Circumventricular Organs - Succinct Presentation - Sanjoy Sanyal

Circumventricular Organs (System) have been well studied, starting with Paul Ehrlich work with Trypan Blue in 1882, and research on their functions is still going on. However, Neuroscience medical students find it difficult to understand them. This short PPTX is meant to succinctly explain the Circumventricular Organs.

Short Video clips pertaining to each CV Organ on a human brain specimen, created and uploaded on YouTube by the author, Dr Sanjoy Sanyal, Professor and Course Director of Neuroscience, are embedded between slides, to provide a narrative highlight to what is mentioned in the slides.

Tags: Median Eminence, Tuber Cinereum, Arcuate Nucleus, Organum Vasculosum, Lamina Terminalis, Subfornical Organ, Pineal, Epiphysea, Subcommissural Organ, Area Postrema, Supraoptic Nucleus, Suprachiasmatic nucleus, Preoptic nucleus

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1. Circumventricular Organs Dr Sanjoy Sanyal MBBS, MS (Surgery), MSc (Royal College of Surgeons of Edinburgh), ADPHA Professor and Course Director of Neuroscience – FCM-III Neurology

2. No Blood Brain Barrier (BBB) Paul Ehrlich (1882) After IV injections of Trypan Blue, most areas of Brain did not get stained These areas are inside the BBB Some areas of Brain did get stained with Trypan Blue These structures are outside the BBB; i.e. they do not have a BBB

3. Circumventricular Organs Five of these areas were identified around the Third Ventricle , and one on the floor of the Fourth Ventricle They are called Circumventricular Organs (around the Ventricle) They are bathed by CSF and are also in contact with the Capillaries

4. Functions of CV Organs Chemosensitive Organs Allow ‘sampling’ of Blood Endocrine Feedback and Regulation Homeostasis Metabolic Regulation Fluid Electrolyte Balance Detect Toxins in Blood CSF Circulation(?)

5. Structure of CV Organs Highly Vascularized Fenestrations of Endothelial Cells Permeable Basement Membrane Astrocyte Podocytes do not form complete circle Exception : Sub-Commissural Organ has Non-fenestrated Capillaries

6. 1. Median Eminence of Tuber Cinereum ME-TC#1 Has Arcuate Nucleus that releases RH / IH, P-IH Detects Endocrine Feedback to Hypothalamus Mediated by Tancytes lining the ME-TC Maintains Basal Levels of Hormones (FSH-LH) In Floor of 3 rd Ventricle : Raised Central Part of a Convex gray matter in the Ventral-most part of Hypothalamus #1

7. 2. Organum Vasculosum of Lamina Terminalis (OV-LT) #2 Has Osmoreceptors Regulates ADH release by Supraoptic Nucleus Provides Vascular Outlet for LH-RH by Pre-optic and GH-IH by Suprachiasmatic (Both are adjacent to LT) A.k.a . Vascular Organ of Lamina Terminalis #2

8. 3. Subfornical Organ (SFO) #3 On inferior surface of Fornix, at level of Foramen of Monroe (#3) Angiotensin II Receptors Neurons from SFO project to SO Nucleus and OV-LT (Both are Osmoreceptors ) Fluid Electrolyte balance

9. 4. Pineal Gland #4 Pinealocytes ( Epiphyseal Cells) # 4 Highly Vascular Fenestrated Capillary Release Melatonin into 3 rd Ventricle Transported by Tancytes in Floor of 3 rd Ventricle Act on Pituitary Gland

10. 5. Subcommissural Organ #5 Special Epithelial / Glial Cells Non-fenestrated Capillaries Functions : (a) Circulation of CSF (Hydrocephalus); (b) Clearance of certain compounds (?) Below Posterior Commissure #5 At 3 rd Ventricle–Aqueduct of Sylvius Junction

11. 6. Area Postrema Modified Astrocyte -like Neurons Fenestrated Capillaries 5-HT 3 Receptors (Excitatory Ionotropic ) Induces Vomiting from Morphine, Blood 5-HT Gets Afferents from CTZ and GIT Plays Role in Food Intake / CVS Control In Floor of 4 th Ventricle, Between Vagal Triangle and Inferolateral margin of Rhomboid Fossa , just Rostral to Obex