Perivascular nerves with immunoreactivity to vasoactive intestinal polypeptide in cephalic arteries of the cat: distribution, possible origins and functional implications

Central projections of the sensory innervation to the middle cerebral artery in the squirrel monkey

To analyze the brainstem projections of the innervation to the middle cerebral artery (MCA) in the squirrel monkey, transganglionic tracing of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) was used. After application of WGA-HRP to the middle cerebral artery (MCA), labelled cell bodies were identified in the ipsilateral trigeminal and superior cervical ganglia. In the brainstem, positive labelling indicative of preterminals and terminals occurred in a discontinuous pattern throughout the trigeminal brainstem nuclear complex. At the level of the obex, nerve terminations were identified in the nucleus tractus solitarius, nucleus motorius dorsalis nervi vagi and the nucleus nervi hypoglossi. Positive WGA-HRP profiles were also observed in the periaqueductal gray matter.

Selective excitation of parasympathetic nerve fibers to elicit the vasodilatation in cat lip

Electrical stimulation of the tongue and the proximal cut end of the lingual nerve caused a blood flow to increase in a stimulus-intensity dependent manner in the ipsilateral lower lip of the cats. Pretreatment with hexamethonium (an autonomic ganglionic blocker, 1.0 mg/kg) abolished the vasodilator response, while atropine, phentolamine, propranolol and tripelennamine had no effect on these vasoresponses. Ipsilateral sections of either the glossopharyngeal nerve root, inferior alveolar nerve or mental nerve at the main mental foramen, but not at the posterior mental foramen, abolished the vasodilator response caused by electrical stimulation of the tongue and the lingual nerve. Electrical stimulation of the distal cut ends of the glossopharyngeal nerve root and inferior alveolar nerve caused the vasodilator and vasoconstrictor responses, whereas stimulation of the tongue and the proximal cut ends of the lingual nerve did not elicit the vasoconstrictor response. These results suggest that reflex vasodilatation in the cat mandibular division is exclusively mediated via activation of the parasympathetic nerve fibers, and that selective excitation of the parasympathetic nerve fibers in the oral area is possible.

Prepro-vasoactive intestinal polypeptide-derived peptide sequences in cerebral blood vessels of rats: on the functional anatomy of metabolic autoregulation

This study describes the distribution of peptide sequences derived from the prepro-vasoactive intestinal polypeptide (preproVIP) molecule in perivascular nerves of rat brain arteries and arterioles. The peptides were identified by immunohistochemistry using highly specific antibodies. Five peptide sequences (preproVIP 60-76, peptide histidine isoleucine (PHI), preproVIP 111-122, VIP, and preproVIP 156-170) were identified in the perivascular nerves throughout the arterial cerebral circulation. The density of the immunoreactive fibers was highest in the nerves of the larger extracerebral arteries, declining in smaller branching arteries. All peptide sequences were identified in the nerves of small pial arterioles overlying the cortical convexity, whereas capillaries and veins contained no immunoreactive material. Dendritic processes of neocortical neurons immunoreactive for VIP and PHI could be followed towards the brain surface where the processes penetrated into the pial layer, often close to the pial vasculature. Some of the processes were also observed to enter the Virchow-Robin space, close to the arterioles. It is possible that cortical nerve cells containing VIP and PHI release the peptides in the perivascular space during periods of activity and thereby contribute to local vasodilatation associated with changes of neuronal function.

Vasoactive intestinal polypeptide receptors in rat cerebral vessels: an autoradiographic study

1. Localization and pharmacological properties of the vasoactive intestinal polypeptide (VIP) receptors in rat circle of Willis arteries and in the arteries of pial-arachnoid membrane were studied using light microscope autoradiography combined with radioreceptor binding techniques. 2. [125I]-VIP was specifically bound to sections of rat cerebral arteries with a dissociation constant value of 0.5 nM and a binding site density of 80 fmol mg protein-1. Radioreceptor binding experiments revealed that the binding characteristics of [125I]-VIP were consistent with the labelling of specific VIP receptors. The rank order of potency of various substances tested to inhibit [125I]-VIP binding was the following: VIP greater than peptide histidine methionine greater than secretin greater than glucagon. 3. Light microscope autoradiography revealed the localization of [125I]-VIP binding sites in the medial layer of circle of Willis and pial arteries. Quantitative determination of [125I]-VIP binding site density in the different circle of Willis arteries demonstrated a higher accumulation of silver grains in the anterior than in the posterior cerebral arteries. Pial arteries are richer in VIP receptor sites than circle of Willis arteries. 4. These results suggest that the physiological neurogenic vasodilation elicited by VIP on cerebral arteries is mediated by the interaction with specific receptor sites located primarily within cerebral vessels structures involved in the control of cerebrovascular resistances.

Vasodilator responses following intracranial stimulation of the trigeminal, facial and glossopharyngeal nerves in the cat gingiva

The effects of electrical stimulation of the trigeminal, facial and glossopharyngeal nerves on gingival blood flow in the cat were studied. The intracranial part of these nerves was stimulated electrically, and gingival blood flow was measured by the laser Doppler technique. Electrical stimulation of the trigeminal, facial and glossopharyngeal nerves caused blood flow to increase in the ipsilateral gingiva both with the cranial nerve intact and after cutting it to the medulla. Stimulation of the distal cut ends of the facial and glossopharyngeal nerves elicited an increase in blood flow but no increase in systemic blood pressure. Pretreatment with hexamethonium reduced the increase in blood flow elicited by electrical stimulation of the facial and glossopharyngeal nerves, but had no effect on that elicited by stimulation of the trigeminal nerve. In contrast, pretreatment with tripelennamine attenuated the trigeminal nerve-stimulated blood flow increase, but not that elicited by stimulation of the facial and glossopharyngeal nerves. Atropine, propranolol and phentolamine had no effect on these responses. These results suggest that the autonomic nervous system, particularly the parasympathetic nervous system, is responsible for the blood flow increase elicited by facial and glossopharyngeal nerve stimulation, and that the trigeminal nerve-stimulated blood flow increase is induced by antidromic vasodilatation of the trigeminal sensory nerve.

