Noradrenergic action in the developing rat cerebellum: interaction between norepinephrine and gamma-aminobutyric acid applied microiontophoretically to immature Purkinje cells.

In this study, we examined the action of norepinephrine (NE) on developing cerebellar Purkinje cells. Responses of immature Purkinje cells to microiontophoretically applied NE were assessed both in terms of the direct depressant effect of the catecholamine as well as its ability to interact synergistically with gamma-aminobutyric acid (GABA). Sensitivity for NE, GABA, taurine and beta-alanine was found to be present by postnatal day 3. In addition, NE enhanced inhibitory responses of Purkinje cells to GABA but not those to beta-alanine by at least postnatal day 5, before periods of extensive morphological differentiation and synaptic investment. The modulation by NE persisted into adulthood with no qualitative changes in characteristics. The results of this study support and extend the hypothesis that 'chemosensitivity' antedates synaptogenesis' to include responsiveness of developing Purkinje cells to interactions between putative cerebellar neurotransmitters.