CHAPTER 17The Hypothalamus: Vegetative and

Endocrine Imbalance

General Features of Hypothalamic Function

• Controls visceral activity• Output of emotions from limbic system• Neural and endocrine functions exerted via

axonal pathways and vascular system• Functions include self-preservation (such as

eating and drinking) and preservation of the species (reproduction)

• Involved in water balance, food intake, endocrine control, reproduction, sleep, behavior, output of endocrine system

Hypothalamus: Inferior and Midsagittal Views

Coronal Sections Through the Hypothalamus

Hypothalamus: General Anatomical Features

• Very small area of brain, 4 g or about 0.3% of total

• Lamina terminalis rostral

border; mamillary bodies at caudal border

• Divided into 3 regions in rostral caudal axis:– anterior/supraoptic– middle/tuberal– posterior/mamillary

• Preoptic area rostral extends to septal region

Hypothalamus Has 3 Sagittal Zones

• Lateral Zone– lateral to fornix

– diffuse neurons

– medial forebrain bundle connecting HT, septum and brainstem

• MFB also functions in reward

– autonomic functions

• Medial and Periventricular Zones are divided up into several nuclei

Hypothalamic Nuclei By Region• Anterior region

– preoptic– supraoptic– paraventricular– anterior– suprachiasmatic

• Middle – dorsomedial– ventromedial– arcuate/tuberal

• Posterior– mamillary– posterior

Neural Inputs to the Hypothalamus

• Most neural inputs from limbic system:– hippocampus via fornix– amygdala via ventral amygdaloid path– orbitofrontal cortex– midline thalamic nuc– retina– medial forebrain bundle connects septal

area, lateral HT and brainstem– reticular formation sends sensory info

Humoral Inputs to the Hypothalamus

• Humoral input via vasculature– glucose, hormones– blood osmolality and

temperature• Circumventricular organs detect

changes in CSF and relay info to HT

Neural Outputs of the Hypothalamus

• Mamillary bodies to anterior thalamic nucleus (hippocampus projects to mamillary bodies via fornix)

• Midbrain reticular formation from medial forebrain bundle and mamillotegmental tract

• Amygdaloid nuclei via ventral amygdaloid path• Brainstem and spinal cord autonomic centers both directly

and via reticular formation– in the midbrain and rostral pons near periaqueductal gray and floor of

4th ventricle– lateral part of the reticular formation through the pons and medulla

Humoral Outputs of the Hypothalamus

• Direct secretion of hormones into the circulation

• Indirect by secretion of releasing factors into the hypophysial portal system that travel to the anterior pituitary

Direct Hormonal Secretion

• Magnocellular neurons in supraoptic and paraventricular nuclei

• Axons project to posterior pituitary• Release vasopressin and oxytocin• Vasopressin or anti-diuretic hormone acts

on kidney to increase water resorption • Oxytocin stimulates smooth muscle

contraction in uterus and mammary gland• Both also thought to be involved in other

neural functions such as pair bonding, maternal & sexual behavior, and learning

Indirect Hormonal Secretion

• Small neurons in mediobasal HT have axons projecting to median eminence

• Vessels in ME travel to anterior pituitary

• Hypothalamic regulatory hormones (releasing factors) are released into extravascular space, enter vessels and are carried to the anterior pituitary

• Control release of ant pit hormones including ACTH, growth hormone, FSH, LH, TSH, and prolactin

Hypothalamic Functions 1

• Body temperature: heat loss center in anterior HT (preoptic area)stimulates sweating and peripheral vasodilation, lesions cause hyperthermia; heat gain center in posterior HT stimulates cutaneous vasoconstriction, piloerection, shivering; lesions cause poikilothermy

• Food intake: ventromedial and paraventricular nuclei are satiety centers, lesion causes obesity; lateral HT stimulates food and water intake

Hypothalamic Functions 2

• Reproduction and sexual function: preoptic and ventromedial nuclei, estrogen and testosterone sensitive neurons control releasing factor neurons in mediobasal HT

• Tuberal and arcuate nuclei also involved in endocrine function

• Sleep/wake cycle: suprachiasmatic nuc is biological clock; preoptic nuc can initiate sleep; lat HT can change cortical arousal; post HT lesion can cause coma or impaired arousal

Hypothalamus Functions 3

• Emotions and behavior: ventromedial lesions can cause viciousness/rage

• Posterior HT stimulates sympathetic functions

• Anterior HT stimulates parasympathetic functions

• Mamillary nuclei: recent memory