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The effects of post-trial injections of nicotine on the learning of an underwater discrimination task by rats
Anim . Behav., 1067, 15, 2 87-290
THE Er r'ECTS OF POST-TRIAL INJECTIONS OF NICOTINE ON THE LEARNING OF AN UNDERWATER DISCRIMINATION TASK BY RATS BY K. B. WRAIGHT, E. WELDON, B . D . GUPTA & H . C . HOLLAND Institute of Psychiatry, University of London
An increasing number of experimental reports are concerned with the effects of drugs and other treatments on the modification of neural processes in learning . Most of these reports deal with the effects of pre-trial treatments in the belief that the efficiency of learning depends upon the enhanced or reduced efficiency of the organism during performance . In contrast, a great deal of interest has recently been evoked by the reintroduction of the `consolidation theory', which advances the view that the establishment of the underlying neuro-physiological modification in learning is dependent upon the perseverance of neural activity initiated by the training procedure after the cessation of performance . Several authors (McGaugh et al., 1962 ; Pare, 1961 ; Stratton & Petrinovich, 1963) have administered drug and other treatments after the completion of the designated daily performance in the belief that such treatments can have no effect on the independent conditions of the task and must be assumed to act on the perseverating activity which continues after it has ceased. The modes of action of the treatments so far employed may be classified into the broad polar categories of stimulant (enhancement of the perseverating activity) and depressant (reduction or blocking of the activity) . Both procedures have on the whole tended to support the proposition that learning can be facilitated or reduced by compounds and treatments, which can only have their effect after performance . Clearly any drug or other treatment hypothesized to have its main effect upon the posttrial neural activity must be quickly absorbed and utilized by the organism, and it should also be completely excreted from the body tissues before the commencement of a following trial so as not to confound pre- and post-trial augmentation . Nicotine was chosen to fulfil these conditions (Warwick, 1963), the prediction being that the group of rats given immediate post-performance doses of nicotine would learn less well than the group given the drug after a 5-min delay, and further that this second group
would be inferior in learning to the placebo group. Method In this experiment 48 animals from the 22nd generation of the Maudsley Reactive (MR) and Maudsley Non-Reactive (MNR) strains of rats were employed as the experimental subjects . These animals have been bred over many years for `emotionality' (Broadhurst, 1960) . The subjects were divided into three equal treatment groups which were balanced for sex and strain . Group I received an immediate placebo injection (within 15 sec of the end of training) ; Group II, an immediate nicotine injection, and Group III, a delayed nicotine injection . The delayed injection was administered 5 min after the final trial on each day. The nicotine dose was 0 . 25 mg/kg, a dose level arrived at after a perusal of the literature, e.g . Macht (1920), Pechstein (193.7), Essenberg (1948), and some preliminary work which had shown 0 .5 kg/mg intraperitoneal nicotine to lead to debility . The dose is approximately five times the threshold dose and about one tenth of the average convulsive dose for rats . The placebo was an equivalent volume of distilled water . The apparatus was a Y maze, constructed to force the animals to make a light-discrimination whilst swimming submerged in water (Broadhurst, 1956) . The experimental routine demanded five massed trials of underwater maze learning