Caffeine attenuates Aβ-induced hippocampal dysfunction alongside changes in adenosine receptor-linked GABA handling and neuronal excitability.

Abstract

Synaptic and circuit dysfunction in the hippocampus is an early feature of Alzheimer's disease, involving disturbances at both excitatory and inhibitory synapses. Adenosine receptors (ARs) regulate hippocampal glutamatergic and GABAergic signaling. Caffeine, a non-selective AR antagonist, has well-established neuroprotective actions. We examined whether caffeine attenuates amyloid-β (Aβ)-induced changes in neuronal viability, GABA handling, intrinsic excitability and synaptic excitation/inhibition (E/I) balance, and whether these functional effects occur alongside changes in AR and GABA transporter 1 (GAT-1) protein abundance. Primary mouse hippocampal cultures were exposed to Aβ1-42 (1nM) and/or caffeine (0.1, 1, 25, and 50µM) for culture-based assays, whereas acute hippocampal slices were exposed to Aβ1-42 (100nM) and/or caffeine (25µM) during whole-cell patch-clamp recordings from CA1 pyramidal neurons. In cultures, Aβ increased neuronal death, confirming previous reports, and caffeine co-treatment attenuated this effect. Total GAT-1, A1R and A2AR protein levels were unchanged, whereas Aβ reduced neuronal A1R immunoreactivity; this reduction was not observed with caffeine co-treatment. Radiometric assays identified treatment-associated differences in 1-h 3H-GABA accumulation and basal 3H-GABA outflow, including a non-significant trend toward increased accumulation after Aβ exposure and reduced accumulation in the Aβ+caffeine condition. In slices, Aβ flattened the frequency-current relationship and transiently reduced the E/I ratio, whereas these changes were not observed during caffeine co-application; subsequent caffeine exposure restored firing output after 30min of Aβ exposure. Further experiments are required to establish if changes in A1R immunoreactivity or radiometric GABA handling contribute to the electrophysiological effects.