Noradrenergic System Increases Miniature Excitatory Synaptic Currents in the Barrel Cortex

Introduction: Neurons in layer II and III of the somatosensory cortex in rats show high frequency (33 ± 13 Hz) of miniature excitatory postsynaptic currents (mEPSCs) that their rates and amplitudes are independent of sodium channels. There are some changes in these currents in neurodegenerative and psychological disorders. Regarding to well known roles of the neuromodulatory brain systems in these disorders, study the effects of these systems on the miniature currents provides data to understand more precisely pathogenesis of this disorders. Because cortical neurons receive very dense noradrenergic innervations, we examined effects of noradrenergic system on these currents. Methods: Whole cell patch clamp recordings were made on pyramidal neurons of the barrel cortex from brain slices that continuously superfused with artificial cerebrospinal fluid (ACSF) containing tetrodotoxin, sodium channel blocker and picrotoxin, blocker of the GABA receptors. Results: Application of noradrenalin significantly increased frequency and decreased amplitude of the mEPSCs. Using specific agonists and antagonists of the noradrenergic system, it was determined that the effects are mostly mediated by α1 receptor. Conclusion: Our results showed that noradrenergic system controls sodium channel independent synaptic transmission which can be of importance in regulation and induction of many physiological and pathophysiological conditions.