Hypothalamus (from cortex, thalamus and hypothalamus)

Question 1

What 3 groups may the hypothalamic nuclei be organized into?

Answer 1

Anterior group
Intermediate group
Posterior group

Question 2

What nuclei are in the anterior group? What are their functions?

Answer 2

1. Anterior nucleus (pre-optic area) - thermoregulation
2. SCN - clock
3. supraoptic/paraventricular nucleus - posterior pituitary secretion oxytocin & ADH)
4. arcuate nucleus - feeding control by POMC and AGRP (agouti-related protein) neurons that have receptors for many appetite-controlling hormones including, leptin, insulin, and pancreatic polypeptide
5. median eminence/infundibulum - where parvicellular neurons discharge release factors into the portal capillaries → e.g. CRF, GnRH, TRH and GHRH → stimulate anterior pituitary

Question 3

What nuclei are in the intermediate group? What are their functions?

Answer 3

1. Ventromedial nucleus – senses metabolites (glucose, free fatty acid); regulates feeding and
   metabolism; ‘satiety centre’; it is also linked to both aggression and sexual behaviour
2. Lateral nucleus – ‘hunger centre’
3. Dorsomedial nucleus – major target of the suprachiasmatic nucleus

Question 4

What nuclei are in the posterior group?What are their functions?

Answer 4

1. Posterior area (nucleus) – central control of sympathetic activation
2. Mammillary bodies – involved in the memory circuit

Question 5

In general, which part of the hypothalamus is responsible for release of hormones to the anterior pituitary? Which specific nuclei release which hormones?

Answer 5

The anterior hypothalamic nuclei
Arcuate → GnRH, GHRH DA
PVN → CRH, TRH

Question 6

Describe how the anterior nucleus is involved in thermoregulation

Answer 6

• pre-optic recieves axons from the parabrachial nucleus of the midbrain parabrachial nucleus of the midbrain reticular formation → a target of the spinoreticular tract that conveys peripheral temperature sensation from DRGs innervating the skin via the spinal cord and
  anterolateral fibre tract
• The pre-optic neurones of hypothalamus have
  TRPV1 receptors so are temperature-receptive

Thermoregulation is driven by sympathetic
outputs (vasculature, sweat glands, hair
smooth muscle)
- Heat loss: peripheral vasodilation, sweating, increased heart rate
- Heat conservation: peripheral vasoconstriction, piloerection, shivering

Question 7

Describe how the thalamus may control circadian rhythms

Answer 7

• melanopsin cells → optic nerve → SCN
• SCN neruoons show rythmic waves of activity which are governed by an intrinsic protein transcription clock - entrained by this retinal input
• Projections to the dorsomedial nucleus which drives circadian cycles in specific hypothalamic nuuclei associated with: thermoregulation, sleep, corticosteroids, feeding, wakefulness

Question 8

Describe how hypothalamus coordinates oxytocin and ADH secretion

Answer 8

SUPRAOPTIC/PARAVENTRICULAR NUCLEI INVOLVED 
Ferguson reflex (oxytocin) & during lactation in response to suckling 

• Hypothalamus contains osmoreceptors in the organum vasculosum of the lamina terminalis (OVLT) and sub-fornical organ (SFO) - in these regions the BBB is leaky, which exposes neurones to osmotic influx - shrinking and swelling - opens and closes stretch receptors of the TRPV family

Question 9

Describe control of food intake by hypothalamus

Answer 9

Arcuate nucleus has two population of feeding-associated neurons: POMC and AgRP:
-AgRP promote feeding
- POMC suppress feeding
The BBB in the arcuate nucleus is leaky, so peripheral hormones such as grehlin, leptin, insulin and
pancreatic polypeptide bind directly to these arcuate AgRP and POMC neurones

Question 10

Describe the mammillary bodies? What happens when they degrade?

Answer 10

Mammillary bodies, and their projections to the anterior thalamus via the mammillothalamic tract, are
important for recollective memory

Rare lesions of the mammillary bodies give complete retrograde amnesia – there are increasing
numbers of cases of Korsakoff’s syndrome, where degeneration of the mammillary bodies is associated
with alcoholism and thiamine deficiency

Question 11

Give an overview of the afferents to the hypothalamus

Answer 11

1. Sensory receptors
   - retina → SCN
   - olfactory → lateral nucleus feeding centre
   - cutaneus (indrect → pain&stress&nipple suckling)
   - visceral (via reticular formation and solitary tract)
2. Brainstem (locus coeruleus, raphe, periaqueductal grey)
3. Higher centres
   - hippocampal formation
   - amygdala
   - orbitofrontal cortex via mediodorsal thalamus

Question 12

Give an overview of the efferents from the hypothalamus

Answer 12

1. Endocrine control via posterior pituitary, and anterior pituitary via portal system
2. Descending control of autonomic centres in brainstem and spinal cord
3. Mammillothalamic tract → motor output

Question 13

Blood supply of hypothalamus

Answer 13

• from the internal carotid → gives superior and interior hypophyseal arteries
• inferior = posterior pituitary directly
• superior = hypothalamus including the CAPILLARY PLEXUS IN THE MEDIAN EMINENCE from which port veins pass to the anterior pituitary

Question 14

Where does the epithalamus lie?

Answer 14

Above the thalamus

Question 15

What is the epithalamus made up of?

Answer 15

the pre-tectal nucleus, the habenular

nuclei and the pineal gland

Question 16

Describe the pretectal nucleus

Answer 16

involved in pupillary constrictor response
– receives inputs from retina and projects bilaterally to
Edinger-Westphal nucleus via posterior commissure

Question 17

Describe the pineal gland

Answer 17

ssecreted melatonin in a circadian cycle

controlled by postganglionic sympathetic fibres

Question 18

Describe the lateral habenular nuclei

Answer 18

Relay nuclei which regulate serotonin and dopamine in the brainstem