Peptidergic and serotoninergic innervation of the rat dura mater

The peptidergic and serotoninergic innervation of the rat dura mater was investigated by reacting dural wholemounts immunohistochemically with antibodies to calcitonin gene-related peptide (CGRP), substance P (SP), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), and serotonin (5-HT). CGRP and SP innervations of the dura were robust and the patterns of distribution of these neuropeptides were essentially the same. The majority of the fibers were perivascular and distributed to branches of the anterior and middle meningeal arteries and to the superior sagittal and transverse sinuses. Other CGRP/SP fibers appeared to end "free" within the dural connective tissue. NPY-immunoreactive fibers were extremely numerous and also distributed heavily to the branches of the meningeal arteries, the venous sinuses, and to the dural connective tissue. The pattern of NPY innervation resembled in many ways that of CGRP/SP; however, NPY innervation of the sinuses was greater and NPY perivascular fibers supplying the meningeal arteries formed more intimate contacts with the walls of the vessels. The pattern of VIP innervation was, in general, similar to that observed for the three previous neuropeptides; however, the overall density was considerably less. Small to moderate numbers of serotoninergic nerve fibers were observed in some, but not all, of the duras processed for 5-HT. The latter fibers were almost exclusively perivascular in distribution. Dural mast cells were prominently stained in the 5-HT preparations because of their serotonin content. Mast cells were also labeled in a nonspecific fashion in some of the tissues reacted immunohistochemically for neuropeptides; some of them were located in close apposition to passing nerve fibers. This study represents, to our knowledge, the first comprehensive work on the peptidergic and serotoninergic innervation of the mammalian dura mater. The results should increase our understanding of the roles that these fibers play in normal dural physiology and of their potential interactions in the pathogenesis of vascular headache.

Parasympathetic denervation of rat pial vessels significantly increases infarction volume following middle cerebral artery occlusion

Studies were undertaken in Long Evans rats to examine the hypothesis that chronic unilateral sectioning of vasodilating nerve fibers (parasympathetic and/or sensory) innervating the circle of Willis increases infarction volume following unilateral branch occlusion of the middle cerebral artery (MCA) combined with temporary (45 min) bilateral common carotid occlusion. Infarct size was measured 24 h after surgical occlusion from seven coronal slices. Infarction volume (mean +/- SD) in sham animals (group A) and surgically naive animals (group B) measured 153 +/- 43 and 131 +/- 38 mm3, respectively. After lesions of both sensory (nasociliary nerve) and parasympathetic efferents at the ethmoidal foramen (group C, combined lesion) or selective lesions of parasympathetic efferents (group D), infarction volume increased [214 +/- 47 mm3 (p less than 0.01) and 209 +/- 46 mm3 (p less than 0.05), respectively]. No increases were detected after cutting the nasociliary nerve alone (group E) or occluding the external ethmoidal artery (group F) [145 +/- 39 mm3 (p greater than 0.05) and 124 +/- 63 mm3 (p greater than 0.05), respectively]. The infarct was predominantly located within cortical gray matter and became enlarged on its superior and inferior aspects after parasympathectomy. Large infarcts were noted whether animals breathed spontaneously (all of the above) or were artificially respired or whether animals were anesthetized with xylazine and ketamine or chloral hydrate. Taken together, these studies suggest a previously unrecognized protective role for autonomic parasympathetic fibers in the pathophysiology of focal cerebral ischemia that is not shared by sensory fibers. The importance of autonomic vasodilating fibers to blood flow in ischemic brain merits further study.

Acetylcholine levels and choline acetyltransferase activity in rat cerebrovascular bed after uni- or bilateral sphenopalatine ganglionectomy

Endogenous acetylcholine (ACh) levels and choline acetyltransferase (ChAT) activity were measured in several vascular segments (major cerebral arteries, cortical pial vessels, and peripheral arteries) and nervous tissues [including the sphenopalatine ganglion (SPG)] in the rat. The effects of uni- or bilateral surgical ablation of the SPG, a putative origin of the cholinergic cerebrovascular innervation, were investigated on these two specific cholinergic markers at various postoperative times. ChAT activity and ACh levels were enriched in the cerebral as compared to the peripheral arteries. Among the cerebrovascular tissues tested, ACh levels were particularly high in the circle of Willis and the vertebrobasilar segments and, to a lesser extent, in the middle cerebral artery. Lower levels were found in the small pial vessels and choroid plexus. Overall, ChAT activity measured in different arterial beds paralleled the distribution of ACh. Following uni- or bilateral removal of the SPG, slight reductions (18-36%, statistically not significant) were observed in ChAT activity in rostral cerebral arteries and pial vessels overlying the frontal cortex. Similarly, bilateral ganglionectomy resulted in minor decreases (11-22%, not significant) in the cerebrovascular contents of ACh in these same vascular segments. These results clearly show that the SPG does not or only partly contributes to the cholinergic fibers that supply the cerebrovascular bed.

Chronic trigeminal ganglionectomy or topical capsaicin application to pial vessels attenuates postocclusive cortical hyperemia but does not influence postischemic hypoperfusion

Marked hyperemia accompanies reperfusion after ischemia in the brain, and may account for the propensity of cerebral hemorrhage to follow embolic stroke or carotid endarterectomy, and for the morbidity that follows head injury or the ligation of large arteriovenous malformations. To evaluate the contribution of trigeminal sensory fibers to the hyperemic response, CBF was determined in 12 symmetrical brain regions, using microspheres with up to five different isotopic labels, in four groups of cats. Measurements were made at 15-min intervals for up to 2 h of reperfusion after global cerebral ischemia induced by four-vessel occlusion combined with systemic hypotension of either 10- or 20-min duration. In normal animals, hyperemia in cortical gray matter 30 min after reperfusion was significantly greater after 20 min (n = 10) than after 10 min (n = 7) of ischemia (312 ml/100 g/min versus 245 ml/100 g/min; p less than 0.01). CBF returned to preischemic levels approximately 45 min after reperfusion and was reduced to approximately 65% of basal CBF for the remaining 75 min. In cats subjected to chronic trigeminal ganglionectomy (n = 15), postocclusive hyperemia in cortical gray matter was attenuated by up to 48% on the denervated side (249 versus 150 ml/100 g/min; p less than 0.01) after 10 min of ischemia. This effect was maximal in the middle cerebral artery (MCA) territory, and was confined to regions known to receive a trigeminal innervation. In these animals, substance P (SP) levels in the MCA were reduced by 64% (p less than 0.01), and the density of nerve fibers containing calcitonin gene-related peptide (but not vasoactive intestinal polypeptide or neuropeptide Y) was decreased markedly on the lesioned side. Topical application of capsaicin (100 nM; 50 microliters) to the middle or posterior temporal branch of the MCA 10-14 days before ischemia decreased SP levels by 36%. Postocclusive hyperemia in cortical gray matter was attenuated throughout the ipsilateral hemisphere by up to 58%, but the cerebral vascular response to hypercapnia (PaCO2 = 60 mm Hg) was unimpaired. The duration of hyperemia and the severity of the delayed hypoperfusion were not influenced by trigeminalectomy, capsaicin application, or the intravenous administration of ATP. These data demonstrate the importance of neurogenic mechanisms in the development of postischemic hyperperfusion, and suggest the potential utility of strategies aimed at blocking axon reflex-like mechanisms to reduce severe cortical hyperemia.

