Physiology & Behavior, Vol. 22, pp. 689--692.PergamonPress and Brain Research Publ., 1979.Printed in the U.S.A.
REM Sleep Deprivation Diminishes Fear in Rats R O B E R T A. H I C K S A N D J O H N D. M O O R E P s y c h o l o g y D e p a r t m e n t , S a n J o s e S t a t e University S a n J o s e , C A 95192 ( R e c e i v e d 28 M a r c h 1977) HICKS, R. A. AND J. D. MOORE. REM sleep deprivation diminishes fear in rats. PHYSIOL. BEHAV. 22(4) 689--692, 1979.--To test the hypothesis that REM sleep deprivation decreases fear, the behavior of 44 rats was measured in an open-field test. Prior to this test, the animals were exposed to 4 days to one of four treatments, i.e., either a dry environment control, a wet environment control, a 2-day REM deprivation period, or a 4-day REM deprivation period. During the test both exploration and three parameters of emotionality were recorded. The results offered convincing evidence in support of the hypothesis. REM sleep deprivation
Exploration
Open-field behavior
S E V E R A L studies [2, 10, 11, 17, 18] have reported that REM sleep deprivation (REMd) increased level of open-field activity in rats. In two of these studies [2,17], this relationship was interpreted as indicative of a general relationship between REMd and emotionality. That is, Albert and his colleagues [2] suggested that REMd had increased emotionality, while Ogilvie and Broughton [17] drew the opposite conclusion, i.e., that REMd diminished level of emotionality. The latter of these diametrically opposed conclusions seems more valid. This because, unlike Albert et al., Ogilvie and Broughton recorded frequency of defecation and urination during their open-field test periods as additional measures of emotionality. They reported that REMd reduced defecation but did not have a significant affect on urination. Thus, they have provided somewhat equivocal evidence for the hypothesis that REMd reduces emotionality. Typically, open-field activity has been used as an index of exploration and when open-field activity is viewed in the broader context of this literature, there is disagreement as to the nature of an exploration-emotionality correlation. To elaborate, some have argued [9,14] that exploration is motivated by fear, or put differently, that increased exploration is a sign of increased emotionality as Albert et al. have suggested. In contrast with this position, there is a fairly substantial body of evidence [1,19] which suggests that increased exploration is an indication of decreased fear. That is the majority of the relevant studies support the position, which Ogilvie and Broughton have adopted, that there is a negative correlation between open-field activity and level of emotionality. Finally, Denenberg and Whimbey [5,21] have, on the basis of factor analytic data which Aitkens [1] has convincingly challenged, concluded that exploration and emotionality are independent dimensions of behavior. In view of this array of interpretations that have been made of increased exploration and the equivocal nature of Ogilvie and Broughton's data, the relationship between
Emotionality
Fear
REMd and emotionality is not at all clear, hence the purpose of this research. As Russell's [19] review suggests, there is disagreement as to what constitutes adequate measurement of exploration and/or emotionality. In view of this conflict, we felt that both a revised measure of exploration and several measures of emotionality should be considered. In part, the interpretation given to level of open-field activity depends on the confidence one has in labelling this activity exploration. In this regard, Corman and his colleagues [3,4] have drawn a useful distinction between locomotor activity and exploration in an open-field apparatus. They feel that exploration is measured by number of excursions into the center of the field, while the well known wall-hugging tendency of rats should be considered as an index of locomotor activity. Thus, it is the pattern rather than the amount of open-field activity which is important. In addition to adopting Corman's logic in measuring exploration, following the implication of Russell's [19] review, we recorded three commonly used indices of emotionality during the open-field test, i.e., defecation, urination and freezing responses. Congruent with the majority of the explorationemotionality literature and consistent with certain of Ogilvie and Broughton's [17] results, we predicted that REMd would increase exploration as measured by excursions into the center of the open-field and decrease the frequency of each of the three indices of emotionality. That is, given the interpretation that is generally given to this combination of behaviors, we predicted that REMd would reduce fear in rats. METHOD Animals The animals were 44 Sprague-Dawley male rats that were 60 days old (weight range=229-280 g) at the time of the
~Now at George Peabody College, Nashville, TN.
C o p y r i g h t © 1979 Brain R e s e a r c h Publications Inc.--0031-9384/79A340689-04502.00/0
690 open-field testing. This age was selected on the basis of Goodrick's [7] finding that Sprague-Dawley rats of this age demonstrated a reduced level of exploration. We felt that the relatively low initial exploration levels of these 60-day animals would be desirable in testing our hypothesis. These animals were randomly assigned to one of four experimental conditions, i.e., either a dry confinement control (DC), a large platform control group (LP), a two day small platform REMd group (SP2), or a four day small platform REMd group (SP4), so that each group was made up of 11 animals.
