Amphetamine promotes cortical Up state: Role of adrenergic receptors

Cortical neurons oscillate synchronously between the Up and Down state during slow-wave sleep and general anesthesia. Using local-field-potential recording in the rat prefrontal cortex (PFC), we have shown that systemic administration of methylphenidate promotes PFC Up states and reduces PFC slow oscillation, suggesting a depolarizing effect of the drug on PFC neurons. Here, we report that systemic injection of d-amphetamine produced similar effects. Our evidence further suggests that norepinephrine (NE) plays a major role in the effects of d-amphetamine since they were mimicked by the NE reuptake inhibitors tomoxetine and nisoxetine and completely blocked by the alpha1 receptor antagonist prazosin. The effects of d-amphetamine persisted, however, in the presence of alpha2 or beta receptor blockade. Experiments with alpha1 subtype-selective antagonists further suggest that d-amphetamine's effects depend on activation of central, but not peripheral, alpha1A receptors. Unexpectedly, the putative alpha1 receptor agonist cirazoline failed to mimic the effects of d-amphetamine. Previous studies suggest that cirazoline is also an antagonist at alpha2 receptors. Furthermore, it is a partial, not full, agonist at alpha1B and alpha1D receptors. Whether or not these properties of cirazoline contribute to its failure to mimic d-amphetamine's effects remains to be determined. Methylphenidate and d-amphetamine are two most common medications for attention-deficit/hyperactivity disorder (ADHD). Both, however, are associated with adverse effects including abuse potential and psychotomimetic effects. Further understanding of their mechanisms of action will help develop safer treatments for ADHD and offer new insights into drug addiction and psychosis.