Vasa nervorum in rat major pelvic ganglion are innervated by nitrergic nerve fibers.

INTRODUCTION: The vasa nervorum comprises a network of small diameter blood vessels that provide blood supply to nerves and ganglia. The cell bodies of autonomic nerves innervating the urogenital organs are housed in the major pelvic ganglia (MPG) in rats. The vasa nervorum of rat MPG have not been characterized previously, and it is not known whether these blood vessels are innervated by neuronal nitric oxide synthase (nNOS) containing nitrergic nerves. AIM: To characterize the blood vessels in and around the rat MPG and to assess their nitrergic innervation. MAIN OUTCOME MEASURES: Characterization of small blood vessels in and around the rat MPG and expression of nNOS in nerve fibers around those blood vessels. METHODS: MPG were obtained from healthy Sprague Dawley rats, fixed in paraformaldehyde, frozen and sectioned using a cryostat. The blood vessels and their nitrergic innervation were assessed with immunohistochemistry using antibodies against alpha-smooth muscle actin (smooth muscle marker), CD31 (endothelial marker), collagen IV (basal membrane marker) and nNOS. The immunofluorescence was imaged using a laser scanning confocal microscope. RESULTS: The neuronal cell bodies were contained within a capsule in the MPG. Blood vessels were observed within the capsule of the MPG as well as outside the capsule. The blood vessels inside the capsule were CD31-positive capillaries with no smooth muscle staining. Outside the capsule capillaries, arterioles and venules were observed. The extra-capsular arterioles and venules, but not the capillaries were innervated by nNOS-positive nerve fibers. CONCLUSIONS: This study, to our knowledge, is the first to demonstrate the blood vessel distribution pattern and their nitrergic innervation in the rat MPG. While similar studies in human pelvic plexus are warranted, these results suggest that the blood flow in the MPG may be regulated by nitrergic nerve fibers and reveal a reciprocal relationship between nerves and blood vessels.

Quantitative assessment of the innervation of epineurial arteries in the peripheral nerve by immunofluorescence: differences between controls and patients with peripheral arterial disease.

The peripheral nerve is supplied by the vasa nervorum. The epi- and perineurial vessels are innervated by an autonomic plexus, which plays a role in regulation of the endoneurial blood flow. This innervation is decreased in diabetes and alcohol polyneuropathy and seems to precede the development of diabetic polyneuropathy. A decreased innervation may therefore play a role in the development of polyneuropathy. In peripheral arterial disease (PAD) clinical and morphological features are present, related to severity of ischemia. To investigate the innervation of the vasa nervorum in severe ischemia, we performed immunofluorescence staining with the general neural marker protein gene product (PGP) 9.5 in whole mount preparations of epineurial vessels of nine sural nerves taken from patients with legs amputated because of severe PAD (59+/-15 years, mean +/- SD) and ten age-matched controls (61+/-24 years). In patients with PAD the nerve density of the perivascular plexus was decreased in comparison with controls (mean intercept density/mm +/- SD) 26.0+/-6.9 in PAD and 39.9+/-10.7 in controls, area% 6.0+/-1.6 in PAD and 9.9+/-2.6 in controls, both P<0.01, t-test). A decreased perivascular plexus may result in a diminished regulation of the endoneurial blood flow in patients with severe PAD.

Presynaptic deficit of sympathetic nerves: a cause for disturbed sciatic nerve blood flow responsiveness in diabetic rats.

Reduced nerve blood flow is thought to play an important role in the pathogenesis of diabetic neuropathy. This disturbance in nerve blood flow might be the consequence of either microangiopathy or an impaired autonomic innervation of the vasa nervorum. In order to differentiate between a vascular or an adrenergic-autonomic defect as the underlying cause of the disturbed nerve blood flow, we investigated the effects of the adrenocorticotropic hormone [ACTH]-(4-9) analogue Org 2766 on sciatic nerve blood flow under basal and adrenergic-stimulated conditions. Org 2766 has neuroprotective effects without cardiovascular effects. Treatment with Org 2766 was started 6 weeks after the induction of experimental diabetes mellitus. At week 12 the sciatic nerve blood flow, measured by laser-Doppler flowmetry, was reduced to 60% of the non-diabetic level; blood pressure was unchanged in diabetic rats compared to non-diabetic rats. Basal haemodynamic values were not affected by Org 2766 treatment. Vasa nervorum adrenergic responsiveness to tyramine (presynaptic) and phenylephrine (postsynaptic) was investigated. Diabetic rats showed adrenergic hyporesponsiveness. Treatment with Org 2766 restored the reduced presynaptic response to tyramine without affecting the reduced postsynaptic response to phenylephrine. It is concluded that a presynaptic-sympathetic deficit of nervi vasorum causes a disturbed flow responsiveness in diabetic rat sciatic nerve and that adrenergic autonomic disturbances in the vasa nervorum have only a small role in the reduced basal nerve blood flow of diabetic rats.

