α2-Noradrenergic receptors activation enhances excitability and synaptic integration in rat prefrontal cortex pyramidal neurons via inhibition of HCN currents

Stimulation Of alpha 2-noradrenergic (NA) receptors within the PFC improves working memory performance. This improvement is accompanied by a selective increase in the activity of PFC neurons during delay periods, although the cellular mechanisms responsible for this enhanced response are largely unknown. Here we used current and voltage clamp recordings to characterize the response of layer V-VI PFC pyramidal neurons to alpha 2-NA receptor stimulation- alpha 2-NA receptor activation produced a small hyperpolarization of the resting membrane potential, which was accompanied by an increase in input resistance and evoked firing. Voltage clamp analysis demonstrated that alpha 2-NA receptor stimulation inhibited a caesium and ZD7288-sensitive hyperpolarization-activated (HCN) inward current. Suppression of HCN current by alpha 2-NA stimulation was not dependent on adenylate cyclase but instead required activation of a PLC-PKC linked signalling pathway. Similar to direct blockade of HCN channels, alpha 2-NA receptor stimulation produced a significant enhancement in temporal summation during trains of distally evoked EPSPs. These dual effects Of a2-NA receptor stimulation - membrane hyperpolarization and enhanced temporal integration - together produce an increase in the overall gain of the response of PFC pyramidal neurons to excitatory synaptic input. The net effect is the suppression of isolated excitatory inputs while enhancing the response to a coherent burst of synaptic activity.