Neuropeptide Y and vasoactive intestinal peptide in experimental subarachnoid hemorrhage: immunocytochemistry, radioimmunoassay and pharmacology

The involvement of noradrenaline (NA), neuropeptide Y, (NPY), 5-hydroxytryptamine (5-HT), acetylcholine (ACh) and vasoactive intestinal polypeptide (VIP) has been examined in the late phase of spasm after an experimental subarachnoid hemorrhage (SAH) in a rat model. Immunocytochemistry and radioimmunoassay of blood vessels from the circle of Willis did not show significant differences in NPY- and VIP-like immunoreactivity 2 days post SAH as compared to control vessels. The postjunctional effects of NA, NPY, 5-HT, ACh and VIP were studied two days after SAH using a sensitive in vitro system. NPY induced contractions were significantly (p less than 0.01) weaker (lower Emax) in SAH as compared to control rats while the relaxant responses to ACh and VIP were slightly increased after SAH. These observations reveal that in a rat model of SAH, with an approximately 20% in vivo constriction at two days, dynamic changes occur in cerebral artery reactivity despite any obvious change in sympathetic or parasympathetic perivascular nerve networks.

Parasympathetic innervation of cutaneous blood vessels examined by retrograde tracing in the rat lower lip

The origin of vasoactive intestinal polypeptide (VIP)-immunoreactive and acetylcholinesterase (AChE)-positive perivascular nerve fibers in the lower lip of rats was investigated using the retrograde tracer, wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase gold complex (WGAapoHRP-Au), in combination with immunohistochemistry and enzyme histochemistry, by comparing the cells of origin of projection to the parotid gland. After the application of the tracer to the lip, small- to medium-sized nerve cells were labelled exclusively in the ipsilateral otic ganglion. Most of them showed moderate VIP-immunoreactivity and AChE activity. In contrast, injection into the parotid gland resulted in labelling of mostly large-sized cells of the otic ganglion which showed intense VIP-immunoreactivity and AChE activity. These results confirmed that the parasympathetic innervation of the rat lip originates from the otic ganglion. It was further suggested that there are at least two subpopulations in the otic ganglion cells, different from each other in size and in VIP-immunoreactivity, which separately innervate the salivary gland and the blood vessels.

Evidence that neuropeptide Y and norepinephrine mediate electrical field-stimulated vasoconstriction of rabbit middle cerebral artery

We investigated the contractile response of isolated rabbit middle cerebral artery (MCA) segments to electrical field stimulation (EFS). The dynamics of the EFS contraction were compared with a similar-sized branch of rabbit ear artery. In comparison with the ear artery, the EFS contractions of the MCA displayed a longer latency and a higher stimulus frequency threshold. Greater stimulation train lengths were required to attain equilibrium, and the time course of EFS response--including force development, plateau, and return to rest tension--was significantly slower than in the ear artery. Morphological and pharmacological studies of the MCA showed that it receives sympathetic adrenergic innervation: whole-mount preparations displayed catecholamine histofluorescence; electron micrographs of MCA sections revealed a population of varicosities containing chromaffin positive large and small vesicles; and EFS contractions were blocked by tetrodotoxin (30 nM) and guanethidine (5 microM) and by chronic surgical sympathectomy. Exposure to prazosin (10 microM) or phenoxybenzamine (1 microM) blocked norepinephrine contractions but did not significantly influence the EFS contraction. Procedures and drugs that antagonized the responses to neuropeptide Y, serotonin, or histamine were also ineffective in blocking the EFS contraction. The involvement of ATP could not be assessed, since the purinergic P2 agonist alpha,beta-methylene ATP was ineffective in blocking ATP-mediated contractions. The EFS contraction, however, could be blocked by a combination of neuropeptide Y desensitization and phenoxybenzamine (30 nM) or prazosin (0.1 microM). These results suggest that norepinephrine and neuropeptide Y are released from sympathetic nerves and mediate EFS contraction by occupation of postjunctional alpha-adrenoceptor and neuropeptide Y receptors. Since the blockade of only one of these components does not diminish the response to EFS, the adrenergic neuroeffector system in this artery may involve complex prejunctional regulatory mechanisms.

Distribution of postganglionic parasympathetic fibers originating in the pterygopalatine ganglion in the maxillary and ophthalmic nerve branches of the trigeminal nerve; HRP and WGA-HRP study in the guinea pig

The distribution of the postganglionic parasympathetic fibers originating in the pterygopalatine ganglion (PTPG) has been traced in the guinea pig by means of the HRP and WGA-HRP methods. The greatest number of labeled cells were observed when WGA-HRP was injected in the lacrimal gland. After applying HRP to all the ramifications of the maxillary and ophthalmic divisions of the trigeminal nerve, labeled neurons were found in the PTPG. Numerous PTPG fibers were detected in the ethmoidal and sphenopalatine nerves. The presence of PTPG fibers in the supraorbital, infratrochlear, zygomaticotemporal, zygomaticofacial-inferior palpebral, sphenopalatine and infraorbital-superior alveolar nerves has not hitherto been reported in mammals.

Stimulation of the superior sagittal sinus in the cat causes release of vasoactive peptides

External jugular vein blood was sampled in the anesthetized cat during electrical stimulation of the superior sagittal sinus (SSS), and the levels of calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), substance P (SP) and neuropeptide Y (NPY) were measured with sensitive radioimmunoassays. CGRP levels rose by 85% and VIP levels by 300% while there was no change in SP or NPY levels in the same samples. These data provide the first evidence that activation of the trigeminovascular system, by selective stimulation of nociceptive craniovascular afferents, causes releases of vasodilator peptides and further implicates this system in the pathophysiology of migraine.

High-frequency stimulation of the facial nerve results in local cortical release of vasoactive intestinal polypeptide in the anesthetised cat

Local cortical release of vasoactive intestinal polypeptide (VIP) was measured using a sensitive radioimmunoassay following direct electrical stimulation of the facial nerve in the anaesthetised cat. During activation of the facial nerve dilator pathway VIP was released at the cortex and collected into a physiological superfusate, its concentration increasing from 4.2 +/- 1.2 to 15.5 +/- 2.4 pmol/l. Administration of the nicotinic ganglion blocking agent hexamethonium (10 mg/kg i.v.) eliminated this response demonstrating that the release is mediated via an autonomic ganglion. Given previous experiments that have demonstrated that stimulation of the facial nerve leads to a neurogenically mediated dilatation of the cerebral vasculature, these data further implicate VIP as the transmitter in this pathway.

