Perspectives on gender differences in food intake and frequency of disease

Dissociable effects of Sry and sex chromosome complement on activity, feeding and anxiety-related behaviours in mice

Whilst gonadal hormones can substantially influence sexual differentiation of the brain, recent findings have suggested that sex-linked genes may also directly influence neurodevelopment. Here we used the well-established murine ‘four core genotype’ (FCG) model on a gonadally-intact, outbred genetic background to characterise the contribution of Sry-dependent effects (i.e. those arising from the expression of the Y-linked Sry gene in the brain, or from hormonal sequelae of gonadal Sry expression) and direct effects of sex-linked genes other than Sry (‘sex chromosome complement’ effects) to sexually dimorphic mouse behavioural phenotypes. Over a 24 hour period, XX and XY gonadally female mice (lacking Sry) exhibited greater horizontal locomotor activity and reduced food consumption per unit bodyweight than XX and XY gonadally male mice (possessing Sry); in two behavioural tests (the elevated plus and zero mazes) XX and XY gonadally female mice showed evidence for increased anxiety-related behaviours relative to XX and XY gonadally male mice. Exploratory correlational analyses indicated that these Sry-dependent effects could not be simply explained by brain expression of the gene, nor by circulating testosterone levels. We also noted a sex chromosome complement effect on food (but not water) consumption whereby XY mice consumed more over a 24hr period than XX mice, and a sex chromosome complement effect in a third test of anxiety-related behaviour, the light-dark box. The present data suggest that: i) the male-specific factor Sry may influence activity and feeding behaviours in mice, and ii) dissociable feeding and anxiety-related murine phenotypes may be differentially modulated by Sry and by other sex-linked genes. Our results may have relevance for understanding the molecular underpinnings of sexually dimorphic behavioural phenotypes in healthy men and women, and in individuals with abnormal sex chromosome constitutions.

Role of hypothalamic monoamines in nicotine-induced anorexia in menopausal rats

BACKGROUND

Nicotine reduces body weight by reducing appetite. Estradiol modulates food intake. Menopause or ovariectomy (Ovx) increases food intake and body weight. Nicotine and estradiol individually influence hypothalamic dopamine (DA) and serotonin (5-HT), whose interaction influences food intake and body weight. We investigated whether lower weight gain in menopausal smokers is mediated via changes in hypothalamic DA/5-HT.

METHODS

Ovx or sham-operated female rats had 2 microdialysis guide cannulas simultaneously implanted in ipsilateral ventromedial nucleus of hypothalamus (VMN) and contralateral lateral hypothalamic area (LHA). Rats were divided into 4 groups and received a continuous subcutaneous infusion of nicotine or saline Ovx and sham. DA and 5-HT in LHA and VMN were measured by in vivo microdialysis.

RESULTS

Nicotine infusion decreased food intake and body weight in Ovx and sham groups. Increase in LHA-DA and VMN-5-HT in sham group occurred with nicotine, whereas an increase in VMN-DA in Ovx groups with and without nicotine and VMN-5-HT in Ovx group with nicotine was observed.

CONCLUSIONS

In the presence of estradiol (ovary intact sham-operated rats), nicotine lowers food intake and body weight via increased LHA-DA and VMN-5-HT. In menopause (Ovx rats), nicotine lowers food intake and body weight only via increased VMN-DA and 5-HT. Data show that lower weight gain is mediated via changes in hypothalamic monoamines, primarily via ventromedial hypothalamus.