Maturational changes in neonatal rat motor system with early postnatal administration of nicotine

Experiments were designed to assess the effects of chronic maximum 'smoking dose' nicotine administration on neonatal motor behavior and neuromuscular structural maturation. Thus, Sprague-Dawley rat neonates received daily subcutaneous injections of nicotine (0.05 mg/kg/day) from postnatal days 1 to 14. Motor behavior (ambulations, stop and go movements) was not affected, but a marked increase in grasping duration resulted, indicating increased neuromuscular maturation. Concomitantly, neuromuscular morphological and dynamic contractile changes were observed in the in situ extensor digitorum longus (EDL) muscle. The EDL muscle showed accelerated morphological dimensions of the endplate at postnatal day 7 and a more rapid twitch at 2 weeks of age. The results suggest that this maximum 'smoking dose' of nicotine induces time-dependent maturational changes in the neuromuscular model.