The CA1 hippocampal region is involved in organizing several neuropsychological processes. Pyramidal cell dendritic spines in the CA1 field of rats subjected to chronic tryptophan diet restriction were quantified at 21, 40, and 60 days of age. At 40 days of age, the number of spines in the distal third of the apical dendrite was smaller in experimental animais. The same was true for the medial third of the apical dendrite and the basal dendrite at 60 days of age. The results could be interpreted as a trans-synaptic plastic response due to understimulation of serotoninergic receptors located in the hippocampal Ammon's horn and, particularly, on the CA1 pyramidal neurons as well as on aferences to the hippocampus. Since the present is a model of generalized tryptophan restriction, neurochemical studies are needed to dilucidate this hypothesis.