Guanfacine's mechanism of action in treating prefrontal cortical disorders: Successful translation across species

The selective norepinephrine (NE) alpha 2A-adrenoceptor (alpha 2A-AR) agonist, guanfacine (IntunivTM), is FDA-approved for treating Attention Deficit Hyperactivity Disorder (ADHD) based on research in animals, a translational success story. Guanfacine is also widely used off-label in additional mental disorders that involve impaired functioning of the prefrontal cortex (PFC), including stress-related disorders such as substance abuse, schizotypic cognitive deficits, and traumatic brain injury. The PFC subserves high order cognitive and executive functions including working memory, abstract reasoning, insight and judgment, and top-down control of attention, action and emotion. These abilities arise from PFC microcircuits with extensive recurrent excitation through NMDAR synapses. There is powerful modulation of these synapses, where cAMP-PKA opening of nearby potassium (K+) channels can rapidly and dynamically alter synaptic strength to coordinate arousal state with cognitive state, e.g. to take PFC "offline" during uncontrollable stress. A variety of evidence shows that guanfacine acts within the PFC via post-synaptic alpha 2A-AR on dendritic spines to inhibit cAMP-PKA-K+ channel signaling, thus strengthening network connectivity, enhancing PFC neuronal firing, and improving PFC cognitive functions. Although guanfacine's beneficial effects are present in rodent, they are especially evident in primates, where the PFC greatly expands and differentiates. In addition to therapeutic actions in PFC, stress-related disorders may also benefit from additional alpha 2-AR actions, such as weakening plasticity in the amygdala, reducing NE release, and antiinflammatory actions by deactivating microglia. Altogether, these NE alpha 2-AR actions optimize top-down control by PFC networks, which may explain guanfacine's benefits in a variety of mental disorders.