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Effect of water deprivation and cues associated with water on the heart rate of the rat
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Effect of Water Deprivation and Cues Associated with Water on the Heart Rate of the Rat' ROBERT GOLDSTEIN,- JOHN A. STERN AND STEPHEN L ROTHE'NBERG Department of Psychiatry, Washington University School o[" Medicine, St. Lottls, Mis.ff)uri (Received 6 D e c e m b e r 1965) G C ) I , I ) s l E i N , R . , J. A . STFRNANt) S. J. ROTHENBFRG.
Eff('Cl o f water deprh;ation and cues a~soci'ated with water o , t h e
heart rate of the rat. PHYsioL. BI~H^v. 1 (3) 199-203, 1966.~Heart rate (H R) was recorded from rats prior to and. during 10 cycles of adaptation to 0. 23.5 and 47.5 hr water deprivation ~hedules. Drinking was permitted in the last 5 rain of each 10 rain recording session during deprivation. Though the 23.5 hr group was excluded from the analysis due to it predePrivation artifact, their data agreed with that of the remaining groups reported. Results showed no differeno= in the 5 rnin predrink period between the 47.5 and the 0 hr deprived groups even after 4 deprivation cyclcs. As a function of repeated exposures to the situation the ttR of the 47 5 hr group ncreas ng y exceeded that of the 0 hr group result ng ill a sMgmficant groups X days nteraction. During drinking a clear accelerative ctt't,et was noted in both deprived groups, The outcome was interpreted as being compatible With the theoretical position of Campbell in demonstrating the in~ortance of cues associated with water in the activation of a deprived animal. W~tter' deprivation and heart• rate conditioning uon Conditioning of heart rate
Drinking
Tt~e COnDtTtONS Under which food and water deprivation are translated into arousal or activation have received considerable attention m the psychological literature. In,several recent studies it was ft)und that only during the inslrumentalconsummatory response sequence was a relationship between level of deprivation and heart rate (HR) demonstrable [I, 6]. In describing their procedure, Bdlanger and Feldman commented that deprived animals separated from the lever and reinforcement device by a sheet of glass showed a lower and more variable HR than those bar pressing for water. Therefore they included for analysis only those records taken during either bar pressing or drinking. However, in the Hahn et al,, study, the HR of deprived rats during free drinking was shown not to reflect deprivation level. Since neither the state of deprivation nor the drinking response will produce a depri',ation related cardiac accelcration independently, we are led to the tentative conclusion that this dependency obtains only when animals are performing an instrumental response. That we arc not simply dealing with an artifact of mu',cular exertion associated with bar pressing response was demonstrated by Hahn. Stern, and Fehr [5], The amount of energy expended on the bar press was experinaentally increased in that study and ft~und not to augment the HR at any level of deprivation. The fact that deprivation pc, se was not sufficient to cause a cardiac acceleration in the two studies cited earlier is of theoretical significance. Malmo [7], referring to Belanger and Feldman's results, suggested the importance of en~ ironmental
Heart rate
Water deprivation
Drive
Activa..
stimuli in evoking the otherwise "latent" effects of deprivation on HR. in support of this view Maline cited the work of Campbell and Sheffield [2] in which it was shown that by far the greatest portion of the variance in general activity observed during deprivation could be accounted for by that occurring during the presentation Of stimuli associated with reward. From the Bdlanger and Feldman report it is impossible to determine whether the situation in their preliminary tests was appropriate for the conditi0na~l e components of the drinking response to become associafed with the sightof-lever (the CS). In the Hahn study'such a n opportunity either did not exist or could not be manifested. That is, it is probable that their procedure, not conceive~l for the purpose, was not adequate for conditioningto have occurred: but even in the event that it had, the fact that all animals were drinking during the test trials might well have obscured such an effect. The purpose of the present investigation was to study the effect of water deprivation on HR in the ab~nce of an instrumental response: (a~ prior to the introduction of any cc~nditioned cues and (b) under conditions favorable to the development and manifestation of conditioning. , METtIOD
Subjects and apparatus Thirty male albino rats (Hohzman) abouf [00 days old at the initiation of the study served as subjects. The recording cage wits a plywood box partitioned into 6 compartments, each one 5~ in. by !1 in. by 20 in. high. The grid floor consisted of rods ~.~ in. in dia~ spaced ½in. apart,
tThis investigation was supported by Public Health Scrv~ce Research Grants Mt! 07140, MH 02755, MH 7081 and MH 5938 from the National Institute of Mental Health and was conducted at the Malcolm Bliss Mental Health C.enter, St. Louis, Me. 199
GOLDSTEIN, STERN AND ROFllENBERG
