Back to full list
|
|
Research Interests
Neuroendocrine Control of Reproduction
Research Summary
Research centers on investigations of the neural mechanisms controlling reproduction in seasonally breeding mammals. A complex and poorly understood interaction between environmental and endogenous signals (e.g. changes in daylength, steroid hormones) modulates the activity of a subset of neurons secreting the decapeptide, gonadotropin releasing-hormone (GnRH), to ultimately affect gamete production in both males and females. GnRH neurons and their projections to the median eminence represent the final common pathway in the neural control of reproduction for all vertebrates. To ensure that young are born at favorable times, temperate zone species have adapted a highly successful strategy of restricting reproductive activity to limited portions of the sidereal year. Changes in daylength (photoperiod) serve as the predominant factor responsible for causing reproductive transitions ('Nature's contraceptive') in many of these species. Yet, how the photoperiod signal is conveyed to the GnRH neurons remains a key unanswered question in the field. The bulk of evidence suggests that photoperiodic information (via the endocrine signal for daylength - melatonin) reaches GnRH neurons indirectly through neural inputs from other brain regions. Some of these neurons likely bind the ovarian steroid, estradiol, whose influence on the neuroendocrine axis varies with season and is considered a key processes responsible for causing seasonal reproductive variation. Because GnRH neurons themselves contain little, if any, gonadal steroid receptors a major thrust of the work involves identify estrogen-responsive neural systems that convey information indirectly to GnRH neurons. Using the sheep as a model, our goal is to advance a more unified hypothesis of the mechanisms underlying the seasonal control of reproduction by using neuroanatomical, molecular, and systems approaches.
Research Publications
Stefanovic I, Adrian B, Jansen HT, Lehman MN,
Goodman RL: (2000) The ability of estradiol to
induce fos expression in a subset of estrogen receptor a-containing
neurons in the ewe is dependent upon reproductive status.
Endocrinology 141:190-196.
Viguie C, Jansen HT, Glass JD, Watanabe M, Billings HJ, Coolen L, Lehman MN, Karsch FJ. ·2001) Potential for polysialylated form of neural cell adhesion molecule-mediated neuroplasticity within the gonadotropin-releasing hormone neurosecretory system of the ewe. Endocrinology. 142(3):1317-24.
Jansen HT, West C, Lehman MN, Padmanabhan V. 2001. Ovarian estrogen receptor-beta (ERbeta) regulation: I. Changes in ERbeta messenger RNA expression prior to ovulation in the ewe.Biol Reprod. 65(3):866-72.
Sleipness EP, Sorg BA, Jansen HT. 2005 Time of day alters long-term sensitization to cocaine in rats. Brain Res. 1065(1-2):132-7.
Jansen HT, Cutter C, Hardy S, Lehman MN, Goodman
RL. 2003 Seasonal Plasticity within the Gonadotropin-Releasing
Hormone (GnRH) System of the Ewe: Changes in Identified GnRH Inputs
and Glial Association. Endocrinology. 144(8):3663-76.
Romeo RD, Wagner CK, Jansen HT, Diedrich SL, Sisk
CL. 2002 Estradiol induces hypothalamic progesterone receptors but
does not activate mating behavior in male hamsters (Mesocricetus
auratus) before puberty. Behav Neurosci.116(2):198-205.