Sensory convergence on central visual neurons in Hermissenda.

Abstract

In the isolated circumesophageal nervous system of Hermissenda, 2 classes of central visual neurons were identified in a restricted region of the dorsal cerebropleural ganglion. Visual, statocyst and chemosensory inputs to these neurons were investigated. Of 46 central visual neurons, 26 cells received EPSP [excitatory postsynaptic potential] with light stimulation, 16 cells received IPSP [inhibitory postsynaptic potential] and 4 cells received EPSP and IPSP. For 14 of the 26 cells that received EPSP during light, the EPSP followed one-for-one impulses of ipsilateral type B photoreceptors. The amplitude of these EPSP decreased rapidly with increasing frequency. For 10 of the 16 cells that received IPSP during light, discrete IPSP followed one-for-one impulses of ipsilateral type B photoreceptors. Latencies of these EPSP and IPSP were in the same range as that measured for the monosynaptic inhibitory interactions between the type B photoreceptors in the same eye. A dual synaptic action of the type B photoreceptor is indicated: inhibition of neighboring photoreceptors and excitation of central visual neurons. Statocyst and chemosensory pathway stimulation produced on these central visual neurons synaptic effects that paralleled the effect of light. Central visual neurons that received EPSP (IPSP) during light also, for most cases, received EPSP (IPSP) during statocyst and chemosensory pathway stimulation.