Vascular relaxation properties of calcitonin gene-related peptide and vasoactive intestinal polypeptide in subarachnoid hemorrhage

The vascular relaxation effects of calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) on the dog basilar artery after experimentally produced subarachnoid hemorrhage (SAH) were examined in vitro by an isometric tension recording method. Both CGRP and VIP induced dose-dependent relaxations in ring segments of the intact basilar artery of control dogs. The vasorelaxant action of CGRP was more potent than that of VIP. The single-injection model of SAH was produced by injection of fresh autologous arterial blood (1 ml/kg body weight) into the cisterna magna on Day 0 of the post-SAH period, and the double-injection model was produced by two injections of blood (0.5 ml/kg each) on Days 0 and 2. Narrowing of the basilar arteries on vertebral angiograms was most prominent on Day 3 or 7 in the single- or double-injection model, respectively. Relaxation of the basilar artery induced by CGRP and VIP was to some extent decreased on Days 3 and 7 of the post-SAH period in the single-injection model, and on Days 7 and 14 in the double-injection model. However, the vasorelaxant effects of CGRP and VIP were significantly enhanced on Day 14 of the post-SAH period in the single-injection model, and on Days 28 and 42 in the double-injection model. Subsequently, these effects returned to control levels by Days 28 or 63 in the single- or double-injection model, respectively.

Target-related patterns of co-existence of neuropeptide Y, vasoactive intestinal peptide, enkephalin and substance P in cranial parasympathetic neurons innervating the facial skin and exocrine glands of guinea-pigs

The patterns of co-existence of neuropeptides in cranial autonomic neurons of guinea-pigs have been examined with quantitative double-labelling immunofluorescence and retrograde axonal tracing using Fast Blue. Within the sphenopalatine, otic, sublingual and submandibular ganglia, and a prominent intracranial ganglion associated with the glossopharyngeal nerve, most neurons contained immunoreactivity of vasoactive intestinal peptide, neuropeptide Y, enkephalin and substance P in combinations that were correlated with their projections. Hair follicles in the facial skin formed a major target of sphenopalatine ganglion cells. The combinations of peptides co-existing in these neurons depended upon the region of the skin where the follicles were located. The parotid gland was innervated by neurons with cell bodies in the otic ganglion or the intracranial ganglion. Most of these neurons contained immunoreactivity to all four peptides. The sublingual gland was innervated by local ganglion cells usually containing immunoreactivity to neuropeptide Y, vasoactive intestinal peptide and substance P. The submandibular gland was innervated by local ganglion cells containing enkephalin immunoreactivity and low levels of immunoreactivity to neuropeptide Y. Presumptive vasodilator neurons, containing immunoreactivity to vasoactive intestinal peptide but no other peptide examined here, comprised less than 10% of cranial autonomic ganglion cells. These results demonstrate that the patterns of co-existence of neuropeptides in cranial autonomic neurons show a high degree of target specificity. The discovery that hair follicles form a major parasympathetic target implies a broader range of actions of cranial autonomic neurons than has been suspected until now.

Long-term chemical sympathectomy leads to an increase of neuropeptide Y immunoreactivity in cerebrovascular nerves and iris of the developing rat

Short-term (surgical) and long-term (chemical) sympathectomy have revealed the presence of a population of neuropeptide Y-like immunoreactive nerve fibres which do not degenerate in parallel with noradrenaline-containing nerves supplying cerebral vessels and the iris of the rat. Two days after bilateral removal of the superior and middle cervical ganglia of 7-week-old rats, noradrenaline-containing nerves could not be detected along any of the arteries of the rat circle of Willis or of the iris, but 18-32% of neuropeptide Y-like immunoreactive nerves remained. Long-term treatment (6 weeks) with guanethidine commencing in developing 1-week-old rats caused degeneration of the sympathetic neurons in cervical ganglia and disappearance of 5-hydroxydopamine-labelled nerves (that showed dense-cored vesicles at the electron microscope level) from rat cerebral vessels, but did not significantly change the density of neuropeptide Y-like immunoreactive axons on the vessels. Furthermore, whilst in control rats neuropeptide Y-like immunoreactivity was localized largely within 5-hydroxydopamine-labelled cerebrovascular nerves, after long-term sympathectomy with guanethidine, neuropeptide Y-like immunoreactivity was seen only in nerves lacking small dense-cored vesicles. A small number of catecholamine-containing nerves appeared along the internal carotid and anterior cerebral arteries after long-term sympathectomy; these may arise from neurons of central origin. These results suggest that as a consequence of long-term sympathectomy with guanethidine, compensatory changes occur, involving an increase in the expression of neuropeptide Y-like immunoreactivity in non-sympathetic axons in cerebrovascular nerves and iris of the rat. In contrast, the neuropeptide Y-like immunoreactive nerves in the dura mater appear to be entirely sympathetic, since none were present after short-term sympathectomy and none appeared after long-term sympathectomy.

Sphenopalatine ganglion stimulation increases regional cerebral blood flow independent of glucose utilization in the cat

Regional cerebral blood flow was determined using the tracer [14C]iodoantipyrine and regional brain dissection, and regional cerebral glucose utilization determined using the 2-deoxyglucose method, in the alpha-chloralose-anesthetized cat to evaluate the effect of electrical stimulation of the sphenopalatine (pterygopalatine) ganglion. Unilateral stimulation for either a short period (7-10 min) or a longer period (45 min) resulted in increases in blood flow in the ipsilateral cerebral cortex of up to 45% (parietal cortex) with, in addition, increased flow in the white matter of the corpus callosum (42%). The flow changes for both brief and prolonged stimulation were not significantly different. Flow was not altered in either the brainstem or basal ganglia (caudate nucleus). In contrast to these changes in cerebral blood flow no changes in cerebral glucose utilization were seen in any of the brain areas studied and in particular there were no changes in the areas in which blood flow increased. These data provide clear evidence that the innervation of the cerebral vasculature from the main parasympathetic ganglion can alter cerebral blood flow independent of cerebral metabolism.

Noradrenergic and peptidergic innervation of the extrinsic vessels and microcirculation of the rat cremaster muscle

The noradrenergic and peptidergic innervation of the extrinsic vessels and microcirculation of the rat cremaster muscle was examined. Catecholamine-containing nerves were identified histochemically by glyoxylic acid-induced fluorescence and tyrosine hydroxylase immunoreactivity (TH-IR). The extrinsic pudic-epigastric artery and vein as well as the entire intramuscular arteriolar network was innervated by noradrenergic axons. The capillaries and intramuscular venules of the cremaster muscle were devoid of a noradrenergic innervation. Immunohistochemical double-labeling demonstrated that most, if not all, of the TH-IR axons also possessed neuropeptide Y immunoreactivity (NPY-IR), implying colocalization of the norepinephrine and NPY in the perivascular nerves. No vasoactive intestinal peptide immunoreactivity (VIP-IR) was found, except for occasional VIP-IR axons associated with the pudic-epigastric artery. Substance P immunoreactive (SP-IR) axons formed a sparse plexus around the arteries and larger arterioles. Calcitonin gene-related peptide immunoreactivity (CGRP-IR) had a similar distribution to the SP-IR axons. CGRP-IR was also observed in axons alongside some smaller arterioles and capillaries. The extrinsic vessels and intramuscular arteriolar network of the rat cremaster muscle are innervated by noradrenergic axons which contain NPY and by presumed sensory nerves containing SP and/or CGRP. Both types of nerves may contribute to regulation of microvascular function.

