Adenosine induces initial hypoxic-ischemic depression of synaptic transmission in the rat hippocampus in vivo

The present study was designed to investigate the role of adenosine in the hypoxic depression of synaptic transmission in rat hippocampus. An in vivo model of hypoxic synaptic depression was developed in which the common caro tid artery was occluded on one side in the urethane-anesthetized rat. Inspi red oxygen levels were controlled through a tracheal cannula. Rats were pla ced in a stereotaxic apparatus for stimulation and recording of bilateral h ippocampal field excitatory postsynaptic potentials. The percent inspired o xygen could be reduced to levels that produced a reversible and repeatable depression of evoked synaptic transmission restricted to the hippocampus ip silateral to the occlusion. Further reduction in the level of inspired oxyg en depressed synaptic transmission recorded from both hippocampi. The adeno sine nonselective antagonist caffeine and the A(1) selective antagonist 8-c yclopentyltheophylline prevented the initial depression in synaptic transmi ssion. We conclude that the initial depression of synaptic transmission obs erved in the rat hippocampus in vivo is due to endogenous adenosine acting at neuronal adenosine A1 receptors.