[Blocking action of adenosine and ATP on synaptic transmission in isolated slices of the rat brain]

Effects of ATP and adenosine on the background activity, orthodromic responses of single neurons and focal potentials were investigated in neocortex, hippocampus, fascia dentata and cerebellum slices in vitro. Both agents exerted a double action: excitatory and inhibitory. Excitation was observed only at large concentrations of ATP (10(-2)-10(-3)M), and it was insignificant for adenosine. It was apparently due to a direct depolarizing action of those agents on cell membrane. Similar inhibitory effects of both ATP and adenosine were observed at concentrations as low as 10(-6)-10(-7)M and were manifested in depression of evoked unit responses and their background activity at a presynaptic level. Hippocampal neurons proved to be the most sensitive to these agents, while the cerebellar neurons displayed the lowest sensitivity to them. Apamine did not effect the inhibitory action of ATP. The data obtained indicate that ATP and adenosine cannot be considered as central neurotransmitters. Their possible role as modulators of synaptic transmission in the CNS is discussed.