Hypothalamus

Question 1

What part of the hypothalamus is derived developmentally from the Telencephalon?

Answer 1

Lateral Preoptic Nucleus

Question 2

What region is traversed by many myelinated and unmyelinated axons of the medial forebrain bundle?

Answer 2

Lateral zone of the Hypothalamus

Question 3

What is the rest of the hypothalamus developmentally derived from? (aside from the Lateral Preoptic Nucleus)

Answer 3

Diencephalon

Question 4

What is the Lateral Hypothalamic Area involved in?

Answer 4

• Involved in the regulation of feeding behavior
  
  • ablation ⇒ anorexia and starvation

Question 5

What are the nuclei of the Lateral zone of the hypothalamus

Answer 5

1. Lateral Preoptic Nucleus
2. Lateral Hypothalamic Nucleus
3. Tuberomammillary/Lateral Tuberal Nucleus

Question 6

What does the Tuberomammillary/Lateral Tuberal nucleus release? Role of it?

Answer 6

• Histamine attention and arousal
  
  • just inhibited before you fall asleep

Question 7

What are the regions of the Medial Zone of the hypothalamus?

Answer 7

1. Preoptic
2. Anterior (Supraoptic)
3. Middle (Tuberal)
4. Posterior (Mammillary)

Question 8

What does the Preoptic region contain? What does this do?

Answer 8

• Contains the medial preoptic nucleus
• Houses neurons regulating gonadotropin secretion from the adenohypophysis (anterior pituitary)
• Also contains the interstitial nuclei of the anterior hypothalamus
  
  • one of which is sexually dimorphic
  • developmentally regulated by testosterone

Question 9

What subnuclei are contained in the Anterior (supraoptic) region and what does each do?

Answer 9

1. Suprachiasmatic nucleus (located at the base):
   
   • Receives collateral axons from optic nerve and regulates circadian rhythmicity
2. Anterior nucleus: Responds response to warmth
   
   • bilateral damage ⇒ hyperthermia
3. Paraventricular nucleus (located adjacent to the ventricle): Contains three distinct types of neurons
   
   1. Magnocellular = contain AVP OR oxytocin
   2. The other two types are parvocellular:
      
      • Release CRH at median eminence using portal veins to stimulate production of ACTH
      • Project to the spinal cord (hypothalamalspinal tract)
      • responsible for activating sympathetic arm of the ANS
4. Supraoptic nucleus:
   
   • Mini version of the magnocellular neurons of the Paraventricular nucleus, making either AVP or oxytocin

Question 10

What are the nuclei of the Middle/Tuberal region?

Answer 10

1. Dorsomedial Nucleus: BP regulation
2. Ventromedial Nucleus:
   
   • inhibits the urge to eat when stimulated
     
     • “satiety center”
   • neurons relay ingestion-related signals to the brainstem
   • bilateral destruction ⇒ eating
   • **Opposite as lateral hypothalamic area **
3. Arcuate Nucleus:
   
   • Controls release into portal vasculature of adenohypophyseal hormones
   • Produce hypothalamic releasing and inhibiting factors
   • Play a role in feeding behavior

Question 11

What are the nuclei of the Posterior/Mammillary region?

Answer 11

1. Posterior nucleus:
   
   • Cold-sensing neurons
   • Opposite as anterior nucleus
   • Conserve heat
2. Mammillary nucleus:
   
   • Receives major input from hippocampus
   • Involved in memory
   • lesions ⇒ short term memory loss

Question 12

What is the importance of the Periventricular zone of the hypothalamus?

Answer 12

• Cells lining the wall of the third ventricle, mostly at the supraoptic and tuberal levels (mid-levels)
• No functional designation
• Just convergent or overlapping with the other nuclei

Question 13

List the major tracts of the hypothalamus (7):

Answer 13

1. Fornix
2. Mammillothalamic tract
3. Stria terminalis
4. Medial forebrain bundle
5. Supraopticohypophyseal tract
6. Tuberoinfundibular tract
7. Hypothalamospinal tract

Question 14

Fornix:

Answer 14

• mammillary bodies of the hypothalamus receive a large axonal projection from the hippocampus via this pathway
  
  • Also contains axons that serve as inputs to the hippocampus from multiple brain regions

Question 15

Mammillothalamic tract:

Answer 15

• projects from the mammillary bodies (nuclei) to the anterior nucleus of the thalamus
  
  • a key component of the “Papez Circuit” of the limbic system

Question 16

Stria terminalis:

Answer 16

prominent pathway interconnecting the amygdaloid complex (i.e. amygdala) with the medial zone of the hypothalamus

Question 17

Median Forebrain Bundle:

Answer 17

• most complex fiber pathway in the CNS
  
  • contains at least 50 distinct constituent parts or pathways
• Extends throughout the entire lateral hypothalamic zone
  
  • ​interconnects regions from the septal nuclei (rostrally) to the brainstem (caudally)

Question 18

Supraopticohypophyseal tract:

Answer 18

• Conducts fibers from the supraoptic and paraventricular nuclei to the neurohypophysis
• Specifically, these are axons of the large (magnocellular) neurons
  
  • synthesize either AVP or oxytocin

Question 19

Tuberoinfundibular tract:

Answer 19

• Conducts fibers from the arcuate nucleus to the hypophyseal portal system at the median eminence of the infundibulum
• These axons carry neuropeptide releasing or inhibiting factors which act upon anterior pituitary cells
  
  • corticotrophs, lactotrophs, gonadotrophs, somatotrophs, thyrotrophs

Question 20

Hypothalamospinal tract:

Answer 20

• Contains descending axons that regulate spinal cord preganglionic neurons of both sympathetic and parasympathetic divisions
  
  • Originates primarily from the paraventricular nucleus
  • Damage may induce Horner’s Syndrome

Question 21

Major Regulatory Functions of the Hypothalamus (5):

Answer 21

1. Body Temperature
2. Feeding and Energy Metabolism
3. Emergency Responses to Stress
4. Blood Pressure and Electrolyte Composition
5. Reproductive Functions

Question 22

Describe the thermoregulation process in the anterior hypothalamus:

Answer 22

• Anterior hypothalamic nucleus (and portions of the medial preoptic area) contains neurons that are sensitive to warmth
  
  • trigger heat dissipation through multiple mechanisms:
    
    • including sweating, cutaneous vascular dilatation and accelerated respiration
  • activate portions of the parasympathetic nervous system
• Inflammatory cytokines and pyrogens also act in the anterior hypothalamus:
  
  • alter body temperature set points
  • initiate a disease-associated fever

Question 23

Describe the **thermoregulation **process in the posterior hypothalamus:

Answer 23

1. posterior hypothalamic nucleus contains neurons that are sensitive to cold
2. triggers heat conservation via sympathetic outflow
   
   • shivering, cessation of sweating, cutaneous vascular constriction
3. activation of appropriate endocrine (e.g. thyroid) responses to alter (increase) metabolic rate

Question 24

Which part of the brain has a major influence on thermoregulation nuclei?

Answer 24

limbic forebrain

Question 25

Heat dissipation and conservation are also accomplished by initiation of appropriate __________ responses

Answer 25

**behavioral** * seeking a warmer/colder environment

Question 26

What is the result of **bilateral destruction of the anterior hypothalamic area?**

Answer 26

**hyperthermia**

Question 27

What is the result of **bilateral lesions to the posterior hypothalamic nucleus and surrounding area?** Why does this happen?

Answer 27

**inability to thermoregulate altogether** * "poikilothermia" * **loss of both the cold-sensitive neurons in the region, and the descending projections of the warm-sensitive neurons** * **​**which course through the region en route to the brainstem

Question 28

Describe the role the hypothalamus plays in coordinating the "fight-or-flight" response:

Answer 28

* Neuroendocrine control of the release of: * stress hormones from the adrenal cortex * glucocorticoids * epinephrine and norepinephrine * adrenal medulla * **Sympathetic connections** with the viscera **initiate physiological changes:** * diversion of blood from the viscera to skin and muscles * increased cardiac output * pupillary dilation * bronchodilation * decreased GI motility and renal activity * **Parasympathetic activity is inhibited**

Question 29

Describe the **regulatory control** of the stress response:

Answer 29

* hypothalamus is under afferent regulatory control by numerous brain regions: * **pre-frontal cortex, limbic forebrain, and brainstem** * **integrates** signaling from these areas * **produce an appropriately coordinated set of responses** * **hippocampus and amygdala**, are extensively interconnected with the hypothalamus

Question 30

What areas of the hypothalamus have a role in **feeding/appetite and energy metabolism?**

Answer 30

1. **arcuate nucleus** * **​central role ** * located on the ventral surface of the hypothalamus at the middle or tuberal level 2. lateral hypothalamic area * feeding 3. ventromedial hypothalamic nucleus * satiety

Question 31

What sets of **neurons of the arcuate nucleus** are involved in feeding/metabolism?

Answer 31

**Two distinct sets:** 1. first set co-expresses two neuropeptides: 1. **agouti-related peptide (AgRP)** 2. **neuropeptide Y (NPY)** * **​​**have a number of **local hypothalamic projections** that serve to **signal increased feeding and a concomitant decrease in metabolism** 2. ​second set co-expresses and releases the neuropeptides: 1. melanocyte-stimulating hormone (MSH), a product of the cleavage of POMC 2. cocaine- and amphetamine-responsive transcript (CART) * synthesize and release and **act upon secondary hypothalamic neurons** * Activation of POMC/CART neurons signals **decreased feeding accompanied by increased metabolism** 3. Output from both sets of neurons is integrated in the brainstem * specifically in the NTS

Question 32

What other hormones act at the hypothalamus to modulate feeding?

Answer 32

1. **ghrelin** * released from the stomach just prior to a meal * act on the two sets of arcuate neurons to stimulate feeding 2. **PPY** (polypeptide Y) * released from the GI tract immediately following a meal * act on the two sets of arcuate neurons to inhibit feeding 3. Gastric distension and CCK release * produce satiety at the brainstem (NTS) level 4. **leptin** * released by fat cells * signals a decrease in feeding * insulin serves a similar function * inhibition of the AgRP/NPY neurons * stimulation of MSH/CART neurons

Question 33

**Craniopharyngioma:**

Answer 33

* **Congenital tumor** (usually calcified) * originating from remnants of Rathke’s pouch * Most common supratentorial tumor in children * **Pressure on optic chiasm** ⇒ **bitemporal hemianopsia** * **Pressure on overlying hypothalamus** ⇒ **“hypothalamic syndrome”:** * adiposity, diabetes insipidus, temperature regulation disturbances, and somnolence

Question 34

**Hypothalamic Memory Disturbances:**

Answer 34

* **posterior hypothalamic lesions involving mammillary bodies** * associated with **inability to form new memories** (episodic) for context- and time-specific events

Question 35

**Klein-Levin Syndrome:**

Answer 35

* **hypothalamic disorder primarily in adolescent males** * possibly autoimmune * hypersomnolence * episodic compulsive eating * hypersexuality * associated with **decrease in dopaminergic tone** during symptomatic phase