Neuroendocrinology

Neuroendocrinology is the study of the interaction between the nervous system and the endocrine glands and their secretions. The study of neuroendocrinology spans across the globe as evidenced by neuroendocrine societies such as the International Neuroendocrine Federation and the American Neuroendocrine Society. Research is presented in journals such as Neuroendocrinology, Journal of Neuroendocrinology, and Hormones and Behavior. On June 14, 1917, the Association for the Study of Internal Secretions (currently the Endocrine Society) was founded to further investigate the field of endocrinology. Research in this field has led to a greater understanding of the human body, as evidenced by the 1977 Nobel Prize in Physiology and Medicine being awarded to Roger Guillemin and Andrew Schally for their work on the hypothalamus.

This field of study primarily encompasses the hypothalamus and pituitary glands and the corresponding organs that they regulate. The hypothalamus is located just below the thalamus and is a derivative of the diencephalons. This part of the brain is involved with many functions including maintaining an individual's circadian rhythm and regulating homeostasis. It receives multiple inputs from various parts of the brain including the brainstem and the limbic forebrain. It also receives feedback inputs such as gonadal steroids and glucocorticoids. The hypothalamus is responsible for releasing the following hormones: corticotrophin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), growth hormone releasing hormone (GHRH), somatostatin, thyrotropin-releasing hormone (TRH), hypocretin, antidiuretic hormone (ADH), and dopamine. In addition to releasing hormones, the hypothalamus sends projections to many areas of the brain via the medial forebrain bundle, the mammillotegmental tract, the dorsal longitudinal fasciculus, the mammillothalamic tract, the stria terminalis, and the fornix.

The pituitary gland resides in the pituitary fossa and is functionally connected to the hypothalamus via the median eminence. It is also responsible for maintaining homeostasis and regulating other endocrine glands via hormone secretions. Anatomically and functionally, it is divided into two lobes. The anterior lobe or adenohypophysis is derived from ectoderm and is responsible for regulating other endocrine glands via the release of hormones. It is regulated largely by the hypothalamus via the hypo-thalamic-hypophyseal portal system and by feedback mechanisms. The finding of this relationship was attributed to Geoffrey Harris in the early 20th century, who is now considered by most to be the father of neuroendocrinology. The anterior pituitary gland releases growth hormone, prolactin, follicle-stimulating hormone, luteinizing hormone, thyroid stimulating hormone, adrenocorticotropic hormone, and endorphins. The posterior pituitary lobe or neurohypophysis is connected to the hypothalamus via the infundibulum or tuberoinfundibular pathway. Oxytocin and antidiuretic hormone (vasopressin) are produced in the paraventricular nucleus and supraoptic nucleus of the hypothalamus, respectively. These hormones then travel down the infundibulum and are secreted from by the posterior pituitary gland.

Dysfunction or disease of the hypothalamus or pituitary gland can lead to pathologies affecting their target organs. These pathologies may either be due to an overproduction or underproduction of hormones. For instance, individuals with excessive growth hormone may suffer from acromegaly, a condition associated [Page 1225]with macrocephaly and coarse facial features. Conversely, an underproduction of growth hormone leads to growth hormone deficiency and shorter stature as well as other signs and symptoms. There may also be overproduction or underproduction of posterior pituitary hormones. For example, an overproduction of vasopressin may lead to the syndrome of inappropriate antidiuretic hormone (SIADH), while underproduction of vasopressin will cause diabetes insipidus.

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