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DEVELOPMENT AND TISSUE PLASTICITY

Developmental changes in spontaneous smooth muscle activity in the neonatal rat urinary bladder

Eniko A. Széll,^1,2 George T. Somogyi,¹ William C. de Groat,¹ and Gyula P. Szigeti^2,3

¹Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261; ³Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, New York 14214; and ²Departments of Pediatrics and Physiology, Health Science Center, University of Debrecen, Debrecen, Hungary H4012

Submitted 16 October 2002 ; accepted in final form 10 May 2003

Changes in spontaneous activity of the urinary bladder during postnatal development were examined in muscle strips from the base and dome of bladders from 1- to 5-wk-old rats. Activity was analyzed using fast Fourier transformation (FFT), nonlinear cross prediction, and the Shannon entropy test. Spontaneous activity was not detected in strips from 1- to 5-day-old rats but was observed in 50% of strips from 6- to 7-day-old rats and was prominent in strips from 2-wk-old animals. FFT analysis revealed one peak in activity, which was significantly faster in the bladder base (0.21 ± 0.03 Hz) than in the dome (0.08 ± 0.01 Hz). A second peak at 0.5 Hz was detected at 3-5 wk of age. Atropine but not tetrodotoxin decreased the amplitude of spontaneous contractions, whereas carbachol, a muscarinic agonist, unmasked or stimulated spontaneous activity. These data suggest that slow rhythmic activity observed previously in neonatal whole bladders is generated by pacemaker cells in the bladder base or dome. The emergence of faster activity in bladders from older animals may reflect the development of multiple pacemaker sites, which would reduce coordination within the bladder wall and improve storage function in the mature bladder.

spontaneous contractions; fast Fourier transformation; nonlinear analysis

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