We examined 5-HT7 receptor mRNA expression with in situ hybridization histochemistry in the brains of young (3 months), middle-aged (12 months) and old rats (24 months). In the ventral CA3 area of the hippocampus 5-HT7 mRNA expression is reduced by approximately 30% between young and middle age without further decline between middle and old age. In other brain areas 5-HT7 mRNA expression is unaffected by age.