Last Tuesday evening approximately 100 people gathered at the New York Academy of Sciences to hear a talk on the neurobiology behind many of the sex differences found in men and women. The speaker was Dr. Donald W. Pfaff of Rockefeller University, well-known for his work in behavioral neuroscience and his studies on sex hormones.
Before the talk started, however, I was already impressed with the Academy’s presentation. Settling into a room boasting incredible Manhattan skyline views was a diverse group of individuals, all buzzing with excitement and anticipation for the event. Speaking with others I quickly concluded that this evening was drawing not only those interested in neuroscience, but those interested in women’s rights, autism, molecular biology, and numerous other relevant topics. Various ages and races abounded, and it was evident that this diverse group of people was brought together by a passion for information.
Dr. Pfaff, upon taking the podium, seemed as eager to provide this information as we were to receive it. The evening centered around the presentation of Dr. Pfaff’s recently published book “Man and Woman: An Inside Story of Neurobiology and Sex Differences.” He began the evening discussing the social implications of his work. The topic Dr. Pfaff will most likely receive high praise for is his “3 Hit Theory” of Autism Spectrum Disorders. Taking his cue from the 2 Hit Theory of cancer causation, Dr. Pfaff theorizes that in ASD there is not only the genetic and pre/neonatal stressors involved, but also androgenic hormones. These hormones can cause neuroanatomical sex differences which are controlled by the preoptic area in males and the medial basal hypothalamus in females. Males with ASD have been shown to have enlarged preoptic areas, presumably caused by an over absorption of testosterone in the prenatal period.
This led Dr. Pfaff into his next topic: the different ways in which he has been working with steroid hormone action. Much of Dr. Pfaff’s previous work has dealt with the absorption of hormones, and how this creates individual sex differences, or masculinization of the brain. During the administration of hormones one can simply raise hormone dosage, or they can raise tissue sensitivity, making hormone co-regulators more efficient. Dr. Pfaff introduced the possibility of “re-hooking” hormone responsive axons in order to make them more responsive to hormone absorption. This could make hormone therapy an easier ongoing process for individuals needing long-term treatment.
After this explanation, Dr. Pfaff, like a kid in a candy store, began to talk about new research he has done since the publication of his book; research on nucleosome remodeling. Dr. Pfaff’s research highlights that approximately 9% of the human brain contains nucleosomes which are specifically geared for sex differences. Through researching whether these nucleosomes continue to express gender differences at the genetic level throughout life, Dr. Pfaff began looking at the DNA around histone proteins. From this he has pinpointed how lysine and arginine can change inactive DNA into active nucleotides, which then allows estrogen dependent genes to turn on. This histone modification accounts for the sexual differentiation seen in the medial preoptic area for males, and the central medial hypothalamus in females. Future research can use these findings to better map specific genes which cause sex differences, and the period of development in which these genes are “on.”
After his talk Dr. Pfaff took questions, the nature of which again highlighted the diversity of the audience. Questions were asked about autism, women’s rights, and protein reproduction. Dr. Pfaff answered all to the best of his ability, and was generous enough to point people in the direction of his colleagues in order to better their understanding of anything he could not personally clarify. The evening hummed with a buzzing excitement of his findings, and I felt a sense of contentment that the study of sex differences is heading in directions that will help us better understand the opposite sex, as well as to help treat those with hormone maladies.
Kimberly Epperson is a full-time neuropsychology student in New York City who previously studied musical theater, and hopes to run a research clinic for mentally handicapped adolescents.