in which the unlighted arm of the maze Was locked . The subject was thus compelled to swim to the lighted side, which was changed randomly for each trial, using a Gellerman Series (Gellerman, 1933) . Trials were timed from the moment of release from the confining box to the moment at which the animal's nose broke surface . Two people were involved in the testing ; one manipulated the animal and the other the maze . Intervals between trials were not timed but were in the region of four or five seconds . The `preliminary training' procedure, under which the animals learnt to swim underwater and to master a light discrimination task, lasted 5 days. On the first day the animals had five 287
288
ANIMAL BEHAVIOUR, 15, 2-3
untimed trials of free surface swimming in a linear alley. On the second day there were five further trials, but the animals were released from the confining box underwater . On each of days 3 and 4, the animals had five trials, being released from the confining box underwater and swimming underwater through the alley . On day 5, the Y maze was used ; during the first trial both of the doors were open, but on four further trials the discrimination procedure was used . Following the above was the `training' phase . On each of days 6 to 10, the animals had five massed and timed trials in the Y maze followed by the appropriate injections . At the end of the daily number of trials they were injected (intraperitoneally) with the placebo or nicotine
(according to the group to which they belonged), dried and returned to their home cages . After an interval of 14 days, during which the animals were kept under ordinary laboratory conditions, they were re-tested (on day 24) but without the subsequent injections . The animals were weighed at the beginning and end of the experiment . Average weight loss was negligible, i.e. Group I, 1 .3 g ; Group II, 1 .6 g ; Group III, 2 .0 g . Results An examination of the mean log transformed trial scores (Table I) indicated no `strain' main effect and no `treatment' effect in total trial scores (i.e. all trials with the exception of the 24th day) but there was a strong and highly
Table I. Mean (log transformed) Time Scores for the Underwater Y Maze Discrimination Task Maudsley Non-Reactive strain
Maudsley Reactive strain Trials
Group I
Group II
Group III
Group I
Group II
Group III
I II III IV V
0 . 82 0 .79 0 .58 0 .67 0 .53
0 . 84 0 . 94 0 . 73 0 . 69 0 . 69
0 . 89 0 . 93 0 . 60 0 . 79 0 . 60
0 .98 0 .73 0 .71 0 .73 0 .79
0 .84 0 . 85 0 . 62 0 . 61 0 . 65
0 . 67 0 . 57 0 . 49 0 . 66 0 . 54
I II
IV V
0 .96 0 . 49 0 . 62 0 . 40 0 . 51
0 . 76 0 . 63 0 .52 0 .55 0 .52
0 . 76 0. 53 0 . 50 0 . 50 0 . 43
0 .62 0 .60 0 . 63 0 . 43 0 . 66
0 . 59 0 . 59 0 .48 0. 59 0. 54
0. 64 0 .52 0 . 62 0 . 47 0 . 59
Day 3
I II III IV V
0 .46 0. 57 0.43 0 .38 0 .33
0.45 0 .57 0 . 38 0 . 38 0 . 38
0 . 47 0 . 56 0 . 37 0 .41 0 . 35
0 . 54 0 . 55 0 .45 0 .45 0 .52
0.67 0 . 49 0 . 50 0 . 56 0 . 46
0 . 55 0 . 60 0 . 41 0 .49 0 . 55
Day 4
I 11 III IV V
0 . 55 0 . 41 0 . 36 0 . 36 0 . 35
0 . 52 0 .39 0 . 55 0 . 33 0 .41
0.43 0.67 0. 48 0 . 41 0 . 43
0 . 48 0 . 43 0 . 56 0 . 36 0 . 45
0 . 49 0 .49 0 .44 0 .47 0 .44
0 . 61 0 .48 0 .46 0 .36 0 . 46
Day 5
I II III IV V
0 . 51 0 .45 0. 33 0.46 0.48
0 .45 0 .36 0 .37 0 . 46 0 .36
0 . 41 0 . 48 0 . 34 0 . 42 0 . 33
0 . 59 0 .49 0 .45 0.44 0.45
0 .41 0 . 44 0 . 43 0 . 44 0 . 51
0 . 41 0 . 48 0 . 44 0 . 42 0 . 34
Day 24
I II III IV V
0.43 0. 33 0.44 0.41 0. 33
0 . 37 0 .44 0 .44 0 . 38 0 . 47
0 .45 0 . 32 0 .41 0 . 33 0 .40
0 .46 0. 36 0 .40 0 .29 0 .31
0 . 43 0 . 47 0 . 38 0 . 43 0 .46
0 . 53 0 .49 0 .45 0 . 39 0 .44
Day I
Day 2
in
Each value in the table represents the average score obtained from eight animals on that trial . Group I (Placebo), Group II (Nicotine, immediate injection), Group III (Nicotine, delayed injection) .