200 center to center. The lower 15 in. of the front of each c o m partment was plexiglas consisting of a door hinged on the bottom about 4 in. from the grid. Hinged onto the rear of the cage and of the same outer dimensions as the cage itself was a rectangular frame on which were mounted six 50 ml eudiometer tubes with glass drinking spouts. When the frame was rotated against the box, the drinking spouts projected through slots in the back about ~ in. into the individual compartments and about 1½ in. from the floor. In the withdrawn position, the spouts were about 6 in. from the box. The recording leads passed through the open top and were brought to a nearby EEG jack box. About a foot above the recording box a light nylon line was tied to each set of leads. Each of these lines was brought through an overhead pulley and counterweighted. The entire apparatus was placed in a 6 ft by 10 ft sound attenuated and electrically shielded room illuminated by a fluorescent fixture (two 20 W bulbs) centered in the ceiling. A one-way vision glass made observation possible from outside the room where the recording apparatus (Gilson EEG machine) was located. Procedure
Under light ether anesthesia, 2 wire loops of 18 gauge stainless steel wire were implanted in each rat according to the method devised by Stern and Word [1 I]. At this point the 30 subjects were randomly divided into 3 groups composed of 9, 9 and 12 animals each. Three to 4 days later, habituation to the recording box was begun. The animals were divided into 5 squads of 6 subjects each. 2 rats from each group represented in 4 of the squads and the remainder in the fifth. Squads were run at the same time each day. A squad was brought into the recording room. leads were attached to the f i R loops, the experimenter exited, closed the door and returned to the polygraph. A 10 sec record was taken at this point and at I rain intervals for 5 rain. Immediately following the sixth reading (at 5 rain), the investigator entered the room and inserted the empty tubes. After closing the door again, another 10 sec record was taken at once and again at I rain intervals until 6 "posttube" records were taken. The animals remained in the box for an additional 10 rain upon which a final HR sample was obtained. Therefore, a total of thirteen 10 sec samples were taken from each animal: 6 prior to introduction of the tubes ("pre-tube") and 6 after insertion including one final record at about 20 rain. The animals were then returned to their home cages. This sequence was repeated for 7 days with one exception : commencing on the fourth day and on all following days, only 5 pre-tube records were taken, i.e. the animals were in for only 4 rain prior to the insertion of the tubes. After the seventh daily recording session, the water bottles were removed from the home cages of the Twenty-three-andone-half hr IT group) and Forty-seven-and-one-half hr (F group) animals (N 9 and 12. respectively). On the following deprivation days, all eudiometer tubes were filled prior to the recording sessions and the final 10 rain in the box v, as omitted. For the Zero deprivation rats (Z group, N 9) and T group the procedure was as before except that immediately following the recording se~ion the animals from both groups were placed in individual drinking cages in another room for 25 rain before returning to their home cages. The F group was run on alternate days in the identical manner for 10 deprivation recording sessions, the same total as the Z and T groups received on consecutive days.
Measures All HR scores were based on beats/2 sec intervals. For every 10 sec HR sample the first three 2 sec periods were taken which yielded a readable record for all 6 animals in that squad. Each of these three 2 sec periods for each rat was scored to the nearest whole cardiac cycle and the representative score for that 10 sec for each animal was the median of these 3 measures. The median was used here rather than the mean simply to facilitate scoring and analysis. In all graphs and analyses where a representative measure was needed for individual animals, which involved more than one median, e.g. the HR in the entire first 5 rain period, and/or the HR across several grouped days, the mean was used. The choice of medians as the basic data should not in any way be interpreted as reflecting a high degree of variability since in fact the opposite was true. Body weights were taken at the time of implantation, again at the beginning of deprivation and prior to every deprivation recording session. Water intake during the five minutes in the test chamber and the following 25 rain in the drinking boxes was recorded on all deprivation days. RESULTS
Since the HR records were not scored until the experiment was completed, a rather large pre-deprivation difference in baseline H R between the T group and the other two groups was not discovered until after it was too late to balance out by reassigning animals. An F test performed on the mean HR in the first 5 rain of the last 4 adaptation days for the 3 groups (16.4, 15.5 and 16.2 beats/2 sec in the Z, T and F groups, respectively) resulted in an F =- 3.37, significant at the 0.05 level (dr : 2, 27). In all subsequent analyses the T group data were omitted since it was felt that there were no a priori grounds to assume an absence of interaction between factors deterxnining this initial difference on the one hand and the experimental treatments on the other. However, the graphic displays include the T group performance which in each case is in agreement with the conclusions based on the remaining data. ,'~DA PTA F!ON DE I:~IVA TIO~'J
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W,'~]FR r)FPRIVA'I'I()N AND tIEART RATE
201
