The consumption of caffeine (an adenosine receptor antagonist) correlates inversely with depression and memory deterioration, and adenosine A 2A receptor (A 2A R) antagonists emerge as candidate therapeutic targets because they control aberrant synaptic plasticity and afford neuroprotection. Therefore we tested the ability of A 2A R to control the behavioral, electrophysiological, and neurochemical modifications caused by chronic unpredictable stress (CUS), which alters hippocampal circuits, dampens mood and memory performance, and enhances susceptibility to depression. CUS for 3 wk in adult mice induced anxiogenic and helpless-like behavior and decreased memory performance. These behavioral changes were accompanied by synaptic alterations, typified by a decrease in synaptic plasticity and a reduced density of synaptic proteins (synaptosomal-associated protein 25, syntaxin, and vesicular glutamate transporter type 1), together with an increased density of A 2A R in glutamatergic terminals in the hippocampus. Except for anxiety, for which results were mixed, CUS-induced behavioral and synaptic alterations were prevented by (i) caffeine (1 g/L in the drinking water, starting 3 wk before and continued throughout CUS); (ii) the selective A 2A R antagonist KW6002 (3 mg/kg, p.o.); (iii) global A 2A R deletion; and (iv) selective A 2A R deletion in forebrain neurons. Notably, A 2A R blockade was not only prophylactic but also therapeutically efficacious, because a 3-wk treatment with the A 2A R antagonist SCH58261 (0.1 mg/kg, i.p.) reversed the mood and synaptic dysfunction caused by CUS. These results herald a key role for synaptic A 2A R in the control of chronic stress-induced modifications and suggest A 2A R as candidate targets to alleviate the consequences of chronic stress on brain function.R epeated stress elicits neurochemical and morphological changes that negatively affect brain functioning (1, 2). Thus, repeated stress is a trigger or a risk factor for neuropsychiatric disorders, namely depression, in both humans and animal models (2, 3). Given the absence of effective therapeutic tools, novel strategies to manage the impact of chronic stress are needed, and analyzing particular lifestyles can provide important leads. Notably, caffeine consumption increases in stressful conditions (4) and correlates inversely with the incidence of depression (5, 6) and the risk of suicide (7,8). However, the molecular targets operated by caffeine to afford these beneficial effects have not been defined.Caffeine is the most widely consumed psychoactive drug. The only molecular targets for caffeine at nontoxic doses are the main adenosine receptors in the brain, namely the inhibitory A 1 receptors (A 1 R) and the facilitatory A 2A receptors (A 2A R) (9). A 2A R blockade affords robust protection against noxious brain conditions (10), an effect that might result from the ability of neuronal A 2A R to control aberrant plasticity (11, 12) and synaptotoxicity (13-15) or from A 2A R's impact on astrocytes (16) or microglia (17). T...
