The postnatal development of the inferior oblique muscle of the cat: II. Effects of repetitive stimulation on isometric tension responses

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Abstract
The changes with postnatal age in post-tetanic potentiation (PTP) and fatigue of the inferior oblique muscle were studied in the cat. PTP of the twitch amplitude increased steadily with age up to 20 wk after birth. Twitch contraction time (ct) and half relaxation time (hrt) was not significantly changed. The potentiation of the tetanic response also became more prominent with age. Young muscles (10 wk and below) were slightly more susceptible to fatigue than older muscles, but recovery was rapid in muscles of all ages. Intensive stimulation induced post-tetanic depression of twitch responses in muscles older than 1 wk, but none in muscles of new-born cats. Ct and hrt were greatly prolonged in muscles above 6 wk of age. In these muscles, but never in the very youngest, repetitive firing was observed in response to post-tetanic single nerve stimulation. Results are compared with those obtained in similar experiments on hindlimb muscles. Slow eye muscle fibers probably developed quicker and reached maturity earlier than fast fibers.