WRAIGHT et al. : NICOTINE AND THE LEARNING OF RATS
significant `sex' effect, (F=43.68 ; P<0.01) which persisted through first and second order interactions with the other variables . This difference was thought to be exclusively due to the superior swimming speed of the males (average log trial score 0-49 sec) over that of the females (average log trial score 0 . 56 sec) ; in terms of non-transformed scores the males were thus about 15 per cent faster . However two further analyses, of the differences between the first three scores on day 1 and the last three scores on day 5, and the variance of regression lines derived from the progressively shortening scores, failed to support this view. In both these cases `sex' appeared only as a second order interaction, and although `strain' effects were found in both, in neither were there `treatment' effects . Analysis of variance of the average differences observed between the last trial of one day and the first trial of the next day (reminiscence) for the two strains under the three treatment conditions and the interactions of these variances on the summed scores for the 4 days, resulted in only a `strain' effect achieving the acceptable level of significance (i .e . F between strains = 7 . 25 ; P<0.01) . The Non-Reactives demonstrated more reminiscence than the Reactives . The overall `strain' differences in reminiscence was confirmed by individual analyses of variance for each daily score where it was found that the overall strain effect was largely due to a highly significant strain difference for the scores between day one and two (i .e . trials 5 and 6) ; thereafter there was no difference which was statistically acceptable . No `treatment' effect emerged for the combined reminiscence scores but in the individual analyses a 5 per cent difference occurred between the last trial of the fifth day and the first trial of the sixth (following the two weeks rest) . Discussion In this experiment, no effect of administering nicotine after performance could be detected ; no treatment effects emerge from the analyses conducted on either the individual trial scores, the regression score designed to outline general practice tendencies, or the reminiscence values except in one case which does not fall within the true scope of the experiment . Fairly consistent strain differences occur which are probably due to either the differential learning capacity of the Reactives and Non-Reactives demonstrated on a number of occasions (Eysenck & Broadhurst,
289
1964), or to a relatively small differential strain reaction to nicotine . The failure to demonstrate treatment effects may be due to the drug dosage used (0 .25 mg/kg) which, on the basis of some reports, might have been too small to be effective as a stimulant, whilst according to other reports this dose might have been large enough to impair performance . Bovet et al . (1963) have used a range of nicotine doses, of which some were smaller and some larger than the one used here, and found that there is a tendency for the agent to augment learning in an escape-avoidance task . It was noticeable that the nicotine injection caused a degree of irritation in most of the animals in the drug groups, producing squealing and muscular spasms in the later stages of the experiment below the level of magnitude which could be called convulsions ; this intolerance was not the case with placebo injections . This finding might suggest a cumulative effect of the daily nicotine injections. However, no `treatment x trial' interaction achieved a level of significance sufficient to give any confidence in this suggestion. Whether this traumatic aspect of the treatment militated against the hypothesis can only be speculated upon, but it seems not unreasonable to surmise that local irritation and discomfort might act against the rehearsal process implicit in both consolidation theory and learning . A second feature of the experiment which could have obscured an improvement in performance of the type predicted was the failure of many animals to manifest any reminiscence whatsoever . Many were still improving their individual trial scores at the end of their five massed trials . Another reason for the failure to obtain the predicted result might lie in the method of massing the trials ; the time interval between two successive trials (i .e . the massing) depended in part on the swimming speed, which differed somewhat with individual animals . It may be recalled that the average trial score was of the order of 4 sec and that for the inter-trial interval was approximately the same . It might be argued that a between-trial interval which is the same as the trial duration constitutes a distributed trial regime rather than one of massed practice ; if this were valid then it is unlikely that any systematic reminiscence could have been observed .
290
ANIMAL BEHAVIOUR, 15, 2-3
Summary Animals (N=48) of the Maudsley Reactive and Non-Reactive strains of rats were subjected to a procedure which involved an underwater discrimination task employing massed trials . At the end of each daily series the experimental subjects were injected with 0 . 25 mg/kg of nicotine either immediately or after a delay of 5 min ; a control group was administered a placebo . The experiment failed to produce any evidence of augmentation of learning due to the post-trial stimulant treatment whether applied immediately or delayed . REFERENCES Bovet, D ., Bignami, G ., Robustelli, F . & Courrier, M . R . (1963) . Action de la nicotine sur la conditionnement et la reaction d'6vitement chez le rat . C.R . Acad. Sci ., 256, 778-780 . Broadhurst, P . L. (1956) . Emotionality in the rat : a study of its determinants, inheritance and relation to some aspects of motivation . pp. 31, 32 . Ph .D . Thesis, University of London . Broadhurst, P. L . (1960) . Experiments in psychogenetics. In Experiments in Personality . Vol. I (Ed. by H . J. Eysenck) . London : Routledge & Kegan Paul . Catalogue of Uniform Strains of Laboratory Animals maintained in Great Britain (1958), 2nd Edition.