Microvascular spasm is mediated by vasopressin fibers in the rat hippocampal slice

Microvessels in the rat hippocampal slice can be used as an in vitro model for the study of cerebral vasospasm. Serum from coagulated blood causes prompt and long-lasting microvascular constriction that is neurogenic in nature. Here we show that a candidate spasmogen, thromboxane B2, has excitatory action on neural elements in the slice. However, spasmogenic serum lacks this excitatory effect. Instead, it is inhibitory for a major population of slice neurons. Thus, neurogenic microvascular spasm is produced by a subpopulation of slice neurons or projection fibers, not all neurons acting in concert. Arginine vasopressin (AVP) is contained in fibers that project to the hippocampus, and hippocampal microvessels contain pressor (V1) receptors for the peptide. AVP causes vasoconstriction in the slice, and a specific V1 antagonist for the peptide blocks the microvascular spasm induced by blood serum. The results are interpreted to mean that neurogenic microvascular spasm is mediated by locally released AVP.

Acetylcholine and vasoactive intestinal peptide in cerebral blood vessels: effect of extirpation of the sphenopalatine ganglion

The innervation of cerebral blood vessels by nerve fibers containing acetylcholinesterase (AChE) and vasoactive intestinal peptide (VIP) and the vasomotor effects of the two neurotransmitters have been analyzed in the rat following the uni- or bilateral removal of the sphenopalatine ganglion (SPG), which is thought to be the major origin of this innervation. Histochemistry of AChE-positive nerve fibers and the immunoreactivity toward VIP revealed only a 30% reduction in the innervation pattern of the rostral part of the cerebral circulation following the operation. At approximately 4 weeks postoperatively, the original nerve network was restored. Quantitative measurements of cholineacetyltransferase activity and VIP revealed similar reductions in the levels of collected large cerebral arteries at the base of the brain and in small pial vessels overlying the cerebral cortex at the various postoperative times following uni- or bilateral removal of the SPG. The two techniques thus complemented each other. Vasomotor reactivity to acetylcholine (ACh) and VIP was examined in proximal segments of the middle cerebral artery at the various postoperative times. Generally, the removal of the SPG had no effect on the responses to ACh or VIP. The evidence indicates that only approximately one-third of the cholinergic/VIP innervation of the rostral part of the cerebral circulation originates in the SPG.

Effect of stimulation of the sphenopalatine ganglion on cortical blood flow in the rat

The effects of electrical stimulation of the sphenopalatine ganglion on cortical blood flow and gas partial pressures (PO2 and PCO2) were studied in the anesthetized rat. Tissue PO2, PCO2, and local CBF were measured simultaneously in both parietal cortices by means of mass spectrometry. Stimulation of the sphenopalatine ganglion increased CBF and tissue PO2 by approximately 50 and 20%, respectively, in the ipsilateral parietal cortex. Smaller but significant increases in CBF and tissue PO2 were simultaneously seen in the contralateral parietal cortex. These variations were also accompanied by small decreases in PCO2 in both parietal cortices and a 5% increase in mean arterial pressure, whereas cortical electrical activity did not change. We conclude that the cholinergic (and vasoactive intestinal polypeptidergic) innervation of the cerebral blood vessels, arising from the sphenopalatine ganglion has significant vasomotor potential and that this system may be of functional importance.

Origins and pathways of cerebrovascular vasoactive intestinal polypeptide-positive nerves in rat

In order to clarify the origins and pathways of vasoactive intestinal polypeptide (VIP)-containing nerve fibers in cerebral blood vessels of rat, denervation experiments and retrograde axonal tracing methods (true blue) were used. Numerous VIP-positive nerve cells were recognized in the sphenopalatine ganglion and in a mini-ganglion (internal carotid mini-ganglion) located on the internal carotid artery in the carotid canal, where the parasympathetic greater superficial petrosal nerve is joined by the sympathetic fibers from the internal carotid nerve, to form the Vidian nerve. VIP fiber bridges in the greater deep petrosal nerve and the internal carotid nerve reached the wall of the internal carotid artery. Two weeks after bilateral removal of the sphenopalatine ganglion or sectioning of the structures in the ethmoidal foramen, VIP fibers in the anterior part of the circle of Willis completely disappeared. Very few remained in the middle cerebral artery, the posterior cerebral artery, and rostral two-thirds of the basilar artery, whereas they remained in the caudal one-third of the basilar artery, the vertebral artery, and intracranial and carotid canal segments of the internal carotid artery. One week after application of true blue to the middle cerebral artery, dye accumulated in the ganglion cells in the sphenopalatine, otic and internal carotid mini-ganglion; some of the cells were positive for VIP. The results show that the VIP nerves in rat cerebral blood vessels originate: (a) in the sphenopalatine, and otic ganglion to innervate the circle of Willis and its branches from anterior and caudally and (b) from the internal carotid mini-ganglion to innervate the internal carotid artery at the level of the carotid canal and to some extent its intracranial extensions.

Immunohistochemical study of neuropeptides in vagal and glossopharyngeal afferent neurons in the rat

The presence and distribution of multiple neuropeptides in vagal and glossopharyngeal afferent ganglia of the rat were studied using immunohistochemistry. Substance P-, calcitonin-gene related peptide-, cholecystokinin-, neurokinin A-, vasoactive intestinal polypeptide-, and somatostatin-immunoreactive neurons were detected in each visceral afferent ganglion. Neurotensin-immunoreactive cells were not observed. In the nodose ganglion (inferior ganglion of the vagus nerve) occasional immunoreactive cells were scattered throughout the main (caudal) portion of the ganglion with small clusters of cells seen in the rostral portion. The pattern of distribution of the various peptides in the nodose ganglion was similar, with the exception of vasoactive intestinal polypeptide-immunoreactive neurons which exhibited a more caudal distribution. The relative numbers of immunoreactive cells varied, with the greatest numbers being immunoreactive for substance P or vasoactive intestinal polypeptide, and the lowest numbers being immunoreactive for neurokinin A and somatostatin. A build-up of immunoreactivity for each of the peptides, except somatostatin and neurotensin, was detected in vagal nerve fibers of colchicine-injected ganglia. Numerous peptide-immunoreactive cells were also found in the petrosal (inferior ganglion of the glossopharyngeal nerve) and jugular (superior ganglion of the vagus nerve) ganglia. No specific intraganglionic distribution was noted although the relative numbers of cells which were immunoreactive for the different peptides varied considerably. Substance P and calcitonin-gene related peptide were found in large numbers of cells, cholecystokinin was seen in moderate numbers of cells, and neurokinin A, vasoactive intestinal polypeptide and somatostatin were seen in fewer cells. These data provide evidence for the presence and non-uniform distribution of multiple peptide neurotransmitters in vagal and glossopharyngeal afferent neurons. In general, relatively greater numbers of immunoreactive cells were located in the rostral compared with caudal nodose ganglion, and in the petrosal and jugular ganglia compared with the nodose ganglion. Thus, multiple neuropeptides may be involved as afferent neurotransmitters in the reflexes mediated by vagal and glossopharyngeal sensory nerves.