In Fig. I a summary (ff the HR changes observed within and across session is presented starting from the fourth adaptation day and running through the remainder of the experiment. The designations "4a" and "4b" refer to the periods immediately before and immediately following presentation of the tubes. The interval between the~e measures ~as approximately ~ rain. For convenience of presentation and analysis the data was condensed into 2 day blocks. The relalively slow HR of the T group referred to above can be scen clearly in both adaptation blocks (Figs. IA and B), especially the latter where it is noted there is considerable ovcrlap between the Z and F groups. The initial effect of the deprivation depicted in Fig. IC, was minimal. In fact, the apparently higher HR of the F group was due completely to the second rather than the first of the two days making tip this block, In Fig. ID, the absence of any deprivation effect corroborates the conclusion that deprivation p e r s e does not induce a HR change. Following this. however, a clear disparity between the groups becomes manifest. Generally, the difference can be ascribed to the progressive habituation of the control animals' HR rather than to an absolute increase in the HR of the F animals. For statistical treatment of this trend the 5 pre-tube HR measures were averaged for the last adaptation block and the 5 deprivation blocks. The resultant means are plotted in Fig. 2. A 2 by
relationship. However, the possible bias introduced by the lower initial rate of the T group should be stressed again. Turning to the effects of drinking on HR, Fig. 3B depicts the HR immediately before the experimenter entered the ~,D~,PTATIC)NDAYS4-7 A
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room (4a) and the changes attendant upon drinking (4b-9) averaged over all deprivation days. A 2 by 6 analysis of variance on the F and Z data presented in Fig. 3B (excluding the 4a measure) yielded significant deprivation, minutes, and interaction effects (F values ~ 21.1, 64.5 and 56.0 respectively, all beyond the 0.05 level). For purposes of comparison the corresponding measures for the last 2 adaptation blocks are graphed in Fig, 3A. It can be seen that the complex stimulus commencing with the experimenter's entrance into the test toom resulted in a reliable cardiac response pattern essentially identical in all groups and comparable to the Z group pattern exhibited during deprivation. Patently, ingestion of water is associated with cardiac acceleration, a phenomenon in close agreement with data presented by O'Kelly e t a L [9] from whose study we may further conclude that with respect to the accelerative effect the route by which water is introduced (drinking or stomach loading) is irrelevant.
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6 analysis of variance (m this data Iornittlng the r group data for reasons mentioned above) yielded significant deprivation, day and interaction effects, (t: values 5.65, 4.43 and 8.71, respectively; all beyond the 0.05 level). The significant interaction is the critical effect in this context since it indicates that the declining HR of the control animals over days ~as not paralleled by a like decrement in the F g r o u p l l R . As can be seen in tlg. 2, the slope of the T group is somewhere between that of the F and Z groups, aN expected
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202
GOLf)STEIN, STERN AND ROTHENP, I RG
In Fig. 4 the water intake of the three groups on all deprivation days is presented. This is given as two volumes: the 5 rain intake in the recording box , and the "total daily intake" which includes the intake in the ~'ecording box plus that of the subsequent 25 rain watering period, Ob~,iously, this is not the daily intake of the Z group who drank in their home cages as well. Though possibly confounded with trials it is of passing interest that the high total intake of the F group on block 4 (days 7 and 8) is consistent with the higher HR observed on these days (Fig. 2). We may note again that despite the fact that asymptotic intake was achieved by the F g-roup on approximately the fourth day, there existed no apparent HR effect of deprivation on this trial block. Finally, in comparing HR acceleration during drinking in the T and F groups (Fig. 4), the amount ingested in the recording box and so presumably the time spent drinking there, was almost identical in the two groups. DISCUSSION
These data are consistent with the hypothesis that the state of water deficit is not a sufficient condition for the excitation of physiological processes generally associated with activation. Heart rate during the first four deprivation cycles of a 47.5 hr schedule was essentially the same as that of a d libitum controls. This is consistent with the results reported by both B~langer and Feldman [1] and Hahn et al. [6]. After about five or six exposures to the stimulus conditions which regularly preceded water presentation (handling and other manipulations leading up to and including the first 5 min in the recording box), the deprived animals manifested a significantly higher HR when subsequently placed in that situation. Thus, contrary to the conclusions based on the above studies, instrumental behavior is unnecessary in order to activate the "latent" effects of deprivation. Rather, relevant environmental stimuli, i.e. those associated with the needed substance, are decisive in the activation of such effects. We may infer, therefore, that Campbell's [3] deprived rats, which he demonstrated to be behaviorally inactive in the absence of cues associated with water, were autonomically quiescent as well (accepting HR as an index of autonomic activat ion). The compatibility of this and the O'Kelly et al. data [9] concerning the incremental effect of water intake on HR has already been pointed out. However, the effects of thirst obtained here seem to be in direct contradiction to the HR depression their rats exhibited during saline-induced dehydration. The assumption implicit in O'Kelly's study is that thirst induced by hypertonic saline administration is equivalent to that resulting from normal deprivation. A recent study by Grimsley [4] is germane to this issue: rats injected with hypertonic saline demonstrated extreme decreases in activity, decrements which were inversely related to dose level. The opposite was true for water deprived rats, a fact substantiating Campbell's [3] earlier observations. In the same vein, O'Kelly and Heyer [10] have reported evidence suggesting a difference between the normal and saline modes of inducing thirst. The extrapolation of HR effects from saline-thirst to normal thirst, in the light of these behavioral