Essenberg, J . M . (1948) . The effect of nicotine on maze learning ability of albino rats. Fed. Proc. Balt., 7, 31-32. Eysenck, H . J. & Broadhurst, P . L . (1964) . Experiments with animals . In Experiments in Motivation (Ed. by H. J . Eysenck) . Oxford : Pergamon Press. Gellerman, L . W. (1933) . Chance order alternating stimuli in visual discrimination experiments . J. genet . Psychol., 42, 206-208 . Macht, D . I . & Bloom, W . (1920). Comparative study of ethanol, caffeine and nicotine on behaviour of albino rats . Proc. Soc. exp. Biol., 18, 241-242. McGaugh, J . L., Thomson, C . W ., Westbrook, W . H. & Hudspeth, W . J . (1962) . A further study of learning facilitation with strychnine sulphate. Psychopharm, 3, 352-360 . Pare, W. (1961). The effect of caffeine and seconal on a visual discrimination task . J. comp . physiol . Psychol., 54, 506-509 . Pechstein, L. A. & Reynolds, W . R. (1937) . The effect of tobacco smoke on the growth and learning behaviour of the albino rat and its prodigy . J. comp . physiol. Psychol., 24, 459-469 . Stratton, L . O. & Petrinovich, L. (1963). Post-trial injections of an anti-cholinesterase drug and maze learning in two strains of rats . Psychopharm ., 5, 47-54 . Warwick, K . M . (1963) . An experimental study of the effects of nicotine on certain psychological functions . Unpublished Ph .D . Thesis, University of London . (Received 2 April 1965 ; revised 13 January 1967 ; Ms. number: 562)
THE Er r'ECTS OF POST-TRIAL INJECTIONS OF NICOTINE ON THE LEARNING OF AN UNDERWATER DISCRIMINATION TASK BY RATS BY K. B. WRAIGHT, E. WELDON, B . D . GUPTA & H . C . HOLLAND Institute of Psychiatry, University of London
An increasing number of experimental reports are concerned with the effects of drugs and other treatments on the modification of neural processes in learning . Most of these reports deal with the effects of pre-trial treatments in the belief that the efficiency of learning depends upon the enhanced or reduced efficiency of the organism during performance . In contrast, a great deal of interest has recently been evoked by the reintroduction of the `consolidation theory', which advances the view that the establishment of the underlying neuro-physiological modification in learning is dependent upon the perseverance of neural activity initiated by the training procedure after the cessation of performance . Several authors (McGaugh et al., 1962 ; Pare, 1961 ; Stratton & Petrinovich, 1963) have administered drug and other treatments after the completion of the designated daily performance in the belief that such treatments can have no effect on the independent conditions of the task and must be assumed to act on the perseverating activity which continues after it has ceased. The modes of action of the treatments so far employed may be classified into the broad polar categories of stimulant (enhancement of the perseverating activity) and depressant (reduction or blocking of the activity) . Both procedures have on the whole tended to support the proposition that learning can be facilitated or reduced by compounds and treatments, which can only have their effect after performance . Clearly any drug or other treatment hypothesized to have its main effect upon the posttrial neural activity must be quickly absorbed and utilized by the organism, and it should also be completely excreted from the body tissues before the commencement of a following trial so as not to confound pre- and post-trial augmentation . Nicotine was chosen to fulfil these conditions (Warwick, 1963), the prediction being that the group of rats given immediate post-performance doses of nicotine would learn less well than the group given the drug after a 5-min delay, and further that this second group
