SPATIAL AND TEMPORAL VARIATIONS IN LOCAL SPIKE PROPAGATION IN THE MYOMETRIUM OF THE 17-DAY PREGNANT RAT

Detailed spatial analysis of propagation of individual action potentia l was performed during spontaneous bursts of activity in the isolated 17-day pregnant rat myometrium. Use was made of high-resolution mappin g with simultaneous recordings from 240 extracellular electrodes. Posi tioning of the electrode assembly by itself did not have any adverse e ffects, and no differences were found in the period or duration of spo ntaneous bursts recorded with and without the electrode assembly touch ing the tissue. The spread of propagation of individual action potenti als was reconstructed at several moments during myometrial spike burst s. Both the direction and the sequence of activation of the myometrium were found to be highly variable and depended on 1) the level and spa tial dispersion of excitability and 2) whether conduction occurred pre dominantly in the longitudinal or the circumferential direction. Furth ermore, conduction was frequently complicated by the spontaneous occur rence of 1) lines of conduction block, 2) focal sites of pacemaking, o r 3) merging of two or more wavelets into a single wave. In contrast, when the myometrium was divided into small segments, activity became m uch more regular, and both the location of the pacemaker and the direc tion of propagation were much more stable than in the whole myometrium . In conclusion, spontaneous spatial variations in local spike propaga tion at the preterm stage could provide for the necessary asynchrony i n activation and play a role in the prevention of forceful contraction s and premature labor.