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 AND GEORGE!3 CHAPOUTHIER Dkptrrternent de Psychoph_vsiologie, L.P.N.-C.N.R.S. 91 IW-Gif-sur-Yvette (Frunce) (Received 3 March 1978) ALEXINSKY, T. AND G. CHAPOUTHIER. Hdothcrne wwesthesicr und DMS perfwmcmce in ruts: Memory impairment or trwicl~trrce hehcwiortr? PHYSIOL. BEHAV. 22J1) ‘99-105, 1979.- Halothane anaesthesia administered after the presen- tation 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 Memory disruption Aversion ANAESTHETIC agents have been widely used to impair memory consolidation. Pearlman et cl/. [ 141 and Hen. et al. [I l] showed in rodents that ether inhalation following learn- ing 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. responsible for the long term learning of the rule are impor- tant 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. We have devised a delayed match to sample (DMS) tech- nique in the rat [2] which seems to be suitable, on both theoretical and practical grounds, for the study of the physi- ological bases of memory 171. The stimulus-test intervals that we can use with this ex- perimental protocol (up to 20 mm before significant perform- ance 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 ef- fects 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? The principle of the test is as follows: to obtain rein- forcement (water), the rat must choose, out of 3 com- partments 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 in- troduced between the stimulus and testing sessions (DMS). METHOD Animals 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. Thirty male Sprague-Dawley rats from the IFFA CREDO rearing center were used. At the beginning of the experi- ments, 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 Our test therefore permits the study of 2 aspects of mem- Three stimulus boxes and a test device made up the train- ory. Firstly, during the learning stage (very long), processes ing apparatus. The floor and sides of the boxes and of the Copyright c 1979 Brain Research Publications Inc.-0031-9384/79/010099-07$02.00/O