LHRH neurons express cFos on the afternoon of proestrus in association with the ovulatory LH surge. This study determined whether LHRH neurons express another proto-oncogene product, Jun, during the estrous cycle. By using immunocytochemical double staining techniques, localization of Jun proteins and LHRH was compared with expression of cFos in LHRH neurons. LHRH neurons expressed Jun proteins on the afternoon of proestrus with detection of Jun through the morning of cstrus. The time course of Jun expression in LHRH neurons during proestrus suggests a common stimulus for both Jun and cFos expression in LHRH neurons, with Jun proteins persisting somewhat longer than cFos. Pentobarbital, which blocks the preovulatory LH surge and cFos expression in LHRH neurons, blocked Jun expression in LHRH neurons; the LHRH neurons similarly expressed Jun and cFos on thp following afternoon at the time of the expected delayed LH surge. There was a similarity in the patterns (in terms of numbers and distribution) of Jun-positive and cFos-positive LHRH neurons. Both were, localized in the preoptic area and anterior hypothalamus; LHRH neurons above the anterior commissure or rostral to the OVLT did not express Jun or cFos. For the first time, these data provide direct evidence that both proto-oncogene products, Jun and cFos, are expressed in LHRH neurons in association with the proestrous LH surge. Taken together, these results suggest that changes in gene expression mediated by Jun-cFos hclcrodimcrs may accompany LHRH activation on the afternoon of proestrus.
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