[Memory and aging: changes in the mammillary body and anterior thalamic nuclei due to age]

Karyometric changes and variation of neuron number in mammillary body and anterior thalamic nuclei, dependent of the age, have been studied in humans and rats. The behaviour of the neurons number is very similar in all studied nuclei of both species: there is a constant and gradual loss of neurons from the first until the last period of the life. The intensity of the neuronal loss, however, is different according the nuclei and is more pronounced in rats than in humans. The evolution of the nuclear area of the human mammillary body is similar to that of the anterior thalamic nuclei: there is a significant decrease until the age of 60-70 years and then begins an increase up to the end of the life. This increase is more intense in the mammillary nuclei than in the thalamic ones. In rats, the behaviour of the mammillary nuclei is different to that of the anterior thalamic nuclei. In the mammillary body there is an increase of the nuclear are until 18 months of age, followed by a decrease until the end of the life. The anterior thalamic nuclei show a double inflexion: first, it appears a marked decrease of the nuclear area during the first 6 months, then the area remains unchanged until the age of 15 months, but from this period up to the end of the 2nd year undergoes an increase and, finally, during the 3 year shows a significant decrease. There is not a complete correlation between neuronal loss and nuclear area increase. Although the neuronal loss is constant during the entire life, the nuclear are increase only in a certain period: in rats during the second year and in humans in the final period of life. The signification of this partial correlation is discussed.