Do nigro-striatal neurones possess a discrete dendritic modulatory mechanism? Electrophysiological evidence from the actions of amphetamine in brain slices.

Dopamine released from dendrites of nigrostriatal neurones in the substantia nigra exerts an inhibitory action on these cells. However, the spatio-temporal characteristics of the action of dendritic dopamine is still unclear. The aim of the present study was to investigate the responses of these neurones in the guinea-pig to amphetamine, applied locally in the region of the distal dendrites in pars reticulata. During intracellular recording in vitro it was found that amphetamine hyperpolarizes the membrane and causes a decrease in the input resistance, probably by increasing a potassium conductance. This response was resistant to blockade of sodium channels but sensitive to dopamine depletion by reserpine and alpha-methyl-p-tyrosine. The response showed tachyphylaxis and proved to be highly dependent on the site of administration of amphetamine. It is concluded that the release and action of dopamine occurs locally, in a heterogeneous pattern, within the dendritic field of nigrostriatal neurones. The possibility is discussed that this phenomenon underlies a modulatory mechanism, localized in dendrites.