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Sex Differences and Motivation

Women now account for approximately 40% of regular cocaine users. The increase in cocaine use, especially among young women, is a serious public health concern since women begin using cocaine at a younger age than men. Furthermore, women enter treatment after a shorter period of time, with more severe drug problems, and poorer psychological functioning than do men. Research in my laboratory is investigating how sex differences in the brain may underlie the sex differences in drug addiction. We are also interested in the role of ovarian hormones in expression of these sex differences and the mechanisms mediating the rapid effects of estradiol in the brain.

A little background: What is a sex difference in the brain?

The brains of mammals undergo sexual differentiation during development. In rats this occurs during the perinatal period, in humans during the second trimester. Exposure to androgens (which is converted to estrogen in some areas of the brain) during this sensitive period, influences neuronal survival, differentiation and connectivity. There may also be sex chromosome effects on development of mesencephalic dopamine neurons. As a result, the brains of gonadal hormones in the adult. Sex differences in the brain can be seen when males and females are compared after gonadectomy. In addition to the sexual dimorphisms caused by sexual differentiation, there may also be sex differences in brain function that are a result of sex differences in the gonadal hormones produced in the adult. This second type of sex difference can be due the effect of the gonadal hormones acting on the sexually dimorphic brain, or because males and females produce different hormones.

Why study sex differences in the brain?

Sexual differentiation results in permanent structural changes in the brains of male mammals that make them different from females (i.e., neuroplasticity). The study of the relations between brain morphology, neurochemistry, etc. and behavior in males vs. females is a strategy that has provided useful insights into structure-function relations in the hypothalamus. This approach can be applied to other neural systems as we come to better understand sex differences in non-reproductive behaviors, such as those induced by the psychomotor stimulants. Thus, sexual differentiation induces consistent individual differences in brain and behavior that can help us to better understand neuroplasticity and the neural mechanisms of behavior.

In addition, basic research on the role of gender/sex and ovarian hormones in the neurochemical and behavioral responses to acute and repeated exposure to cocaine is important to enhance our understanding of the underlying neural processes involved in sex differences in drug abuse. An understanding of the mechanisms through which ovarian hormones act in the brain is important in order to develop treatments for many disorders in which an individual’s gender and a female’s reproductive status and ovarian cycle may impact outcome. A long-term goal of mine is to identify the quantitative and qualitative changes in the brains of male and female rats associated with behavioral sensitization to psychomotor stimulants and to identify those changes necessary for the development or expression of addictive behaviors.