Physkdo~.v & Brhtrvio~r. Vol. 22, pp. 99-105. Rrgamon

Press and Brain Research Pd.,

1979. Printed in the U.S.A

Halothane Anaesthesia and DMS Performance in Rats: Memory Impairment or Avoidance Behaviour? TATIANA ALEXINSKY Dkptrrternent

de Psychoph_vsiologie,

AND GEORGE!3 CHAPOUTHIER L.P.N.-C.N.R.S.

(Received

91 IW-Gif-sur-Yvette

(Frunce)

3 March 1978)

ALEXINSKY, T. AND G. CHAPOUTHIER. Hdothcrne wwesthesicr und DMS perfwmcmce in ruts: Memory impairment or trwicl~trrce hehcwiortr? PHYSIOL. BEHAV. 22J 1) ‘99-105, 1979.- Halothane anaesthesia administered after the presentation of a stimulus to he memorized for a short time leads to an impairment of performance in a delayed matching to sample (DMS) task. Such an effect, which would he classically interpreted as a memory disruption, is here re-evaluated. Our data show: (I) That the animals tend to systematically avoid the stimulus associated with the halothane treatment; (2) That they are still able to remember the stimulus presented just before treatment. These results suggest an aversive rather than amnesic effect of the halothane anaesthesia. Rat

Delayed matching to sample (DMS)

Halothane anaesthesia

ANAESTHETIC agents have been widely used to impair memory consolidation. Pearlman et cl/. [ 141and Hen. et al. [I l] showed in rodents that ether inhalation following learning produced retrograde amnesia. The anaesthetic most often used in our laboratory is halothane. This drug does not seem to cause aversive effects in the animals and onset of, and recovery from, anaesthesia are rapid: a few minutes after narcosis, the motor and perceptual capabilities of the animal appear normal. Post-trial halothane anaesthesia has been shown to impair retention both in chicks [5, 13,201 and in rats [3, 4, 151. We have devised a delayed match to sample (DMS) technique in the rat [2] which seems to be suitable, on both theoretical and practical grounds, for the study of the physiological bases of memory 171. The principle of the test is as follows: to obtain reinforcement (water), the rat must choose, out of 3 compartments placed symmetrically in front of it (test session), the one identical to that in which it had been previously placed by the experimenter (stimulus session). The rat must therefore learn the rule which is an association between the stimulus and goal boxes (the stimulus and hence the goal box are changed randomly between session). A delay can be introduced between the stimulus and testing sessions (DMS). The conception of this test has been influenced by the methodological concepts of experimentation on animal memory published by Weiskrantz [19]. He considered appropriate tests to be “tests involving a unique relation*‘. They can be solved only by reference to a single past event. In all such tasks the animal must learn a rule or a strategy but the rule can be applied only by reference to a unique event. Our test therefore permits the study of 2 aspects of memory. Firstly, during the learning stage (very long), processes

Copyright

c 1979 Brain Research

Memory disruption

Aversion

responsible for the long term learning of the rule are important and secondly, during each test when a stimulus-test delay is present, the animal must conserve the memory of the unique event over a short period. The stimulus-test intervals that we can use with this experimental protocol (up to 20 mm before significant performance drop occurs) are much longer than those previously reported and, allow the use of treatments which demand a certain time to be effective (anaesthesia, biochemical agents). We chose halothane anaesthesia for these tests. Our experimental protocol appeared to us to be adequate for the study of two related but different problems: (1) Are the effects of halothane the same as those previously described for transient memory (stimulus) and long term memory (the rule)? (2) How can one interpret these effects? METHOD Animals

Thirty male Sprague-Dawley rats from the IFFA CREDO rearing center were used. At the beginning of the experiments, the rats weighed 120 g each; they were housed in individual wire mesh cages measuring 35 x 20x 18 cm; by the end of the experiments they had reached 400 g. The animals were trained under partial water deprivation; food was given ad lib. During the experiment, the weight increase of the animals was compared with control animals given water ad lib. Trtrining

Apparcttus

Three stimulus boxes and a test device made up the training apparatus. The floor and sides of the boxes and of the

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ALEXINSKY testing apparatus were made of opaque 5 mm plastic sheet with a transparent Plexiglas ceiling. The ceiling could be removed in order to introduce the animals into the stimulus boxes. The stimulus boxes (30x 15 cm) differed in their visual characte+ristics: a white, a black and a blackand-white striped one. Cues chosen for their tactile and olfactory characteristics were added in each of the boxes; smooth floor and rat food gratings in the white box, sand paper and eau de Cologne discrete scent in the black box, grid floor and orange peel raspings in the striped one. The test device consisted of a (20x20 cm) start box followed by a choice chamber, both made of beige plastic sheet. The choice chamber allowed entry to the 3 goal boxes, in which visual, tactile and olfactive cues were identical to the ones of the stimulus boxes. At the end of the goal boxes were situated the front parts of the drinking troughs. Swinging doors, situated at the entrance of the goal boxes prevented the return of the rats during early phases of the training. The stimulus boxes and the starting box were provided with doors which, when lifted, allowed animals to move into another box. Occasionally a side opening in the starting box, allowed the waiting rats to see the stimulus.

