Submitted on September 25, 2008
Revised on November 25, 2008
Accepted on December 1, 2008
Polysensory Interneuronal Projections to Foot Contractile Pedal Neurons in Hermissenda
Terry J. Crow1* and Lian-Ming Tian2
1 University of Texas Medical School - Houston
2 Univ TX med sch
* To whom correspondence should be addressed. E-mail: terry.crow{at}uth.tmc.edu.
A Pavlovian conditioning procedure may produce modifications in multiple behavioral responses. As an example conditioning may result in the elicitation of a specific somatomotor conditioned response (CR), and in addition, other motor and visceral CRs. In the mollusk Hermissenda conditioning produces two conditioned responses; foot-shortening and decreased locomotion. The neural circuitry supporting ciliary locomotion is well characterized, however the neural circuit underlying foot-shortening is poorly understood. Here we describe efferent neurons in the pedal ganglion that produce contraction or extension of specific regions of the foot in semi-intact preparations. Synaptic connections between polysensory type Ib and Is interneurons and identified foot contractile efferent neurons were examined. Type Ib and Is interneurons receive synaptic input from the visual, graviceptive, and somatosensory systems. Depolarization of type Ib interneurons evoked spikes in identified tail and lateral foot contractile efferent neurons. Mechanical displacement of the statocyst evoked complex EPSPs and spikes recorded from type Ib and Is interneurons and complex EPSPs and spikes in identified foot contractile efferent neurons. Depolarization of type Ib interneurons in semi-intact preparations produced contraction and shortening along the entire rostral-caudal extent of the foot. Depolarization of Is interneurons in semi-intact preparations produced contraction of the anterior region of the foot. Taken collectively, the results suggest that type Ib and Is polysensory interneurons may contribute to the neural circuit underlying the foot-shortening CR in Hermissenda.