results, would appear to be unwarranted at the present time. A problem arising in the interpretation of the present data is the potentially confounding effect of general activity on HR. What makes this point singularly critical is the fact that the present procedure, designed to elicit a HR increase as a conditioned autonomic response, would be optimal for the evocation of general activity as a behavioral anticipatory response. However, assuming that the activity level of the F group was indeed higher than that of the Z group, it still remains to be demonstrated that this activity entirely accounts for the HR differences observed. The data of Hahn, Stern, and Fehr [5] mentioned earlier, tend to oppose such an alternative. Despite a substantial increase in the force requited to bar press (from ! 5 to 60 g), their rats showed no accomganying rise in HR. This was so even at the lowest deprivation level where correspondingly low bar pressing and heart rates permitted the effects of the added work load to be manifested. In the second experiment of the Hahn, Stern and Fehr investigation, the HR effects of hypertoni¢ saline injections were studied Though saline concentration was reflected in bar pressing rate, slight "decrements" in HR were found, again pointing to the independence of activity and cardiac rate under their test conditions (and reminiscent of the point made earlier concerning saline thirst ). What might be an important difference between the above and the present experimental conditions should, however. be mentioned. Where the group showing the lowest activity level in their study could be represented by those rats who were bar pressing at the slowest rate, the low level in the present report was of animals in an essentially resting condition. It is conceivable that the higher HR of the F group in this study represented the difference between resting and generally active animals. The latter, according to this view, would be functioning at a level near the low rate subjects in the Hahn et al. study. That this variable might be critical was suggested by an experiment on humans by Means and Newburgh [8]. They found a considerable increase in pulse rate and heart output]beat in the transition from the resting state to the lowest work load condition studied (270 kg-m/min). From this point to about 700 kg-m/ min the pulse rate remained relatively stable (105 b/m) ~.hile output/beat steadily increased. At the maximum load reported, 1000 kg-m/min, pulse rate had again increased from 105 to about 132 b/m while output showed no further change over the previous level. If the same dynamic principles apply to the rat and if the work load analogy is apt, then the HR increase in the pre~nl study might be conceived of as the initial rise due to a minimal level of activity while the Hahn, Stern and Fehr animals were operating only in the work load range of HR stability. One can only speculate at this juncture how crucial the activity level was in giving rise to the comparatively rapid HR of the F group in the present study. Despite the rationale given for an activity interpretation of these data, the sizeable difference in HR between the Z and F groups on the final trial block (Fig. 2) would seem to place a heavy burden on this variable. Nevertheless, the effect of activity on HR in general and the involvement of this relationship in the present study deserves further investigation.
WATER DEPRIVATION AND HEART RATE
203
REFERENCES I. BElanger, D. and S. M. Feldman. Effects of water deprivation upon heart rate and instrumental activity in the rat. J. (~m~p. Phy.~h,I. Ps.t'chol. 55: 220-225, 1962. 2. Campbell, B. A. and F. D. Sheffield. Relation of random activity to food deprivation. J. Comp. Physhd. Psychol. 46: 320-322, 1953. 3. ('ampbell, B. W. Effects of water deprivation on random activity. J. Comp. Physiol. Psychol. 53: 240.-241, 1960. 4. Grimsley, D. L. Effect of water deprivation and injections of hypertonic saline on the activity of rats. Psycho/. Rep. 16: 1081-1085, 1965. 5. Hahn, W. W., J. A. Stern and F. S. Fehr. Generalizability of he:~rt rate as a measure of drive state. J. Comp. Physiol. P~3'chol. 58: 305-309, 1964. 6. Itahn, W. W., J. A. Stern and D. G. McDonald. Effects of water deprivation and bar pressing activity on heart rate of the male albino rat. J. Comp. Physiol. Psychol. 55: 786-790, 1962.
7. Malmo, R. B. Activation: a neurophy,,iologieal dimen,~ion, Psychol. Rev. 66: 367--.186. 1959. 8. Means. J. H. and L. H. Newburgh. The effect ofcaffeine upol~ the blood flow in norn'ml human subjects. J. Pharmacol. Erp. Therape,th'~, 7: 449--465, I ql 5. 9. O'KclIy, t.. I., (;. I. Hatton, I.. Tucker and D. Weslall. Water regula'ion in the rat: Heart rate as a function of hydration, anesthesia, and association with reinfi~rccment. J. Comp. Physiol. Psychol, 59: 159-165, 1965. I0. O'Kelly, I_. !. aJld A. W. Heyer, Jr..Studies in motivation and retentii~n. ('mop. Psychol. Ahm. 20: 251-31)1, 1951. I I. Stern, J. A. and T. J. Word. Changes in cardiac response of the albino rat as a function of electroconvulsive seizures. J. Cmnp. Physiol. PsychoL 54: 389-394, 1961.