REM Sleep Deprivation REMd was achieved using an adaptation of the technique developed by Jouvet and her colleagues [13,20] (we are well aware of the criticisms of Jouvet's technique, but recent reviews [6, 8, 12, 15, 16] have convincingly dealt with the major criticisms of this procedure) and in general our REMd apparatus was similar to the equipment Ogilvie and Broughton [17] used in their study. That is, all the animals were housed in 18.9 liter buckets that were modified so that food was delivered ad lib from a feeder on the side of the bucket. The feeder was positioned to be within easy reach of the animals. The top of each bucket was covered with wire mesh. Drinking water was continuously available from a bottle that was attached to the top of the bucket so that the spout was within easy reach of the animal. For the LP, SP2 and SP4 conditions the buckets were filled with water (19°C) to 1 cm from the surface of the platform. The water in the buckets was changed daily. Room temperature was a constant 22°C. All the animals were confined in the REMd apparatus for a 4-day period, i.e., the LP group spent 4 days on the large platform (dia. = 16.5 cm); the SP~ group spent the first 2 days on the large platform and the remaining 2 days on the small platform (dia. =6.5 cm); the SP4 group spent 4 days on the SP; and finally each member of the DC group spent 4 days in a dry REMd apparatus with the large platform in place. Thus, all the animals had experienced relatively equal exposure to the novel environment of the REMd apparatus at the time of the open-field test.
HICKS AND MOORE allowed a 10-min rest period, before being tested in the open-field apparatus (which was thoroughly cleaned after each animal was run). After testing, each animal was weighed. All testing was done by two experimenters who were naive to the treatment condition under which each animal had been maintained. One experimenter recorded the pattern of activity, while the other recorded emotionality. R E S U L T S AND DISCUSSION
First as a check on the possibility of a stress×treatment confounding, the pre-post experimental weight change scores for the four groups were tested and were found to be not significant, i.e., F(3,40)= 1.22. Further, we should note that the mean weight change over the four treatment days for all groups was less than 1 g, i.e., -0.91 g. Thus, it seems unlikely that there were differential levels of stress between the treatment conditions. To test for exploration changes, we adopted the procedure [3,4] that was mentioned earlier. First the data were scored so that each animal received two scores, i.e., number of grids crossed which were adjoining the wall and number of grids crossed in the central area of the field. These values were combined into a single exploration index using the following formula: exploration i n d e x = n u m b e r central crossings/total crossings xl00. The mean exploration indexes (and the standard deviations) for the DC, LP, SP2, and SP4 groups were 5.8 +- 5.1; 12.1 _+ 10.0; 35.6 - 7.6; and 4 5 . 8 _ 7.0, respectively. The differences between these means were tested using a one-way ANOVA; F(3,40)=46.22, p
REM Sleep Deprivation Diminishes Fear in Rats R O B E R T A. H I C K S A N D J O H N D. M O O R E P s y c h o l o g y D e p a r t m e n t , S a n J o s e S t a t e University S a n J o s e , C A 95192 ( R e c e i v e d 28 M a r c h 1977) HICKS, R. A. AND J. D. MOORE. REM sleep deprivation diminishes fear in rats. PHYSIOL. BEHAV. 22(4) 689--692, 1979.--To test the hypothesis that REM sleep deprivation decreases fear, the behavior of 44 rats was measured in an open-field test. Prior to this test, the animals were exposed to 4 days to one of four treatments, i.e., either a dry environment control, a wet environment control, a 2-day REM deprivation period, or a 4-day REM deprivation period. During the test both exploration and three parameters of emotionality were recorded. The results offered convincing evidence in support of the hypothesis. REM sleep deprivation
Exploration
Open-field behavior
S E V E R A L studies [2, 10, 11, 17, 18] have reported that REM sleep deprivation (REMd) increased level of open-field activity in rats. In two of these studies [2,17], this relationship was interpreted as indicative of a general relationship between REMd and emotionality. That is, Albert and his colleagues [2] suggested that REMd had increased emotionality, while Ogilvie and Broughton [17] drew the opposite conclusion, i.e., that REMd diminished level of emotionality. The latter of these diametrically opposed conclusions seems more valid. This because, unlike Albert et al., Ogilvie and Broughton recorded frequency of defecation and urination during their open-field test periods as additional measures of emotionality. They reported that REMd reduced defecation but did not have a significant affect on urination. Thus, they have provided somewhat equivocal evidence for the hypothesis that REMd reduces emotionality. Typically, open-field activity has been used as an index of exploration and when open-field activity is viewed in the broader context of this literature, there is disagreement as to the nature of an exploration-emotionality correlation. To elaborate, some have argued [9,14] that exploration is motivated by fear, or put differently, that increased exploration is a sign of increased emotionality as Albert et al. have suggested. In contrast with this position, there is a fairly substantial body of evidence [1,19] which suggests that increased exploration is an indication of decreased fear. That is the majority of the relevant studies support the position, which Ogilvie and Broughton have adopted, that there is a negative correlation between open-field activity and level of emotionality. Finally, Denenberg and Whimbey [5,21] have, on the basis of factor analytic data which Aitkens [1] has convincingly challenged, concluded that exploration and emotionality are independent dimensions of behavior. In view of this array of interpretations that have been made of increased exploration and the equivocal nature of Ogilvie and Broughton's data, the relationship between