would be inferior in learning to the placebo group. Method In this experiment 48 animals from the 22nd generation of the Maudsley Reactive (MR) and Maudsley Non-Reactive (MNR) strains of rats were employed as the experimental subjects . These animals have been bred over many years for `emotionality' (Broadhurst, 1960) . The subjects were divided into three equal treatment groups which were balanced for sex and strain . Group I received an immediate placebo injection (within 15 sec of the end of training) ; Group II, an immediate nicotine injection, and Group III, a delayed nicotine injection . The delayed injection was administered 5 min after the final trial on each day. The nicotine dose was 0 . 25 mg/kg, a dose level arrived at after a perusal of the literature, e.g . Macht (1920), Pechstein (193.7), Essenberg (1948), and some preliminary work which had shown 0 .5 kg/mg intraperitoneal nicotine to lead to debility . The dose is approximately five times the threshold dose and about one tenth of the average convulsive dose for rats . The placebo was an equivalent volume of distilled water . The apparatus was a Y maze, constructed to force the animals to make a light-discrimination whilst swimming submerged in water (Broadhurst, 1956) . The experimental routine demanded five massed trials of underwater maze learning in which the unlighted arm of the maze Was locked . The subject was thus compelled to swim to the lighted side, which was changed randomly for each trial, using a Gellerman Series (Gellerman, 1933) . Trials were timed from the moment of release from the confining box to the moment at which the animal's nose broke surface . Two people were involved in the testing ; one manipulated the animal and the other the maze . Intervals between trials were not timed but were in the region of four or five seconds . The `preliminary training' procedure, under which the animals learnt to swim underwater and to master a light discrimination task, lasted 5 days. On the first day the animals had five 287
288
ANIMAL BEHAVIOUR, 15, 2-3
untimed trials of free surface swimming in a linear alley. On the second day there were five further trials, but the animals were released from the confining box underwater . On each of days 3 and 4, the animals had five trials, being released from the confining box underwater and swimming underwater through the alley . On day 5, the Y maze was used ; during the first trial both of the doors were open, but on four further trials the discrimination procedure was used . Following the above was the `training' phase . On each of days 6 to 10, the animals had five massed and timed trials in the Y maze followed by the appropriate injections . At the end of the daily number of trials they were injected (intraperitoneally) with the placebo or nicotine
(according to the group to which they belonged), dried and returned to their home cages . After an interval of 14 days, during which the animals were kept under ordinary laboratory conditions, they were re-tested (on day 24) but without the subsequent injections . The animals were weighed at the beginning and end of the experiment . Average weight loss was negligible, i.e. Group I, 1 .3 g ; Group II, 1 .6 g ; Group III, 2 .0 g . Results An examination of the mean log transformed trial scores (Table I) indicated no `strain' main effect and no `treatment' effect in total trial scores (i.e. all trials with the exception of the 24th day) but there was a strong and highly
Table I. Mean (log transformed) Time Scores for the Underwater Y Maze Discrimination Task Maudsley Non-Reactive strain
Maudsley Reactive strain Trials
Group I
Group II
Group III
Group I
Group II
Group III
I II III IV V
0 . 82 0 .79 0 .58 0 .67 0 .53
0 . 84 0 . 94 0 . 73 0 . 69 0 . 69
0 . 89 0 . 93 0 . 60 0 . 79 0 . 60
0 .98 0 .73 0 .71 0 .73 0 .79
0 .84 0 . 85 0 . 62 0 . 61 0 . 65
0 . 67 0 . 57 0 . 49 0 . 66 0 . 54
I II
IV V
0 .96 0 . 49 0 . 62 0 . 40 0 . 51
0 . 76 0 . 63 0 .52 0 .55 0 .52
0 . 76 0. 53 0 . 50 0 . 50 0 . 43
0 .62 0 .60 0 . 63 0 . 43 0 . 66
0 . 59 0 . 59 0 .48 0. 59 0. 54
0. 64 0 .52 0 . 62 0 . 47 0 . 59
Day 3
I II III IV V
0 .46 0. 57 0.43 0 .38 0 .33
0.45 0 .57 0 . 38 0 . 38 0 . 38
0 . 47 0 . 56 0 . 37 0 .41 0 . 35
0 . 54 0 . 55 0 .45 0 .45 0 .52
0.67 0 . 49 0 . 50 0 . 56 0 . 46
0 . 55 0 . 60 0 . 41 0 .49 0 . 55
Day 4
I 11 III IV V
0 . 55 0 . 41 0 . 36 0 . 36 0 . 35
0 . 52 0 .39 0 . 55 0 . 33 0 .41
0.43 0.67 0. 48 0 . 41 0 . 43
0 . 48 0 . 43 0 . 56 0 . 36 0 . 45
