5,7-dihydroxytryptamine (5,7-DHT) (150 µg; 4.5 µl/ventricle), a serotonergic neurotoxin, significantly decreased spontaneous alternation in Y-maze task and working memory in radial arm-maze task, suggesting effects on short-term memory, without affecting long-term memory, explored by reference memory in radial arm-maze task. Parachlorophenylalanine (PCPA) (3 days treatment 200µg, i.c.v.), a serotonin synthesis inhibitor, significantly decreased spontaneous alternation in Y-maze task, suggesting effects on short-term memory. These results suggest that serotonin, among other neurotransmitters, plays an important role in cognitive functions, especially in short-term memory, with relevance for treatment of cognitive impairment in schizophrenia.