Abstract

Parasol cells are multimodal sensory interneurons of the hemi-ellipsoid body in the decapod forebrain. In reptant crustaceans, the hemi-ellipsoid body resides in the base of the eyecup, as an appendage to the terminal medulla. Parasol cells exhibit periodic depolarizations at a frequency of 0.5-1.0 Hz. I have investigated the role of these periodic depolarizations and their superimposed impulse bursts in affecting the input/output properties of these neurons. Parasol cells receive input from photic, olfactory, and mechanosensory pathways. Strong stimulation over any one of these pathways can lead to the generation of one or more impulse bursts in a subset of parasol cells, timed to occur at the peak of successive periodic depolarizations. A role for the periodic depolarizations in the function of the parasol cells has yet to be established. I suggest the possibility that they may act as a nonlinear amplifier that boosts spatially-summated excitatory synaptic potentials from strong or appropriate stimuli above threshold for burst generation. Another possibility includes modification of voltage-sensitive ion channels in the dendritic membrane, permitting a more effective spread of excitatory synaptic currents to impulse or burst initiating zones. Impulse bursts may be a highly effective mode of output for these neurons, especially so as they occur synchronously in a subset of cells in response to strong sensory input. Furthermore, backfiring of bursts into the dendritic tree has a brief (2-3 second) but effective suppressive action upon weak sensory input, which can thereby be masked by stronger, burst-generating input. This masking phenomenon is seen in other arthropod sensory interneurons, where its physiological basis appears to be a transient accumulation of intracellular Ca(++) ions that open calcium-sensitive potassium channels.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.