Published by Miroslawa Manko, Raffaella Geracitano & Marco Capogna in the Journal of Physiology.
Abstract: Intercalated cells (ITCs) of the amygdala are clusters of GABAergic cells that surroundthe basolateral complex of the amygdala (BLA). Growing evidence suggests that ITCs are requiredfor the expression of fear extinction. The main intercalated nucleus (Im) is the largest of the ITCclusters and could also be important for emotional processing.We usedwhole-cell recordings fromIm neurons in acute slices of mouse amygdala.We found that these neurons were medium-sizedspiny projection cells. Their passive and active membrane responses were consistent with thosepreviously reported in other ITC clusters. The axon of Im neurons was, in many cases, cut atthe slice boundaries, suggesting long-range projections. Axonal branches could be detected inseveral amygdala nuclei where they made functional synapses. We also functionally studied Imcell inputs. Excitatory postsynaptic currents (eEPSCs) were evoked by the stimulation of theIm, intermediate capsula (IC), external capsula (EC) or BLA, when GABAergic transmission waspharmacologically blocked.An occlusion test indicated that fibres recruited by stimulating ImandIC, or Imand EC were distinct. These eEPSCs had both NMDA and AMPA receptor components.Inhibitory postsynaptic currents (eIPSCs) were evoked after the stimulation of the Im, the ECand the BLA, when glutamatergic transmission was pharmacologically blocked. Furthermore,dopamine reversibly hyperpolarised, and decreased the firing frequency and the input resistanceof Im cells via dopamine type 1 receptor. Our data suggest that the Im is functionally connectedto other amygdala nuclei and is under neuromodulatory influence.We propose that the Imservesas key neuronal substrate of fear extinction.