|Unwinding the snail's clock: cellular analysis of a retinal circadian pacemaker|
Block, G.D.; Guesz, M.; Khalsa, S.B.; Manivannan, K.; Michel, S.; Withmore, D. (1994). Unwinding the snail's clock: cellular analysis of a retinal circadian pacemaker. Neth. J. Zool. 44(3-4): 550-562
In: Netherlands Journal of Zoology. E.J. Brill: Leiden. ISSN 0028-2960, more
|Authors|| || Top |
- Block, G.D.
- Guesz, M.
- Khalsa, S.B.
- Manivannan, K.
- Michel, S.
- Withmore, D.
The eye of the cloudy bubble snail, Bulla gouldiana, expresses a circadian rhythm in spontaneous optic nerve impulse frequency. The circadian rhythm is generated among a group of approximately 100 neurons (basal retinal neurons-BRNs) at the base of the retina. Each BRN appears to be a competent circadian pacemaker. Using the Bullaretina as a model pacemaker system our laboratory has adressed three central issues of circadian physiology:Synchronization: Entertainment of the ocular rhythm to light cycles is mediated by depolarization of pacemaker neurons with a resultant transmembrane calcium flux. Phase shifts of the rhythm are prevented when calcium entry or membrane depolarization is blocked and light-induced phase shifts can be mimicked by depolarization. Depolarization leads to a persistent increase in intracellular calcium in pacemaker neurons.Expression: The circadian rhythm in impulse frequency is driven by a rhythm in membrane conductance. Membrane conductance is relatively high during the subjective night and decreases by approximately 50 percent near subjective dawn. The 'clock-controlled' conductances are TEA sensitive and recent experiments reveal a circadian modulation in a sustaned calcium-independant potassium conductance.Rhythm generation: Protein synthesis and transcription appear to play critical roles in rhythm genesis. Alterations in the rates of transcription and translation profoundly affect the velocity of the circadian pacemaker in a phase-dependent manner. Transmembrane ionic fluxes, while not involved in rhythm generation, play critical roles in pacemaker synchronization and rhythm expression.