Dopaminergic and noradrenergic responses in the hippocampal slice preparation. Evidence for different receptors

The effects of iontophoretic applications of dopamine (DA) and noradrenaline (NA) on potentials evoked by the stimulation of the hippocampal slice preparations were investigated. Dopamine, ejected at the soma, produced an increase of the amplitude of the population spike of CA1 pyramidal cells; NA had an excitatory action on some responses, inhibitory on others. The field-excitatory postsynaptic potentials (EPSPs) were unaffected by ejection of DA and NA on the dendritic tree. Domperidone, a dopaminergic antagonist, blocked the increase of the population spike induced by DA, but was unable to antagonize noradrenergic responses. Timolol, a beta-adrenergic antagonist, blocked the excitatory action of NA, but did not modify either the effect of DA or the inhibition induced by NA. Phentolamine, an alpha-antagonist, antagonized only the inhibition induced by NA. These results indicate that DA and NA modulate the activity of hippocampal neurones by interacting on different receptors.