Effect of Water Deprivation and Cues Associated with Water on the Heart Rate of the Rat' ROBERT GOLDSTEIN,- JOHN A. STERN AND STEPHEN L ROTHE'NBERG Department of Psychiatry, Washington University School o[" Medicine, St. Lottls, Mis.ff)uri (Received 6 D e c e m b e r 1965) G C ) I , I ) s l E i N , R . , J. A . STFRNANt) S. J. ROTHENBFRG.
Eff('Cl o f water deprh;ation and cues a~soci'ated with water o , t h e
heart rate of the rat. PHYsioL. BI~H^v. 1 (3) 199-203, 1966.~Heart rate (H R) was recorded from rats prior to and. during 10 cycles of adaptation to 0. 23.5 and 47.5 hr water deprivation ~hedules. Drinking was permitted in the last 5 rain of each 10 rain recording session during deprivation. Though the 23.5 hr group was excluded from the analysis due to it predePrivation artifact, their data agreed with that of the remaining groups reported. Results showed no differeno= in the 5 rnin predrink period between the 47.5 and the 0 hr deprived groups even after 4 deprivation cyclcs. As a function of repeated exposures to the situation the ttR of the 47 5 hr group ncreas ng y exceeded that of the 0 hr group result ng ill a sMgmficant groups X days nteraction. During drinking a clear accelerative ctt't,et was noted in both deprived groups, The outcome was interpreted as being compatible With the theoretical position of Campbell in demonstrating the in~ortance of cues associated with water in the activation of a deprived animal. W~tter' deprivation and heart• rate conditioning uon Conditioning of heart rate
Drinking
Tt~e COnDtTtONS Under which food and water deprivation are translated into arousal or activation have received considerable attention m the psychological literature. In,several recent studies it was ft)und that only during the inslrumentalconsummatory response sequence was a relationship between level of deprivation and heart rate (HR) demonstrable [I, 6]. In describing their procedure, Bdlanger and Feldman commented that deprived animals separated from the lever and reinforcement device by a sheet of glass showed a lower and more variable HR than those bar pressing for water. Therefore they included for analysis only those records taken during either bar pressing or drinking. However, in the Hahn et al,, study, the HR of deprived rats during free drinking was shown not to reflect deprivation level. Since neither the state of deprivation nor the drinking response will produce a depri',ation related cardiac accelcration independently, we are led to the tentative conclusion that this dependency obtains only when animals are performing an instrumental response. That we arc not simply dealing with an artifact of mu',cular exertion associated with bar pressing response was demonstrated by Hahn. Stern, and Fehr [5], The amount of energy expended on the bar press was experinaentally increased in that study and ft~und not to augment the HR at any level of deprivation. The fact that deprivation pc, se was not sufficient to cause a cardiac acceleration in the two studies cited earlier is of theoretical significance. Malmo [7], referring to Belanger and Feldman's results, suggested the importance of en~ ironmental
Heart rate
Water deprivation
Drive
Activa..
stimuli in evoking the otherwise "latent" effects of deprivation on HR. in support of this view Maline cited the work of Campbell and Sheffield [2] in which it was shown that by far the greatest portion of the variance in general activity observed during deprivation could be accounted for by that occurring during the presentation Of stimuli associated with reward. From the Bdlanger and Feldman report it is impossible to determine whether the situation in their preliminary tests was appropriate for the conditi0na~l e components of the drinking response to become associafed with the sightof-lever (the CS). In the Hahn study'such a n opportunity either did not exist or could not be manifested. That is, it is probable that their procedure, not conceive~l for the purpose, was not adequate for conditioningto have occurred: but even in the event that it had, the fact that all animals were drinking during the test trials might well have obscured such an effect. The purpose of the present investigation was to study the effect of water deprivation on HR in the ab~nce of an instrumental response: (a~ prior to the introduction of any cc~nditioned cues and (b) under conditions favorable to the development and manifestation of conditioning. , METtIOD
Subjects and apparatus Thirty male albino rats (Hohzman) abouf [00 days old at the initiation of the study served as subjects. The recording cage wits a plywood box partitioned into 6 compartments, each one 5~ in. by !1 in. by 20 in. high. The grid floor consisted of rods ~.~ in. in dia~ spaced ½in. apart,
tThis investigation was supported by Public Health Scrv~ce Research Grants Mt! 07140, MH 02755, MH 7081 and MH 5938 from the National Institute of Mental Health and was conducted at the Malcolm Bliss Mental Health C.enter, St. Louis, Me. 199
GOLDSTEIN, STERN AND ROFllENBERG
200 center to center. The lower 15 in. of the front of each c o m partment was plexiglas consisting of a door hinged on the bottom about 4 in. from the grid. Hinged onto the rear of the cage and of the same outer dimensions as the cage itself was a rectangular frame on which were mounted six 50 ml eudiometer tubes with glass drinking spouts. When the frame was rotated against the box, the drinking spouts projected through slots in the back about ~ in. into the individual compartments and about 1½ in. from the floor. In the withdrawn position, the spouts were about 6 in. from the box. The recording leads passed through the open top and were brought to a nearby EEG jack box. About a foot above the recording box a light nylon line was tied to each set of leads. Each of these lines was brought through an overhead pulley and counterweighted. The entire apparatus was placed in a 6 ft by 10 ft sound attenuated and electrically shielded room illuminated by a fluorescent fixture (two 20 W bulbs) centered in the ceiling. A one-way vision glass made observation possible from outside the room where the recording apparatus (Gilson EEG machine) was located. Procedure
Under light ether anesthesia, 2 wire loops of 18 gauge stainless steel wire were implanted in each rat according to the method devised by Stern and Word [1 I]. At this point the 30 subjects were randomly divided into 3 groups composed of 9, 9 and 12 animals each. Three to 4 days later, habituation to the recording box was begun. The animals were divided into 5 squads of 6 subjects each. 2 rats from each group represented in 4 of the squads and the remainder in the fifth. Squads were run at the same time each day. A squad was brought into the recording room. leads were attached to the f i R loops, the experimenter exited, closed the door and returned to the polygraph. A 10 sec record was taken at this point and at I rain intervals for 5 rain. Immediately following the sixth reading (at 5 rain), the investigator entered the room and inserted the empty tubes. After closing the door again, another 10 sec record was taken at once and again at I rain intervals until 6 "posttube" records were taken. The animals remained in the box for an additional 10 rain upon which a final HR sample was obtained. Therefore, a total of thirteen 10 sec samples were taken from each animal: 6 prior to introduction of the tubes ("pre-tube") and 6 after insertion including one final record at about 20 rain. The animals were then returned to their home cages. This sequence was repeated for 7 days with one exception : commencing on the fourth day and on all following days, only 5 pre-tube records were taken, i.e. the animals were in for only 4 rain prior to the insertion of the tubes. After the seventh daily recording session, the water bottles were removed from the home cages of the Twenty-three-andone-half hr IT group) and Forty-seven-and-one-half hr (F group) animals (N 9 and 12. respectively). On the following deprivation days, all eudiometer tubes were filled prior to the recording sessions and the final 10 rain in the box v, as omitted. For the Zero deprivation rats (Z group, N 9) and T group the procedure was as before except that immediately following the recording se~ion the animals from both groups were placed in individual drinking cages in another room for 25 rain before returning to their home cages. The F group was run on alternate days in the identical manner for 10 deprivation recording sessions, the same total as the Z and T groups received on consecutive days.
Measures All HR scores were based on beats/2 sec intervals. For every 10 sec HR sample the first three 2 sec periods were taken which yielded a readable record for all 6 animals in that squad. Each of these three 2 sec periods for each rat was scored to the nearest whole cardiac cycle and the representative score for that 10 sec for each animal was the median of these 3 measures. The median was used here rather than the mean simply to facilitate scoring and analysis. In all graphs and analyses where a representative measure was needed for individual animals, which involved more than one median, e.g. the HR in the entire first 5 rain period, and/or the HR across several grouped days, the mean was used. The choice of medians as the basic data should not in any way be interpreted as reflecting a high degree of variability since in fact the opposite was true. Body weights were taken at the time of implantation, again at the beginning of deprivation and prior to every deprivation recording session. Water intake during the five minutes in the test chamber and the following 25 rain in the drinking boxes was recorded on all deprivation days. RESULTS
Since the HR records were not scored until the experiment was completed, a rather large pre-deprivation difference in baseline H R between the T group and the other two groups was not discovered until after it was too late to balance out by reassigning animals. An F test performed on the mean HR in the first 5 rain of the last 4 adaptation days for the 3 groups (16.4, 15.5 and 16.2 beats/2 sec in the Z, T and F groups, respectively) resulted in an F =- 3.37, significant at the 0.05 level (dr : 2, 27). In all subsequent analyses the T group data were omitted since it was felt that there were no a priori grounds to assume an absence of interaction between factors deterxnining this initial difference on the one hand and the experimental treatments on the other. However, the graphic displays include the T group performance which in each case is in agreement with the conclusions based on the remaining data. ,'~DA PTA F!ON DE I:~IVA TIO~'J
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W,'~]FR r)FPRIVA'I'I()N AND tIEART RATE
