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Introduction to Histology of the Hypothalamic-Pituitary Axis
Department of Cell Biology, University of Oklahoma Health Science Center, Oklahoma City, Oklahoma
The hypothalamic-pituitary axis represents an important pathway in the control of the body’s endocrine
systems. As classically described, specialized groups of
neurons within the hypothalamus control the release of
a variety of hormones from the adenohypophysis (anterior pituitary gland), or release hormones directly into
the blood within the neurohypophysis (posterior pituitary gland). These hormones regulate the major metabolic and reproductive functions of the body.
Since the discovery of the dual origins of the pituitary
from diencephalon and oral ectoderm by Martin Heinrich Rathke in the early 1800s, much has been learned
concerning the anatomy and neurochemistry of the
neuronal relationships with the pituitary. However, the
very complex and dynamic nature of pituitary secretion
warrants a much more extensive examination of these
neural control systems.
Because this topic is very broad and new information
is being generated at a fast pace, it is not possible to
cover all the hypothalamic systems in detail. Rather
the goal of the topical issue ‘‘Histology of the Hypothalamic-Pituitary Axis’’ is to provide examples of the
modern anatomical approaches that are being used to
provide new information about specific (immunocytochemically-identified) hypothalamic-pituitary systems
from a comparative and functional perspective.
The first two papers deal with the gonadotropinreleasing hormone (GnRH) system. These neurons are
unique in that they are born within the nasal cavity and
migrate into the forebrain during development. Those
that reach the preoptic-hypothalamic area are responsible for controlling the secretion of luteinizing hor-
mone and follicle stimulating hormone from the pituitary gland. The neural activity of these neurons is
coordinated so that they all fire simultaneously to elicit
hormonal secretion. The first two papers address: (1)
what molecular guidance mechanisms subserve the
migration of GnRH neurons to the appropriate brain
areas during development (Schwanzel-Fukuda), and
(2) what structural mechanisms are involved in GnRH
neuron coordinated activity (Witkin).
The second set of papers covers a variety of hypothalamic neural systems related to the anterior and posterior pituitary, including those containing vasopressin,
oxytocin, gonadotropin-releasing hormone, and corticotropin-releasing hormone, among others. These papers
cover aging and comparative issues and specifically
address: (3) what age-related changes occur in hypothalamic neurons (Zhou and Swaab), and (4) how the
teleost adenohypophysis receives direct innervation
from hypothalamic neurons (Batten, Moons, and Vandesande).
Far from being comprehensive, this topical issue on
the ‘‘Histology of the Hypothalamic-Pituitary Axis’’
serves to highlight some recent advances in our knowledge regarding the complex relationship between the
brain and the master gland of the body. It also serves to
illustrate the wealth of information on this system still
awaiting discovery.
I wish to thank all the authors for their contributions,
and Dr. John E. Johnson, Jr., Editor-in-Chief of Microscopy Research and Technique, for his guidance and
support during the process of compiling this series of
topical papers.
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