ドパミンによる海馬苔状線維シナプス伝達の増強

抄録

Dopamine is thought to play important roles in various brain functions including learning and memory. In the hippocampus, dopamine has been shown to modulate synaptic transmission and plasticity in the CA1 region. However, it remains largely unknown how dopamine affects synaptic transmission in the CA3 region where forms of synaptic plasticity distinct from those in the CA1 region have been demonstrated. In the present study, we show that application of dopamine reversibly potentiates synaptic transmission between the mossy fibers (MFs) and CA3 pyramidal cells. Pharmacological experiments showed that D1-like receptors mediate the potentiation induced by dopamine. This potentiation was accompanied by a decrease in the magnitude of synaptic facilitation and occluded by application of forskolin, an adenylate cyclase activator, suggesting the involvement of presynaptic cAMP-dependent mechanisms. The MF synaptic transmission is kept inhibited by tonic activation of presynaptic adenosine A1 receptors and GABA_B receptors. It is known that dopamine and adenosine counteract each other in some brain regions and that adenosine receptor antagonists can enhance effects of dopamine receptor agonists. At the MF synapse, application of an adenosine receptor antagonist alone, or together with a GABA_B receptor antagonist, enhanced the synaptic transmission, but suppressed the dopamine-induced potentiation. These results suggest that dopamine-induced presynaptic potentiation of the MF synaptic transmission is unmasked by the tonic presynaptic inhibition mainly mediated by adenosine. [J Physiol Sci. 2006;56 Suppl:S84]