Figure 4. Mixed-mode membrane oscillations in a single neuron.
(A) A non-cholinergic (putative GABAergic) cell in the rat medial septum displays rhythmic alternations at theta frequency between ‘clusters’ of spikes and epochs of sub-threshold membrane potential oscillations. (B) A model of GABAergic neurons in the medial septum. Upper: a membrane trace. The simulated oscillation is faster than the experimental data (see the different time scales), because the model simulation was done at body temperature (37°C), whereas the in vitro trace was recorded at 32°. Lower left: membrane potential versus the inactivation gating variable q for a low-threshold potassium channel (IKS). IKS gradually de-inactivates (increase of q, hence IKS) during the hyperpolarizing phases of spikes (arrows to the right), whereas it inactivates (decreasing q) during subthreshold membrane oscillations (arrows to the left). Lower right: the frequency of subthreshold oscillations (open circle) and intra-cluster spike firing rate (filled circle) co-vary as a function of the input current intensity. (C) Similar behavior of principal (mitral) cells of the rat olfactory bulb. Left: mixed subthreshold oscillation and clustered spike firing of a mitral cell in response to three current intensities. Right: frequencies of subthreshold oscillation and intra-cluster spike firing versus the mean membrane potential which was varied by current injection. (A) Reproduced with permission from [858]; (B) from [1031]; (C) from [231].