MUSCULAR BASIS OF BUCCAL PRESSURE - INFLATION BEHAVIOR IN THE STRIPEDBURRFISH CHILOMYCTERUS-SCHOEPFI

We examined the relationship between commonly measured features of cra nial muscle activity and the magnitude of sub- and superambient pressu re measured inside the buccal cavity of the striped burrfish Chilomyct erus schoepfi during inflation behavior. Buccal pressure was recorded simultaneously with electromyographic (EMG) records of activity from t hree expansive-phase muscles (levator operculi, levator pectoralis and and three hyohyoideus abductor) compressive-phase muscles (adductor m andibulae, protractor hyoideus and protractor pectoralis) in eight ind ividuals. We quantified EMG activity in approximately 30 inflation cyc les per fish by measuring the burst duration, rectified integrated are a, intensity of activity (area divided by duration) and onset time rel ative to the onset of subambient pressure at the beginning of the cycl e. Multiple regressions were calculated separately for data from each fish to investigate the relationships between pressure and EMG variabl es. The percentage of variation in minimum buccal pressure or area und er the subambient pressure curve explained by the multiple-regression models ranged among individuals from approximately 52 to 84 %. The reg ression models accounted for more variation in peak pressure and the i ntegrated area of superambient pressure; r(2) ranged from 76 % to 97 % . The strong relationship between EMG activity and superambient buccal pressure suggests that the latter is probably a direct function of th e strength of compressive-muscle contraction. In contrast, the magnitu de of subambient pressure is a complex function of the area of the ora l opening and the rate of buccal expansion, factors that do not appear to be as directly indicated by the degree of muscle activity.