Heterogeneous vasomotor responses of anatomically distinct feline cerebral arteries

1. The vasomotor reactivity to a number of neurotransmitters and blood-borne substances was evaluated in several anatomically distinct arteries of the cat cerebral circulation. Few regional differences were observed in their vasoconstrictor responses to noradrenaline, dopamine, 5-hydroxytryptamine and prostaglandin F2 alpha. Only the anterior cerebral artery reacted strongly to all vasoconstrictor agents. 2. Adenosine, acetylcholine and histamine induced pronounced relaxation in the vast majority of the major cerebral arteries. The relaxation elicited by adenosine showed a slight degree of heterogeneity between the arteries and the overall response accounted for 81 +/- 6% of the pharmacologically-induced tone. On the other hand, the dilatation induced by acetylcholine and histamine varied as a function of the anatomical localization of the cerebral arteries. The acetylcholine-induced vasodilatation was significantly more pronounced in the middle cerebral, anterior communicating and anterior cerebellar arteries, with respective responses of 72, 66 and 83% of the induced tone as compared to 43% in the other vessels. However, all arteries were equally sensitive to acetylcholine with an overall mean pD2 value of 7.47 +/- 0.06. The most heterogeneous results were obtained with histamine and applied both to the magnitude of the maximal response and the sensitivity of the various arteries to this amine. The intensity of the relaxation varied from 20% (anterior communicating artery) to 118% (posterior cerebellar artery). 3. Among the neuropeptides studied, substance P and bradykinin were considerably less potent than vasoactive intestinal peptide on all the cerebral arteries. The least responsive vessel to bradykinin was the anterior cerebral artery with a maximal response of 22 +/- 5% of the induced-tone and a pD2 value of 7.56 +/- 0.24. All vessels responded weakly to substance P and those from the vertebrobasilar circulation were significantly less sensitive to this neuropeptide with pD2 values around 8.07 as compared to 9.82 in the more rostral arteries. Although all vessels were equally sensitive to vasoactive intestinal peptide, the dilator responses were significantly less pronounced in the middle cerebral and basilar arteries (maximal response of 86 +/- 5% and 69 +/- 6% of the induced-tone, respectively, as compared to 110 +/- 9% in the other vessels). 4. The vertebrobasilar arteries were as reactive, if not more reactive, to vasoconstrictors than the vessels originating from the carotid circulation. In contrast, the dilator responses were less marked in most caudal arteries. Such dichotomies may be important in the regulation of local cerebral blood flow. 5. The results emphasize the considerable heterogeneity in the vasomotor responses to a given substance among the various cerebral arteries. Further, they suggest the presence of multiple receptor populations which mediate opposite effects and which are distributed in different proportions among the cephalic arteries.

Cerebral arterial innervation by nerve fibers containing calcitonin gene-related peptide (CGRP): I. Distribution and origin of CGRP perivascular innervation in the rat

The origin, density and distribution of calcitonin gene-related peptide (CGRP) immunoreactivity in cerebral perivascular nerves and the trigeminal ganglion of rats were examined in this study. CGRP immunoreactive axons were abundant on the walls of the rostral circulation of the major cerebral arteries in the circle of Willis. The fibers form a grid- or meshwork of longitudinal and circumferential axons studded with numerous varicose swellings. The density of CGRP fibers was particularly high at the bifurcation of major arteries. A few CGRP fibers cross the midline to innervate arteries on the contralateral side of the arterial tree. The arteries of the caudal circulation were sparsely innervated by CGRP fibers. In the trigeminal ganglion, about 30% of the ganglion cells had CGRP immunoreactivity. The cell size of most (75%) of CGRP neurons was less than 30 micron in diameter. There was no significant difference in staining density between small and large CGRP neurons. Unilateral transection of the maxillary and mandibular divisions of the trigeminal nerve caused a substantial decrease of CGRP immunoreactivity in the ipsilateral dorsal two-thirds of the trigeminal nucleus and cervical spinal cord but did not noticeably change the diameter of the vascular lumen or the densities of CGRP fibers in the walls of the cerebral arteries. In contrast, unilateral transection that included the ophthalmic division eliminated CGRP fibers on the ipsilateral cerebral arteries and eliminated CGRP immunoreactivity throughout the trigeminal nucleus in the brainstem and rostral cervical cord. In addition, these lesions caused a significant reduction in the diameter of the denervated arteries. The present study demonstrates that CGRP, a putative neurotransmitter/neuromodulator, is especially abundant in the rostral cerebral circulation and is derived from the ipsilateral ophthalmic division of the trigeminal nerve. In addition, the loss of CGRP perivascular nerves is associated with a reduction of the arterial lumen. This suggests that CGRP is a strong candidate as a nerve-derived trophic factor at trigeminal terminals and provides additional evidence that CGRP is a component in the trigeminovascular system influencing vascular diameter.

Possible origins of cerebrovascular nerve fibers showing vasoactive intestinal polypeptide-like immunoreactivity: an immunohistochemical study in the dog

Changes of vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) in perivascular nerve fibers of the major cerebral arteries were examined immunohistochemically in the dog. The density of cerebrovascular nerve fibers showing VIP-LI (the average number of nerve fibers with VIP-LI in a unit area of the major cerebral arteries) was estimated, by using whole-mount preparations after extirpation of the pterygopalatine, otic or superior cervical ganglion. After pterygopalatine ganglionectomy, the density was markedly decreased in major cerebral arteries of both anterior circulation (the anterior cerebral and middle cerebral arteries) and posterior circulation (the basilar, superior cerebellar, posterior cerebral and posterior communicating arteries). After otic ganglionectomy, the density was moderately reduced in the major arteries of the posterior circulation, but was not decreased in those of the anterior circulation. After superior cervical ganglionectomy, the density was decreased markedly in the major cerebral arteries of the posterior circulation, and moderately in those of the anterior circulation. The results also indicate that the pterygopalatine, otic and superior cervical ganglia supply perivascular nerve fibers showing VIP-LI to the major cerebral arteries bilaterally with an ipsilateral dominance.

