Meeting Abstract

45.4  Monday, Jan. 5  Changes in synaptic connections between mechanosensory neurons in leeches mediates species-specific behavior patterns. BALTZLEY, MJ*; GAUDRY, Q; KRISTAN, JR., WB; St. Mary’s College of Maryland; University of California, San Diego; University of California, San Diego mjbaltzley@smcm.edu

We characterized the behavioral responses of two species of leeches, Hirudo verbana and Erpobdella obscura, to mechanical skin stimulation. In response to mechanical stimulation, Hirudo showed the well-characterized local bending behavior, in which the body wall shortened only on the side of the stimulation. Erpobdella, in contrast, contracted both sides of the body in response to touch, producing a behavior we call tensing. To investigate the neuronal basis for this behavioral difference, we studied the interactions between the pressure mechanosensory neurons (P cells) that innervate the skin. Each midbody ganglion has four P cells; each cell innervates a different quadrant of the body wall. Consistent with the local bending behavior, activating any one P cell in Hirudo elicited polysynaptic inhibitory potentials in the other P cells. In contrast the P cells in Erpobdella had excitatory polysynaptic connections, consistent with the segment-wide contraction observed in this species. Preliminary data in a third leech species, Macrobdella decora, indicate that the P cells in Macrobdella have excitatory polysynaptic connections. Because Erpobdella and Macrobdella are basal to Hirudo within the leeches, these results suggest that Hirudo may have evolved a more localized pressure mechanosensory system through lateral inhibition of P cells.