In comparison with the large number of studies that have examinedproperties of cells in the basolateral complex and centralnucleus, there are very few detailed studies of cells in theremaining amygdaloid nuclei.
A. Intercalated Cell Masses
The GABAergic intercalated cells (202) that lie in the fiberbundles between the basolateral complex (173) and the centralnucleus act as feed-forward interneurons to cells in the CeA,leading to the generation of a disynaptic inhibitory synapticpotential in these neurons following stimulation in the basolateralcomplex (47, 203, 239). There are two main types of neuronfound in the intercalated cell masses. The first, which accountsfor the vast majority of cells, has medium (
10–15 µm)ovoid cell bodies with spiny, largely bipolar dendritic treesand axons that send collaterals into the lateral, basal, andcentral nuclei (173). The other type are very large cells(50 µm) with very long thick spiny or aspiny dendritesthat travel in parallel to the borders of the basal, lateral,and central nuclei (173, 203). These two cell types are verysimilar to striatal neurons. Although detailed electrophysiologicalstudies of these neurons have not been reported, trains ofaction potentials in these neurons are followed by an afterdepolarization(ADP) lasting several seconds (240). Activation of this ADPimparts a heightened excitability to these cells. As the intercalatedcells inhibit neurons in the CeA, modulation of the activityof these neurons will have a significant impact on the outputof the CeA. In addition, intercalated neurons are connectedin local networks oriented in the lateral to medial directionsuch that activation of intercalated cells preferentially inhibitsneurons in the medial direction (241). This organization withinthe intercalated cell masses leads to a very specific controlof inhibition in the central nucleus as information passingthrough the basolateral complex activates different populationsof intercalated cells (241).
B. Medial Nucleus
The medial nucleus contains just one cell type that resemblesthe main neurons located in the CeM. They are small to medium-sizedovoid cells with two to four moderately spiny primary dendrites(156). There do not appear to be any local circuit neuronsin this structure. Neurons in the bed nucleus of the striaterminalis, which are similar to the main cell types found inthe medial and intermediate subdivisions of the central nucleus,have medium-sized somata and multipolar spiny dendrites (151).The anterior amygdaloid area contains cells that have ovoidsomata and three to four primary dendrites that branch sparinglyand have few spines (73). Thus they resemble the second classof neuron found in the CeM. The cell types observed in the nucleus of the lateral olfactory tract, the amygdalohippocampalarea, and the cortical nuclei are similar to those in the basolateralcomplex. The majority of the cells are pyramidal-like withsmaller stellate cells (which resemble the local circuit neurons),spiny stellate cells, and neurogliaform cells also presentto lesser degrees (156, 152). Orientation of neurons in theolfactory areas is more cortical-like with apical dendritesoriented parallel to each other. To our knowledge there havebeen no detailed studies of the electrophysiological propertiesof neurons in these other nuclei.
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