Gonadectomy before puberty increases the number of neurons and glia in the medial prefrontal cortex of female, but not male, rats

Abstract

The human prefrontal cortex, important for executive functions, loses gray matter throughout the adolescent period. In rats, our laboratory demonstrated that a loss of neurons between adolescence and adulthood partially underlies the loss of volume, and this loss is greater in females than males. Here, we examine whether being deprived of gonadal hormones before puberty through adulthood influences the number of neurons in the medial prefrontal cortex (mPFC). Prior to puberty, the testes or ovaries were removed in male and female rats. In adulthood, the number of neurons and glia in the mPFC were quantified using unbiased stereology, and the volume of the frontal white matter was measured. Prepubertal ovariectomy resulted in a higher number of neurons and glia and a larger volume of white matter compared to sham control littermates. Castrated males were not different from sham males on any measure. Thus ovarian hormones secreted after puberty influence the cellular composition of the medial prefrontal cortex.

Keywords: adolescence; gonadectomy; ovariectomy; prefrontal cortex; puberty.

Figure 1

The anatomical methods for counting cells. (a) A photograph illustrating the parcellation of the mPFC and the division into layers which is necessary for the calculation of volume. The white matter (WM) under the cortex is also labeled. (b) A photograph showing a neuron (N) and glial cell (G) under high magnification used for counting. (From Koss et al., 2012).

Figure 2

The number of neurons (a) and glia (b) (mean±SEM) in the mPFC. Significant differences were found between OVX females and sham control females in the number of both neurons and glia. No differences were found between GDX males and control males. *p<.05; **p<.01

Figure 3

The number of neurons and glia (mean±SEM) in the upper and lower layers of the mPFC. In the upper layers, no change in the number of neurons was found after male or female gonadectomy (a), but there was a significant difference in the number of glia between OVX and sham control females (b). In the lower layers, the number of both neurons (c) and glia (d) were significantly different between OVX and sham control females. GDX males were not affected by castration. *p<.05; **p<.01

Figure 4

The volume (mean±SEM) of the frontal white matter. OVX females had a larger volume than control females. No significant differences were found between castrated and control males. **p<.01