The Effect of Sleep Deprivation on Conditioned Taste Aversion

Animals can acquire conditioned taste aversion when they experience unconditioned stimulus (US) while sleep deprived. 14, 60 days old, Long-Evans rats (Teklad) were water deprived except for 15-minute exposure to 20 millilitres of tap water for one day in phase 1. During the second phase, there was 15 minutes of drinking Grape juice (the conditioned stimuli (CS)), followed immediately by intraperitoneal injection of Lithium Chloride (LiCl). In phase 3, both sleep deprived and non-sleep deprived rats were given 20ml of both water and conditioned stimuli simultaneously in separate tubes and allowed 15 minutes of drinking or until one test tube is completely consumed . Sleep deprived were allowed time to groom before giving both test tubes of water and conditioned stimuli. Results showed that the Nonsleep deprived rats were not significantly different in their decrease in consumption of fruit juice following the injection of LiCl than the sleep deprived rats. The procedure carried out is discussed as a means to effect of sleep deprivation on conditioned taste aversion (CTA)

Introduction

Living organisms learn to develop food aversion when some of its constituents are associated with some kind of metabolic discomforts such as sleep deprivation and gastrointestinal discomfort . Conditioned taste aversion (CTA) is a crucial aspect for the survival of living things since it mitigates the repetitive consumption of toxic substances available in the environment. In human beings, sleep deprivation is usually associated with physiological side effects such as weight loss, cognitive function impairment, hypothermia, hyperphagia, and impaired immune function ( Hinderliter, Musci , Misanin & Anderson, 2 004 ) . Sleep deprived humans usually display increased irritability, learning recall, restlessness, aggressiveness, discrimination, and impairment of vigilance and mood. In experimental studies, rats have shown increased exploratory activities, aggression, and locomotor, but reduced fear and emotionality ( Hinderliter, 2 004 ) .

In the behavioral laboratory, Pavlovian conditioning has been utilized in the study of the conditioned taste aversion. The procedure involves associating a cause of physiological discomfort (unconditioned stimulus) with a customarily consumed food ( conditioned stimulus). After performing some trials, the subject of study (usually rats) develops a conditioned response by associating the physiological discomfort to the consumed food. According to Schafe and Bernstein (1995), the main indicator of conditioned taste aversion is the availability of a certain selective associability; attaining conditioned response depends on the association of a specific discomfort (like sleep deprivation) with a certain stimulus or taste ( Hinderliter, 2 004 ) . In the past experimental situations, a considerable number of substances has been used to induce a conditioned aversion to certain stimuli. Frequently, Lithium Chloride (LiCl) has been used as the unconditioned stimulus, normally administered through intraperitoneal (I.P) injections. The symptoms of the unconditioned stimulus are usually observed after 5-10 minutes; the subject experiences increase in peristalsis, remain motionless among others.

Past experiment documentations reveals the effect of associating LiCl with stimulus intake in Pavlovian condition is so effective such that its extinction can be observed even in the first trial ( Youngblood, Zhou, Smagin, & Harris, 1997 ) . However, in the case of sweetened solutions like Grape juice, this procedure has been applied only in a few experiments. Archer and Sjödén (1979) revealed that intraperitoneal injection of LiCl was associated with a decrease in intake of saccharine sweetened solutions ( Hinderliter, 2 004 ) . According to Peck and Ader (1974), it is possible to reduce the intake of saccharine sweetened solutions in rats by exposing a group of rats to deprivation conditions then giving them saccharine sweetened solutions and intra-peritoneal injection of cyclophosphamide simultaneously.

Nevertheless, these procedures utilized saccharine solutions which lack calories. A procedure conducted by Nachman and Ashe revealed that association between administering an I.P injection of LiCl and a solution containing 15% sucrose successfully resulted in conditioned taste aversion. In the study, groups of rats were administered a considerable intra-peritoneal injection of LiCl. A part of the group was given the LiCl dose in an ascending manner, while another group is receiving the dose in a descending manner . The findings of the study showed that the efficiency of the experiment was exclusively dependent on the amount of LiCl dosage; it was not associated with the manner of administering, available solution, or the order of dose administration. A similar study was conducted by Loy and Hall (2002), Martínez and López-Espinoza (2007) which confirmed that the LiCl is effective in establishing conditioned aversion of sucrose solutions ( Li , Hsiao & Li, 2013 ) .

