Excitatory effects of adenosine receptor agonists and antagonists on neurotransmission in guinea pig superior collicular slices

Abstract

Adenosine has excitatory actions on neurotransmission in the superior colliculus. To investigate whether adenosine A 1 or A 2 receptors are involved in mediating these excitatory actions, the effect of A 1 and A 2 receptor agonists and antagonists on the evoked postsynaptic potentials (PSP) in the superficial grey layer were tested using slices of the superior colliculus. Application of both A 1 agonists, such as CHA, R-PIA, and the A 2 agonist, CGS-21680 increased the amplitude of the PSP. The increase in PSP amplitude occured gradually over 20–30 min after application of these adenosine agonists. Application of the A 1 antagonist 8-CPT, and the A 2 antagonists, DMPX and CGS-15943, increased the amplitude of the PSP and could not antagonize the excitatory effect of adenosine. These results suggest that the mechanism of the excitatory effect of adenosine cannot be explained by the classical concept of A 1 and A 2 adenosine receptor subtypes which were identified by their effect on adenylate cyclase activity.