Trigeminal orosensation and ingestive behavior in the rat

A deafferentation procedure was used to examine the contributions of trigeminal orosensation to the control of ingestive behavior in the rat. The procedure removed somatosensory input from the mouth, sparing olfaction, lingual taste, and vibrissae inputs as well as proprioceptive afferents from and efferents to the jaw muscles. Rats with sections of tongue or jaw muscle efferents served as oromotor controls. Bilateral trigeminal orosensory deafferentation was followed by an array of effects on ingestive behavior whose magnitudes were proportional to the extent of the deafferentation. The "trigeminal syndrome" includes a disruption of food and water intake (aphagia, adipsia), impairments in the sensorimotor control of eating and drinking, decreased responsiveness to food and water, and a reduction in the level of body weight regulation. Trigeminal deafferentation spared elementary ingestive movement patterns (biting, licking, chewing) but disrupted their control by the perioral stimuli, which normally elicit them, so that eating and drinking sequences were either aborted or inefficient. Deficits in food intake varied with the sensory properties of the diet. Recovery of intake took place along a palatability gradient, and recovery of water intake paralleled that of dry food. The chronically reduced body weight was caused by a persistent hypophagia and reflects reduced responsiveness to food. These findings suggest a considerable degree of overlap in the neural mechanisms mediating the sensorimotor and motivational control of intake in the rat.