AND CHAPOUTHIEK

covered

Genenrl

FIG. I. Effect of delay between stimulus and test on the performance level. Note the stability

of performance

up to 24 mn delay.

E (n= 15) and group C (n= 15). During the halothane session, only group E was submitted to anaesthesia. Group C, manipulated the same way, was used as a non-anaesthetized control. Non-halothanc control sessions during which none of the group were anacsthetized were interspersed with the halothane sessions.

Procedure

The training procedure has been described in detail elsewhere [2]: a modified delayed matching to sample technique was employed (DMS). The rat was placed in one of the stimulus boxes for 2 mn (stimulus session) and was then removed and placed in the start box of the test apparatus (test session). The door was opened by the experimenter and the rat proceeded to the choice chamber, where the 3 goal boxes were in view. A correct choice is the goal box which is the same as the stimulus box which was previously presented to the animal. Water is present in all 3 water-troughs in order to eliminate all possible water-associated sensory cues. The rat had access to water by pulling the trough into the correct box; the troughs were blocked in the incorrect boxes. The training proceeded in 3 stages. The animals were habituated to the experimental situation for 1 week. During pretraining spatial habits were eliminated and a correction procedure was used so that an animal making a wrong choice had another look at the stimulus and another opportunity to choose. The pretraining phase consisted of 110 trials distributed over 14 weeks. The training detailed above was begun when fX% of the rats made correct choices for 3 consecutive days. During the first 12 trials the animals could see the stimulus box through a window in the start box. Then the window was closed and the choice had to be made using only immediate memory. The details of this training procedure have been described in an earlier article [2]. Animals used for the following experiments were trained with this procedure. Once the procedure had been learned, a delay was introduced between stimulus and test sessions. Previous results [2] showed that this delay could be as long as 24 min, without any impairment in performance (Fig. I).

Anaesthesia was administered in a plastic box, similar to the waiting box, with an atmosphere of 3.5% halothane in an equal mixture of 2 Vmn of air and 2 Vmn of oxygen, which produced narcosis within approximately 15 sec. The animals were divided into 2 groups of equivalent performance: group

FIRST SERIES OF EXPERIMENTS Principle

The purpose of the first experimental series was to study the effects on our model of an agent classically considered as amnesic: halothane. The experimental paradigm for this series comprised the following stages:

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delay between the end of the stimulus session and the beginning of the testing session was 16 mn. Under normal conditions (see Fig. l), it was shown that such a delay does not impair information retention; in the present study performance of the controls confirm this result. During the 16 mn delay, experimental animals (group E) were submitted to an 8 mn anaesthesia, followed by an 8 mn recovery. This 8 mn delay was sufficient for the animal to recover its motor ability. (A complementary experiment was devised with 30 animals. It allowed us to measure the minimum duration for anaesthesia and recovery necessary to obtain performance (choice response latency of any one of the compartments) identical to that of non-treated animals.) Control animals (group C) were submitted to the same handling but without anaesthesia. During successive trials, each rat was presented with each of the 3 possible stimuli.

perf~mnttnce.

Control

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Between each experimental trial (during which experimental animals were anaesthetized) 3 normal trials, during which these animals were treated as controls (no anaesthesia), were inserted. These control trials were run 2 hr and 24 hr after a given experimental trial and 24 hr before the next one. The 2 triais following the experimental trial enabled us tocheck the existence of proactive effects of the habthane treatment over the medium (2 hr) or long (24 hr) term. Such proactive effects wouki mean an impairment in the stable memory (rule) through non-specifi factors (i.e., not specifically related to the memory of a given stimulus). Corrtrol of shout trrwr c#iTt of’ hrrlotkci~r~~ trmttmwt. It was also necessary to verify on the experimental animals

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HALOTHANE

ANAESTHESIA

AND

ment) that there was no impairment in performance after anaesthesia given just before the stimulus session. Such an effect could be due to either non-specific impairment of the rule or an impairment of the perceptive abilities of the animals. We therefore designed an experiment in which the anaesthetic treatment (8 mn anaesthesia followed by 8 mn recovery) was administered just before the stimulus session. In a subsequent test 16 mn after the stimulus session, performance of the experimental animals was compared to that of controls given the same handling but without anaesthesia. Control trials, with both groups non-treated, were carried out before and after the experimental trial. Effect of the ktervcrl hetweerr stimulrrs session cmd onuesthesicr. The onset of anaesthesia was delayed for one, then 2

min in the experimental group. Performance was compared with that of non-anaesthetized animals. Because of the delay in the onset of the treatment, testing was carried out 17 or I8 mn after the end of the stimulus session, instead of I6 mn as in the preceding experiments. We have shown however (Fig. 1) that performance remains stable up to a 24 mn delay. Control trials were also designed as before. Results EfflJct of post-stirllrrllrs

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DMS PERFORMANCE

treatment

otl retention

Results are presented in Fig. 2, second group of columns. Performance of the anaesthetized animals is lower than that of the control animals (xX= 13.88; p

Halothane anaesthesia and DMS performance in rats: memory impairment or avoidance behaviour?

Physkdo~.v & Brhtrvio~r. Vol. 22, pp. 99-105. Rrgamon Press and Brain Research Pd., 1979. Printed in the U.S.A Halothane Anaesthesia and DMS Perfor...
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