Parasympathetic innervation of cutaneous blood vessels by vasoactive intestinal polypeptide-immunoreactive and acetylcholinesterase-positive nerves: histochemical and experimental study on rat lower lip

The distribution and origin of perivascular acetylcholinesterase-active and vasoactive intestinal polypeptide-immunoreactive nerve fibers were studied in the rat lower lip by means of acetylcholinesterase histochemistry and vasoactive intestinal polypeptide immunohistochemistry. The perivascular nerve fibers stained intensely with both histochemical techniques and were widely distributed on small arteries and arterioles of the lower lip, especially in the transitional zone between the hairy skin and the mucous membrane. The distributions of the two types of fibers were very similar and most of them showed overlapping coloration, on consecutive staining for vasoactive intestinal polypeptide and acetylcholinesterase. Both acetylcholinesterase-positive and vasoactive intestinal polypeptide-immunoreactive fibers were completely lost on removal of the otic ganglion, while they were not affected by sympathetic ganglion removal or sensory nerve sectioning. In the otic ganglion, most cells exhibited acetylcholinesterase activity, and about 60% of the cells showed light to heavy vasoactive intestinal polypeptide immunoreactivity. These findings indicate that vessels in the rat lip are innervated by parasympathetic fibers originating from the otic ganglion and support the view that vasoactive intestinal polypeptide is present in cholinergic neurons. This may suggest the possible control by the parasympathetic nervous system of cutaneous blood vessels through vasoactive intestinal polypeptide-containing cholinergic neurons, in general or at least in the facial area.

Co-existence of immunoreactivity to neuropeptide Y and vasoactive intestinal peptide in non-noradrenergic axons innervating guinea pig cerebral arteries after sympathectomy

We have used double-labelling immunofluorescence to examine the coexistence of immunoreactivity (IR) to neuropeptide Y (NPY), tyrosine hydroxylase (TH) and vasoactive intestinal peptide (VIP) in autonomic neurons innervating guinea pig cerebral arteries. In the rostral circle of Willis of control animals. NPY-IR was detected in 86% of axons with TH-IR (noradrenergic) and 18% of VIP-IR (non-noradrenergic) axons. No axons contained both VIP-IR and TH-IR. Ten to 12 days after bilateral removal of the superior cervical ganglia all TH-IR axons had disappeared. The density of VIP-IR axons was unchanged but now 70% of VIP-IR axons contained NPY-IR. These results show that NPY is not exclusively associated with noradrenergic axons in the cerebral vasculature. Furthermore, NPY levels in non-noradrenergic axons increased following sympathetic denervation.

Pathway of nerves with vasoactive intestinal polypeptide-like immunoreactivity to the major cerebral arteries of the rat

The pathway of nerves with vasoactive intestinal polypeptide (VIP)-like immunoreactivity to the major cerebral arteries was studied in rats by means of the indirect immunofluorescent method. The fibers are densely distributed in the ethmoidal nerves and in the adventitia of both the external and internal ethmoidal arteries. Section of both ethmoidal nerves and external ethmoidal arteries before they enter the cranial cavity induced a marked reduction of VIP-like immunoreactive fibers in the walls of the vessels of the circle of Willis and its major branches. However, section of the external ethmoidal artery alone did not result in visible changes of the nerves around major cerebral arteries. The present study suggests that VIP-like immunoreactive fibers surrounding major cerebral arteries of the rat arise from fibers in the ethmoidal nerve showing immunoreactivity to VIP.

Changes of vasoactive intestinal polypeptide-like immunoreactivity in cerebrovascular nerve fibers after cervical sympathectomy in the dog

The presence of vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) was confirmed in many neuronal perikarya of the superior cervical ganglion (SCG), as well as in many perivascular nerve fibers of the major cerebral arteries in the dog. After bilateral extirpation of the SCG, VIP-LI was decreased markedly in the basilar artery and the posterior cerebral artery, and moderately in the middle and anterior cerebral arteries.

Nerve fibers surrounding intracranial and extracranial vessels from human and other species contain dynorphin-like immunoreactivity

Dynorphin B(20-32) was visualized by immunohistochemistry in guinea-pig and rat perivascular nerve fibers and was measured by radioimmunoassay within the walls of feline, canine, bovine and human cephalic and systemic arteries and veins. Canine vessels contained the highest levels. When human blood vessels or trigeminal ganglia were subjected to reverse-phase high-performance liquid chromatography, dynorphin immunoreactivity exhibited a retention time identical to that of synthetic dynorphin B. No differences in dynorphin-like immunoreactivity were measurable between feline systemic arteries and veins, or between cephalic and systemic vessels. The highest amounts were present in leptomeninges devoid of large pial arteries. Relatively high levels were also measured in feline and human trigeminal ganglia and feline superior cervical and sphenopalatine ganglia, three sources of projecting perivascular axons. Levels did not diminish, however, in ipsilateral feline cephalic vessels following either unilateral trigeminal or superior cervical ganglionectomies. Hence, dynorphin-containing fibers may project from parasympathetic cell bodies or perhaps from intrinsic brain sources. Previously published reports indicate that the kappa agonist dynorphin does not modify vessel tone when added in vitro but does inhibit release of neurotransmitters from afferent and sympathetic axons via prejunctional receptors. These observations suggest a pharmacological role for dynorphin on sensory and autonomic functions of the vasculature.

Perivascular innervation of the cerebral circulation: involvement in the pathophysiology of subarachnoid hemorrhage

The authors describe the perivascular innervation of cerebral circulation. The different nerve fiber systems can be classified as follows: 1. Sympathetic (noradrenaline, neuropeptide Y), 2. Parasympathetic (acetylcholine, vasoactive intestinal peptide/peptide histidine isoleucine (methionine), 3. Sensory (tachykinins, calcitonin gene-related peptide). Each of these systems is outlined by their basic anatomical and physiological facts. Then, the etiology of cerebral vasospasm after subarachnoid hemorrhage is discussed in relation to the cerebrovascular innervation.

