Masticatory movements and EMG activity following electrolytic lesions of the trigeminal motor nucleus in growing guinea pigs.

Unilateral electrolytic lesions were produced in the left trigeminal motor nucleus (TMN) of six guinea pigs at 49 days of age. Masticatory mandibular movement and EMG data were collected prior to lesioning and at 4 and 12 days postlesion. After the animals were killed 60 days postlesion, dissection and maceration revealed muscular atrophy and craniofacial asymmetries on the lesion side. Analyses of prelesion and postlesion mandibular movement and EMG data indicated significant (p less than 0.05; p less than 0.01) changes in chew cycle durations, dimensions, and EMG activity patterns. Shifts in EMG durations of working- and balancing-side muscles were strongly related to most of the observed skeletal asymmetries. Data indicated that muscular paresis and altered neuromuscular activity can effect skeletal changes in the mammalian craniofacial complex; total muscular paralysis is not a prerequisite for profound morphologic changes. Altered manifestation of masticatory central pattern generators within the central nervous system may also account for variations in craniofacial form and function.