Concomitant activation of D₁ dopamine and α_2A adrenergic receptors improves cognition compared with methylphenidate

Methylphenidate is commonly prescribed to manage symptoms of attention-deficit/hyperactivity disorder (ADHD), but like other stimulants it has limited effectiveness. Methylphenidate works by increasing the synaptic availability of dopamine and norepinephrine, resulting in stimulation of dopaminergic and adrenergic receptors. One hypothesis is that selective receptor targeting may be more effective clinically and have fewer side effects than non-selective stimulants.

To test this hypothesis, we compared methylphenidate with three compounds: the selective D_1/5 dopamine agonist 2-methyldihydrexidine; the selective α_2A adrenergic agonist guanfacine; and the cannabinoid compound cannabigerol that has α_2A agonist properties. Acute effects on temporal order memory, cognitive flexibility, and spatial working memory were evaluated using two rodent behavioral tasks.

Co-administration of an α_2A agonist and a D₁ agonist produced greater cognitive improvement than methylphenidate. The performance improvement from these selective agents, however, was only observed in rats that had poor performance at baseline.

These findings suggest that synergistic effects may emerge from the coadministration of selective agents (e.g., α_2A and D₁ agonists) and should be considered for further study, especially as regards individuals with decrements in cognitive function.