Cellular components of the human medial amygdaloid nucleus

Abstract

The medial nucleus (Me) is a superficial component of the amygdaloid complex. Here we assessed the density and morphology of the neurons and glial cells, the glial fibrillary acidic protein (GFAP) immunoreactivity, and the ultrastructure of the synaptic sites in the human Me. The optical fractionator method was applied. The Me presented an estimated mean neuronal density of 1.53 × 10⁵ neurons/mm³ (greater in the left hemisphere), more glia (72% of all cells) than neurons, and a nonneuronal:neuronal ratio of 2.7. Golgi-impregnated neurons had round or ovoid, fusiform, angular, and polygonal cell bodies (10-30 μm in diameter). The length of the dendrites varied, and pleomorphic spines were found in sparsely spiny or densely spiny cells (1.5-5.2 spines/dendritic μm). The axons in the Me neuropil were fine or coarsely beaded, and fibers showed simple or notably complex collateral terminations. The protoplasmic astrocytes were either isolated or formed small clusters and showed GFAP-immunoreactive cell bodies and multiple branches. Furthermore, we identified both asymmetrical (with various small, clear, round, electron-lucent vesicles and, occasionally, large, dense-core vesicles) and symmetrical (with small, flattened vesicles) axodendritic contacts, also including multisynaptic spines. The astrocytes surround and may compose tripartite or tetrapartite synapses, the latter including the extracellular matrix between the pre- and the postsynaptic elements. Interestingly, the terminal axons exhibited a glomerular-like structure with various asymmetrical contacts. These new morphological data on the cellular population and synaptic complexity of the human Me can contribute to our knowledge of its role in health and pathological conditions.

The human medial amygdala: structure, diversity, and complexity of dendritic spines

“…The selection criteria were the same described in Dall'Oglio et al. (), and included adult men with no violent cause of death and no neurological infectious diseases or stroke. Clinical data and information regarding prior comorbidities were obtained by direct interviews with the family members or legal representatives.…”

“…() and Bolam (), and adapted for the human nervous tissue by Dall'Oglio et al. (, ). Briefly, bilateral brain blocks of the anterior temporal lobe (cases 1 to 3, Table ) were sectioned to approximately 1.5 cm 3 to contain the Me.…”

“…The human amygdala is a group of nuclei with different cytoarchitectonical, connectional, and functional features in the subcortical part of the dorsomedial pole of the temporal lobe, rostral to the hippocampus, and close to the inferior margins of the claustrum, putamen, and globus pallidus (Brodal, ; Everitt, ; de Olmos, ; Yilmazer‐Hanke, ; Dall'Oglio et al. ; Janak & Tye, ). The medial nucleus of the amygdala (Me) has a superficial position and an irregular shape in the rostrocaudal axis, located lateral to the optic tract and at the fundus of the endorhinal sulcus (Everitt, ; Gloor, ; de Olmos, ; Yilmazer‐Hanke, ), and forming a continuum with part of the bed nucleus of the stria terminalis (BST) in monkeys and humans (Martin et al.…”

“…The definitive subdivision of the human Me has not as yet been established (Dall'Oglio et al. and references therein).…”

“…Output projections reach the medial areas of the BST, the medial preoptic area and the anterior medial hypothalamus, including the paraventricular and supraoptic nuclei as well as the hypothalamic ventromedial, the dorsal and ventral premammillary nuclei, and the midline thalamic nuclei (Everitt, ; Freese & Amaral, ; reviewed in Dall'Oglio et al. ).…”