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Neuroendocrinology

Maya Lottati, DVM, PhD, DACVIM (SAIM)
TrueCare for Pets, Studio City, CA, USA

Neuroendocrinology refers to the orchestration between system and act as endocrine hormones on distant target
the nervous system and the endocrine system to main- tissues. The unique capability of the hypothalamus to
tain homeostasis by regulating various bodily functions convert neural signals into hormonal output is called
such as stress responsiveness, growth and development, neuroendocrine transduction.
and metabolism. To achieve homeostasis, the body Hypothalamic hormones enter the general circulation
appropriately senses and responds to alterations in the in one of two ways (Figure 5.1). Some hypothalamic hor-
external and internal environment through the modula- mones are transported along axons to the median emi-
tion of chemical messengers, or hormones. The key play- nence where they enter the portal circulation to reach
ers of the neuroendocrine system are the hypothalamus the anterior pituitary. Here, they stimulate or inhibit
and pituitary gland which are intricately linked via secre- anterior pituitary hormone release into the general
tory peptides and neuronal connections, as well as target circulation. Other hypothalamic nuclei have axons that
end‐organs (adrenal, thyroid, gonads, liver, and breast terminate at the posterior pituitary. These particular
tissue) whose role is to exert a physiologic response. hypothalamic hormones (e.g., vasopressin and oxytocin)
These players are integrated with one another through a are transported to the posterior pituitary where they can
series of feedback loops that allow controlled secretions be released into the general circulation. The intermedi-
of endocrine hormones throughout the body. In this way, ate lobe of the pituitary gland is under direct neural con-
the hypothalamus, pituitary gland, and target tissues trol by the hypothalamus.
regulate physiologic function. Alterations to these path- Hypophysiotropic hormones can be releasing or inhib-
ways and regulatory mechanisms may result in hormone itory in nature. The hypothalamic and pituitary hor-
disturbances that lead to disease processes. mones and their primary effects are listed in Table 5.1.

The Pituitary Gland
Anatomic Considerations of the
Hypothalamus and Pituitary System The pituitary gland is referred to as the hypophysis, and
it is situated beneath the hypothalamus at the base of the
brain. It is securely nestled within a depression of the
The Hypothalamus
sphenoid bone called the sella turcica whose shape is
The hypothalamus is a highly specialized region of the described as “saddle‐like.” The pituitary is composed of
posterior forebrain that is critical to regulation of vital an anterior lobe (AL; adenohypophysis) and a posterior
bodily functions, including temperature regulation, lobe (PL; neurohypophysis). Their diverse function is a
immune function, growth, stress responsiveness, water reflection of their distinct embryologic origin.
balance, sexual behavior and reproduction, and metabo-
lism. It is situated below the thalamus just above the Adenohypophysis and Intermediate Lobe
midbrain, and arises from the diencephalon during The adenohypophysis is the glandular portion of the
embryologic development. pituitary gland. During embryologic development, it
The hypothalamus is composed of neurosecretory arises from an ectodermal pouch (Rathke’s pouch) grow-
neurons that produce various peptide hormones and ing upwards from the oral cavity. In many mammalian
biogenic amines (dopamine), which enter the circulatory species, there is a distinct intermediate lobe (IL) that

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical