.
authors.forename: M E
authors.initials: ME
authors.lastname: Geusz
authors.forename: T L
authors.initials: TL
authors.lastname: Page
mesh_terms: D000200:Action Potentials; D000818:Animals; D002940:Circadian Rhythm; D066298:In Vitro Techniques; D008974:Mollusca / Q000502:physiology*; D009799:Ocular Physiological Phenomena; D009900:Optic Nerve / Q000502:physiology*; D010775:Photic Stimulation