Response of colonic smooth muscle from newborn and adult rabbits to electrical field stimulation.

Electrical field stimulation (EFS) of circular smooth muscle from the proximal and distal colon of adult rabbits elicits region-specific patterns of contraction and relaxation referred to as on and off responses. The present study examined EFS-mediated on and off responses in neonatal (3- to 5-d-old), juvenile (2-wk-old), and adult rabbits to determine whether colonic motility undergoes a period of postnatal maturation with respect to the pattern of contraction/relaxation that develops in response to stimulation of the enteric nervous system. Muscle strips from the proximal and distal colon were oriented parallel to the circular muscle layer and stimulated electrically (80 V;0.5-ms pulse width) for 10 s using platinum wire electrodes. Stimulus frequency varied between 1 and 64 Hz. EFS stimulation of circular smooth muscle from the proximal colon of neonatal, juvenile, and adult rabbits was characterized by the development of atropine-sensitive on-contractions. The frequency-response curves were similar for each age group. In the distal colon, EFS of circular smooth muscle from neonatal, juvenile, and adult rabbits produced on-relaxations and atropine-insensitive off-contractions. The frequency-response data for the off-contractions were similar for each age group. Although no age-related differences were observed with respect to the pattern of contractile response to EFS, the force of the proximal colon on contractions and the distal colon off-contractions increased as the animals matured. The results suggest that the pattern of colonic enteric neurotransmission is established early in the neonatal period and does not undergo any significant change during the postnatal period.(ABSTRACT TRUNCATED AT 250 WORDS)