Somatostatin-281–12-like immunoreactivity is reduced in Alzheimer's disease cerebral cortex

A deficiency in somatostatin is the most consistently described neurochemical alteration in Alzheimer's disease (AD) attributable to intrinsic cortical neurons. Somatostatin-28 (SOM-28), an N-terminal-extended form of somatostatin, can be cleaved to form somatostatin-28(1-12)(SOM-28(1-12) ) and somatostatin-14 (SOM-14). We have measured concentrations of SOM-28(1-12)-like immunoreactivity in 8 cortical regions from 12 patients with AD and 13 controls. Significant reductions (P less than 0.001) were found in all cortical regions examined with the largest decrease in temporal lobe. Reductions were significantly correlated with decreases in somatostatin-14-like immunoreactivity in the same regions. The similar reductions of two prosomatostatin-derived peptides in AD cerebral cortex supports the contention that decreased somatostatin immunoreactivity in AD is caused by a degeneration of somatostatin cortical neurons and terminals.