Summary
The isolatedBulla eye expresses a circadian rhythm in optic nerve impulse frequency. In an effort to determine the anatomical location of the circadian pacemaking system within the retina we surgically reduced the eye. We report that:
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1.
The approximately 1000 large photoreceptors which form a cell layer immediately surrounding the lens, are not required for the expression of a circadian rhythm. Eyes which are surgically reduced so that only the basal retinal neuron population remains, continue to express a circadian rhythm indistinguishable in period to intact eyes.
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2.
The photoreceptor layer is also not required for light-induced phase shifts of the ocular rhythm. Retinal fragments containing only basal retinal neurons can be phase advanced or delayed by 6 h light pulses provided at the appropriate circadian phase.
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3.
Of the approximately 100 basal retinal neurons in theBulla eye, only a small proportion are required for the expression of a circadian rhythm in optic nerve frequency. Ocular fragments with as few as 6 basal retinal neuron somata remain rhythmic, and exhibit a free-running period indistinguishable from intact eyes.
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4.
Intact basal retinal somata are required for the expression of a circadian rhythm in optic nerve impulse frequency. Retinal fragments consisting of an optic nerve with a small amount of neuropil region produce spontaneous action potentials without evidence for a circadian modulation.
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5.
An explicit model for the organization of the circadian pacemaker system in theBulla retina is proposed.
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Abbreviations
- BRN :
-
basal retinal neuron
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Block, G.D., McMahon, D.G. Cellular analysis of theBulla ocular circadian pacemaker system. J. Comp. Physiol. 155, 387–395 (1984). https://doi.org/10.1007/BF00610592
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DOI: https://doi.org/10.1007/BF00610592