PIRTLE, T.J.*; SATTERLIE, R.A.; Abilene Christian University; University of North Carolina at Wilmington: The Relative Contribution of Cellular and Circuit Level Properties to Swim Acceleration in Clione limacina
Serotonin induced swim acceleration in Clione limacina involves changes in cellular and circuit level properties. At the cellular level, swim interneurons exhibit several changes in intrinsic properties. At the circuit level, general excitor motoneuron recruitment and enhanced activity of type 12 interneurons occurs. Here we examine the contribution of the type 12 interneurons to increased swim speed. One type 12 interneuron is located in each of the two pleural ganglia. To demonstrate the role of the type 12 interneuron in mediating swim speed change we cut the pleural-pedal connective to remove the influence of this interneuron from the swim circuit. Following cutting, the preparation was refrigerated at 4-6oC for 48 hours to ensure that the axons of the type 12 interneuron were sufficiently destroyed. After 48 hours the fictive swim activity was monitored by intracellularly recording from the swim interneurons. The fictive swim activity was measured first in normal sea water and then in sea water containing 10-6M serotonin. Serotonin increased swimming speed by 70% in cut preparations which was not significantly different from the effects of serotonin in uncut preparations. To determine that the type 12 interneurons were completely removed from the swim circuit we filled the type 12 interneuron with biocytin, cut the pleural-pedal connective, and kept the preparation at 4-6oC for 48 hours. Preliminary data from a type 12 biocytin filled preparation suggests that axons of this neuron were sufficiently damaged to remove the influence of this cell from the swim system. This work suggests that cellular and circuit properties contribute equally to mediate swim acceleration.
