NEU 257
The diencephalon
• “between brain”
• Posterior part of embryonic forebrain
• Lies between brainstem and cerebral
• Includes: thalamus, hypothalamus,
subthalamus, epithalamus
Hypothalamus: General description
• Below rostral thalamus (hypo =“under”/”beneath)
• Vital regulatory functions include: temperature, heart
rate, blood pressure, blood osmolarity, goal seeking
behavior, emotional behavior, visceral nervous system,
sexual activity, food & water intake, aggression
• Forms floor and lower walls of third ventricle
• Contains various classes of peptidergic neuroendocrine
cells which control endocrine function
• Communicates with cortex via limbic system and also
via direct projections
Involvement with 3 major systems
• Endocrine system (HPA: hypothalamopituitary-adrenal axis)
• Autonomic nervous system
• Motivation system
….Also adaptive emotional behavior
Gross anatomy of the Hypothalamus
science.tjc.edu/ images/brain/Index.htm
Main Inputs to Hypothalamus
• receives info on external and internal
– specific sensory info (e.g., direct retinal projection)
- input from visceral senses (NTS: nucleus of the
solitary tract: taste)
– contains many neurons that are sensitive to local
temperature, osmolarity, glucose, sodium
– circulating hormones influence it via the
circumventricular organs
Retinohypothalamic tract
Circumventricular organs
•Brain regions near ventricles
that lack a blood-brain barrier,
e.g., subfornical organ, OVLT,
median eminence, area
•Highly vascularized
•Influenced by circulating
hormones, osmotic changes,
substances in CSF, afferent
fibers from other parts of the
nervous system
Peptidergic neuroendocrine cells:
Magnocellular neurons
• “Large” neurons
• Located in paraventricular and supraoptic
• Secrete oxytocin and vasopressin into
general circulation via posterior pituitary
• Oxytocin
uterine contraction & milk
• Vasopressin
vasoconstriction, water
resorption by the kidney
Magnocellular Secretory System
clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm
Peptidergic neuroendocrine cells:
Parvocellular neurons
• “small” neurons
• Located in medial basal region, arcuate and
tuberal nuclei, periventricular region, preoptic
and paraventricular nuclei
• Secrete releasing and inhibiting hormones
into portal vasculature via anterior pituitary
• Nobel prize awarded to Guillemin (Salk),
Schally and Yalow in 1977 for their
(independent) work in proving the hypothesis
that the hypothalamus releases hormones
that regulate the pituitary
Hypothalamic Portal System
clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm
Hypothalamic inhibitors
Hypothalamic hormone
Anterior pituitary hormone
Prolactin release-inhibiting hormone
(PIH), dopamine
Growth hormone release-inhibiting
hormone (GIH; somatostatin)
GH, thyrotropin
Melanocyte-stimulating hormone release
inhibiting factor (MIF)
Hypothalamic releasers
Hypothalamic hormone
Anterior pituitary hormone
Thyrotropin-releasing hormone
Thyrotropin, prolactin
Corticotropin-releasing hormone
Adrenocorticotropin, b-lipotropin
gonadotropin-releasing hormone
Growth-hormone releasing
hormone (GHRH)
Prolactin-releasing factor (PRF)
Melanocyte-stimulating hormonereleasing factor (MRF)
MSH, b-endorphin
Peripheral Influence of Hypothalamus
clem.mscd.edu/~raoa/ bio2320/endo1/sld003.htm
•Also known as “orexin”
•Peptide involved in arousal
and feeding behavior
•Project to thalamus, cortex
and brainstem regions
associated with arousal,
cardiovascular control, and
autonomic functions
•Few thousand neurons
•Loss of hypocretin neurons
implicated in human
From Thannickal et al., Neuron 27: 469, 2000