CREB1 and Alzheimer disease: Although the molecular mechanisms that underlie these morphological changes are not completely understood, emerging evidence supports at least two important signaling pathways that have been linked to dendrite spine formation and AD etiology: (1) cAMP-dependent activation of PKA has been shown to be critical for the maintenance of the late phase of LTP, and downstream phosphorylation of CREB has been linked to formation of new spines [93].