It is not surprising that chemicals may affect biological functions. In a new study, by Andrea Gore of the University of Texas on rats, has shown that PCB-induced brain changes delayed puberty in male offspring and disrupted reproductive cycles in the adult female offspring. Rats and humans are very similar biochemically in the hypothalmus whose functions influence reproduction which is what she studied. In addition, the researchers identified five genes that PCB disrupted. Gore said that all five are critical to the normal hypothalamic control of reproduction.

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The hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland.



The hypothalamus is responsible for certain metabolic processes and other activities of the autonomic nervous system. It synthesizes and secretes certain neurohormones and these in turn stimulate or inhibit the secretion of pituitary hormones. The hypothalamus controls body temperature, hunger, thirst, fatigue, sleep, and circadian cycles.



"By identifying five genes that are most perturbed by PCBs in the developing rat brain, we may one day be able to develop targeted interventions or therapeutics for reproductive problems, focusing on these molecular endpoints," Gore said.



PCBs were widely used as dielectric and coolant fluids, for example in transformers, capacitors, and electric motors. Due to PCBs' toxicity and classification as a persistent organic pollutant, PCB production was banned by the United States Congress in 1979 and by the Stockholm Convention on Persistent Organic Pollutants in 2001. Concerns about the toxicity of PCBs are largely based on compounds within this group that share a structural similarity and toxic mode of action with dioxin. Toxic effects such as endocrine disruption and neurotoxicity are also associated with other compounds within the group.



In this study, funded by the National Institutes of Health, the investigators exposed rats late in pregnancy to low levels of a mixture of PCBs, as one might encounter in the environment, Gore said. Control rats received an inactive substance. After birth, the offspring had monitoring throughout their life to determine if their reproductive development was disrupted. The research team also examined the brains of some of the animals at different ages to determine whether and how prenatal exposure affected gene expression in the hypothalamus.



Effects on gene expression depended on age, the scientists found. Effects were most profound on day 15 in the life of males and day 45 in females, corresponding roughly to childhood and just after puberty, respectively.



In females, PCB exposure also resulted in altered reproductive cycles in adulthood, and in males, puberty was delayed, compared with the offspring of nonexposed control rats.



Depending on age and sex, five genes in the hypothalamus were affected by PCB treatment. These genes are known to be very important for the control of reproduction. However, because the effects of PCBs on the brain were specific to age, sex and developmental stage, Gore suggested that PCBs might alter development of the hypothalamus, rather than just altering individual genes.



For further information see Exposure.



Hypothalmus image via Wikipedia.