Immunolocalisation of protein phosphatase inhibitor-1 in the cerebral cortex of the rat, cat and ferret

The distribution of inhibitor-1 was analysed in the neocortex of cat, ferret and rat by immunocytochemistry (at the light and electron microscope levels) and by immunoblotting using an affinity purified antibody which recognises both the phosphorylated and dephosphorylated forms of the protein. In each mammalian cortex immunocytochemical techniques identified inhibitor-1 predominantly in infragranular pyramidal neurons and, at a lower concentration, in supragranular pyramidal neurons of cortical layers II-III, and V-VI. Within the cortical layers, neuronal cell bodies and apical dendrites were stained strongly but no immunoreactivity was associated with dendritic spines. Regional differences in intensity of staining were revealed when appropriate antibody concentrations were used; the concentration of inhibitor-1 appeared to follow a gradient with the highest levels in layer VI and the lowest in layer I. The results were confirmed by immunoblotting of microdissected cortical regions which identified the inhibitor-1 protein unambiguously. The distribution of inhibitor-1 is different from that reported by other investigators.