2019B13 Briefly outline the roles of the hypothalamus.

Anterior stimulation

·      Depressor area -> PSNS response

Posterior stimulation

·      SNS response

o  Effect via hindbrain (e.g. RVLM) and spinal cord (intermediolateral horn)

o  Organ-specific projections: e.g. skeletal muscle vs skin vs splanchnic

o  Stimulation by ARAS maintains wakefulness

Via posterior pituitary

·      Releases into infundibulum from the SON and PVN:

o  ADH -> water retention, vasoconstriction

o  Oxytocin -> myometrial contraction in labour, behavioural effects

Via anterior pituitary

·      Secretes into hypophyseal portal system

o  CRH -> ↑ACTH -> ↑cortisol -> stress response

o  TRH -> ↑TSH -> thyroid hormones -> metabolic homeostasis

o  GHRH -> ↑GH -> ↑IGF -> tissue growth, metabolic effects

o  GnRH -> ↑FSH, LH -> reproductive function

o  ↓Dopamine -> ↑PRL -> lactation
(note negative feedback from pituitary hormones and target organ-derived hormones)

Temperature

·      Senses temperature (anterior); controls set point (posterior); responds outside inter-threshold range

·      Anterior stimulation (pre-optic nuclei): triggers autonomic and behavioural heat loss responses (e.g. sweating, cutaneous vasodilatation)

·      Posterior stimulation (tuberal nuclei): triggers autonomic and behavioral heat gain and conservation responses (e.g. shivering, cutaneous vasoconstriction)

Water

·      Paraventricular region: contains a thirst centre activated by hypertonicity, hypovolaemia, dry mouth, other

o  ↑ADH synthesis

o  ↑Thirst -> water-seeking

·      Contains internal osmoreceptors: supraoptic (and paraventricular) nuclei

·      Receives input from external osmoreceptors: SFO, OVLT

Food

·      Ventromedial: senses [glucose], induces satiety

·      Lateral: induces hunger and food-seeking

Sleep-wake

·      Suprachiasmatic nucleus: generates circadian rhythm (input from photosensitive cells)

VLPO nuclei vs brainstem ARAS: the awake-NREM flip-flop

Emotion

·      Well connected to other limbic structures (e.g. limbic lobe, amygdala, hippocampus)

·      Mediates emotional expression via autonomic and somatic nervous systems

·      Defence area: anterior perifornical region

o  Activated by the limbic system

o  Stimulation -> ↑HR, ↑BP, vasodilatation of skeletal muscle arterioles, splanchnic and renal vasoconstriction

o  i.e. fight-or-flight response

·      Depressor area: anterior region

o  Stimulation -> ↓HR, ↓BP

o  ?Accompanies the ‘playing dead’ response in some young animals

Sexual function

·      By control of pituitary hormones: onset of puberty; menstrual cycle

·      Medial region control sexual behaviour