A comparison of intact and in-vitro locomotion in an adult amphibian.

Locomotion was compared in an intact and in-vitro preparation of the adult mudpuppy (Necturus maculatus). The intact animals walked on an aquatic treadmill while in-vitro preparations were made to walk with a bath application of the excitatory amino acid NMA (N-methyl DL-aspartate). EMG recordings of shoulder muscles (pectoralis, latissimus dorsi, dorsalis scapulae, and procoracohumeralis) and elbow muscles (brachialis and extensor ulnae) were obtained from intact animals while recordings were made from only the elbow muscles in-vitro. The in-vitro preparation required magnesium in the bath to initiate and maintain locomotion, consistent with an NMDA mediated response. Also consistent with an NMDA response was the finding that glycine potentiated the NMA induced locomotion in-vitro. The range of cycle durations seen in-vitro was well within the range seen in the intact animal, while gait analysis demonstrated the similarity of intact and in-vitro locomotor cycles. In spite of these very similar locomotor patterns there are interesting differences in the patterned output seen in-vitro, such as the absence of a second burst in the brachialis muscle in-vitro.