Modelling the electrotonic structure of starburst amacrine cells in the rabbit retina: a functional interpretation of dendritic morphology.

A detailed morphometric analysis of a Lucifer yellow-filled Cb amacrine cell was undertaken to provide raw data for the construction of a neuronal cable model. The cable model was employed to determine whether distal input-output regions of dendrites were electrically isolated from the soma and each other. Calculations of steady state electrotonic current spread suggested reasonable electrical communication between cell body and dendrites. In particular, the centripetal voltage attenuation revealed that a synaptic signal introduced at the distal end of the equivalent dendrite could spread passively along the dendrite and reach the soma with little loss in amplitude. A functional interpretation of this result could favour a postsynaptic rather than a presynaptic scheme for the operation of directional selectivity in the rabbit retina. On the other hand, dendrites of starburst amacrine cells process information electrotonically with a bias towards the centrifugal direction and for a restricted range of membrane resistance values the voltage attenuation in the centripetal direction suggests that the action of these dendrites can be confined locally. A functional interpretation of this result favours a presynaptic version of Vaney's cotransmission model which attempts to explain how the neural network of starburst amacrine cells might account for directionally selective responses observed in the rabbit retina.