Beschreibung:
AbstractIn many neurons, strong excitatory stimulation causes an after‐hyperpolarization (AHP) at stimulus offset, which might give rise to activity‐dependent adaptation. Graded‐potential visual motion‐sensitive neurons of the fly Calliphora vicina respond with depolarization and hyperpolarization during motion in their preferred direction and their anti‐preferred direction, respectively. A prominent after‐response, opposite in sign to the response during motion, is selectively expressed after stimulation with preferred‐direction motion. Previous findings suggested that this AHP is generated in the motion‐sensitive neurons themselves rather than in presynaptic processing layers. However, it remained unknown whether the AHP is caused by membrane depolarization itself or by another process, e.g. a signaling cascade triggered by activity of excitatory input channels. Here we showed by current injections and voltage clamp that the AHP and a corresponding current are generated directly by depolarization. To test whether the generation of an AHP is linked to depolarization via a Ca2+‐dependent mechanism, we used photoactivation of a high‐affinity Ca2+ buffer. In accordance with previous findings the AHP was insensitive to manipulation of cytosolic Ca2+. We propose that membrane depolarization presents a more direction‐selective mechanism for the control of AHP than other potential control parameters.