Monday, January 9, 2012

The Area Postrema is not the only place where the BBB is lacking

I'll paraphrase a question posed by one of my 2nd-year students at Southern Illinois University School of Medicine:

I understand that the Area Postrema was a site where there was increased penetrability of the blood brain barrier. I am not sure, but thought I had come across additional sites of increased penetrability last year in my reading. Are there other sites where there is increased permeability of the BBB?

In pondering an answer to this question, I immediately thought of the illustrious Dr. John Donahue, consummate neurologist, neuropathologist, and neuroanatomist.  I posed the question to him and got the following response:

Dr. John Donahue, Brown University, Providence, RI
"Not increased permability of the BBB.  NO BBB!  Area postrema is one of the circumventricular organs, areas in the brain that lack a BBB.  Being the vomiting center, it is imperative that it lacks a BBB so that it can sample the systemic circulation.  Being in the medulla, it is the only circumventricular organ that is adjacent to the fourth ventricle; all of the others are adjacent to the third.  It is the only paired circumventricular organ; all of the others are single and midline.  The other circumventricular organs are subfornical organ, organum vasculosum of the lamina terminalis, median eminence, posterior pituitary gland, subcommissural organ, and pineal gland."

There you have it!

7 comments:

Agent86 said...

Good thing Descartes didn't know about the subfornical organ, organum vasculosum of the lamina terminalis, median eminence, posterior pituitary gland, and subcommissural organ, or he never would have found the soul!

Brian E. Moore, MD said...

Nicely stated, Agent86. For those who do not know what the heck he is talking about:
http://plato.stanford.edu/entries/pineal-gland/

Anonymous said...

Also of note the choroid plexi are not in the BBB, and if I remember correctly neither is the induseum griseum, (although I'm less sure of that).
--Douglas C Miller, posting as "anonymous" after multiple failures of known passwords to work with this blog's access system

jd said...

The literature is mixed on the subject. Some list the CP with the circumventricular organs, and some don't. In retrospect, it probably is outside the BBB based on this study: Wuerfel E, Infante-Duarte C, Glumm R, Wuerfel JT, "Gadofluorine M-enhanced MRI shows involvement of circumventricular organs in neuroinflammation," J Neuroinflammation 2010; 7: 70. The MRI Gadofluorine signal intensity of the CP in this study was similar to that of the subfornical organ and area postrema in experimental autoimmune encephalomyelitis.

Do not know about the indusium griseum.

jd said...

Just to clarify, I know what the indusium griseum is; I just don't know if it's outside the BBB.

Anonymous said...

Whether the choroid plexus is to be considered part of the cirumventricular organs or not, and also regardless of one's interpretation of MRI gadolinium enhancement, in adult patients with jaundice those areas outside the BBB turn green (in formalin fixed brain) from the bilirubin whereas the rest of the brain, if not infarcted or otherwise damaged, has the bilirubin excluded by the BBB. The choroid plexus tissues are always green in these cases.

DCM, anonymous as far as google is concerned.

jd said...

I think that's a good interpretation: outside the BBB, but not usually grouped with the other circumventricular organs. The CVO's have a distinctive, loose histologic architecture, while the CP has its own, unique histologic architecture.