BUCKLEY, C.A.*; SCHNEIDER, J.E.; CUNDALL, D.; Lehigh University: How Syrian hamsters fill their cheek pouches: Co-opted masticatory motor patterns and the role of the retractor muscle

The rodent cheek pouch is an evolutionary novelty that allows quick transport of large amounts of food to a safe environment for storage and consumption. Hamsters are unusual in responding to internal energy deficits by increasing hoarding rather than consumption of food. The hamster cheek pouch opens into the oral cavity, so that the mouth must be opened in order to pouch food. This suggests that pouching motor patterns might be derived from ingestive behavior. We recorded Syrian hamsters (Mesocricetus auratus) chewing and pouching in a mirrored box that provided simultaneous frontal, lateral, and ventral perspectives using video recorded at 60 fps with frame exposures of 1/500 sec. Jaw cycles were evident during pouching, and assisted insertion of food into the pouch. Pouching jaw cycles were similar to masticatory jaw cycles but a delay was often evident between normal fast-open and fast-close phases, particularly when pouching large food items, suggesting modulation of the most complex part of the masticatory motor pattern. The gross anatomy of the cheek pouch and its trapezius-derived retractor muscle combined with visual records of the timing of retractor contraction suggest that the retractor plays a role in filling the pouch. Contraction of the retractor muscle tightens the pouch walls around the food while pulling the pouch and enclosed food caudally, leaving an empty rostral region of the pouch available for more food. We speculate that the neuroanatomical circuits that control the cheek pouch and hoarding behavior might provide a unique opportunity to study the neural basis of hunger motivation vs. food consumption.