Roles of ATP and adenosine derivatives for frequency-dependent changes of synaptic connections, long-term potentiation (LTP) and long-term depression (LTD).

Abstract

Synaptic connections in the brain are functionally and morphologically changed depending on environmental stimuli. A "tracing circuit" model is proposed that a "tracing circuit" of neurons corresponding to human descriptive memory is established by synaptic competition and kept by the following sprouting and increase of the number of synapses in the circuit. The physiological roles of adenosine derivatives are considered to be agonists of two mechanisms of synaptic competition: lateral inhibition and central facilitation. Released ATP can facilitate novel synapse formation through ecto-protein kinase. A new hypothesis is proposed that the occurance of long-term potentiation (LTP) or of long-term depression (LTD) depends on the frequency of conditional stimulation and can be induced by different presynaptic adenosine receptors.