Ocellar interneurons in the honeybee

Summary

Morphologically identified spiking ocellar interneurons (L_B and L_D-neurons) of the honeybee (Apis melliferd) were investigated by combined intracellular recording and staining techniques using multimodal stimulus programs.

Response patterns containing both graded and action potentials (mixed response), and pure spiking responses were analysed. Mixed responses allow a comparison of information coded simultaneously by graded and action potentials in one neuron. In most cases the intensity dependence coded by spikes was found to be similar to the intensity dependence coded by one of two different parameters evaluated from the graded signal. Lneurons with mixed responses were unimodal, i.e. they reacted exclusively to stationary illumination of the ocelli, as do nonspiking L-neurons.

In contrast, spiking L-neurons that lacked a graded response component could also respond to stimuli of other sensory modalities: moving patterns, compound eye illumination, airstreams, mechanical and gustatory stimulation. One L_D-neuron was also excited by the wing beat.

Recordings from the same type of neuron in different individuals demonstrate that the input modalities and response patterns of L-neurons vary remarkably. Consequently many recordings are required to properly characterise the physiological properties of these neurons even though anatomically they are identified.

The existence of graded and action potentials in the same cell and the fact that these two signals carry different information is discussed in the context of a possible role for information transmission from L-neurons to postsynaptic cells.