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The effects of alpha-conotoxin Im1 on the intact, swimming medicinal leech

  • Author(s): Ries, David Christopher
  • et al.

We are studying the effects of [alpha]-conotoxin Im1 on the swimming behavior of the intact medicinal leech. Injection with Im1 leads to abnormal, circular swimming patterns. First, we observed the change in amplitude of the swimming movements of toxin treated leeches, and then we recorded the motor output of dorsal longitudinal excitor Cell 3 in an intact animal. Our purpose was to characterize the effects of Im1 both behaviorally and physiologically, and then decide whether the toxin was affecting the swim CPG at the muscle, the motor neuron input, or higher up in the swim circuit. We discovered that Im1 affects behavior by increasing the amplitude of troughs during swimming and increasing the delay before the onset of the following peak. By observing firing patterns in the DP nerve, Cell 3 was seen to fire for longer durations after treatment with Im1. These observations have led us to conclude that Im1 is affecting the swimming CPG at a higher level, altering the timing between ventral and dorsal muscle contractions

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