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In Fig. I a summary (ff the HR changes observed within and across session is presented starting from the fourth adaptation day and running through the remainder of the experiment. The designations "4a" and "4b" refer to the periods immediately before and immediately following presentation of the tubes. The interval between the~e measures ~as approximately ~ rain. For convenience of presentation and analysis the data was condensed into 2 day blocks. The relalively slow HR of the T group referred to above can be scen clearly in both adaptation blocks (Figs. IA and B), especially the latter where it is noted there is considerable ovcrlap between the Z and F groups. The initial effect of the deprivation depicted in Fig. IC, was minimal. In fact, the apparently higher HR of the F group was due completely to the second rather than the first of the two days making tip this block, In Fig. ID, the absence of any deprivation effect corroborates the conclusion that deprivation p e r s e does not induce a HR change. Following this. however, a clear disparity between the groups becomes manifest. Generally, the difference can be ascribed to the progressive habituation of the control animals' HR rather than to an absolute increase in the HR of the F animals. For statistical treatment of this trend the 5 pre-tube HR measures were averaged for the last adaptation block and the 5 deprivation blocks. The resultant means are plotted in Fig. 2. A 2 by
relationship. However, the possible bias introduced by the lower initial rate of the T group should be stressed again. Turning to the effects of drinking on HR, Fig. 3B depicts the HR immediately before the experimenter entered the ~,D~,PTATIC)NDAYS4-7 A
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room (4a) and the changes attendant upon drinking (4b-9) averaged over all deprivation days. A 2 by 6 analysis of variance on the F and Z data presented in Fig. 3B (excluding the 4a measure) yielded significant deprivation, minutes, and interaction effects (F values ~ 21.1, 64.5 and 56.0 respectively, all beyond the 0.05 level). For purposes of comparison the corresponding measures for the last 2 adaptation blocks are graphed in Fig, 3A. It can be seen that the complex stimulus commencing with the experimenter's entrance into the test toom resulted in a reliable cardiac response pattern essentially identical in all groups and comparable to the Z group pattern exhibited during deprivation. Patently, ingestion of water is associated with cardiac acceleration, a phenomenon in close agreement with data presented by O'Kelly e t a L [9] from whose study we may further conclude that with respect to the accelerative effect the route by which water is introduced (drinking or stomach loading) is irrelevant.
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202
GOLf)STEIN, STERN AND ROTHENP, I RG
In Fig. 4 the water intake of the three groups on all deprivation days is presented. This is given as two volumes: the 5 rain intake in the recording box , and the "total daily intake" which includes the intake in the ~'ecording box plus that of the subsequent 25 rain watering period, Ob~,iously, this is not the daily intake of the Z group who drank in their home cages as well. Though possibly confounded with trials it is of passing interest that the high total intake of the F group on block 4 (days 7 and 8) is consistent with the higher HR observed on these days (Fig. 2). We may note again that despite the fact that asymptotic intake was achieved by the F g-roup on approximately the fourth day, there existed no apparent HR effect of deprivation on this trial block. Finally, in comparing HR acceleration during drinking in the T and F groups (Fig. 4), the amount ingested in the recording box and so presumably the time spent drinking there, was almost identical in the two groups. DISCUSSION
These data are consistent with the hypothesis that the state of water deficit is not a sufficient condition for the excitation of physiological processes generally associated with activation. Heart rate during the first four deprivation cycles of a 47.5 hr schedule was essentially the same as that of a d libitum controls. This is consistent with the results reported by both B~langer and Feldman [1] and Hahn et al. [6]. After about five or six exposures to the stimulus conditions which regularly preceded water presentation (handling and other manipulations leading up to and including the first 5 min in the recording box), the deprived animals manifested a significantly higher HR when subsequently placed in that situation. Thus, contrary to the conclusions based on the above studies, instrumental behavior is unnecessary in order to activate the "latent" effects of deprivation. Rather, relevant environmental stimuli, i.e. those associated with the needed substance, are decisive in the activation of such effects. We may infer, therefore, that Campbell's [3] deprived rats, which he demonstrated to be behaviorally inactive in the absence of cues associated with water, were autonomically quiescent as well (accepting HR as an index of autonomic activat ion). The compatibility of this and the O'Kelly et al. data [9] concerning the incremental effect of water intake on HR has already been pointed out. However, the effects of thirst obtained here seem to be in direct contradiction to the HR depression their rats exhibited during saline-induced dehydration. The assumption implicit in O'Kelly's study is that thirst induced by hypertonic saline administration is equivalent to that resulting from normal deprivation. A recent study by Grimsley [4] is germane to this issue: rats injected with hypertonic saline demonstrated extreme decreases in activity, decrements which were inversely related to dose level. The opposite was true for water deprived rats, a fact substantiating Campbell's [3] earlier observations. In the same vein, O'Kelly and Heyer [10] have reported evidence suggesting a difference between the normal and saline modes of inducing thirst. The extrapolation of HR effects from saline-thirst to normal thirst, in the light of these behavioral
