Sex Differences in Maturation and Attrition of Adult Neurogenesis in the Hippocampus

Abstract

Sex differences exist in the regulation of adult neurogenesis in the hippocampus in response to hormones and cognitive training. Here we investigated the trajectory and maturation rate of adult-born neurons in the dentate gyrus (DG) of male and female rats. Sprague-Dawley rats were perfused one, two or three weeks after BrdU injection, marking newly dividing cells.Adult-born neurons (BrdU/NeuN-ir) matured faster in males compared to females. Males had a greater density of neural stem cells (Sox2-ir) in the dorsal, but not in the ventral, DG and had higher levels of cell proliferation (Ki67-ir) than females. Males had a greater reduction in neurogenesis between one and two weeks after mitosis, while females showed similar levels of neurogenesis throughout. The faster maturation and attrition of new neurons suggests greater potential for neurogenesis to respond to external stimuli in males compared to females and emphasizes the importance of studying sex on adult hippocampal neurogenesis.(Fisher Scientific) solution for cryoprotection and remained in the solution until sectioning. Brains were sliced into 30 μ m coronal sections using a Leica SM2000R microtome (Richmond Hill, Ontario, Canada). Sections were collected in series of ten throughout the entire rostral-caudal extent of the hippocampus and stored in anti-freeze solution consisting of ethylene glycol, glycerol and 0.1M PBS at -20°C until immunostaining. Complete series of sections were immunohistochemically stained for BrdU/DCX and BrdU/NeuN to examine sex differences in the maturation timeline of new neurons, for Sox2 to examine the number of neural stem cells, and for Ki67 to examine actively dividing progenitor cells. In addition, the brain sections were double-stained for BrdU/Sox2 to examine changes of Sox2 expression over the three weeks after BrdU injection. Radioimmunoassay for 17β-estradiol and testosteronePrevious studies reported that 17β-estradiol increases cell proliferation in females but not males (Tanapat et al., 1999;Barker and Galea, 2008) and androgens can influence survival of new neurons in males but not females (Spritzer and Galea, 2007;Duarte-Guterman et al., 2019).Thus, we examined serum levels of 17β-estradiol and testosterone in females and males, respectively.Blood samples were stored at 4℃ overnight and centrifuged at 10g for 15 minutes to collect serum.Serum 17β-estradiol levels in female rats and serum testosterone levels in male rats were assayed using commercially available radioimmunoassay (RIA) kits from Beckman Coulter (Brea, USA) or MP Biomedicals (Santa Ana, USA) respectively. The sensitivity of the RIA kits was 0.75 ng/mL for 17β-estradiol and 0.03ng/mL for testosterone. The intra-and inter-assay coefficient of variation were <8.9% and <12.2% respectively for 17β-estradiol and <8.2% and <13.2% for testosterone.None of the females were in proestrus at the time of sacrifice. 4. Immunohistochemistry 4. 1. BrdU/NeuN, BrdU/DCX or BrdU/Sox2 double-stainingThe exogenous DNA synthesis marker, 5-bromo-2'-deoxyuridine (BrdU) is i...

Sex-Specific Effects of Early-Life Iron Deficiency and Prenatal Choline Treatment on Adult Rat Hippocampal Transcriptome

“…Choline activates the GRIN3A pathway in IDch male rats, whereas it was inhibited in ID male rat, suggesting choline could enhance activity of glutamatergic neurons to improve learning and memory function in the hippocampus. Choline supplementation may lower neurogenic potentials of neural stem cell pools via the SOX2/TCF7L2 gene network (54)(55)(56)(57), thus reducing the proliferation of neuroglia (Figure 4A). Unlike IDch males, choline supplementation did not rescue the active neuroinflammation in the ID female hippocampus, contributing to a lower expression of GRIN2A and 2B, and thus lower activity of glutamatergic system.…”

The Effects of Anesthesia on Adult Hippocampal Neurogenesis

“…It is unclear how propofol might affect males and females differently, but it could potentially be related to differences in the maturation rate of new granule neurons. Death of adult-born granule cells is normally undetectable after 28 days in male rats (Dayer et al, 2003), but a recent study in adult rats showed that maturation and attrition of new cells in the DG is prolonged in females relative to males (Yagi et al, 2019). A change in the maturation time course could shift or lengthen the window of susceptibility to a propofol-induced activity decrease in new neurons in females relative to males.…”