|Dr. John Donahue, Brown University, Providence, RI|
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:
"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!