ABSTRACT
The rat corpus callosum (CC) is larger in males than females, and is responsive to hormone manipulations during development. Previous data suggest that CC sensitivity to testosterone ends by postnatal day 8 (P8). In contrast, responsivity to ovarian hormones extends as late as P25. The current series of experiments investigates whether ovarian hormone effects on the callosum are permanent and whether CC sensitivity to ovarian hormones extends beyond P25. We found that P70 ovariectomy (Ovx) did not affect callosal size, suggesting that ovarian hormone exposure sometime prior to P70 is sufficient to feminize the CC, and that once the callosum is feminized, the effects can not be reversed. We also found that P25 ovariectomy enlarged, or defeminized, adult female CC, whereas ovary transfer starting on P55 or P70 counteracted this enlarging effect, resulting in feminized adult CC. Thus, although a previously feminized callosum is not affected by P70 ovarian hormone removal, a not-yet feminized callosum can still be feminized after P70. These findings indicate that there is flexibility in the developmental window within which the female brain is responsive to the active feminization process initiated by ovarian hormones.
Subject(s)
Corpus Callosum/growth & development , Estrogens/physiology , Ovary/physiology , Sex Differentiation , Age Factors , Animals , Corpus Callosum/anatomy & histology , Estrus/physiology , Female , Feminization/embryology , Feminization/physiopathology , Male , Organ Size , Ovariectomy , Ovary/transplantation , Rats , Rats, WistarABSTRACT
Perinatal gonadal hormones significantly affect subsequent sex differences in reproductive and non-reproductive behaviors in rodents. However, the influence of the sex chromosomes on these behaviors has been largely ignored. To assess the influence of the non-pseudoautosomal region of the Y chromosome, C57BL/JEi male and female mice and mice from the C57BL/6JEi-Y(POS) consomic strain were given behavioral tests known to distinguish males from females. The C57BL/6JEi-Y(POS) strain contains sex-reversed XY-females which, when compared to their XX-female siblings, allow assessment of the influence of the Y chromosome in a female phenotype. XX-females and XY-females did not differ on open-field activity, the Lashley maze, or active avoidance learning, but XY-females were significantly better than XX-females on the Morris hidden platform spatial maze. These findings suggest that males may have both a genetic and a hormonal mechanism to ensure visuospatial superiority.
Subject(s)
Behavior, Animal/physiology , Disorders of Sex Development , Sex Characteristics , Space Perception/physiology , Y Chromosome/physiology , Animals , DNA Primers , Estrogens/physiology , Female , Male , Maze Learning/physiology , Mice , Mice, Inbred C57BL , Myogenin/genetics , Phenotype , Polymerase Chain Reaction/methods , Testosterone/physiologySubject(s)
Brain Diseases/psychology , Cerebral Cortex , Choristoma/psychology , Maze Learning , Neocortex , Animals , Mice , Mice, Neurologic MutantsABSTRACT
The inbred 129 substrains have been characterized as poor learners that display hypoplasia of the corpus callosum. However, they are used extensively as a source of embryonic stem (ES) cells for creating mice carrying altered copies of a targeted gene ('knockout mice'). The present research investigated callosal agenesis and behavior in the 129/SvEvTac substrain and compared their behavior to that of C57BL/6J mice. In addition, the degree to which callosal agenesis affected behavior was assessed. Nearly 80% of 129/SvEvTac mice in the current sample exhibited callosal hypoplasia, although this was not subsequently found to be associated with any measure of cognition. They learned the Morris maze and a non-spatial pattern discrimination task, though at a level inferior to C57BL/6J mice. They were unable to learn shuttlebox avoidance or the Lashley III maze. The only measure on which they performed better than C57BL/6J mice was a simple water escape task. Thus, 129/SvEvTac mice, in addition to displaying aberrant neuroanatomy, perform poorly on many behavioral tasks, resulting in potential interpretational difficulties.