To the author’s knowledge, no studies have compared the association of sleep deprivation with solution intake. In the view of the above experiments, the question rose whether sleep deprivation is effective in establishing conditioned taste aversion. The general purpose of this paper is to determine the effects of sleep deprivation in conditioned taste aversion. The study will also determine whether the taste of the solution affects the aversive condition. During the procedure, water and grape juice intake amounts will be recorded and analyzed to answer the research question.

Methods 

Subjects: 14 Male Rats: 60 Days Old 

Long-Evans rats (n=14) from the Teklad laboratory, Envigo were used. Their body weight ranged between 230 and 250g at the beginning of the experiment. The rats were housed in Plexiglas home cages with corn-cob bedding under 15:9 h light-dark cycle at 22 0 C and were fed ad lib. The sleeping chamber is a 68-litre plastic tube with a 10-inch terracotta flower-pot with a 5-inch base. Also, grape juice fruit at 10% concentration was used . 0.15% of Lithium Chloride (LiCl) solutions were prepared (Carolina Biological Supply) for each of the rats in the in the procedure. The dosage depended on the weight of the rat; the dosage was given at 2% of the total body weight. All the procedures in the experimental study were conducted in line with the framework provided by the Guide for Care and Use of Laboratory Animals, 8 th Edition.

Procedure and Materials 

The subjects were randomly assigned into two groups: Sleep Deprived Group (N=7) and Nonsleep Deprived Group (N=7). During phase 1 of the experiment, all rats were water deprived except for one 15-minute exposure to 20 ml of tap water in day 1. The volume of water drank by each rat was recorded. In phase 2 of the study, 15 minutes of drinking 20ml of 10% grape juice (conditioned stimuli) followed immediately with intraperitoneal (I.P) injection of 0.15% Lithium Chloride (LiCl) (Carolina Biological Supply. The last phase of this experiment was retention test in day 3. The subjects were given 20ml of both water and Conditioned Stimuli (20ml of 10% grape juice) simultaneously in separate tubes and allowed 15 minutes of drinking or until one test tube is completely consumed . Sleep Deprived (SD) rats were allowed 15-20 minutes to groom before giving both test tubes of water and Conditioned Stimuli (CS). The volume of water and grape juice intake in both Sleep Deprived group and No Sleep Deprived group were then recorded .

Results 

On the conditioning trial, both groups drank almost all the grape juice that was made available (at least 5ml grape juice as anticipated). A Student’s t-test was carried out on the test data, with Sleep Deprived and NonSleep Deprived as the variables. This showed that there was no significant difference between the groups in the amount of grape juice consumed: The Nonsleep Deprived rats (Mean=5.93, standard deviation=2.59) were not significantly different in their decrease in consumption of fruit juice (t(12)=0.31,p>0.10) following the injection, than the Sleep Deprived rats (M=5.29, SD=2.14). However, there was a significant decrease between the groups in the amount of water taken; The Nonsleep Deprived rats (Mean = -9.92, SD =4.8) were significantly different in their decrease in water consumption (t(12)= 0.00099, p<0.10) following the injection than Sleep Deprived (Mean -2.57, SD =2.3).Fig.1 below shows a bar graph of average difference scores in Nonsleep and Sleep groups.

