Endocrine Abstracts

Background: By providing a non-invasive, functional insight into brain chemistry, MRS has the potential to provide objective longitudinal data on mammalian brain development.

Aims: To assess the sexual dimorphism in rodent brain chemistry and development using in vivo MRS.

Methods: 26 (19 males) Sprague–Dawley rats were scanned at 6 weeks and 12 male rats at 10 weeks using a 7T MRI scanner. Testosterone concentrations were measured by ELISA and reproductive organs and brain tissue collected. Metabolites were expressed as a ratio to creatine and full width at half-maximum (FWHM) of the water peak was used as a guide to the reliability of the ratios.

Results: Median weight in 6 wk males, 6 wk females and 10 wk males was 197 g (142–230), 131 g (121–135) and 316 g (274–365) respectively. Median anogenital distance (AGD) in 6 wk males, 6 wk females and 10 wk males was 2.46 cm (1.89–2.9), 1.17 cm (1.04–1.19) and 3.25 cm (2.8–3.6). Median male serum testosterone at 6 and 10 weeks were 1.33 ng/ml (0.23–5.45) and 3.36 ng/ml (1.75–8.26). Median brain weight at 6 weeks in three male and three female rats was 1.84 g (1.8–1.84) and 1.78 g (1.75–1.8). Median prostate weight at 6 and 10 weeks in 3 and 12 male rats was 0.22 g (0.20–0.47) and 0.56 g (0.44–0.76). Median testes weight at 6 weeks was 0.83 g (0.8–0.94). Median phallus weight at 6 weeks was 0.12 g (0.11–0.14). 14 metabolites were identified in the occipitofrontal cortex. FWHM range was 12–38 Hz. In the 6 wk male rats, myo-inositol ratios showed a positive association with testosterone levels (P=0.04), and AGD was correlated with phosphocreatine (P=0.033) and glutamate (P=0.045). In addition, there was an increase from 6 to 10 weeks in three metabolite ratios: taurine (P=0.025), myo-inositol (P=0.012) and phosphocholine (P=0.005).

Conclusions: MRS is a reliable tool for studying the brain in maturing rats and may be a useful tool for studying the link between longitudinal changes in sex steroids and brain development.

Declaration of funding

Yorkhill Children’s Foundation Charity.