Excitation of rat prefrontal cortical neurons by dopamine: an in vitro electrophysiological study

The effects of dopamine (DA) on prefrontal pyramidal neurons were studied in vitro on rat cerebral cortex slices using intracellular recordings. Pyramidal neurons were first identified by Lucifer yellow and some of their basic bioelectrical properties were analysed. At resting potential, white matter stimulation mainly evoked depolarizing inhibitory postsynaptic potentials (IPSPs) which reversed between -60 and -50 mV and were almost totally abolished by bicuculline. Furthermore, pyramidal cells often exhibited spontaneous depolarizing IPSPs abolished by bicuculline. Under tetrodotoxin (TTX) this synaptic noise was partly blocked suggesting that it was due both to the spontaneous firing of presynaptic gamma-aminobutyric acid (GABA)ergic neurons and to a spontaneous quantal release from these afferent fibers. In pyramidal cells, DA enhanced the number of spikes evoked by depolarizing current pulses, and the input resistance was increased by 10-20%. DA also clearly increased the inhibitory synaptic noise. This effect was blocked by fluphenazine. In contrast, evoked IPSPs were not consistently affected by DA. Taken altogether, these results suggest, that in the prefrontal cortex, dopamine has a mild excitatory effect on both pyramidal cells and GABAergic interneurons impinging on them.