2 Neuroscience2.8 Modulators, hormones and inflammatory responses
2.8 Modulators hormones and inflammatory responses
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Written by Resident Doctor Committee · Published
Hypothalamic, pituitary and peripheral axes
Axis | Hypothalamus and pituitary | Output |
|---|---|---|
Adrenal | Corticotrophin-releasing hormone drives adrenocorticotrophic hormone | Cortisol |
Thyroid | Thyrotrophin-releasing hormone drives thyroid-stimulating hormone | Thyroxine, triiodothyronine |
Gonadal | Gonadotrophin-releasing hormone (GnRH) drives luteinising hormone (LH) and follicle-stimulating hormone (FSH) | Oestrogen, progesterone, testosterone |
Growth | Growth hormone-releasing hormone and somatostatin regulate growth hormone | Hepatic insulin-like growth factor 1 |
Oxytocin and vasopressin are hypothalamic hormones released into blood from posterior pituitary terminals.
Feedback, rhythm and stress
Cortisol feedback limits hypothalamic-pituitary-adrenal activation.
Pulsatile release keeps receptors responsive, and continuous GnRH agonism eventually suppresses LH and FSH.
Cortisol peaks in the morning and is lowest at night. After stress it peaks at 20 to 30 minutes, later than catecholamines, and mobilises fuel and restrains inflammation.
Receptor | Affinity | Occupied |
|---|---|---|
Mineralocorticoid | High | Even at the trough |
Glucocorticoid | Lower | Only at peak and under stress |
Brief stress can strengthen emotional consolidation but impairs retrieval.
Sustained exposure alters hippocampal and prefrontal dendrites and neurogenesis.
Endocrine findings in psychiatric disorders
Condition | Finding |
|---|---|
Melancholic or psychotic depression | Dexamethasone non-suppression in roughly half |
Hypothyroidism | Depressive and cognitive symptoms |
Anorexia nervosa | Low LH, FSH and triiodothyronine, with amenorrhoea |
Dopamine receptor blockade | Raised prolactin |
Dexamethasone non-suppression also occurs in other illnesses, so it cannot diagnose depression.
Immune to brain signalling
Peripheral inflammation reaches the brain through circumventricular organs, endothelial prostaglandins and vagal afferents.
Indoleamine 2,3-dioxygenase diverts tryptophan to kynurenine. Quinolinic acid then activates N-methyl-D-aspartate receptors, and kynurenic acid opposes them.
Interferon treatment shows that sustained immune signalling can contribute to depression.