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The acquisition and extinction of a conditioned taste aversion in Egyptian spiny mice and Long-Evans rats was compared during 20 posttest sessions using a cross-over design and double-blind control procedures. Spiny mice preexposed to a sucrose CS demonstrated more latent inhibition and a faster rate of extinction than did Long-Evans rats preexposed to the same CS. Preference indices did not differ between control animals or as a function of gender. The present results are the first report of the effects of latent inhibition on learning taste aversion in Egyptian spiny mice.

The influences of hypothyroidism on behavioral measures of the taste function in male and female Long-Evans rats were determined. Experimental rats' preferences for and ability to detect NaCl, HCl, sucrose, and quinine sulfate were examined before, during, and after 9 weeks of maintenance on 0.1% propylthiouracil (PTU), an agent that produces marked hypothyroidism, with similar determinations made for control animals. Despite significant decreases in PTU-treated rats' serum triiodothyronine (T3) and thyroxin (T4), there were no changes in sensitivity or responsivity to the target tastants. However, altered preferences for NaCl, HCl, and quinine sulfate were observed for PTU-treated rats; elevated consumption of HCl and quinine sulfate was present at the end of the study when serum T3 and T4 had returned to near-baseline levels. The data confirm observations that PTU-induced hypothyroidism alters rats' taste preference behavior.

The influences of three methyl xanthines (MX) on human taste responsivity, caffeine, theophylline, and theobromine, were examined using blind control procedures. Taste responsivity in the same subjects was determined using the matching procedure described by Schiffman (Study 1) and the whole-mouth procedure described by Sheperd (Study 2). In each study, the duration of MX pretreatment necessary to enhance taste responsivity was examined. No potentiation of overall- and taste-quality specific intensity ratings was observed for any tastant, independent of test procedure, type, and concentration of MX pretreatment, or length of MX pretreatment. Taste intensity ratings, especially for NaCl, were higher following pretreatment with water than methyl xanthine or adenosine combined with caffeine. Adenosine, added at several concentrations to caffeine pretreatments, influenced neither taste responsivity nor taste intensity ratings.

Taste sensitivity and responsivity, two-tastant and taste-mixture discrimination performance, and taste preferences were examined prior to and after the selective desalivation of 48 male Long-Evans rats. Altered preference behavior was observed in rats after removal of the major salivary glands, as well as after removal of only the submandibular-sublingual complexes. In 9 of 12 desalivated rats, decreased sensitivity and increased responsivity to near-threshold sodium chloride solutions were observed, although these changes were less than one-half an order of magnitude. No between-group differences in performance on two-tastant and taste-mixture discrimination tasks were observed. These results suggest that decrements in absolute sensitivity do not result in concomitant deficits in the discrimination of taste qualities.

The influence of 33 days of combined dietary sodium and water deprivation on the taste sensitivity and responsivity of the rat to a wide range of NaCl solutions and discrimination tasks was examined using double-blind procedures, high-precision gustometry, and an automated operant go/no-go task. Sodium concentration in urine and saliva but not plasma decreased significantly only in the sodium-deficient rats. The same measures remained unchanged in control animals. Nonparametric measures of taste sensitivity and responsivity to NaCl did not differ between sodium-deficient and control animals and performance on taste discrimination, reversal learning, and lick-rate tasks remained the same between the groups as well. The present results support and extend previous findings that dietary-induced sodium deficiency increases NaCl and water consumption, but alters neither the sodium-deficient rat's taste sensitivity and responsivity nor performance on simple and complex tasks in which tastants serve as cues for discriminative responding.

An operant conditioning procedure is described for assessing taste detection and discrimination in rats. Rats were trained to lick at a 10-barrel stimulus delivery tube for a 0.005-ml sample of a positive (S+) or negative (S-) stimulus and to switch to a water delivery tube after presentation of S+. The system is computer controlled and selection of stimuli can be made interactive with performance. After preliminary training, absolute and intensity-difference thresholds can be determined in 1-2 sessions. Mean absolute thresholds in 10 rats for NaCl, sodium-saccharin, and sucrose were 0.0049%, 0.0012%, and 0.035%, respectively. Intensity-difference thresholds (not reported previously in the rat) for NaCl and saccharin were 16.1% and 12.3%, respectively. With these procedures rats also rapidly acquired 2-tastant discriminations, including those involving taste mixtures.

The effects of dietary copper and Vitamin B-6 deficiency on NaCl sensitivity in adult male rats were assessed in separate studies using a double-blind protocol, high-precision gustometry, computer-controlled go/no-go operant procedures and signal detection measures of sensitivity and responsivity. The dietary manipulations reduced plasma copper ion content to 40% of baseline levels in the copper deficient group and plasma 5'-pyridoxalphosphate content to 5% of baseline levels in the Vitamin B-6 deficient group and, as expected, altered hematocrit and hemoglobin levels in both groups. These metabolic changes resulted in increased NaCl preference in the Vitamin B-6 deficient group but did not alter sensitivity or responsivity to NaCl, and similar results were obtained in simple and complex taste discrimination tests. The present results demonstrate that dietary copper and Vitamin B-6 deficiencies do not result in altered taste sensitivity in the adult male rat.

Taste detection thresholds for sodium chloride, sucrose, citric acid and quinine sulfate were determined with the Henkin three drop forced-choice method at stimulus volumes 0.05 ml, 0.50 ml, and 0.90 ml, with and without water rinses. Taste thresholds were inversely related to stimulus volume (median rs = -.68 and, within each volume, thresholds did not differ as function of water rinsing. The detection thresholds for sodium chloride (range: 15.06 mM to 6.7 mM), sucrose (range: 24.22 mM to 14.13 mM), citric acid (range: 1.47 mM to 0.5 mM) and quinine sulfate (range: 0.35 mM to 0.12 mM) were similar to those of other investigators using considerably larger stimulus volumes and different psychophysical procedures. The present results demonstrate that the Henkin three drop method provides a more optimal measure of changes in taste sensitivity when stimulus volumes of approximately 1 ml are used in place of the standard 0.05 ml stimulus volume.

The influence of adrenalectomy on the taste sensitivity and responsivity of Long-Evans rats to sodium chloride and sucrose tastants presented separately and in mixtures was examined using high precision gustometry, computer-controlled go/no-go operant procedures, and nonparametric signal detection measures. Relative to baseline levels, adrenalectomized rats' plasma corticosterone levels decreased by 328% while sodium chloride and water consumption increased by 548% and 165%, respectively. The same measures remained unchanged in sham-operated animals. Taste sensitivity and responsivity to sodium chloride and sucrose did not differ between adrenalectomized and sham-operated animals and discrimination performance remained the same between the groups as well. The present results support and extend previous findings that adrenalectomy and the resultant corticosteroid deficiency does not influence taste sensitivity or responsivity in the rat.