Figure 4.

Illustration of the [Ca]_i location during depolarization of a thalamic cell to the level of fast membrane potential oscillations. (A) Fura-2 control fluorescent image of an iontophoretically filled neuron. (B) [Ca]_i image obtained from subtracting background fluorescence from recordings acquired during a depolarizing step to membrane potential level positive to the threshold for oscillation. Note the increase in [Ca]_i at dendritic level. (C) Diagram of the proposed thalamocortical neuronal circuit depicting the somatic and dendritic calcium conductances in thalamic neurons. A thalamic projection neuron is shown synapsing on a pyramidal cell at layer IV. The return pathway to the thalamus terminates mostly on the dendritic compartments of TCNs, where dendritic high-threshold calcium-dependent oscillations are observed (red). The corticothalamic input gives collaterals to the reticular nucleus (green) reinforcing thalamocortical resonance by inhibitory reset.