Ketaset-Rompun extends the temporal gradient for hypothermia-induced retrograde amnesia

In studies of experimentally induced retrograde amnesia (RA), as the interval between training and the amnestic treatment is lengthened, amnesia decreases (4). This temporal gradient for RA has been reported with a wide variety of amnestic agents, including RA produced by thermoregulatory disturbances (8). This temporal gradient for RA is not unlike certain characteristics of classical conditioning, where weaker conditioned responding occurs when the interval between the conditioned stimulus (CS) and unconditioned stimulus (US) is lengthened. Furthermore, there is evidence that administration of anesthetics can lengthen the "effective conditioning" interval between the CS and US, as demonstrated in a conditioned taste-aversion (CTA) procedure (10). In that study, little conditioning was observed when a 3-h delay (or more) was incorporated between presentations of the CS (flavor) and the US (toxin). However, if subjects were anesthetized immediately after the CS was delivered and remained anesthetized during the CS-US interval, strong conditioning was observed with CS-US intervals of up to 9 h. The aim of the present experiment was to determine if the temporal gradient for hypothermia-induced RA could also be lengthened. That is, we tested whether the interval between training and hypothermia treatment could be lengthened by anesthetizing subjects with Ketaset-Rompun. The results indicate that the training-to-amnestic agent interval could be lengthened within moderate limits. The implications for hypothermia-induced RA is further discussed.