Figure 1: Average Difference Score 

Figure 2: Statistical Analysis

					Col B-C (DV 1)	Col C-D (DV 2)
	Grape Juice	Grape Juice test (FT)	Water		GJ-GJT	GJT-Water
No Sleep	7	0	9		7	-9
Deprived	6	1	7.5		5	-6.5
	2	0	10		2	-10
	7.5	0	18		7.5	-18
	7	1	9		6	-8
	10	0	13		10	-13
	6	2	7		4	-5
Mean	6.5	0.5714286	10.5		5.92857143	-9.92857143
SD	2.3979158	0.7867958	3.8405729		2.5888957	4.382052139
					DATA SET 2
Sleep Dep	7	1	2		6	-1
	4	2	2		2	0
	8.5	1.5	2.5		7	-1
	5	2	5		3	-3
	6	0	3		6	-3
	8	0	7		8	-7
	5	0	3		5	-3
Mean	6.2142857	0.9285714	3.5		5.28571429	-2.57142857
SD	1.6797109	0.9322272	1.8484228		2.13808994	2.299068134

Figure 3: t-Test

t-Test: Two-Sample Assuming Equal Variances
	Variable 1	Variable 2
Mean	5.92857143	5.28571429
Variance	6.70238095
Observations	7
Pooled Variance	5.63690476
Hypothesized Mean Difference	0
Df	12
t Stat	0.5065568
P(T<=t) one-tail	0.31082208
t Critical one-tail	1.78228756
P(T<=t) two-tail	0.62164416
t Critical two-tail	2.17881283

Discussion 

The results show that there was no significant difference in the amount of grape juice consumed between the two groups after the experimental procedure in CTA was applied. This could have been as a result of; 1. the rats have an intrinsic attraction towards sweet solutions.2) the energetic properties of sweet solutions resulted in this preference. 3) The amount of unconditioned stimulus (LiCl) was too low to trigger a conditioned response in rats. 4) Sleep deprivation does not affect conditioned taste aversion in rats.

The Nonsleep Deprived rats showed a normal intake of both water and grape juice. There was no evidence of conditioned response as a result of administering LiCl. This could be due to a low dosage of LiCl which was not effective. Furthermore, Sleep Deprived rats showed a normal intake of the grape juice and a significant decrease in water intake. Sleep deprived rats associated water intake with physical discomfort of sleep deprivation. However, they were intrinsically attracted to sleep deprivation.

Base on the past experiments, it was expected that there would be a significant difference in both water and grape juice consumption between Sleep Deprived and Nonsleep Deprived groups. Nachman and Ashe (1973), Peck and Ader (1974), and Loy and Hall (2002) confirmed in their studies that it is possible for the subjects to show aversion to sweet solutions. In this case, the aversive condition was not established in the grape juice solution. This result is supported by the study of Houpt, Zahorik and Swartzman-Ander (1990) which suggested that it is difficult to establish aversive conditioning with sweetened foods. Bures (1998) suggested that administering LiCl had an instant effect on the subject at the first trial. It was not possible in the current experiment since aversive conditioning was not established . The results show that sleep deprivation causes aversive conditioning. However, this conditioning is not established in sweet foods.

Conclusion 

In conclusion, the results showed sleep deprivation causes conditioned aversive taste. However, aversive conditioning could not be established for sweet solutions; rats are innately attracted to the sweet solution. It is satisfactory to conclude that organisms repeatedly consume toxic or harmful substances as long as they are tasty; they fail to establish an aversive condition for sweet foods. On the other hand, they easily develop aversive conditioning for not-tasty foods. It is important to note from this study that sleep deprivation or other physical discomforts can sometimes fail to cause aversive conditioning under some specific circumstances favorable to the organism,

References  

Hinderliter, C. F., Musci, J. A., Pollack, C. A., Misanin, J. R., & Anderson, M. J. (2004). Hypothermia modifies the effective CS–US interval in conditioned taste aversion in rats.  Neuroscience letters ,  369 (2), 142-144. 

Li, K. C., Hsiao, S., & Li, J. S. (2013). Conditioned taste aversion as instrumental punishment.  Journal of Experimental Psychology: Animal Behavior Processes ,  39 (3), 294. 

Youngblood, B. D., Zhou, J., Smagin, G. N., Ryan, D. H., & Harris, R. B. (1997). Sleep deprivation by the “flower pot” technique and spatial reference memory.  Physiology & behavior ,  61 (2), 249-256.