Module 10: Figure theta oscillatory mechanism
Hippocampal theta oscillatory mechanisms.
The inhibitory oriens-lacunosum moleculare (O-LM) cell (red) and the excitatory CA3 pyramidal neuron (green) interact with each other to form a network oscillator that is tuned to generate theta oscillations. The collateral axons of CA3 neurons release glutamate that depolarizes the O-LM cell whose axon terminals innervate the distal dendrites of the CA3 neurons to releases GABA, which then acts on GABAA receptors (GABAARs) to provide the inhibitory postsynaptic potentials (IPSPs) that hyperpolarize the membrane to temporarily curtail the firing of the CA3 neurons. Operation of this self-contained network oscillator is regulated by a tonic excitatory drive provided by the septal cholinergic input that releases acetylcholine (ACh), which acts through muscarinic 1 receptors (M1Rs). These metabotropic receptors appear to act by stimulating channels (dashed box) to provide a pacemaker depolarization that drives oscillatory activity. See the text for information on the different signalling mechanisms that control this network oscillator.