Emotionality
Fear
REMd and emotionality is not at all clear, hence the purpose of this research. As Russell's [19] review suggests, there is disagreement as to what constitutes adequate measurement of exploration and/or emotionality. In view of this conflict, we felt that both a revised measure of exploration and several measures of emotionality should be considered. In part, the interpretation given to level of open-field activity depends on the confidence one has in labelling this activity exploration. In this regard, Corman and his colleagues [3,4] have drawn a useful distinction between locomotor activity and exploration in an open-field apparatus. They feel that exploration is measured by number of excursions into the center of the field, while the well known wall-hugging tendency of rats should be considered as an index of locomotor activity. Thus, it is the pattern rather than the amount of open-field activity which is important. In addition to adopting Corman's logic in measuring exploration, following the implication of Russell's [19] review, we recorded three commonly used indices of emotionality during the open-field test, i.e., defecation, urination and freezing responses. Congruent with the majority of the explorationemotionality literature and consistent with certain of Ogilvie and Broughton's [17] results, we predicted that REMd would increase exploration as measured by excursions into the center of the open-field and decrease the frequency of each of the three indices of emotionality. That is, given the interpretation that is generally given to this combination of behaviors, we predicted that REMd would reduce fear in rats. METHOD Animals The animals were 44 Sprague-Dawley male rats that were 60 days old (weight range=229-280 g) at the time of the
~Now at George Peabody College, Nashville, TN.
C o p y r i g h t © 1979 Brain R e s e a r c h Publications Inc.--0031-9384/79A340689-04502.00/0
690 open-field testing. This age was selected on the basis of Goodrick's [7] finding that Sprague-Dawley rats of this age demonstrated a reduced level of exploration. We felt that the relatively low initial exploration levels of these 60-day animals would be desirable in testing our hypothesis. These animals were randomly assigned to one of four experimental conditions, i.e., either a dry confinement control (DC), a large platform control group (LP), a two day small platform REMd group (SP2), or a four day small platform REMd group (SP4), so that each group was made up of 11 animals.
REM Sleep Deprivation REMd was achieved using an adaptation of the technique developed by Jouvet and her colleagues [13,20] (we are well aware of the criticisms of Jouvet's technique, but recent reviews [6, 8, 12, 15, 16] have convincingly dealt with the major criticisms of this procedure) and in general our REMd apparatus was similar to the equipment Ogilvie and Broughton [17] used in their study. That is, all the animals were housed in 18.9 liter buckets that were modified so that food was delivered ad lib from a feeder on the side of the bucket. The feeder was positioned to be within easy reach of the animals. The top of each bucket was covered with wire mesh. Drinking water was continuously available from a bottle that was attached to the top of the bucket so that the spout was within easy reach of the animal. For the LP, SP2 and SP4 conditions the buckets were filled with water (19°C) to 1 cm from the surface of the platform. The water in the buckets was changed daily. Room temperature was a constant 22°C. All the animals were confined in the REMd apparatus for a 4-day period, i.e., the LP group spent 4 days on the large platform (dia. = 16.5 cm); the SP~ group spent the first 2 days on the large platform and the remaining 2 days on the small platform (dia. =6.5 cm); the SP4 group spent 4 days on the SP; and finally each member of the DC group spent 4 days in a dry REMd apparatus with the large platform in place. Thus, all the animals had experienced relatively equal exposure to the novel environment of the REMd apparatus at the time of the open-field test.
HICKS AND MOORE allowed a 10-min rest period, before being tested in the open-field apparatus (which was thoroughly cleaned after each animal was run). After testing, each animal was weighed. All testing was done by two experimenters who were naive to the treatment condition under which each animal had been maintained. One experimenter recorded the pattern of activity, while the other recorded emotionality. R E S U L T S AND DISCUSSION
First as a check on the possibility of a stress×treatment confounding, the pre-post experimental weight change scores for the four groups were tested and were found to be not significant, i.e., F(3,40)= 1.22. Further, we should note that the mean weight change over the four treatment days for all groups was less than 1 g, i.e., -0.91 g. Thus, it seems unlikely that there were differential levels of stress between the treatment conditions. To test for exploration changes, we adopted the procedure [3,4] that was mentioned earlier. First the data were scored so that each animal received two scores, i.e., number of grids crossed which were adjoining the wall and number of grids crossed in the central area of the field. These values were combined into a single exploration index using the following formula: exploration i n d e x = n u m b e r central crossings/total crossings xl00. The mean exploration indexes (and the standard deviations) for the DC, LP, SP2, and SP4 groups were 5.8 +- 5.1; 12.1 _+ 10.0; 35.6 - 7.6; and 4 5 . 8 _ 7.0, respectively. The differences between these means were tested using a one-way ANOVA; F(3,40)=46.22, p
