Intermittency in mastication and apomorphine-induced gnawing

Rhythmic behaviors like mastication, gnawing, and locomotion, are character ized by temporal segmentation or intermittency. That is, they frequently oc cur as a series of short bursts interrupted by pauses rather than as one lo ng uninterrupted burst. The function of intermittency as well as the mechan isms that produce it are unknown. Biogenic amine systems may play a role in producing intermittency; however, experimental work to confirm this is onl y in its infancy. The current study evaluates the structure of intermittenc y associated with mastication and apomorphine-induced gnawing in the guinea pig. Thirteen free-roaming animals were videotaped while masticating or gn awing. Eight animals were given 0.5 mg/kg i.m. apomorphine and videotaped w hile gnawing. The remaining five animals received no apomorphine injections , but were taped while feeding on alfalfa pellets. Custom software was used to score instances of maximum jaw closures in videotaped mastication and g nawing sequences. The time between successive maximum jaw closures, called the interocclude interval (IOI), was calculated for all scored sequences. A cutoff IOI value of 0.26 s differentiated pauses (IOI values equal or grea ter than 0.26 s) from chews or gnaws (IOI values less than 0.26 s). Two or more successive chews or gnaws, without intervening pauses, defined behavio r bursts. Chew, gnaw, and burst durations were quantified and compared. Che w and gnaw durations were similar. However, chewing bursts were significant ly longer than gnawing bursts. The significance of these results is present ed in light of previous neurophysiological work on rhythmic jaw movements a na intermittency. (C) 1998 Elsevier Science Inc.