Age-related changes in the subcortical afferents to the medial frontal cortex in mice: a WGA-HRP study

The subcortical afferent projections to the mediodorsal part of the frontal cortex were studied both qualitatively and quantitatively in young (3 months), adult (12 months) and aged (22 months) Balb/c mice by means of the retrograde transport of wheat germ agglutinine-horseradish peroxidase (WGA-HRP). A progressive decrease in the number of afferents was observed during aging with a differential pattern of reduction as a function of the subcortical structures. In adult mice a large reduction of afferents occurs in the diagonal band of Broca, the posterior thalamic nucleus, the zona incerta, the lateral hypothalamic area, the nuclei of amygdaloid complex, the posterior hypothalamic nucleus, the reticular pontine nucleus, the dorsal and medial raphe nuclei and the dorsal tegmental nucleus. In aged animals, only the anteromedial and mediodorsal thalamic nuclei, as well as the locus coeruleus appear to be clearly affected.