Vessel Wall - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 366

choroid epithelium that are separated by the brain interstitial fluid. Epithelial cells
produce 90% of CSF ( 4 ml/mn/g) [ 679 ]. Cerebrospinal fluid is composed of

water (99%), vitamins, ions, glucose, amino acids, etc. The choroid plexi also have
a CSF purification role.

∼ 0 .

7.6 Perivascular Nerves

Vascular tone undergoes a dual regulation by perivascular nerves and endothelial
cells. Endothelial cells can provoke both vasodilation and -constriction. Endothelial
cells indeed produce, store, and release vasoactive substances, either vasodilators,
such as nitric oxide and acetylcholine, or vasoconstrictors such as endothelin
(Sect. 9.10 ). Perivascular nerves and endothelial cells interact.
Perivascular nerves are not limited to adrenergic or cholinergic axons. Four
types of perivascular nerves exist: sympathetic, parasympathetic, sensory-motor,
and projection neurons from intrinsic ganglia of the heart and other organs [ 680 ].
Cotransmission usually occurs, as: (1) sympathetic nerves use the transmitters
noradrenaline, adenosine triphosphate, and neuropeptide-Y (NPY); (2) parasym-
pathetic nerves signal via acetylcholine and vasoactive intestinal peptide (VIP);
and (3) messages of sensory-motor nerves 38 are coded by calcitonin gene-related
peptide (CGRP), substance-P, and adenosine triphosphate. (4) Neurons from organ
ganglia release many types of neurotransmitters, such as peptides (peptidergic
nerves [transmission]), 39 purines (purinergic nerves [transmission]), nitric oxide
(nitrergic nerves [transmission]), and classical transmitters.
Artemin (Artn) that is expressed in vascular smooth muscle cells, serves as a
guidance factor for the growth of sympathetic nerve fibers along blood vessels [ 681 ].
Artemin is a member of the glial cell line-derived neurotrophic factor (GDNF)
family of ligands. 40 These ligands signal via a receptor complex composed of
Ret receptor protein Tyr kinase and a glycosyl phosphatidyl inositol-anchored
coreceptor of the receptor- α set for members of the GDNF family .

7.7 Pericytes

Pericytes surround the capillaries. They can also encircle precapillary arterioles and
postcapillary venules. These periendothelial cells are rich in stress actin bundles.

38 Certain afferent nerves have an efferent function and axonic reflex control of vascular tone.
39 Peptidergic nerves contain substance-P, CGRP, and VIP transmitters.
40 The glial cell line-derived neurotrophic factor family ligands include glial cell-derived neu-
rotrophic factor (GDNF), neurturin (Ntn), persephin (Pspn), and artemin (a.k.a. enovin [Evn] and
neublastin [Nbn]).