ELECTROMYOGRAPHIC ANALYSIS OF ORAL HABITUATION IN RAT PUPS

Rat pups show decreases in mouthing activity in response to a series o f repeated oral infusions of a diet. This decrease in mouthing activit y has been termed ''oral habituation'' and these changes have been rea dily recorded with simple behavioral observations. Oral habituation ap pears to be a component of satiety in young rats. In the present study , to more specifically characterize changes in motor response topograp hy during habituation ill muscle groups used for mastication, mouthing activity was recorded by implanting fine wire electromyographic elect rodes in the superficial masseter, anterior digastric, sternohyoideus, and genioglossus muscles of 12-day-old rat pups. During testing, pups received a series of brief oral infusions of a 10% sucrose diet deliv ered through an oral cannula. The results demonstrated that mouthing a ctivity as observed and scored behaviorally was highly correlated with mouthing behavior recorded by EMG, with oral habituation distinctly e merging in both measures. In addition, the pattern of motor activity i n the four masticatory muscles changed during the course of oral habit uation. Within the minute following a single infusion, the cycle frequ ency, duration of activity, and relative onset time of activity in the four muscles changed. In addition, across the course of habituation, both cycle frequency and relative onset times of muscle activity chang ed. These results demonstrate the general reliability of behavioral ob servations of masticatory motor activity in young rats and provide fur ther information on how the pattern of activity of muscles involved in the mouthing motor pattern is altered during the course of oral habit uation. (C) 1998 Elsevier Science Inc.