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Experimental evidence suggests an important role of serotonin in the process of learning and memory. The present study investigated the effect of 5HT3-receptor antagonist (ICS 205-930) on retrieval of a previously learned aversive habit in the mouse. The effect of ICS 205-930 on scopolamine (3 mg/kg) induced amnesia was also studied. ICS 205-930 (1, 10 & 100 micrograms/kg) produced a dose-dependent increase in latency to cross into the dark chamber. The scopolamine induced memory impairment was significantly attenuated by ICS 205-930 (10 micrograms/kg). These results suggest that memory deficits may be susceptible to attenuation with non-cholinergic treatments.

The effects of post-training administration of chlordiazepoxide and (-)-baclofen on memory retention was studied in ICRC Swiss mice by measuring the retest stepdown latency 24 hr after foot-shock in a passive avoidance task. Chlordiazepoxide 20 mg/kg impaired memory retention and a similar effect was produced by 10 mg/kg of diazepam. The effect of chlordiazepoxide was antagonised when combined with picrotoxin but not by the addition of a specific GABAB antagonist CGP 35348. The effect of chlordiazepoxide on memory retention seems to be mediated by action at the GABAA-benzodiazepine receptor complex. (-) Baclofen, the active isomer of the GABAB agonist enhanced memory in ICRC mice and this effect was antagonised by CGP 35348 at a dose of 10 mg/kg. The inactive isomer of baclofen, (+)-baclofen did not produce any effect. This indicates that GABAB receptors contribute to the effects of (-)-baclofen on memory.

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