Castration alters the number and structure of dendritic spines in the male posterodorsal medial amygdala

Abstract

The posterodorsal medial amygdala (MePD) is responsive to androgens and participates in the integration of olfactory/vomeronasal stimuli for the display of sexual behavior in rats. Adult gonadectomy (GDX) affects the MePD structural integrity at the same time that impairs male mating behavior. At the cellular level, dendritic spines modulate excitatory synaptic transmission, strength, and plasticity. Here, we describe the effect of GDX on the number and shape of dendritic spines in the right and left MePD using confocal microscopy and 3D image reconstruction. Age-matched adult rats were intact (n = 6), submitted to a sham procedure (n = 4) or castrated and studied 90 days after GDX (n = 5). The MePD neurons have a density of 1.1 spines/dendritic μm composed of thin, mushroom-like, stubby/wide, and few ramified or atypical spines. Irrespective of brain hemisphere, GDX decreased the dendritic spine density in the MePD, but induced different effects on each spine type. That is, compared to control groups, GDX reduced (i) the number (up to 50%) of thin, mushroom-like, and ramified spines, and (ii) the size and the neck length of thin spines as well as the head diameter of ramified spines. Besides, GDX increased the number of stubby/wide and atypical spines (up to 140% and 400%, respectively). These data show that GDX promotes a cellular and synaptic reorganization in a spine-specific manner in the MePD. By altering the number and shape of these connectional elements, GDX can affect the neural transmission and hinder the function of integrated brain circuitries in the male brain.

Remodeling of the number and structure of dendritic spines in the medial amygdala: From prepubertal sexual dimorphism to puberty and effect of sexual experience in male rats

“…The present methodological approach is similar to that reported by Zancan et al. ( and references therein).…”

“…In adulthood, sex differences in the density of dendritic spines (~30% higher in males than in cycling females in proestrus) and effects of ovarian hormones fluctuations (~30% reduction from diestrus to proestrus) are evident in the MePD of Wistar rats (Rasia‐Filho et al., ). Considering the MePD activity and connections in both sexes, these data can be related to the sequencing expression of the copulatory behavior in males and, in females, the disinhibition of sexual behavior concomitant with the increase in gonadotrophin‐releasing hormone secretion for ovulation (as reviewed in Rasia‐Filho et al., , and references therein; Zancan et al., ). It is noteworthy that the density of proximal spines in the MePD reduces following castration of postpubertal males (~20% after 90 days of the testes removal; de Castilhos et al., ).…”

“…Length was defined as the distance from the base at the dendritic shaft to the top of the spine or its neck; diameter was defined as the maximum distance perpendicular to the long axis of the spine and was measured for the neck or and the head of the spine (Ryu et al., ). Then, from the 3D reconstructed images, spines were classified and counted according to morphological criteria based on spine length (SL), neck length (NL), neck diameter (ND), head diameter (HD) and the number of protrusions from a single stalk (Dall'Oglio, Dutra, Moreira, & Rasia‐Filho, ; Zancan et al., and references therein). Based on their shapes, spines were classified into the following: (a) thin (when SL > HD and HD > ND), (b) mushroom‐like (HD ≫ ND), (c) stubby/wide (HD > SL), (d) ramified (with a single stalk that branches in two heads) or (e) atypical (when showing a transitional aspect between classes or an unusual shape not classified in the other classes (based on Arellano, Benavides‐Piccione, DeFelipe, & Yuste, ; Brusco et al., , ; Dall'Oglio et al., ; Harris et al., ; Stewart, Popov, Kraev, Medvedev, & Davies, ; Zancan et al., and references therein).…”

“…Morphometric data from up to 15 spines of each type in each studied dendrite were obtained after further enhancing (400×) the 3D reconstructed images. Similar sampling density (pixel size and z ‐step) and image acquisition procedures were held constant, and both blurring “pixelated” aspects of the spine borders were kept to as minimal as possible (Zancan et al., ). Measurements (in micrometers) were made on the “z” stack images that provided the best visualization of well‐defined borders of the spine and its components using the software Image Pro Plus 7.0 (Media Cybernetics, USA).…”

“…Spines are classified in different types which, based on region‐specific characteristics, can reflect their synaptic functions (Bourne & Harris, ; Harris, Jensen, & Tsao, ; Spruston et al., ; Tønnesen & Nägerl, ; Yuste, ). Dendritic spines in the rat MePD are pleomorphic (Brusco et al., ), and detailed morphometric data have recently unraveled additional features regarding the modifications in the spine number, shape and structure after adult male castration (Zancan et al., ). No such detailed data are currently available for the dendritic spines comparing the prepubertal differences between sexes or after puberty and sexual experience in the male rat MePD.…”