Early testosterone modulated sex differences in behavioral outcome following neonatal hypoxia ischemia in rats

Abstract

Hypoxia ischemia (HI; reduced blood oxygenation and/or flow to the brain) represents one of the most common injuries for both term and preterm/very low birth weight (VLBW) infants. These children experience elevated incidence of cognitive and/or sensory processing disabilities, including language based learning disabilities. Clinical data also indicate more substantial long-term deficits for HI injured male babies as compared to HI injured females. Previously, we reported significant deficits in rapid auditory processing and spatial learning in male rats with postnatal day 1 (P1), P7, or P10 HI injury. We also showed sex differences in HI injured animals, with more severe deficits in males as compared to females. Given these findings, combined with extant clinical data, the current study sought to assess a putative role for perinatal testosterone in modulating behavioral outcome following early hypoxic-ischemic injury in rats. Male, female, and testosterone-propionate (TP) treated females were subjected to P7 HI or sham surgery, and subsequently (P30+) underwent a battery of auditory testing and water maze assessment. Results confirm previous reports of sex differences following HI, and add new findings of significantly worse performance in TP-treated HI females compared to vehicle treated HI females. Post mortem anatomic analyses showed consistent effects, with significant brain weight decreases seen in HI male and TP-treated HI females but not female HI or sham groups. Further neuromorphometric analysis of brain structures showed that HI male animals exhibited increased pathology relative to HI females as reflected in ventricular enlargement. Findings suggest that neonatal testosterone may act to enhance the deleterious consequences of early HI brain injury, as measured by both neuropathology and behavior.

Inhibition of X-Linked Inhibitor of Apoptosis with Embelin Differentially Affects Male versus Female Behavioral Outcome following Neonatal Hypoxia-Ischemia in Rats

“…Given prior findings, a one-tail test was used [37,38]. This analysis revealed a significant effect of sex [F (1, 28) = 4.521, p < 0.03, one-tail], with male HI animals displaying poorer RAP abilities than female HI animals (fig.…”

“…Tests of RAP have been successfully developed for use in animal models, and such tasks reveal deficits in rodents with induced brain injuries including HI [22,23,24,25,26,37,38], microgyria and/or ectopia [27,28,29,30,31,32,33,34,35], and prenatal teratogenic exposure [36]. However, these models have never shown comparable deficits in female rodents with early injury [30,31,37,38], consistent with clinical data indicating poorer prognosis for male infants suffering HI as compared to matched females.…”

“…Embelin effectively inhibits XIAP by binding to its BIR3 domain (the binding site of caspase-9), rendering it inactive – and thus leading to a potential increase in cell death via the caspase-dependent pathway [66]. We specifically sought to assess the potentially modulating role of embelin following neonatal HI injury and found: (1) evidence of deleterious behavioral effects and increased pathology as a result of early HI injury in males, with no such effects in vehicle-treated HI female subjects (see earlier reports) [37,38]; (2) evidence of increased deleterious behavioral effects and increased pathology as a result of early HI injury in vehicle-treated HI males as compared to vehicle-treated HI females, replicating earlier reports [37,38], and (3) novel and exciting evidence that inhibition of XIAP (via embelin) prior to neonatal HI injury led to both an increase in behavioral deficits in embelin-treated HI females compared to vehicle-treated HI females, and an indication of a similar effect on neuropathology. No comparable effect of XIAP inhibition was seen in males.…”

“…Though it is evident that inhibition of XIAP had a detrimental effect on HI outcome for female animals, recent work exploring testosterone-modulated effects of neonatal HI injury also indicates that perinatal hormone levels (specifically testosterone) may contribute to sex differences in response to early brain injury [37]. Future studies will be needed to assess a potential interaction between the early (or concurrent) presence of specific hormones and activation of sex-specific apoptotic pathways, which may further relate to underlying baseline sex differences in cortical development [71].…”

“…Based on a priori hypotheses that differences would exist between male and female HI animals [37,38], as well as between vehicle-treated HI animals and embelin-treated HI animals, planned comparisons were performed between specific groups. This included separate analyses for sham and vehicle/embelin-treated HI males, sham and vehicle/embelin-treated HI females, and vehicle-treated HI and embelin-treated HI animals.…”