THE MOLECULAR-MECHANISM OF AXONOGENESIS BY SENSORY NEURONS
Hiroshi Segawa-l, Yutaka Kikuchi-2, Naoichi Chino-1, Keiichi Uyemura-2 and Hitoshi Okamoto-2 (Keio Univ., School of Med., 1- Dept. of Rehabilitation., 2-Dept. of Physiol. Tokyo, Japan)
We have been studying the molecular mechanism regulating the axonogenesis by sensory neurons, using zebrafish embryo as a model system. A LIM/homeodomain-type transcription factor, Islet-3, is expressed in the eyes, the midbrain, the sensory neurons, and the myotome in the zebrafish embryo. In this study, we examined the role of Islet-3 in axonogenesis by sensory neurons. Overexpression of LIM domains are known to inhibit a normal function of LIM/homeodomain proteins by competing for the activating molecules. We therefore constructed the DNA which encoded only the LIM domains of Islet-3, and produced its mRNA in vitro. Then, it was miroinjected into the zebrafish embryo at the one-cell stage. Axonogenesis was examined by staining with anti-acetylated α-tubulin antibody. The axonogenesis by sensory neurons was specifically impaired in the 32hr embryo. Our result suggests that Islet-3 regulates the axonogenesis by sensory neurons.
EFFECT OF REDUCED AFFERENT INPUT FROM ANKLE-DORSIFLEXORS ON MOTOR CONTROL OF POSTURE AND GAIT IN HUMANS
Fuk-Tan Tang, Wen-Chung Tsai, *MR Dimitrijevic (Chang Gung Memorial Hospital, Taiwan and *Division of Restorative Neurology and Human Neurobiology, Baylor College of Medicine, USA)
In 4 adult healthy subjects we recorded polyelectromyographically features of motor control during quiet standing, leaning forward and backward and walking forward and backward. Pairs of surface electrodes were placed bilaterally over tile bellies of quadriceps, hamstrings, ankle plantar, dorsal flexors and from the lumbar paraspinals and lower abdominal muscles. EMG signals were amplified and displayed on a multichannel stripchart recorder. After the partial deep peroneal block with 5 ml of 2% xylocaine, the subjects could not lean forward and backward. Simultaneously recorded EMG activity of the anterior muscle compartment of the lower limbs was absent during attempted leaning backward. Leaning forward was also restricted and the motor unit output of tile posterior compartment was larger when compared with the EMG motor unit output of the posterior compartment during the same motor task before partial nerve block. The same partial nerve block altered ankle dorsifiexor activity during walking forward, but did not change motor unit features while the subject walked backward.