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The striatum is the main input stage of the basal ganglia receiving extrinsic input from cortex and thalamus. The striatal projection neurons (SPN) constitute 95% of the neurons in the striatum in mice while the remaining 5% are cholinergic and GABAergic interneurons. The cholinergic (ChIN) and low-threshold spiking interneurons (LTS) are spontaneously active and form a striatal subnetwork involved in salience detection and goal-directed learning. Activation of ChINs has been shown to inhibit LTS via muscarinic receptor type 4 (M4R) and LTS in turn can modulate ChINs via nitric oxide (NO) causing a prolonged depolarization. Thalamic input prefentially excites ChINs, whereas input from motor cortex favours LTS, but can also excite ChINs. This varying extrinsic input with intrinsic reciprocal, yet opposing, effects raises the possibility of a slow input-dependent modulatory subnetwork. Here, we simulate this subnetwork using multicompartmental neuron models that incorporate data regarding known ion channels and detailed morphological reconstructions. The modelled connections replicate the experimental data on muscarinic (M4R) and nitric oxide modulation onto LTS and ChIN, respectively, and capture their physiological interaction. Finally, we show that the cortical and thalamic inputs triggering the opposing modulation within the network induce periods of increased and decreased spiking activity in ChINs and LTS. This could provide different temporal windows for selective modulation by acetylcholine and nitric oxide, and the possibility of interaction with the wider striatal microcircuit., QC 20201210

This chapter reviews the unique microcircuits within the subdivisions of the amygdala. Microcircuits of the amygdala remain somewhat of an enigma. The amygdala itself is comprised of laterally located glutamatergic projection neuron structures, which are cortical-like, and medially located GABA projection neuron structures, which resemble neurons of the striatum. Within these are many nuclei and subnuclei that are distinguished on histologic, hodologic, and functional criteria. Significant progress has been made in understanding the organization of microcircuits in the lateral amygdala (LA) and central amygdala (CE), which play important roles in fear learning and fear memory, and the intercalated neurons (ITC), which regulate fear extinction. Emerging data indicate a structured excitatory microcircuit within the LA. Local axon collaterals of excitatory projection neurons are regulated by transverse modules of local GABA inhibition, which control excitation in the dorsal to ventral and ventral to dorsal planes. Bidirectional excitation in this plane may form recurrent networks that contribute to the temporal coordination of sensory signals integrated into the Lad network. Future work on amygdala microcircuits will continue to yield important data on how microcircuits regulate learning, memory, and behavior.