Introduction:

The impact of general anaesthesia on the postoperative cognitive dysfunction (POCD) is highly controversial. In humans, it has not been possible to distinguish the effects of anaesthesia from those of surgery to identify the cause of POCD. Experimental animal studies have suggested that anaesthesia -e.g. isoflurane- alone may induce cognitive decline and aged rodents appeared to be more susceptible. Therefore, we investigated the influence of repeated propofol anaesthesia on spatial learning and long term memory using the Morris water maze (MWM) in different age groups of rats and additionally in a model of neuronal degeneration (epilepsy induced hippocampal sclerosis).

Material and Methods:

Spatial learning and long term memory before and after propofol anaesthesia were tested on male Wistar rats of different ages (young adult = 3 months, aged = 20 months) and neurodegenerated (= 3 months). To this end, the MWM paradigm was used, consisting of habituation (day 1), acquisition phase (day 2-6) and probe trial without platform (day 7). Following one complete MWM test, a subset of animals was recurrently anaesthetised with propofol. This anaesthetic was applied every 20 minutes (50 mg/kg) until the animals reached a deep anaesthetic state or the maximum dosage of 250 mg/kg. The control groups were not anaesthetised with propofol. 10-13 weeks later, a second trial of MWM was conducted.

Results:

Time to reach the submerged platform (latency), distance travelled and swim velocity were calculated for each trial. The mean of swimming latencies of different groups of rats were compared between the last day of acquisition phase in the first MWM test (day 6) before propofol anaesthesia and the first day of acquisition phase in the second MWM test (day 2) after propofol anaesthesia. Exposure to propofol had no significant effect on the time to reach the hidden platform in either young adult (n=18 vs. n=13, P=0.074) or aged rats (n=11 vs. n=5, P=0.5) compared to their corresponding groups without propofol anaesthesia. Only the group of neurodegenerated animals displayed a significant difference concerning the swimming latencies (n=18 vs. n=11, P=0.008).

Conclusions:

Repeated propofol exposure did not produce significant deficits in spatial learning and long term memory in healthy young and aged rats. However, neurodegenerated animals showed a significant deficit in long term retrieval that may be attributed to the neurodegeneration rather than to propofol exposure.