results, would appear to be unwarranted at the present time. A problem arising in the interpretation of the present data is the potentially confounding effect of general activity on HR. What makes this point singularly critical is the fact that the present procedure, designed to elicit a HR increase as a conditioned autonomic response, would be optimal for the evocation of general activity as a behavioral anticipatory response. However, assuming that the activity level of the F group was indeed higher than that of the Z group, it still remains to be demonstrated that this activity entirely accounts for the HR differences observed. The data of Hahn, Stern, and Fehr [5] mentioned earlier, tend to oppose such an alternative. Despite a substantial increase in the force requited to bar press (from ! 5 to 60 g), their rats showed no accomganying rise in HR. This was so even at the lowest deprivation level where correspondingly low bar pressing and heart rates permitted the effects of the added work load to be manifested. In the second experiment of the Hahn, Stern and Fehr investigation, the HR effects of hypertoni¢ saline injections were studied Though saline concentration was reflected in bar pressing rate, slight "decrements" in HR were found, again pointing to the independence of activity and cardiac rate under their test conditions (and reminiscent of the point made earlier concerning saline thirst ). What might be an important difference between the above and the present experimental conditions should, however. be mentioned. Where the group showing the lowest activity level in their study could be represented by those rats who were bar pressing at the slowest rate, the low level in the present report was of animals in an essentially resting condition. It is conceivable that the higher HR of the F group in this study represented the difference between resting and generally active animals. The latter, according to this view, would be functioning at a level near the low rate subjects in the Hahn et al. study. That this variable might be critical was suggested by an experiment on humans by Means and Newburgh [8]. They found a considerable increase in pulse rate and heart output]beat in the transition from the resting state to the lowest work load condition studied (270 kg-m/min). From this point to about 700 kg-m/ min the pulse rate remained relatively stable (105 b/m) ~.hile output/beat steadily increased. At the maximum load reported, 1000 kg-m/min, pulse rate had again increased from 105 to about 132 b/m while output showed no further change over the previous level. If the same dynamic principles apply to the rat and if the work load analogy is apt, then the HR increase in the pre~nl study might be conceived of as the initial rise due to a minimal level of activity while the Hahn, Stern and Fehr animals were operating only in the work load range of HR stability. One can only speculate at this juncture how crucial the activity level was in giving rise to the comparatively rapid HR of the F group in the present study. Despite the rationale given for an activity interpretation of these data, the sizeable difference in HR between the Z and F groups on the final trial block (Fig. 2) would seem to place a heavy burden on this variable. Nevertheless, the effect of activity on HR in general and the involvement of this relationship in the present study deserves further investigation.
WATER DEPRIVATION AND HEART RATE
203
REFERENCES I. BElanger, D. and S. M. Feldman. Effects of water deprivation upon heart rate and instrumental activity in the rat. J. (~m~p. Phy.~h,I. Ps.t'chol. 55: 220-225, 1962. 2. Campbell, B. A. and F. D. Sheffield. Relation of random activity to food deprivation. J. Comp. Physhd. Psychol. 46: 320-322, 1953. 3. ('ampbell, B. W. Effects of water deprivation on random activity. J. Comp. Physiol. Psychol. 53: 240.-241, 1960. 4. Grimsley, D. L. Effect of water deprivation and injections of hypertonic saline on the activity of rats. Psycho/. Rep. 16: 1081-1085, 1965. 5. Hahn, W. W., J. A. Stern and F. S. Fehr. Generalizability of he:~rt rate as a measure of drive state. J. Comp. Physiol. P~3'chol. 58: 305-309, 1964. 6. Itahn, W. W., J. A. Stern and D. G. McDonald. Effects of water deprivation and bar pressing activity on heart rate of the male albino rat. J. Comp. Physiol. Psychol. 55: 786-790, 1962.
7. Malmo, R. B. Activation: a neurophy,,iologieal dimen,~ion, Psychol. Rev. 66: 367--.186. 1959. 8. Means. J. H. and L. H. Newburgh. The effect ofcaffeine upol~ the blood flow in norn'ml human subjects. J. Pharmacol. Erp. Therape,th'~, 7: 449--465, I ql 5. 9. O'KclIy, t.. I., (;. I. Hatton, I.. Tucker and D. Weslall. Water regula'ion in the rat: Heart rate as a function of hydration, anesthesia, and association with reinfi~rccment. J. Comp. Physiol. Psychol, 59: 159-165, 1965. I0. O'Kelly, I_. !. aJld A. W. Heyer, Jr..Studies in motivation and retentii~n. ('mop. Psychol. Ahm. 20: 251-31)1, 1951. I I. Stern, J. A. and T. J. Word. Changes in cardiac response of the albino rat as a function of electroconvulsive seizures. J. Cmnp. Physiol. PsychoL 54: 389-394, 1961.