The coordination of mastication, oral transport, and swallowing was examined during intake of solids and liquids in four normal subjects. Videofluorography (VFG) and electromyography (EMG) were recorded simultaneously while subjects consumed barium-impregnated foods. Intramuscular electrodes were inserted in the masseter, suprahyoid, and infrahyoid muscles. Ninety-four swallows were analyzed frame-by-frame for timing of bolus transport, swallowing, and phases of the masticatory gape cycle. Barium entered the pharynx a mean of 1.1 s (range -0.3 to 6.4 s) before swallow onset. This interval varied significantly among foods and was shortest for liquids. A bolus of food reached the valleculae prior to swallow onset in 37% of sequences, but most of the food was in the oral cavity at the onset of swallowing. Nearly all swallows started during the intercuspal (minimum gape) phase of the masticatory cycle. Selected sequences were analyzed further by computer, using an analog-to-digital convertor (for EMG) and frame grabber (for VFG). When subjects chewed solid food, there were loosley linked cycles of jaw and hyoid motion. A preswallow bolus of chewed food was transported from the oral cavity to the oropharynx by protraction (movement forward and upward) of the tongue and hyoid bone. The tongue compressed the food against the palate and squeezed a portion into the pharynx one or more cycles prior to swallowing. This protraction was produced by contraction of the geniohyoid and anterior digastric muscles, and occurred during the intercuspal (minimum gape) and opening phases of the masticatory cycle. The mechanism of preswallow transport was highly similar to the oral phase of swallowing. Alternation of jaw adductor and abductor activity during mastication provided a framework for integration of chewing, transport, and swallowing.

An asymmetrically distributed protein in the embryonic mouse retina was identified as an aldehyde dehydrogenase through protein microsequencing. It was characterized as a cytosolic isoform with basic isoelectric point and preference for aliphatic substrates, features that resemble those of the isoform AHD-2 which is known to oxidize retinaldehyde to retinoic acid. Immunohistochemistry with aldehyde dehydrogenase antisera showed strong labeling of the dorsal retina from the early eye vesicle stage into adulthood. In addition, optic axons originating from the dorsal retina were transiently labeled during their outgrowth phase. Whereas in the embryo the enzyme was expressed in undifferentiated cells and in neurons, in the retina of the adult mouse the asymmetrically distributed isoform was mainly expressed in Muller glia, with the number of labeled glial cells varying with retinal position.