Excitatory and inhibitory action of dopamine on hippocampal neurons in vitro. Involvement of D2 and D1 receptors.

The study examined the effects of dopaminergic agonists on the extracellularly recorded spontaneous activity of CA1 neurons in hippocampal slices of the rat. Dopamine evoked excitation or inhibition of the neuronal firing rate, the first reaction being more sensitive to the substance. Having used selective dopaminergic agonists (pergolide and 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepines) and selective antagonists (haloperidol, spiperone, sulpiride and (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3- benzazepine-7-ol), it was concluded that the excitation evoked by dopamine was due to activation of D2 dopamine receptors, while the inhibition was the result of D1 receptor activation. The effects of the dopamine agonists on the firing of CA1 neurons were long-lasting, which suggests a modulating role of dopamine in the hippocampus.