0 . 49 0 .49 0 .44 0 .47 0 .44
0 . 61 0 .48 0 .46 0 .36 0 . 46
Day 5
I II III IV V
0 . 51 0 .45 0. 33 0.46 0.48
0 .45 0 .36 0 .37 0 . 46 0 .36
0 . 41 0 . 48 0 . 34 0 . 42 0 . 33
0 . 59 0 .49 0 .45 0.44 0.45
0 .41 0 . 44 0 . 43 0 . 44 0 . 51
0 . 41 0 . 48 0 . 44 0 . 42 0 . 34
Day 24
I II III IV V
0.43 0. 33 0.44 0.41 0. 33
0 . 37 0 .44 0 .44 0 . 38 0 . 47
0 .45 0 . 32 0 .41 0 . 33 0 .40
0 .46 0. 36 0 .40 0 .29 0 .31
0 . 43 0 . 47 0 . 38 0 . 43 0 .46
0 . 53 0 .49 0 .45 0 . 39 0 .44
Day I
Day 2
in
Each value in the table represents the average score obtained from eight animals on that trial . Group I (Placebo), Group II (Nicotine, immediate injection), Group III (Nicotine, delayed injection) .
WRAIGHT et al. : NICOTINE AND THE LEARNING OF RATS
significant `sex' effect, (F=43.68 ; P<0.01) which persisted through first and second order interactions with the other variables . This difference was thought to be exclusively due to the superior swimming speed of the males (average log trial score 0-49 sec) over that of the females (average log trial score 0 . 56 sec) ; in terms of non-transformed scores the males were thus about 15 per cent faster . However two further analyses, of the differences between the first three scores on day 1 and the last three scores on day 5, and the variance of regression lines derived from the progressively shortening scores, failed to support this view. In both these cases `sex' appeared only as a second order interaction, and although `strain' effects were found in both, in neither were there `treatment' effects . Analysis of variance of the average differences observed between the last trial of one day and the first trial of the next day (reminiscence) for the two strains under the three treatment conditions and the interactions of these variances on the summed scores for the 4 days, resulted in only a `strain' effect achieving the acceptable level of significance (i .e . F between strains = 7 . 25 ; P<0.01) . The Non-Reactives demonstrated more reminiscence than the Reactives . The overall `strain' differences in reminiscence was confirmed by individual analyses of variance for each daily score where it was found that the overall strain effect was largely due to a highly significant strain difference for the scores between day one and two (i .e . trials 5 and 6) ; thereafter there was no difference which was statistically acceptable . No `treatment' effect emerged for the combined reminiscence scores but in the individual analyses a 5 per cent difference occurred between the last trial of the fifth day and the first trial of the sixth (following the two weeks rest) . Discussion In this experiment, no effect of administering nicotine after performance could be detected ; no treatment effects emerge from the analyses conducted on either the individual trial scores, the regression score designed to outline general practice tendencies, or the reminiscence values except in one case which does not fall within the true scope of the experiment . Fairly consistent strain differences occur which are probably due to either the differential learning capacity of the Reactives and Non-Reactives demonstrated on a number of occasions (Eysenck & Broadhurst,
289
1964), or to a relatively small differential strain reaction to nicotine . The failure to demonstrate treatment effects may be due to the drug dosage used (0 .25 mg/kg) which, on the basis of some reports, might have been too small to be effective as a stimulant, whilst according to other reports this dose might have been large enough to impair performance . Bovet et al . (1963) have used a range of nicotine doses, of which some were smaller and some larger than the one used here, and found that there is a tendency for the agent to augment learning in an escape-avoidance task . It was noticeable that the nicotine injection caused a degree of irritation in most of the animals in the drug groups, producing squealing and muscular spasms in the later stages of the experiment below the level of magnitude which could be called convulsions ; this intolerance was not the case with placebo injections . This finding might suggest a cumulative effect of the daily nicotine injections. However, no `treatment x trial' interaction achieved a level of significance sufficient to give any confidence in this suggestion. Whether this traumatic aspect of the treatment militated against the hypothesis can only be speculated upon, but it seems not unreasonable to surmise that local irritation and discomfort might act against the rehearsal process implicit in both consolidation theory and learning . A second feature of the experiment which could have obscured an improvement in performance of the type predicted was the failure of many animals to manifest any reminiscence whatsoever . Many were still improving their individual trial scores at the end of their five massed trials . Another reason for the failure to obtain the predicted result might lie in the method of massing the trials ; the time interval between two successive trials (i .e . the massing) depended in part on the swimming speed, which differed somewhat with individual animals . It may be recalled that the average trial score was of the order of 4 sec and that for the inter-trial interval was approximately the same . It might be argued that a between-trial interval which is the same as the trial duration constitutes a distributed trial regime rather than one of massed practice ; if this were valid then it is unlikely that any systematic reminiscence could have been observed .
290
ANIMAL BEHAVIOUR, 15, 2-3
Summary Animals (N=48) of the Maudsley Reactive and Non-Reactive strains of rats were subjected to a procedure which involved an underwater discrimination task employing massed trials . At the end of each daily series the experimental subjects were injected with 0 . 25 mg/kg of nicotine either immediately or after a delay of 5 min ; a control group was administered a placebo . The experiment failed to produce any evidence of augmentation of learning due to the post-trial stimulant treatment whether applied immediately or delayed . REFERENCES Bovet, D ., Bignami, G ., Robustelli, F . & Courrier, M . R . (1963) . Action de la nicotine sur la conditionnement et la reaction d'6vitement chez le rat . C.R . Acad. Sci ., 256, 778-780 . Broadhurst, P . L. (1956) . Emotionality in the rat : a study of its determinants, inheritance and relation to some aspects of motivation . pp. 31, 32 . Ph .D . Thesis, University of London . Broadhurst, P. L . (1960) . Experiments in psychogenetics. In Experiments in Personality . Vol. I (Ed. by H . J. Eysenck) . London : Routledge & Kegan Paul . Catalogue of Uniform Strains of Laboratory Animals maintained in Great Britain (1958), 2nd Edition.
Essenberg, J . M . (1948) . The effect of nicotine on maze learning ability of albino rats. Fed. Proc. Balt., 7, 31-32. Eysenck, H . J. & Broadhurst, P . L . (1964) . Experiments with animals . In Experiments in Motivation (Ed. by H. J . Eysenck) . Oxford : Pergamon Press. Gellerman, L . W. (1933) . Chance order alternating stimuli in visual discrimination experiments . J. genet . Psychol., 42, 206-208 . Macht, D . I . & Bloom, W . (1920). Comparative study of ethanol, caffeine and nicotine on behaviour of albino rats . Proc. Soc. exp. Biol., 18, 241-242. McGaugh, J . L., Thomson, C . W ., Westbrook, W . H. & Hudspeth, W . J . (1962) . A further study of learning facilitation with strychnine sulphate. Psychopharm, 3, 352-360 . Pare, W. (1961). The effect of caffeine and seconal on a visual discrimination task . J. comp . physiol . Psychol., 54, 506-509 . Pechstein, L. A. & Reynolds, W . R. (1937) . The effect of tobacco smoke on the growth and learning behaviour of the albino rat and its prodigy . J. comp . physiol. Psychol., 24, 459-469 . Stratton, L . O. & Petrinovich, L. (1963). Post-trial injections of an anti-cholinesterase drug and maze learning in two strains of rats . Psychopharm ., 5, 47-54 . Warwick, K . M . (1963) . An experimental study of the effects of nicotine on certain psychological functions . Unpublished Ph .D . Thesis, University of London . (Received 2 April 1965 ; revised 13 January 1967 ; Ms. number: 562)