The Median Raphe Nucleus Lesion Attenuates Amnesic Effects of Ketamine on Short-Term Memory in Rats

The effects of pre-anesthetic dose of ketamine (10 mg per kg) on acquisition of short-term memory in rats with damage of mesolimbic serotonergic system has been investigated. Chemical lesion of serotonergic neurons in the median raphe nucleus was performed by ibotenic acid. The rats injected ketamine (10 mg per kg i. p.) or vehicle (1 ml per kg i. p.) prior to learning were tested after changes in locomotor activity disappeared. Short-term memory was studied using a two compartment single trial passive avoidance chamber for 180 s. In rats with lesion of median raphe nucleus, the pre-anesthetic dose of ketamine produced a significant decrease reduction of acquisition latencies and percentage of animals without amnesia syndrome compared to naive and sham-operated animals-treated with ketamine. These result suggest that deficits in serotonin release of mesolimbic system attenuates amnesic effects of ketamine on short-term memory.