Abstract: Elizabeth Olecki and Rachel Shen
Mentor: Dr. Brodfuehrer
The neuronal control of swimming in the medicinal leech, Hirudo medicinalis, has been studied intensely from the past 30 years, and has led to a model of how swimming is generated in the leech central nervous system (i.e., ventral nerve cord). The ventral nerve cord consists of 21 mid-body ganglia plus a head and tail ganglion, which spans the length of the leech’s body. Each ganglion contains a competent oscillator, a network of oscillatory interneurons whose connections produce the underlying pattern that drives motor neurons to cause alternating contractions of dorsal and ventral longitudinal muscle leading to swimming movements. In the isolated ventral nerve cord, the motor program for swimming can be recorded from a peripheral nerve, the dorsal branch of the posterior nerve (DPs), that innervates the dorsal longitudinal muscles.
Research has implicated cell 208, an oscillatory interneuron, as a critical component of the swim oscillatory network. During swimming, cell 208 is depolarized and its membrane potential oscillates between excited and inhibited states. The Brodfuehrer lab has recently shown that bath application of curare eliminates the inhibitory component of the oscillations in cells 208 in mid-body ganglia, but does not affect the swim motor program recorded from DP nerves along the ventral nerve cord. Curare is a compound that blocks receptors for acetylcholine (ACh), referred to as a nicotinic receptor antagonist. Thus, a re-evaluation of the swim oscillatory network is necessary.
This summer, we continue to investigate the role of cell 208 in generating leech swimming. Specially, we will determine if bath application of curare modifies all cell 208s in the ventral nerve in manner similar to that observed from cell 208 in mid-body ganglia. In addition, we will also confirm that curare’s effects on cell 208 are mediated by blocking nicotinic receptors by trying another type of nicotinic antagonist, hexamethonium chloride. Finally, we will investigate whether curare alters the level of intensity of excitation in cell 208. These findings will provide additional evidence as to the organization of the swim oscillatory network in each segmental ganglion.