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Laboratory
of Neuroendocrinology and Avian Biology
Brain Research Institute, UCLA
Overview:
Sexual selection operates intensively in many bird species. To
visualize this intense selection pressure, one need only compare the
conspicuous and sometimes gaudy plumages of many male birds with the
inconspicuous cryptic plumages of most females. Males use these
ornaments as visual stimuli to attract and stimulate females. Some male
birds enhance this visual stimulation by performing unusual physical
movements: dancing or flying in front of females, inflating air sacs or
rasing individual feather groups. In some species, males also stimulate
and attract females using acoustic displays, using songs or calls or
generating sounds in unusual ways with the wings, tails or airsacs.
From an evolutionary perspective we can imagine why males and females
would develop such different, sexually dimorphic, traits and behaviors.
However, our lab is interested in the mechanisms underlying the
expression of these masculine and feminine anatomical and behavioral
characteristics. In many birds, these characters show remarkable
seasonal changes as well, indicating that birds are capable of
undergoing dramatic transformations periodically throughout life. The
internal signals sculpting these complex transformations must indeed be
powerful.
Steroid
hormones are powerful signalling molecules acting on many body tissues
at various stages in life to regulate a diversity of anatomical,
physiological and behavioral processes. During development steroids
produced by the gonads stimulate the sex specific growth of
reproductive structures. After sexual maturation is complete, the sex
steroids activate sex specific reproductive functions. All sex
steroids, the progestins, androgens and estrogens are derived from
cholesterol. A highly conserved set of enzymes catalyze the conversion
of cholesterol and steroidal substrates into the active signalling
molecules. The study of these enzymes, their location, and activity
tells us a great deal about te steroidogenic capacity and/or steroid
metabolic activity of different vertebrate tissues.
The central
nervous system is an especially important and fascinating target of sex
steroid hormones. Steroids have been shown to stimulate sexually
dimorphic growth of the brain, and then to act on the brain to
stimulate the performance of sexually dimorphic behaviors. The ways
that steroids act on the brain to control growth or cellular function
are diverse, acting on intracellular or on membrane receptors. The ways
in which steroids are made available to distinct neural circuits in
active forms is also quite complex. Steroids can be synthesized
peripherally or centrally and they may be transformed locally in
different brain regions into active or inactive forms.
The research
in my lab asks two questions:
1) How are steroids made available in active forms to distinct neural
circuits at appropriate periods of the animals life?
2) How have some neural circuits, but not others, become sensitive to
control by steroidal signalling molecules?
Experimental
Approaches: We study birds in the lab and in the field to explore
most of these questions, examining species that have evolved unique
behavioral strategies to optimize their reproductive potential.
Techniques regularly used by members of my laboratory include:
Biochemical assays of steroidogenic enzyme activity; steroidogenic
enzyme mRNA expression via Northern blots, rtPCR/Southern blots, in
situ hybridization; protein expression via immunocytochemistry and
Western blots; neuroanatomoical measures via light and flourescence
microscopy and image analysis, and steroid-autoradiography.
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