. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. STATOCYST RESPONSE CHARACTERISTICS Electrotonic coupling CelM Cell 2 5mV Current 50ms 1_ |4nA Figure 5. Intracellular recordings from two nearby secondary sensory hair cells in the statocyst crista of the cuttlefish. Sepia officinalis, showing their electrotonic coupling. A small current (bottom trace) is injected into Cell 1 (top tracel, producing a depolarization, and this causes a simultaneous, but smaller, depolarization in the neighboring cells (Cell 2, middle trace). This provides evidence that the secondary sensory ha
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. STATOCYST RESPONSE CHARACTERISTICS Electrotonic coupling CelM Cell 2 5mV Current 50ms 1_ |4nA Figure 5. Intracellular recordings from two nearby secondary sensory hair cells in the statocyst crista of the cuttlefish. Sepia officinalis, showing their electrotonic coupling. A small current (bottom trace) is injected into Cell 1 (top tracel, producing a depolarization, and this causes a simultaneous, but smaller, depolarization in the neighboring cells (Cell 2, middle trace). This provides evidence that the secondary sensory hair cells in a crista segment are electrotonically coupled along the segment. From Williamson, 1991K neurally controlled electrical coupling is in the vertebrate retina, where the neurotransmitter dopamine alters the coupling ratio between retinal horizontal cells (Knapp and Dowling, 1987). Dopamine has been located in the retinal efferents in Octopus (Suzuki and Tasaki, 1983) and has also been tentatively identified in the statocyst efferents (Budelmann and Bonn, 1982; Williamson, 1989b). It would be an astonishing example of parallel evolution if these two disparate sense organs, the eye and the statocyst, used dopaminergic control of electrical coupling to reg- ulate their sensory input. Efferent system The statocysts have an exceptionally large efferent in- nervation; of the axons in the Octopus statocyst crista nerves, 75% are efferent fibers travelling from the brain to the statocyst (Budelmann el ai, 1987). In contrast, about 8% of axons in a vertebrate vestibular nerve are efferents (Goldberg and Fernandez, 1980). This efferent innervation forms a plexus running beneath the crista epithelium and makes synaptic contact with primary and secondary sensory hair cells, as well as with the afferent and other efferent neurons (Budelmann et ai, 1987). The efferent fibers are active during movements of the animal's head (Williamson, 1986) and can depress or enhance (Fig. 6) the a
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