The Action of Micro‐electrophoretically Applied 1‐3,4‐dihydroxyphenylalanine (Dopa) on Single Cortical Neurones

Abstract

1 The technique of microelectrophoresis was used in order to compare the actions of L-3,4-dihydroxyphenylalanine (DOPA) and noradrenaline on single neurones in the cerebral cortices of cats and rats. 2 DOPA could both excite and depress cortical neurones. Cells excited by DOPA were also excited by noradrenaline and cells depressed by DOPA were also depressed by noradrenaline. 3 In the case of both excitatory and depressant responses, DOPA appeared to be less potent than noradrenaline. 4 Responses to DOPA and noradrenaline could be antagonized by phentolamine and propranolol. Responses to acetylcholine were not affected. 5 Responses to acetylcholine, but not responses to DOPA, were antagonized by atropine. 6 The results indicate that locally applied DOPA may mimic the actions of noradrenaline on cortical neurones. Possible mechanisms for these effects of DOPA are discussed.

The PHARMACOLOGY OF ADRENERGIC NEURONAL RESPONSES IN THE CEREBRAL CORTEX: EVIDENCE FOR EXCITATORY Α‐ AND INHIBITORY Β‐RECEPTORS

“…The results with the adrenoceptor antagonists support our suggestion, based on the action of the agonists, that excitatory responses are mediated by a-, and depressant responses are mediated by /3-receptors. In agreement with previous findings (Johnson et al, 1969;Bevan et al, 1974a;Bevan et al, 1976a), we have found that the a-adrenoceptor blocking agents could reversibly antagonize excitatory responses to adrenoceptor agonists, while excitatory responses to ACh were not affected. On the other hand, depressant responses to adrenoceptor agonists seemed to be resistant to a-adrenoceptor blocking agents (see Figure 4).…”

“…The /-receptor blocking agents, however, were also capable of antagonizing excitatory responses. This finding is in agreement with previous reports (Johnson et al, 1969;Bevan et al, 1974a;Bevan et al, 1976a). This observation might seem to argue against our hypothesis that the excitatory responses are mediated by a-receptors.…”

“…(Johnson et al, 1969;Bevan et al, 1974a;Bevan et al, 1976a). This observation might seem to argue against our hypothesis that the excitatory responses are mediated by a-receptors.…”

“…The animals were anaesthetized with halothane (0.8-1.0%). Our methods for the surgical preparation of the animals and the manufacture of six-barrelled glass micropipettes for extracellular recording and microelectrophoretic drug application, have been described previously (Bradshaw, Roberts & Szabadi, 1973a;Bradshaw, Szabadi & Roberts, 1973b;Bevan, Bradshaw & Szabadi, 1976a). Micropipettes having tip diameters of 3-5 gim were used.…”

“…Some of these results have been presented to the British Pharmacological Society (Bevan, Bradshaw & Szabadi, 1976b of the animals and the manufacture of six-barrelled glass micropipettes for extracellular recording and microelectrophoretic drug application, have been described previously (Bradshaw, Roberts & Szabadi, 1973a;Bradshaw, Szabadi & Roberts, 1973b;Bevan, Bradshaw & Szabadi, 1976a (Bradshaw et al, 1973a,b We have also examined whether the a-adrenoceptor blocking agents can discriminate between excitatory and depressant responses to adrenoceptor agonists on the same cell. In these experiments, excitatory responses were evoked by phenylephrine, depressant responses were evoked by either IPNA or salbutamol, and phenoxybenzamine was used as the antagonist.…”