Differential vulnerability of neuropeptides in nerves of the vasa nervorum to streptozotocin-induced diabetes.

Neuropeptides in perivascular nerves of vasa nervorum supplying blood to rat optic, sciatic, vagus and sympathetic chain nerve trunks are differentially vulnerable to streptozotocin (STZ)-induced diabetes. Immunohistochemical analysis of epineurial/perineurial nerve sheaths showed that 8 weeks after induction of diabetes, the density of neuropeptide Y (NPY)-immunoreactive nerve fibres in optic nerve sheaths was increased, while it was decreased in sciatic, vagus and sympathetic nerve sheaths. Vasoactive intestinal polypeptide (VIP)-immunoreactivity was increased in vasa and nervi nervorum of optic, sciatic, vagus and sympathetic chain nerve sheaths. Immunoassay of NPY confirmed increased levels in optic nerve sheaths and showed that substance P and calcitonin gene-related peptide levels increased in sciatic but not optic nerve sheaths. Neuropeptide levels in the intrafascicular nerve fibres were unaffected. This provides further evidence for a disturbance in the autonomic control of blood flow to peripheral and cranial nerve trunks via vasa nervorum in STZ-induced diabetes, which may lead to ischaemic changes, alter local axon reflexes and contribute to the pathogenesis of the disease.

Influence of perivascular peptides on endoneurial blood flow and microvascular resistance in the sciatic nerve of the rat.

1. A variety of vasoactive peptides has been identified in the axon terminals innervating vasa nervorum but their function is unknown. In mesenteric arterioles, substance P (SP) and calcitonin gene-related peptide (CGRP) have been postulated to have a role in tonic vasodilatation. 2. We explored the effect of epineurial capsaicin, SP, CGRP, spantide (SP antagonist), and hCGRP (8-37) (CGRP antagonist) on blood flow (EBF) and microvascular resistance (EMR) in the endoneurial compartment of the rat sciatic nerve, as measured by hydrogen clearance. 3. Epineurial capsaicin induced a prompt, intense and prolonged increase in EBF and lowering of EMR as compared to epineurial application of the carrier alone in a separate animal group. The hyperaemic response was also confirmed by studying serial clearance curves in individual animals. 4. Multifibre sciatic-tibial motor conduction was not changed by epineurial capsaicin. 5. When co-administered with capsaicin, hCGRP (8-37) completely blocked the hyperaemic response and increased EMR above the pooled control range. Spantide also blocked the capsaicin response. 6. When administered alone, both epineurial hCGRP (8-37) and spantide lowered EBF below and increased EMR above the control measurements in the same animals. 7. At 10(-5) M epineurial CGRP, but not SP lowered EMR. Vasodilatation from intra-arterial administration of CGRP was much greater and was more prolonged compared with that induced by SP. hCGRP (8-37), but not spantide reduced the intra-arterial response to CGRP. 8. The findings suggest that epineurial peptidergic terminals mediate a vasodilatory response (particularly through CGRP) that increases blood flow in the 'downstream' endoneurial compartment. Physiological peptide release (blocked by SP and CGRP receptor antagonism) may be important in maintaining tonic vasodilatation.

The nerves to blood vessels supplying blood to nerves: the innervation of vasa nervorum.

Noradrenergic, serotoninergic and peptidergic nerves have been demonstrated in perivascular plexuses of vasa nervorum of sympathetic, parasympathetic and somatic nerve trunks. 5-Hydroxytryptamine-, vasoactive intestinal polypeptide- and substance P-containing fibers were found by immunohistochemistry to variable extents in whole mounts of the epineurium of sciatic, vagus and paravertebral sympathetic chains of rabbits. Innervation increased with age. This suggests an hitherto unsuspected role for these vasoactive substances in normal blood flow to nerves and in the genesis of experimental and human neuropathies.