Gustatory nerve response to sugars in neonatal puppies.

Sugars were used as stimuli to investigate developmental changes in neural gustatory response in puppies from birth to weaning age. Chorda tympani nerve responses to chemical stimulation of the tongue were present at birth. No developmental changes were detected between birth and weaning, and the relative stimulatory effectiveness of six sugars in the neonate and older puppy was identical to that reported for the adult dog. The steady-state component of the puppy's integrated neural response was absent for many sugars and the immature animal exhibited irreversible decrement in response amplitude with repeated stimulation. Keratinization of tongue epithelium, which thickens after weaning, possibly makes the tongue less permeable so that the gustatory receptors of older animals receive less damage from test stimuli.