Feeding in golden hamsters, Mesocricetus auratus

Abstract

Simultaneous cine and electromyographic records of freely feeding, unanesthetized golden hamsters show that their motion and muscular activity during mastication differ from those of albino rats (Weijs, '75). Rats show only propalinal motion while hamsters show lateral translation as well. The masticatory muscles of hamsters and rats are generally similar, but their molar dentitions differ. The interlocking molar cusps of hamsters restrict propalinal protrusion and retrusion when the molars are in occlusion; however, hamsters readily unlock occlusion by a twisting movement in the horizontal plane. Rats may perform propalinal movements even with the teeth in occlusion.In mastication the hamster's jaw moves laterally as well as vertically and anteroposteriorly. Chewing orbits typically reverse after one to three orbits. Reversal begins at the start of the upstroke and involves a lateral shift in the opposite direction with the mouth closed.Electromyograms show that symmetric and asymmetric activities of closing protrusive and closing retrusive muscles produce a unilateral force couple on both sides. (This couple accompanies a midline closing stroke.) When the mouth is closed, unilateral activity of closing retrusors and closing protrusors also induces lateral translation. A bilateral force couple pits the retrusors of one side against the protrusors on the opposite side. Simultaneous with lateral excursion to the opposite side of midline and the action of these closing muscles, the anterior digastric and lateral pterygoid muscles of one side fire asymmetrically.The mandible moves downward coincidently with bilateral activity of the digastrics and lateral pterygoids. As the jaw opens further, activity differences of the lateral pterygoids accompany a shift of the mandible toward midline. At the end of the downstroke, all masticatory muscles studied are silent. The jaw returns to midline when the adductors fire asymmetrically a t the start of closing.Trituration appears to coincide with an initial simple protrusion, which is subsequently accompanied by lateral translation. Different food types are reduced by distint chewing patterns with the differences clearest when the teeth are near occlusion. During gnawing the lateral pterygoids and digastrics fire longer, and the closing muscles fire less strongly. Chewing patterns in golden hamsters appear more generalized than those of rats; the differences may be directly associated with the ability of hamsters to store food in their cheek pouches.Much of our present understanding of the terns (Turnbull, '70). Although aspects of this function of the mammalian masticatory sys-classification are certainly still open t o questem has been based upon comparative ana-tion (Crompton and Hiiemae, '70; Kallen and tomical studies of teeth, skulls and mastica-Gans, '72), it is clear that rodents show one of tory musculature (cf. Arendsen de Wolff-the extremes of modifications in their mastiExalto, '61; Becht, '53; D'Amico, '65; Hiiemae, catory apparatus. Accordingly, further i...

Kinematic analysis of an appetitive food-handling behavior: the functional morphology of Syrian hamster cheek pouches

“…If this is true, it might also contribute to the considerably faster pouching rate in D. deserti (Nikolai and Bramble, 1983), because the tongue in externally pouched rodents is presumably not involved in pouch filling. A detailed report of the kinematics of masticatory jaw cycles in Syrian hamsters (Gorniak, 1977) gives no indication of any anomalies between FO and FC, and our measurements of masticatory kinematics are in general agreement. Gape phase was only observed during pouching, and was significantly longer for large food items than for small (Fig.·3).…”

“…In Mesocricetus, masticatory jaw cycles occur at a rate of about 4-6·s -1 , depending on the consistency of the food (Gorniak, 1977). Our measurements using 60·frames·s -1 video produced estimates of 0.18·s·cycle -1 for lab chow pellets, or about 5·cycles·s…”

“…The kinematics of pouching jaw cycles in Dipodomys were not described; thus whether or not they resemble masticatory jaw cycles is unknown. Modulation of the jaw cycle (decrease in the length of the slow phase portion) has been observed during gnawing behavior in rodents, including Syrian hamsters (Gorniak, 1977), although kinematic plots of jaw displacement during gnawing were not reported. Our comparison of pouching to mastication shows a relative decrease in the slow phase portion of the jaw cycle during pouching of small food items, but not large items (Figs·3 and 4).…”

“…In Syrian hamsters, cheek pouch function has been examined using electromyographic stimulation (Priddy and Brodie, 1948) and videotaping (Gorniak, 1977), but jaw activity and the role of the retractor muscle in pouch filling have not been described. One externally pouched rodent, Dipodomys deserti, has been shown to coordinate forelimb activity with one jaw cycle per pouching event, defined as the insertion of one load of food from paws into cheek pouches (Nikolai and Bramble, 1983).…”

“…One previous researcher (Gorniak, 1977) captured pouching behavior of Syrian hamsters on film while examining masticatory jaw cycles, and reported little or no forelimb usage for small food items (sunflower seeds), and much more forelimb use for large lab pellets. Our observations confirm and extend those of Gorniak.…”