Model Of Stellate Cells Research Articles

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

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

A computer model of a cochlear-nucleus stellate cell: responses to amplitude-modulated and pure-tone stimuli.

A computer model of a ventral-cochlear-nucleus (VCN) stellate cell with chop-S type response properties is presented and evaluated. The model is based on a simplified model of spike generation preceded by a stage that simulates dendritic low-pass filtering. Input to the model is in the form of simulated auditory-nerve spikes produced by a model of the auditory periphery [Meddis and Hewitt, J. Acoust. Soc. Am. 89, 2866-2882 (1991)]. Outputs from the stellate-cell model are shown to qualitatively replicate a wide range of typical in vivo responses. These include: (a) realistic onset and steady-state rate-level functions, (b) "chopper"-type post-stimulus time histogram responses; (c) typical "chop-S"-type neuron responses characterized by a low coefficient of variance (CV less than 0.3) of interspike intervals as a function of time; (d) level-dependent amplitude-modulation transfer functions; (e) intrinsic oscillations in responses to pure-tone stimuli; (f) amplitude-modulation encoding over a wide dynamic range; and (g) frequency-limited phase locking to pure tones. It is shown that these responses can be explained primarily by the membrane properties of the cells. More specifically, how the model encodes signal amplitude modulation was studied and an explanation was suggested for the generation of the bandpass modulation transfer functions. Such functions are observed neurally in response to amplitude-modulated stimuli presented at moderate to high signal levels.