the abrupt transition from theta to hyper- excitable spiking activity in stellate cells from layer...

The abrupt transition from theta to The abrupt transition from theta to hyper-excitable spiking activity in hyper-excitable spiking activity in

stellate cells from layer II of the medial stellate cells from layer II of the medial entorhinal cortexentorhinal cortex

Horacio G. RotsteinHoracio G. RotsteinDepartment of Mathematical SciencesDepartment of Mathematical Sciences

New Jersey Institute of TechnologyNew Jersey Institute of TechnologyNetwork Synchronization: From dynamical systems to neuroscience Network Synchronization: From dynamical systems to neuroscience

Leiden (NL) - May 27, 2008Leiden (NL) - May 27, 2008

Collaborators

Tilman Kispersky Program in Neuroscience - Boston University

Nancy Kopell Math & Center for BioDynamics – Boston University

Martin Wechselberger Math – University of Sidney

John White Biomedical Engineering – University of Utah

Entorhinal Cortex & Hippocampus

Photomicrograph of a section through the rat hippocampal region (Gluck & Myers). Adapted from Amaral & Witter (1989).

Photomicrograph of a section through the rat hippocampal region (Gluck & Myers). Adapted from Amaral & Witter (1989)

Stellate cells (SCs)

Entorhinal cortex (EC) is the interface between the neocortex and the hippocampus.

Information flows from the neocortex to the hippocampus through the superficial layers (II and III) of the EC. SCs are the most abundant cell type in layer II of the EC.

SCs are putative grid cells.

Subthreshold oscillations (STOs)

SCs develop rhythmic STOs at theta frequencies (8 – 12 Hz).

Spikes occur at the peaks of STOs but not at every cycle.

Interaction between two currents: h- and persistent sodium.

Single cell phenomenon

Depolarization increases from 1 to 3 (Adapted from Dickson et al., J. Neurophysiol., 2000)

SCs: Theta regime (background)

SCs have intrinsic biophysical properties that endow them with the ability to display rhythmic activity in the theta frequency regime (8 – 12 Hz)

Subthreshold oscillations (STOs): interaction between a persistent sodium and a hyperpolarization-activated (h-) current.

Spikes

Mixed-mode oscillations (MMOs): STOs interspersed with spikes

R., Oppermann, White, Kopell (JCNS – 2005) R., Wechselberger, Kopell (Submitted) Focus issue on MMOs (Chaos 2008)

SCs – Hyperexcitable regime (this project)

SCs have intrinsic biophysical properties that endow them with the ability to display spiking activity in the “gamma” frequency regime (~60 Hz).

This time scale can be uncovered by phasic excitation.

The frequency regime depends on a combination of intrinsic and network properties.

Kispersky, White & R. , Work in Progress.

SC dynamic structure

Nonlinearities and multiple time-scales in the subthreshold regime:

How are they created?

How do they depend on the intrinsic SC biophysical properties?

How do they interact with synaptic (excitatory and inhibitory) inputs?

SC biophysical model

Subthreshold oscillations (STOs) and spikes in the SC model

STOs generated by persistent sodium channel noise in the SC model

Subthreshold Regime: Reduction of Dimensions

Multiscale analysis: Identification of the active and inactive currents Identification of the appropriate time scales

Subthreshold regime: reduced SC model

SC biophysical model Subthreshold regime


SC biophysical model Subthreshold regime

Nonlinear Artificially Spiking (NAS) SC model

Inhibitory inputs can advance the next spike by “killing” an STO.

Transition from theta to hyper-excitable (gamma) rhythmic activity

Experimental (in vitro) results:

There exist recurrent connections among SCs.

These connections are “similar” in normal (control) and epileptic cells.

Recurrent inhibitory circuits are reduced in epileptic cells as compared to normal (control) ones.

Recurrent circuits in layer II of MEC in a model of temporal lobe epilepsy. Kumar, Buckmaster, Huguenard, J. Neurosci. (2007)

Minimal S-I network model


A minimal S-S network reproduces the experimentally found transition form normal activity to hyper-excitability in SCs due to lack of inhibition


A minimal SIS network reproduces the experimentally found transition form normal activity to hyper-excitability in SCs due to lack of inhibition

Minimal SC network model (no inhibition)

A small increase in the SC recurrent synaptic conductance causes an explosion of the SC firing frequency


A small increase in the inhibitory input to the SCs brings their frequency back to the theta regime

Single SC + autapse (no inhibition)

The abrupt changes in the SC firing frequency are the result of phasic (synaptic) and not tonic excitation

Single SC model representing a population of synchronized (in phase) SCs.


Effects of changes in the maximal conductances

Single SC (no autapse - no inhibition)


Tilman Kispersky & John White

Dynamic clamp experiments


Voltage record of a stellate cell coupled to itself.

Inset: close up view of a single burst

Under control conditions


Voltage record of a stellate cell coupled to itself.

Inset: close up view of a single burst

Under linopiridine application (M-channel blocker)


Freq. vs. current under control conditions

Summary

SCs have intrinsic biophysical properties that endow them with the ability to display rhythmic activity in the theta and “gamma” frequency regimes (nonlinearities and time scale separation)

In “normal” conditions SCs display theta rhythmic activity (STOs and MMOs.

Abrupt transitions resulting from recurrent excitation.

Theoretical predictions confirmed by dynamic clamp experiments (Tilman Kispersky)

the abrupt transition from theta to hyper- excitable spiking activity in stellate cells from layer...

Documents

sc model slide

sc biophysical model

scs hyperexcitable regime

theta regime background

theta frequency regime

gamma frequency regime

project scs

rhythmic stos