Estradiol rapidly increases GluA2‐mushroom spines and decreases GluA2‐filopodia spines in hippocampus CA1

Abstract

Hippocampal dendritic spine density rapidly increases following estradiol (E2) treatment, but the types of spines and trafficking of synaptic markers have received little investigation. We assessed rapid effects of E2 over time on the density of four spine types (stubby, filopodial, long thin and mushroom) and trafficking of AMPA receptor subunit GluA2 and PSD95 on tertiary, apical dendrites in CA1. Castrated male rats received 20 μg/kg of E2 or vehicle and were sacrificed 30 or 120 min later. Images of Golgi-Cox impregnated and PSD95/GluA2 stained dendrites were captured under the confocal microscope and quantified with IMARIS-XT. Stubby and filopodial spine densities did not change following treatment. Long-thin spines significantly decreased at 30 min while mushroom spines significantly increased at 120 min. GluA2, PSD95 and GluA2/PSD95 colocalization levels in stubby or long thin spines did not change, but filopodial spines had significantly reduced GluA2 levels at 30 min. Mushroom spines showed significantly increased levels for GluA2, PSD95 and GluA2/PSD95 colocalization at 120 min. Since GluA2 is important for memory consolidation, current results present novel data suggesting that trafficking of GluA2 to mushroom spines provides one mechanism contributing to estradiol's ability to enhance learning and memory by the PI3 signaling pathway.

Rapid effects on memory consolidation and spine morphology by estradiol in female and male rodents

“…The important attribute of post training protocols is that enhancements after immediate, but not delayed, post-trial injections show that the enhancing effects on memory do not derive from non-mnemonic effects such as psychological performance variables or learning since the treatments are given after the learning trial. Several labs, using post-training injections in recognition memory tasks, found that E 2 enhances consolidation of memory in OVX rodents when given immediately following T1 but not when given between 45 min to 2 h after T1 (Avila et al, 2017; Fernandez et al, 2008; Inagaki et al, 2012; Inagaki et al, 2010; Jacome et al, 2010; Lewis et al, 2008; Luine et al, 2003; Packard, 1998). The length of time required for memory consolidation varied depending on the dose of E 2 and the inter-trial delay between T1 and T2.…”

“…Micevych’s group has shown that the ability of E 2 to rapidly activate lordosis and increase dendritic spines in the arcuate nucleus is directly linked to mGluR1 receptors (Micevych and Christensen, 2012). Associations of mERs with ionotrophic glutamate receptors (iGluRs) have also been identified: AMPA receptors GluR1 in the prefrontal cortex (Khan et al, 2013), GluR2 in hippocampus (Avila et al, 2017) and NMDA receptors NR1 in cortex (Sellers et al, 2015a) and NR2 in the hippocampus have all been shown to be activated by mERs. Most of these associations with NMDA receptors have been tied to modulation of spine density, memory formation or other behaviors rapidly modulated by estrogens, but further studies are required to establish the connections.…”

“…In an attempt to better understand mechanisms underlying estrogenic effects on memory and spines, we applied Simultaneous Golgi-Cox Laser Scanning Confocal Microscopy and Immunohistochemistry (GC-IHC) to the brains of castrated males who received E 2 at 30 and 120 min before sacrifice (Avila et al, 2017). This dose and time enhances place memory and spine density in CA1 (Avila et al, 2017). Four spine types (stubby, filopodial, long thin and mushroom) were identified by Golgi impregnation.…”

“…The mature spines, long-thin (C) and mushroom (D) both show an overall effect of treatment (long thin; F (2,14) = 3.85, p = 0.046; mushroom F (2,15) = 4.38, p = 0.03 and a significant Tukey post-hoc test (long thin, vehicle vs E 2 30 min, p = 0.04; mushroom, vehicle vs. E 2 120 min, p = 0.03). Figure reprinted from Avila et al, 2017 by permission.…”

“…GluA2/PSD95 co-localization levels within mushroom spines shows an overall significant effect of treatment (F (2,14) = 4.78, p = 0.026) and a significant Tukey post-hoc test (E 2 30 min vs E 2 120, *p = 0.036). Figures reprinted from Avila et al, 2017 by permission.…”