Noradrenaline sensitive cells in cat cerebral cortex

Noradrenaline, isoprenaline, 5-hydroxytryptamine, acetylcholine, glutamate and gaba have been applied iontophoretically onto spontaneously active cortical neurones in cats under different anaesthetic conditions. Neurones were predominantly excited by monoamines in halothane anaesthetised cats and encéphale isolé preparations, and excitation was still seen when careful controls for current, pH and anion effects were made.

Noradrenaline excitations were blocked selectively by α-adrenergic antagonists (dibenamine, thymoxamine and phentolamine) and β-adrenergic antagonists (propranolol, d-INPEA and sotalol) when responses to acetylcholine, 5-hydroxytryptamine and glutamate were unaffected. However, noradrenaline depressions were relatively resistant to these antagonists. Cells tested with both noradrenaline and isoprenaline invariably responded in the same direction, in contrast to cells tested with either noradrenaline and 5-hydroxytryptamine, or noradrenaline and acetylcholine.

The time-course of noradrenaline, isoprenaline and 5-hydroxytryptamine excitation was similar, though slower than that seen with acetylcholine. The time-course of depression was identical for all four substances. The latency of onset of noradrenaline and 5-hydroxytryptamine excitation, but not depression, was inversely related to the spontaneous neuronal discharge rate. Since most neurones discharged at a low rate, there was usually a long latency for monoamine excitation.