THE EFFECT OF ECTOPIC ACTION POTENTIALS ON SENSORY BURSTS DEPENDS ON THE RATIO OF THEIR FREQUENCIES

Publication Date

4-5-2019

Document Type

Poster

Degree Type

Undergraduate

Department

Biological Sciences

Mentor

Wolfgang Stein

Mentor Department

Biological Sciences

Abstract

Animals rely on sensory neurons to encode and transmit information about their environment. Sensory information is encoded in the form of action potentials generated in peripheral dendrites and propagated along axons to the central nervous system. However, axons can also generate secondary (ectopic) action potentials in locations separate from sensory encoding sites. Yet, unlike sensory action potentials, which travel orthodromically towards the central nervous system, ectopic action potentials can travel antidromically towards the periphery. Our lab has previously shown that when ectopic action potentials travel backward into the sensory dendrites they alter how sensory information is encoded. Specifically, we used the crustacean anterior gastric receptor neuron (AGR) - a proprioceptive sensory neuron that elicits two kinds of action potentials: 1) backward traveling ectopic ones and 2) orthodromically traveling ones that occur in bursts. AGR senses tension of two large muscles in the animal's stomach when the animal chews and encodes it as high frequency (~20-30 Hz) bursts of action potentials in its sensory dendrites. In the absence of tension, low frequency (~2-10 Hz) tonic ectopic action potentials are generated. The frequency of these back-propagating action potentials depends on other sensory pathways, which release neuromodulators near an ectopic action potential initiation site on the axon. Our previous studies demonstrate that AGR's sensory burst depends on the frequency of back-propagating ectopic action potentials. To understand the general mechanisms by which ectopic action potential frequency influences neuronal encoding, we created a model neuron that produced ectopic and bursts of action potentials like AGR, but did not include all AGR-specific channels. Instead, its generic structure and channel compliment made it a good representation of neurons in many animals. We hypothesize that the effects that ectopic action potentials have on the encoded burst depends on the ratio between ectopic and burst firing frequencies. To test this, we changed the ectopic firing frequency, while keeping the burst constant, and vice-versa, which changed the ratio. To determine changes in encoding, we measured burst duration and number of action potentials in the burst. Preliminary data suggest that as the ratio increased the number of action potentials in the burst decreased. Our results thus indicate that the relationship between burst and ectopic firing frequencies determines the strength of the influence ectopic action potentials have on encoding.

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