Atropine potentiates neurogenic vasodilatation of the feline infraorbital artery: possible mechanisms

After treatment with guanethidine to inactivate sympathetic nerves, the feline infraorbital artery (IOA) relaxes in response to activation of periarterial nerves in vitro. This response was 60-65% greater in magnitude and 50% longer in duration in the presence of atropine, thus revealing a significant non-adrenergic, non-cholinergic (NANC) dilator response which is potentiated by blockade of muscarinic receptors. Nerve-mediated dilations and the potentiating effect of atropine were endothelial cell-independent. In the presence of atropine the resting membrane potential (-51 +/- 2 mV) of infraorbital vascular smooth muscle cells was not changed by activation of nerves, nor by exogenously applied vasoactive intestinal polypeptide (VIP). Electrical stimulation caused release of VIP from this artery, but atropine did not measurably enhance the degree of release of VIP. Therefore, although presynaptic, muscarinic inhibition of release of a NANC transmitter probably occurs in the IOA, either VIP is not the transmitter involved in this response or the changes in release of VIP are too slight to be detected by the in vitro techniques employed in this study.

Spontaneous and neurogenic constriction of microvasculature in the rat hippocampal slice

The hippocampal slice is characterized by laminar organization and defined synaptic circuitry and provides an in vitro model system for the study of neuronal membrane properties, the action of putative neurotransmitters, and synaptic plasticity. Because the hippocampus is densely vascularized and hippocampal microvessels respond to a variety of stimuli that also affect the activity of neurons in the slice, the preparation is also especially well suited to investigating the physiologic relationship between neurons and intraparenchymal blood vessels. Here we address the issue of potential neurogenic control of cerebral microvasculature using electrical stimuli and specific neurotoxins. A small proportion of slice microvessels displayed spontaneous rhythmic activity that was independent of any exogenous stimulus. The majority of slices examined contained microvessels that responded to a train of electrical impulses delivered to discrete neural pathways. Under particular stimulus conditions, the vascular response could be completely blocked by 1 microM tetrodotoxin. The results are taken to support the existence of a neurogenic influence on penetrating arterioles.

Peptides in the mammalian cardiovascular system

Ample immunocytochemical evidence is now available demonstrating that several peptides are present in the mammalian cardiovascular system where they are localised to nerve fibres and myocardial cells. The neuropeptides (neuropeptide Y, calcitonin gene-related peptide, tachykinins and vasoactive intestinal polypeptide) are localised to large secretory vesicles in subpopulations of afferent or efferent nerves supplying the heart and vasculature of several mammals, including man. Although they often exert potent pharmacological effects on the tissues in which they occur their physiological significance has still to be established. They may act directly via specific receptors and/or indirectly by influencing the release and action of other cardiovascular transmitters. In marked contrast, atrial natriuretic peptide is produced by cardiac myocytes and considered to act as a circulating hormone.

Vasoactive-intestinal-polypeptide (VIP)-like immunoreactive cells in the skull base of rats. A combined study using acetylcholinesterase histochemistry

We investigated the distribution of vasoactive intestinal polypeptide (VIP)-like immunoreactive cell bodies in relation to the major cerebral and internal carotid arteries at the skull base in rats. Acetylcholinesterase (AChE) histochemistry was also applied to investigate the localization of this enzyme. VIP staining revealed a few positive cell bodies in nerves close to the internal carotid artery at the base of the skull as well as in the cerebral arterial wall. Ganglion-like cell bodies were detectable within the greater superficial petrosal (GSP) nerve. AChE activity was observed in VIP-like immunoreactive cell bodies along the whole of the GSP nerve. These cell bodies in the GSP nerve may give rise to at least some of the perivascular VIP- and AChE-containing nerves of the internal carotid arteries at the base of the skull.

Evidence that vasoactive intestinal polypeptide (VIP) mediates neurogenic vasodilation of feline cerebral arteries

In this study the magnitude of non-sympathetic, non-cholinergic neurogenic vasodilation of feline cerebral arteries in vitro was correlated with the extent of innervation by VIP-immunoreactive nerves. Well-innervated arteries underwent nerve-mediated relaxation whereas those that are not supplied with VIP-containing axons did not relax to transmural nerve stimulation. The relaxation of cerebral arteries that are well endowed with VIP-immunoreactive nerves was selectively and reversibly inhibited by VIP-specific antiserum. Substance P-specific antiserum did not affect the dilator responses. We conclude that VIP is a functional neurodilator transmitter in the cerebral circulation.

Effects of capsaicin on vascular smooth muscle

Acute administration of capsaicin in vitro produced either vascular smooth muscle contraction (cat middle cerebral artery) or smooth muscle relaxation (guinea pig carotid artery and thoracic aorta). Prior in vivo treatment with capsaicin abolished the relaxation response of guinea pig vessels to acute capsaicin. Instead a contractile response was seen after chronic capsaicin treatment, suggesting that the relaxation response produced by capsaicin is due to release of a vasodilator substance. Substance P caused relaxation in both cat cerebral arteries and the guinea pig thoracic aorta, an effect which was abolished or reduced by endothelial damage. However, responses to acute capsaicin were not altered by endothelial damage, suggesting that substance P does not mediate the relaxation response to acute capsaicin administration. Exposure to capsaicin in vitro did not affect the neurogenic vasodilator response of cat cerebral arteries and did not alter substance P levels. Therefore, it was concluded that the acute effect of capsaicin is composed of two components. A contractile response is most likely due to direct effects on vascular smooth muscle, while a relaxation response is attributed to release of an as yet unidentified bioactive substance distinct from substance P.

Cerebrovascular projections from the sphenopalatine and otic ganglia to the middle cerebral artery of the cat

The location of the postganglionic parasympathetic cell bodies projecting to cerebral arteries is unknown. Using axonal tracing techniques, we examined whether the sphenopalatine ganglia (associated with the seventh cranial nerve) and otic ganglia (associated with ninth cranial nerve) contain perikarya which send axons to the feline middle cerebral artery (MCA). The tracers horseradish peroxidase (HRP: 3 cats) or wheat germ agglutinin (WGA: 6 cats) were applied to the MCA in a slow release polymeric system. Three days later the SPG, otic ganglia, and rete mirabile were harvested bilaterally and processed for tracer by the TMB method (HRP) or immunohistochemistry (WGA). In a given animal, approximately equal numbers of cells containing axonal tracer were found in both SPG. Labeled fibers occasionally could be seen extending into the vidian nerve. Positive cells were also found in the otic ganglia and in the walls of the internal rete mirabile. These results provide the first identification of parasympathetic cell bodies projecting to cerebral blood vessels.

Circulation during hypoxia in birds

The effects of hypoxia on the avian cardiovascular system are reviewed. The avian cardiovascular system seems well adapted to deal with the stress of hypoxia. In general, birds are remarkably tolerant of hypoxia, with some species being capable of performing vigorous exercise at extreme altitude. During hypoxia at rest, the circulation maintains arterial pressure, increases cardiac output, and redistributes blood flow so oxygen delivery to the heart and brain is maintained. During exercise, further adjustments are required, since exercising muscle has large oxygen requirements. The mechanisms responsible for producing these circulatory changes are largely unknown. The transport steps that limit O2 delivery during hypoxia are also poorly understood.