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females.
Additional neurons in the suprachiasmatic
nucleus regulate our daily rhythms and synchronize them to the light:dark
cycle. 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 (afferents) from other brain regions; these vary with
season. Interestingly, changes
in daylength also modulate the expression of various motivated behaviors,
including sexual activity and drug seeking, amongst others.
Our goal is to advance a more unified hypothesis of the neural
mechanisms underlying these seasonal adaptations.
Biographical Information
Heiko T. Jansen, Associate Professor in VCAPP, received his B.A. in Biology
from Franklin Pierce College, Rindge, NH. He received both his M.S. in
Pharmacology/Toxicology (1987) and Ph.D. in Physiology (1993) from the
University of Illinois at Urbana/Champaign, IL. From 1993-1997 he did
postdoctoral work at the University of Cincinnati and was awarded an NIH
post-doctoral fellowship. In 1997, he was appointed to the faculty at the
University of Cincinnati as Research Assistant Professor and also served as
a member of the Neuroscience Graduate Program. From 1997-1999, he also
served as an adjunct faculty member in the Biology Department of Xavier
University. He joined the Department of VCAPP at Washington State University
and the Neuroscience Graduate Faculty in the summer of 2000.
Recent Publications
Sleipness EP, Sorg BA, Jansen HT.
2007 Contribution of the suprachiasmatic
nucleus to day:night variation in cocaine seeking behavior.
Physiol. Behav.
91(5):523-30.
Jansen HT,
Kirby JD, Cooke PS, Arambepola N, Iwamoto GA.
2007 Impact of neonatal hypothyroidism on
reproduction in the male hamster, Mesocricetus auratus.
Physiol. Behav.
90: 771-81.
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.
Viguié C, Jansen HT,
Glass DG, Watanabe M, Billings HJ, Coolen LM, Lehman MN, Karsch FJ.: (2001)
Potential for PSA-NCAM-mediated neuroplasticity within the GnRH system of
the ewe. Endocrinology 142:1317-1314.
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