Autaptic Excitation Elicits Persistent Activity and a Plateau Potential in a Neuron of Known Behavioral Function

Synaptic connections from a neuron onto Itself (autapses) are not uncommon [1], but their contributions to information processing and behavior are not fully understood. Positive feedback mediated by autapses could in principle give rise to persistent activity, a property of some neurons In which a brief stimulus causes a long-lasting response [2]. We have Identified an autapse that underlies a plateau potential causing persistent activity in the B31/B32 neurons of Aplysia. The persistent activity Is essential to the ability of these neurons to Initiate and maintain components of feeding behavior. Persistent activity In B31/B32 arises from a voltage-dependent muscarinic autapse and from pharmacologically Identical network-based positive feedback. Depolarization via the autapse begins later than network-driven excitation, and the effect of the autapse Is therefore overshadowed by the earlier network-based depolarization. In B31/B32 neurons Isolated In culture only the autapse is present, and the autapse functionally replaces the missing network-based feedback. Properties of B31/B32 provide Insight Into a possible general function of autapses. Autapses might function along with synapses from presynaptic neurons as components of feedback loops.