Descriptive findings on the morphology of dendritic spines in the rat medial amygdala

Abstract

The rat posterodorsal medial amygdala (MePD) is a brain area in which gonadal hormones induce notable plastic effects in the density of dendritic spines. Dendritic spines are post-synaptic specializations whose shape and spacing change neuronal excitability. Our aim was to obtain new data on the dendritic spines morphology and density from MePD neurons using the carbocyanine dye DiI under confocal microscopy. In adult male rats, the dendritic spine density of the medial branches of the left MePD (mean+/-SD) was 1.15+/-0.67spines/dendritic microm. From the total sampled, approximately 53% of the spines were classified as thin, 22.5% as "mushroom-like", and 21.5% as stubby/wide. Other spine shapes (3%) included those ramified, with a filopodium-like or a gemule appearance, and others with a protruding spinule. Additional experiment joining DiI and synaptophysin (a pre-synaptic protein) labeling suggested synaptic sites on dendritic shafts and spines. Dendritic spines showed synaptophysin puncta close to their head and neck, although some spines had no evident labeled puncta on them or, conversely, multiple puncta appeared upon one spine. These results advance previous light microscopy results by revealing features and complexities of the dendritic spines at the same time that give new insight on the possible synaptic organization of the adult rat MePD.

Morphological and Functional Features of the Sex Steroid-Responsive Posterodorsal Medial Amygdala of Adult Rats

“…These neurons are connected to specific hypothalamic nuclei and appear to modulate reproduction [82]. This homogeneity among MePD neurons might explain the low variability in soma size, soma volume, and dendritic spine density density described previously [30,37,65,78,83,84].…”

“…No single morphological characteristic is used to reliably identify these neurons [17,18,37,[78][79][80][81][82][83][84][85] Though gonadal hormone receptors are not present in all cells in the neural regions, the classic Golgi method cannot distinguish neurons that concentrate sex steroids from those that do not [78,81]. However, confocal immunofluorescent microscopy has revealed that transcription factor Lhx6-immunoreactive cells constitute approximately 80% of all neurons in the MePD [82].…”

“…Pleomorphic spines of a continuum of different shapes and sizes are found in the MePD in isolation or in small clusters [2,84]. Spines are classified morphologically as being thin, mushroom-like, stubby/wide, ramified, and other transitional aspects [84,93,99, see further detals in 94].…”

“…Spines are classified morphologically as being thin, mushroom-like, stubby/wide, ramified, and other transitional aspects [84,93,99, see further detals in 94]. In the MePD of adult Wistar males, thin spines are the most abundant (approximately 53%), followed by mushroom-like (22%) and stubby/wide ones (21%) [84].…”

“…Spines are classified morphologically as being thin, mushroom-like, stubby/wide, ramified, and other transitional aspects [84,93,99, see further detals in 94]. In the MePD of adult Wistar males, thin spines are the most abundant (approximately 53%), followed by mushroom-like (22%) and stubby/wide ones (21%) [84]. There is no difference in the density of proximal spines between bitufted and stellate neurons [30], percentage of the different dendritic spines in these cells [84] or spine density of the medial and lateral aspects of the MePD [30].…”