Mechanisms of sex difference: a historical perspective

Emergence of sex differences in the development of substance use and abuse during adolescence

Substance use and abuse begin during adolescence. Male and female adolescent humans initiate use at comparable rates, but males increase use faster. In adulthood, more men than women use and abuse addictive drugs. However, some women progress more rapidly from initiation of use to entry into treatment. In animal models, adolescent males and females consume addictive drugs similarly. However, reproductively mature females acquire self-administration faster, and in some models, escalate use more. Sex/gender differences exist in neurobiologic factors mediating both reinforcement (dopamine, opioids) and aversiveness (CRF, dynorphin), as well as intrinsic factors (personality, psychiatric co-morbidities) and extrinsic factors (history of abuse, environment especially peers and family) which influence the progression from initial use to abuse. Many of these important differences emerge during adolescence, and are moderated by sexual differentiation of the brain. Estradiol effects which enhance both dopaminergic and CRF-mediated processes contribute to the female vulnerability to substance use and abuse. Testosterone enhances impulsivity and sensation seeking in both males and females. Several protective factors in females also influence initiation and progression of substance use including hormonal changes of pregnancy as well as greater capacity for self-regulation and lower peak levels of impulsivity/sensation seeking. Same sex peers represent a risk factor more for males than females during adolescence, while romantic partners increase risk for women during this developmental epoch. In summary, biologic factors, psychiatric co-morbidities as well as personality and environment present sex/gender-specific risks as adolescents begin to initiate substance use.

Rapid comparison of metabolites in humans and rats of different sexes using untargeted UPLC-TOFMS and an in-house software platform

Metabolite differences between sexes have rarely been observed in a global manner, but it has recently been made possible by the advancement in metabolomics techniques. In this study, untargeted ultraperformance liquid chromatography coupled to time-of-flight mass spectrometry and an in-house software platform were used for a rapid comparison of sex differences in urinary metabolites in humans and in urinary and serum metabolites in Sprague Dawley (SD) rats. In addition, the species differences of urinary metabolites between humans and SD rats were also observed. Principle component analysis showed that all the observed metabolite sex differences were more distinct in SD rats than in humans, indicating that the sex differences of human urinary metabolites is small compared with that of SD rats. In SD rats, the observed metabolite sex differences were more distinct in urine than in serum, indicating the importance of urine analysis for metabolomics studies. The species differences in the urinary metabolites of humans and SD rats were much more distinct than any of the observed sex differences. Many sex- and species-related markers were discovered and putatively identified. In both humans and SD rats, steroid metabolites appeared to constitute a major sex difference in urinary metabolites. This provides new proof of the special importance of steroid metabolites in sex differences from an untargeted metabolomics investigation, which is rare for sex differences. Contrary patterns involving adrenocortical activity appeared to exist between rodents and humans, which agrees with previous reports. In the serum metabolites of SD rats, sex differences in ascorbic acid or its isomer and pantothenic acid or its isomer, but not in steroid metabolites, were prominent. Human-specific α-N- phenylacetyl-l-glutamine and androsterone glucuronide were among the putative identities of the markers discriminating humans and SD rats. This study demonstrated the feasibility of an in-house software platform and provides metabolite-related information on sex and species differences.

Sex differences in the physiology and pharmacology of the lower urinary tract

Sexual dimorphism is not only noticed in the prevalence of many diseases, but also in multiple physiological functions in the body. This review has summarized findings from published literature on the sex differences of the pathophysiology and pharmacology of the lower urinary tract (LUT) of humans and animals. Sex differences have been found in several key areas of the LUT, such as overactive bladder, expression and function of neurotransmitter receptors in the bladder and urethra, and micturition patterns in humans and animals. It is anticipated that this review will not only evoke renewed interest for further research on the mechanism of sex differences in the pathophysiology of the LUT (especially for overactive bladder), but might also open up the possibilities for gender-based drug development by pharmaceutical industries in order to find separate cures for men and women with diseases of the LUT.