The odor of taste solutions

Physiology and Behavior.

Vol.

1, p p .

145-146.

Pergamon

Press

Ltd.,

1966

Printed in Great

Britain

The Odor of Taste Solutions' S Y L V I A D. M I L L E R A N D R O B E R T P. E R I C K S O N

Department of Psychology, Duke University, Durham, North Carolina (Received 30 July 1965) MILLER, S. D. AND R. P. ERlCKSON. The odor of taste solutions. PHYSIOL.BEHAV. 1 (2) 145--146, 1966.--Animals run in taste discrimination or preference studies commonly have an intact olfactory sense. It is shown here that rats can smell chloride salts at concentrations near the taste threshold. From this, it seems advisable that animals used in taste experiments be deprived of the olfactory sense. Taste

Olfaction

DUmNG attempts in this laboratory to establish in rats discriminations between taste solutions, it was noticed that successful selection of the correct stimulus was often accom. plished without licking the t u b e s containing the stimuli. Benjamin has indicated that rats may smell solutions of quinine hydrochloride [1], and Henkin has shown that humans can smell NaCI, KC1, NaHCO3, sucrose, urea and HCI [2]. The present experiment was undertaken to determine if rats using olfactory cues could detect certain salt solutions in concentrations normally used in "taste" studies. Four adult, male Sprague-Dawley rats that seemed to be using olfactory cues in the taste discrimination studies mentioned above were used. These rats were trained in the apparatus shown in Fig. 1 using a non.correction "taste" discrimination procedure except that they were not allowed

wo

r.lo

%

r*l o

I

0

I

I

I I]

I

I

5

I0

~

1

15

. . . . .

1. . . . .

20

80

,II ' ' ~ ' ~ ~ ' ~

t/

,,q

'"'""0 ..."" .....-'""

..IP.......

7o O

.:" R'" .... ,'*" °."*" ., ~.." • ff~"

I---

~6o 50

!

x~

I

I

~'~"

0~ J 0003

I I I I. .o01 o03 .Of OJ CONCENTRATION(MOLAR) FIG. 2. Per cent choice of correct door with "taste" solutions of various concentrations. Each data point represents a total of 20 trials each for four rats. O, performance of one of these rats after section of olfactory nerves; S, performance of one sham-operated rat; here, each data point represents 80 trials (NH4C1 stimulus).

to taste the stimuli. They were first trained to sniff through holes in both choice doors (D) behind which were tubes (T) containing the stimuli to be discriminated (salt solutions in distilled water vs. distilled water). These tubes were at a distance which precluded drinking (hole ½ in. in diameter, tube mouth ] in. from front of hole). For each trial the rat was placed in the start-box (S) and allowed to go through either of the two doors. Ten seconds of water reinforcement from tubes (W) mounted behind holes in the end of the apparatus was contingent upon a correct choice at the doors. F o r all rats the correct choice was water, rather than the salt solution, The location of the stimulus tubes was varied randomly. Each rat received 10 trials a day under about 23 hr water deprivation; water was available to them in their home cages for 15 rain after each day's session.

I

25

INCHES FIG. 1. The olfactory discrimination apparatus, plan view. Walls, floor and ceiling of clear ~ in, Plexiglass; height 8 in. Choice do~rs (D) of Black, opaque ~ in. Plexiglass, 5 x 6~in. hinged at top and counterbalanced .to open completely when pushed. Tubes (T) containing "taste" solutions mounted behind holes in choice doors. Holes in choice doors and for water reinforcement (W) ½in. diameter and centered 11 in. above floor. Start box (S) open at top, with hinged cover.

XSupported by NSF Grant GB-2087 and NIFI grant NB--04793, 145

146

MILLER AND ERICKSON

Their performance with various concentrations of choloride salts is shown in Fig. 2. Obviously, the intensities of these as olfactory stimuli were not well controlled; it is only meant to show that the solutions presented as taste stimuli could be smelled. Also, although typical taste stimuli were used, it is not determined, or important for the present experiment, whether the major chemical or the impurities present in the reagent grade chemicals was the olfactory stimulus. According to Henkin (personal communication), this stimulus was probably small amounts of chlorine gas released from the salts.

Clearly, lower thresholds than those evident in Table 1 and Fig. 2 might be obtained in different "tasting" situations, or with more rigid cont~:ol of these stimuli as olfactory stimuli, To assure that olfactory cues had been utilized, the olfactory nerves of one of these rats (phenobarbital anesthesia) were sectioned just caudal to the cribiform plate. As a control, the same operative procedt/re was performed on a second o f these rats, except that the olfactory nerves were not cut. After a relearning period of 19 experimental days of 10 trials each, their performance was as shown in Fig. 2. (O, olfactory nerves sectioned; S, sham-operate). The operated animal's

TABLE 1 ANALYSES OF VARIANCE AND t TESTS FOR MEAN DISCRIMINATION SCORES

Stimulus 0.0003 M KCI NH4CI LiCI NaCI

0 1.19 5.00t 0

t Concentration 0.001 M 0.003 M 0.01 M 2.79 2.35 2.45 2.73

3.90* 3.30* 2.47 1.47

8.68++ 8.19++ 5.02t oc ~+

F 0.1 M 11.00~ 14.70~* 6.60~ 8.57,+

14.45§ 14.98§ 5.36§ 27.91 §

Probabilities of t values (df = 3) and F values ( d f = 4/15); *<0.05, t<0.02, ~<0.01, §<0.001. That the data in Fig. 2 do represent discrimination of some of these stimuli is shown by the analyses of variance and t tests (two-tailed) summarized in Table 1. These analyses are based on the mean percentages correct for the group o f four rats at each concentration. The analyses of variance indicate for each salt other than chance differences in performance with variations in stimulus concentration. The t tests for these same data show that, with the possible exception of 0.0003 M LiCI, only the stronger stimuli are detectable.

performance did not deviate significantly from chance while the sham-operate's performance was significant at the 0.07 level (two-tailed Sign test). These results do not dictate that animals run in other taste experiments with olfactory cues possible have not been primarily or exclusively using gustatory cues. However, it may be suggested from this study that animals run in taste discrimination or preference studies should be deprived of the olfactory sense.

REFERENCES

1. Benjamin, R. M. Effect of removal of olfactory bulbs on taste discrimination in normal and brain operated rats. Physiologist, Wash. 3: 19, 1960.

2. Henkin, R. I. Effect of adrenal insufficiency and of corticos. teroids on smell threshold. Clin. Res. 10: 400, 1962.