FMRF- XXXX -like immunoreactive efferent fibers and FMRF- @entity6346 suppression of pacemaker neurons in eyes of Bulla.

@entity8119 @entity6346
The eyes of certain marine gastropods including Aplysia and Bulla, contain circadian pacemakers, which produce a circadian rhythm of autogenous @entity8119 ( @entity8119 ) activity. The CAPs are generated by the synchronous spike discharge of a distinctive population of retinal pacemaker neurons whose axons convey the @entity8119 activity to the CNS. When @entity8119 activity is recorded from a preparation with eyes attached to the CNS, the @entity8119 activity is modulated by efferent activity. In this study we have identified FMRF- @entity6346 -like immunoreactive efferent axons in the optic nerves of Bulla. These axons arborize in the basal retinal neuropil adjacent to the pacemaker neurons and are in a position to make synaptic contacts with their dendrites. Similar immunoreactive fibers are not observed in Aplysia eyes. Exogenous FMRF- @entity6346 at micromolar concentrations suppresses ongoing @entity8119 activity in isolated eyes but does not suppress the ERG or phase shift the circadian rhythm of @entity8119 activity. Intracellular recordings from the retinal pacemaker neurons reveal that FMRF- @entity6346 hyperpolarizes the membrane potential, suppresses spike discharge, and decreases the input resistance, suggesting that a K conductance is increased. Electrical stimulation of the region of the cerebral ganglion that contains FMRF- @entity6346 immunoreactive neurons suppresses ongoing @entity8119 activity. All these results are consistent with the idea that the FMRF- @entity6346 immunoreactive central neurons and their axons provide a pathway for efferent modulation of the @entity8119 rhythm generated by the retinal pacemaker neurons.
