Early effects of desalivation upon fluid consumption and taste acuity in the rat

Taste preference and acceptance in thirsty and rehydrated [correction of dehydrated] rats

Experiments were designed to determine whether water deprivation affects taste preferences and/or taste acceptance. In experiment 1, both five- and two-bottle preference tests were performed in normally hydrated rats to permit the selection of five groups of rats showing the same taste preference for one of four prototypical tastes. Subsequently, in the same groups of rats, taste preferences were determined by a two-bottle test (experiment 2), and taste acceptance by a one-bottle test (experiment 3), following 12, 24, 36, and 48 h of water deprivation. After both 12 and 24 h of dehydration, during the first 10 min of the tests of experiment 2, all rats ingested greater volumes of either NaCl or sucrose solution than water, but more water than either HCl or quinine solution, and the differences were very significant (P<.0001). After 36 or 48 h of dehydration, the differences became very small and, in some cases, the P-values were at the lowest or borderline level of the significance, suggesting that dehydrated rats poorly discriminate the nature of the fluid drunk. During the 11-60 min interval, all rats preferred either sucrose or NaCl to water, but water to either HCl or quinine. Experiment 3 was performed to ascertain whether the need for fluid might overcome the palatability of solutions. All rats, dehydrated for 36 or 48 h, after 10 min of exposure, drank equal amounts of fluid, independent of its palatability. During the 11-20 and 21-60 min interval, the fluid intake of rats changed in accordance with the palatability of the solution available. In conclusion, severe thirst in rats may override the palatability of the solutions, and the thirst drive may be so strong that they do not reject fluids because body fluid balance would be severely compromised.

Effects of atropine injection on food-associated drinking in rats with superior salivatory nucleus lesions

The neuropharmacological mechanisms involved in the prandial drinking pattern seen in rats with superior salivatory nucleus lesions + parotidectomy were investigated with behavioral methods. Results showed that the administration of low doses (0.1 mg/kg body wt) of atropine in lesioned rats potentiated previously established prandial drinking. Higher doses of atropine (1.0 mg/kg), however, were required to induce a similar degree of prandiality in control rats (parotidectomy alone). These findings suggest that the salivatory nucleus lesions affected a cholinergic brainstem-salivary gland system involved in the neural control of food-associated drinking.

Effects of gustatory deafferentation on ingestion of taste solutions as seen by licking behavior in rats

The role of the taste nerves in licking behavior to various taste solutions was examined in rats. The study consisted of two experiments. In the electrophysiological experiment, the whole nerve recording of the anterior palatine nerve (PN) was performed to examine the response properties of this nerve to taste stimulation applied to the taste buds in the nasoincisal duct. When the moderate concentrations of solutions were used, the PN responded best to HCl, followed by sucrose and NaCl. Quinine hydrochloride elicited the smallest response. In the behavioral experiment, the number of licks/20 sec was measured for each of the test solutions such as 0.5 M sucrose, 0.01-1.0 M NaCl, 0.03 M HCl and 0.0005 M-0.01 M quinine in normal control and experimental rats. The experimental animals received bilateral deafferentation of the PN, chorda tympani (CT) and glossopharyngeal nerve (GN) alone or in various combinations. Rats without one of the 3 taste nerves still rejected the aversive HCl and quinine solutions. However, after lesions of both CT and GN, or all the 3 taste nerves, the rats showed a significant increase in the number of licks to these aversive solutions. These results suggest that taste aversion disappears after denervation of more than 80% of the total taste buds. The interlick interval, lick duration and the amount of intake per lick did not change significantly after sections of the taste nerves in any combinations.

Effects of pharmacologic reductions in salivary flow on taste thresholds in man

The effects of short-term salivary flow reductions on human taste thresholds were measured. Recognition and detection thresholds were obtained from 65 subjects during periods of both normal and reduced salivary flow. Decreased salivary flow was achieved by oral administration of either Elavil, Benadryl or atropine. Thresholds were measured for NaCl, citric acid, quinine sulphate and sucrose with a traditional series of aqueous solutions as well as with a series of dry taste stimuli using a filter-paper base. Whole mouth resting flow and stimulated salivary flow were measured before and after taste testing. The pharmacologic agents produced depressions in salivary flow ranging between 30 and 75 per cent of normal levels. The large decreases in flow produced no measurable changes in taste thresholds with the exception that an increased sensitivity to aqueous and dry citric acid stimuli consistently was observed following atropine administration. Changes in salivary bicarbonate levels, produced by atropine, may have mediated the observed shifts in oral sensitivity to citric acid.

Long-term effects of surgical desalivation upon taste acuity, fluid intake, and taste buds in the rat

Taste bud structure and taste preferences in intact and desalivated animals were evaluated to ascertain whether there was a structure-function relationship. Thirty-three totally desalivated rats and 30 sham-operated controls were tested between 95 and 110 d after surgery with a 48-hour two-bottle preference paradigm; they were then sacrificed, and the tongue epithelium and circumvallate papillae taste buds were examined histologically. Desalivated rats manifested significantly increased preferences for normally avoided solutions. Histological study of the dorsal tongue epithelium revealed increased keratosis. There were qualitative changes in the taste buds of the circumvallate papillae with some taste buds appearing shrunken and disorganized.