TIME-COURSE OF THE DEVELOPMENT OF MOTOR BEHAVIORS IN THE ZEBRAFISH EMBRYO

The development and properties of locomotor behaviors in zebrafish emb ryos raised at 28.5 degrees C were examined. When freed from the chori on, embryonic zebrafish showed three sequential stereotyped behaviors: a transient period of alternating, coiling contractions followed by t ouch-evoked rapid coils, then finally, organized swimming. The three d ifferent behaviors were characterized by video microscopy. Spontaneous , alternating contractions of the trunk appeared suddenly at 17 h post fertilization (hpf), with a frequency of 0.57 Hz, peaked at 19 hpf at 0.96 Hz, and gradually decreased to <0.1 Hz by 27 hpf. Starting at 21 hpf, touching either the head or the tail of the embryos resulted in v igorous coils. The coils accelerated with development, reaching a maxi mum speed of contraction before 48 hpf, which is near the time of hatc hing. After 27 hpf, touching the embryos, particularly on the tail, co uld induce partial coils (instead of full coils). At this time, embryo s started to swim in response to a touch, preferentially to the tail. The swim cycle frequency gradually increased with age from 7 Hz at 27 hpf to 28 Hz at 36 hpf. Lesions of the central nervous system rostral to the hindbrain had no effect on the three behaviors. Lesioning the h indbrain eliminated swimming and touch responses, but not the spontane ous contractions. Our observations suggest that the spontaneous contra ctions result from activation of a primitive spinal circuit, while tou ch and swimming require additional hindbrain inputs to elicit mature l ocomotor behaviors. (C) 1998 John Wiley & Sons, Inc.