Meeting Abstract

101.8  Thursday, Jan. 7  Neural Control of the Snake Leg YOUNG, BA; Univ. Massachusetts Lowell Bruce_Young@uml.edu

In vertebrates rhythmic alternating bilateral movements, such as the movements of the appendages typically seen during locomotion, are generated by a group of spinal motor neurons commonly termed a central pattern generator or CPG. While the CPGs associated with a variety of movements have been described from several vertebrate taxa, little is known about the evolution of this local neural control. The evolutionary loss of the snake leg may be a promising system in which to explore phylogenetic transitions in the CPG. The presumed ancestral varanoid radiation used robust hind limbs for tetrapodal locomotion, early snake fossils have hind limbs, many of the extant basal snakes have pelvic and/or hind limb skeletal elements, while the derived snakes lack all such bony features. Analysis of the neural control of the snake leg can address the central hypothesis that evolutionary loss of the hind limb was not accompanied by change in the associated CPG, thus the controlling neural system evolves in a pattern and rate that is separate from that of the musculoskeletal elements being controlled. The initial exploration of this system has centered on the ball python (Python regius) a basal macrostomatan in which the males have a pelvic girdle coupled to femora that project externally (the cloacal spurs). Stimulation of the femoral protractor coupled with fluorescent retrograde labeling permits identification of the spinal motor neuron pool associated with this muscle. Extracellular recordings from these motor neurons can then identify rhythmic alternating discharge patterns characteristic of CPGs.