Meeting Abstract

P1.98  Monday, Jan. 4  Same wiring, different effect: how pressure mechanosensory neurons interact in the leeches Macrobdella decora and Hirudo verbana GIBBONS, K.R.**; BALTZLEY, M.J. ; St. Mary’s College of Maryland; St. Mary’s College of Maryland krgibbons@smcm.edu

The leech Hirudo verbana has four mechanosensory pressure neurons (P cells) in each midbody ganglion. Within an isolated ganglion, P cells have complex mutually inhibitory connections. When one P cell is stimulated intracellularly, the other P cells have a weak depolarization followed by a strong hyperpolarization. This complex response appears to be mediated by a combination of electrical coupling, monosynaptic excitation and polysynaptic inhibition. We examined the P cell homologues in the American medicinal leech Macrobdella decora. We found that intracellular stimulation of one P cell causes a slight depolarization in the other P cells. The magnitude of the depolarization is greater between ipsilateral P cells than between contralateral P cells. Experiments performed in a high Mg²⁺, 0 Ca²⁺ saline and a high Mg²⁺, high Ca²⁺ saline suggest that the P cells in M. decora have an electrical coupling, a monosynaptic excitation and polysynaptic inhibition, similar to the connections between P cells in H. verbana. Therefore, the difference in net response between these two species seems to be based on differences in the strengths of the electrical and chemical connections. We also tested the connections between P cells in both M. decora and H. verbana in normal leech saline with bicuculline, a GABA-antagonist. Our preliminary results show that the polysynaptic inhibition was eliminated in both species, suggesting that the inhibition is due to GABA-mediated Cl^– channels.