Neurophysiology 1 Contribution of near - threshold currents to intrinsic oscillatory activity in rat medial 2 entorhinal cortex layer II stellate cells

29 30 The temporal lobe is well known for its oscillatory activity associated with exploration, 31 navigation and learning. Intrinsic membrane potential oscillations (MPOs) and resonance 32 of stellate cells (SCs) in layer II of the entorhinal cortex are thought to contribute to 33 network oscillations and thereby to the encoding of spatial information. Generation of 34 both MPOs and resonance relies on the expression of specific voltage-dependent ion 35 currents such as the hyperpolarization activated cation current (IH), the persistent sodium 36 current (INaP) and the non-inactivating muscarine-modulated potassium current (IM). 37 However, the differential contributions of these currents remain a matter of debate. We 38 therefore examined how they modify neuronal excitability near threshold and generation 39 of near-threshold MPOs and resonance in vitro. We found that resonance mainly relied 40 on IH, was reduced by IH blockers and modulated by cAMP and an IM enhancer, but that 41 neither of the currents exhibited full control over MPOs in these cells. As previously 42 reported, IH controlled a theta frequency component of MPOs such that blockade of IH 43 resulted in less regular oscillations that retained low frequency components and high peak 44 amplitude. However, pharmacological inhibition and augmentation of IM also affected 45 MPO frequencies and amplitudes. In contrast to other cell types, inhibition of INaP did not 46 result in suppression of MPOs but only in a moderation of their properties. We 47 reproduced the experimentally observed effects in a single compartment stochastic model 48 of SCs providing further insight into the interactions between different ionic 49 conductances. 50