Differential effects of the aging process on the morphology of the hypothalamic ventromedial nucleus of male and female rats

We investigated the effects of aging on the neuroanatomical sex dimorphisms of the rat hypothalamic ventromedial nucleus (VMN). Stereological methods were used to estimate the volume of the VMN and the total number and size o f its neurons, including their dendritic trees, in males and females aged 6 and 24 months. No cell loss was detected in aged rats. However, in aged fe males, the volume of the VMN and the somatic size of its neurons were incre ased, whereas in aged males the dendritic spine density was augmented. Due to these gender-specific effects, the male-female differences observed in t he morphology of the VMN in adult rats were annulled in aging. Our findings support the notion that some structural sex dimorphisms in the brain are n ot stable throughout the life span. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.