Oral somatosensory factors in dietary self-selection in rats.

For studying the mechanisms of the control of protein intake, rats were subjected to partial trigeminal deafferentation. Oral somatosensory afferents from the lower anterior portion of the oral cavity were selectively sectioned, but somatosensation of the other parts of the mouth as well as gustatory and olfactory afferents were left intact. Animals were allowed to choose from two diets, only one of which contained protein. Before deafferentation, the rats chose a constant portion of their daily intake in the form of protein (12.2%; SE = 0.5). After deafferentation, protein intake was all but eliminated at first but was resumed later; carbohydrate intake was reduced. When total intake had recovered to nearly preoperative values, the protein/total-intake ratio remained impaired, with deficits that ranged from seemingly random selection to extreme preferences. The variability of dietary selection between days was considerably higher than before surgery. The discussion considers the involvement of learning processes in homeostasis.