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We are Juan L. Blazquez,
Montserrat Guerra and Esteban Rodriguez.
The present talk is an update of our former talk of 2008.
All the previous evidence and some new findings continue to support
the concept of the tight hypothalamic blood-brain barrier.
Furthermore, we now provide evidence that
peripheral peptides can reach their brain targets via
the cerebrospinal fluid through specific transport systems
localized at the choroid plexus and probably in hypothalamic tanycytes.
The blood-brain barrier is an efficient system to prevent
the nervous tissue to be directly exposed to the blood stream.
There are, however, discrete brain areas where neural cells,
either neurons or specialized glia may establish an open communication with blood capillaries.
For this to occur without making the blood-brain barrier leaky,
these windows through which the brain looks at the internal milieu,
must have a spatial organization.
The subject to the present talk is about one of these brain windows, the median eminence.
Neurons secreting hormones into the bloodstream
must be in open communication with the blood capillaries.
In the central nervous system,
there are discrete areas localized in
the ventricular walls known as circumventricular organs.
The mammalian circumventricular organs are the pineal gland, the subcommissural organ,
the subfornical organ, the organ of vascular organ of lamina terminalis,
the area postrema, the choroid plexuses and the median eminence.
In most circumventricular organs,
the blood-brain barrier is missing,
all displays special characteristics.
These brain windows may serve two purposes: a)
to allow peptides and proteins secreted by the neural tissue to
reach the blood stream as it occurs in the median eminence or b)
to allow neural cells to sense the plasma as it occurs within the neurons
of the subfornical organ sensoring the plasma levels of angiotensin.