Selective age-related changes in the PKC-sensitive, calmodulin-binding protein, neurogranin, in the mouse brain

Brain ageing is associated with a dysregulation of intracellular calcium (C a2+) homeostasis which leads to deficits in Ca2+-dependent signalling pathw ays and altered neuronal functions. Given the crucial role of neurogranin/R C3 (Ng) in the post-synaptic regulation of Ca2+ and calmodulin levels, age- dependent changes in the levels of Ng mRNA and protein expression were anal ysed in 3, 12, 24 and 31-month-old mouse brains. Ageing produced significan t decreases in Ng mRNA expression in the dorsal hippocampal subfields, retr osplenial and primary motor cortices, whereas no reliable changes were seen in any other cortical regions examined. Western blot indicated that Ng pro tein expression was also down-regulated in the ageing mouse brain. Analysis of Ng immunoreactivity in both hippocampal CA1 and retrosplenial areas ind icated that Ng protein in aged mice decreased predominantly in the dendriti c segments of pyramidal neurones. These data suggest that age-related chang es of postsynaptic Ng in selected brain areas, and particularly in hippocam pus, may contribute to altered Ca2+/calmodulin-signalling pathways and to r egion-specific impairments of synaptic plasticity and cognitive decline.