Kazuo Nakakita

A Light and Electron Microscopic Immunohistochemical Study of Vasoactive Intestinal Polypeptide— And Substance P-Containing Nerve Fibers along the Cerebral Blood Vessels: Comparison with Aminergic and Cholinergic Nerve Fibers

Vasoactive intestinal polypeptide (VIP)– and substance P–containing nerve fibers were observed in the cerebral blood vessels using an immunohistochemical technique. VIP-containing nerve fibers distributed in a spiral pattern, similar to that of muscle cells. Under electron microscopic observation, VIP-immunoreactive terminals lay close to a muscle cell in the inner layer of the adventitia. In contrast, substance P–containing nerve fibers showed a meshwork pattern in the outer layer of the adventitia. Using both acetylcholinesterase (AChE) staining and VIP immunohistochemistry, AChE-positive and VIP-immunoreactive nerve fibers revealed almost the same distribution in the same specimen. The present data suggest that VIP-containing nerve fibers may play a role in the smooth muscle control of the blood vessels, whereas substance P–containing nerve fibers may not take part in muscle control.

Innervation of the Cerebral Veins as Compared with the Cerebral Arteries: A Histochemical and Electron Microscopic Study

The distribution of nerve fibers in the cerebral veins was studied by catecholamine fluorescence simultaneously with acetylcholinesterase (AChE) histochemistry. A comparison of nerve fibers in the cerebral arteries was made, The ultrastructure of terminal boutons in the veins fixed with potassium permanganate was also studied, In the adventitia of the cerebral artery, green fluorescent aminergic fibers and brownish AChE-reactive (probably cholinergic) fibers were observed. In contrast, the cerebral venous system showed no AChE-positive fibers. Catecholamine fluorescent varicose fibers were detected in the dural sinus, the internal cerebral vein, and the superficial vein of Labbé. The highest density of aminergic fibers was found in the dural sinus and the second highest in the internal cerebral vein. Most of the terminal boutons in the adventitia of the cerebral veins were found adjacent to a muscle-like cell and showed only cored vesicles under electron microscopy. Results of our study suggest that the cerebral venous system has a neurogenic innervation, mainly from aminergic fibers, which is different from the neurogenic supply to the cerebral arterial system.

The distribution of adrenergic receptors in cerebral blood vessels: an autoradiographic study

The first morphological evidence of the existence of adrenergic receptors (alpha 1, alpha 2 and beta) within the vascular walls of the central nervous system were presented using the in vitro receptor autoradiographic technique. In the rat pial arteries all three types of adrenergic receptors were demonstrated, whereas the human pial arteries failed to show significant autoradiographic grains of alpha 1 type of adrenergic receptors indicating a considerable inter-species difference in the distribution of adrenergic receptors. alpha 2 and beta receptors in human pial arteries were found not only in the arterial smooth muscle layers but also in the endothelial layers. This suggests a possibility that circulating sympathomimetic agents play some role in controlling the tone or permeability of vascular walls within the central nervous system. A distinct distribution of alpha 1 receptors in cortical layer IV where the vascular plexus was richest may suggest a relation of alpha 1 receptors and blood flow of brain parenchyma.

Peptidergic Innervation in the Cerebral Blood Vessels of the Guinea Pig: An Immunohistochemical Study

The distribution of peptidergic nerve fibers containing substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) in the cerebral arteries and veins of the guinea pig was studied using immunohistochemical techniques. The ultrastructure of these immunoreactive nerve terminals was also compared. The cerebral arteries were innervated by abundant peptidergic nerve fibers with characteristic running patterns, i.e., SP fibers in a meshwork, VIP and NPY fibers in a spiral fashion. Only CGRP fibers showed both meshwork and spiral patterns. In the cerebral veins, the abundant SP fibers innervated the cortical veins, deep cerebral veins, and dural sinuses. However, CGRP, VIP, and NPY fibers in extremely low density were noted merely in the cortical veins. Electron microscopic observations demonstrated that SP-immunoreactive nerve terminals existed apart from the arterial smooth muscle cells, while VIP- and NPY-immunoreactive nerve terminals adjoined them. As for CGRP nerve terminals, some existed close to the arterial smooth muscle cells, and others were found some distance from them. These morphological characteristics observed by light and electron microscopy suggest that SP fibers are not related directly to the vasomotor function, but VIP and NPY fibers are, and that CGRP fibers have a more complicated function. The distribution patterns of the peptidergic nerve fibers are consistent with the suggestion that vasomotor peptidergic fibers may function actively on cerebral arteries and passively on cerebral veins and that SP fibers regarded as sensory fibers may provide information regarding cerebral vascular conditions, innervating every part of both cerebral arteries and veins.

Immunohistochemical Demonstration of Vasopressin Nerve Fibers in the Cerebral Artery

Vasopressin-immunoreactive nerve fibers were demonstrated in the cerebral pial arteries by peroxidase immunohistochemistry. In the large pial artery (proximal part of the middle cerebral artery), they ran longitudinally to the long axis of the vessel. They ran in a spiral pattern in the distal part of the middle cerebral artery. Even in small arteries, vasopressin nerve fibers were found arranged in a longitudinal fashion. The present morphological data suggest that vasopressin nerve fibers in the cerebral artery may play a role in cerebral circulation.

Peptidergic innervation of cerebral blood vessels

Morphological and ohysiological studies concerning the innervation of peptidergic nerve fibers were carried out using inmtmohistochemistry with the PAP and hydrogen clearance method, respectively. Vasoactive intestinal polypeptide (VIP) and substance P (SP) immunoreactive nerve fibers were distributed within the adventitial layer of Dial arteries in the central nervous system, including the spinal cord. In cerebral pial arteries nmny VlP ~reactive fibers ran mainly in a spiral pattern almost identical to that of aoetylcholinesterase-positive fibers, suggestive of the coexistence of VlP and acetylcholine in the Dial arteries, as was reoorted in the autonomic ganglia and the cerebral cortex (H6kfelt and Lundberg 1983, Eckenstelnand Baughmsn 1984). Ultrastructural study of ~stainedmaterial demonstrated that most VIP immunostained fibers and cells were also ntmmrous in the cerebral cortex. Some of thamwere found very close to the intraparenchymal blood vessels, indicating a strong functional correlation between VIP fibers mud arterial smooth muscles. In contrast, SP ~opositive fibers around pial arteries ran in a meshwork pattern and lay relatively apart from the arterial smooth muscle layer. Neither a nerve fiber nor a cell soma immunostainedwith SP was observed within the cerebral cortex. A physiological study to investigate the regional cerebral blood flow (r-CBF) using hydrogen clearance methoddemonstrated that iontophoretically injected VIP increased the r-CBF of the rat cerebral cortex, but SP failed to show significant change in r-CBF. These results suggest an important role of VIP neurons in regulating the cerebral blood flow.