Parasympathetic cerebrovascular innervation: an anterograde tracing from the sphenopalatine ganglion in the rat

Sphenopalatine Ganglion Stimulation Upregulates Transport of Temozolomide across the Blood-Brain Barrier

Sphenopalatine ganglion (SPG) stimulation has been shown to reversibly alter blood-brain barrier (BBB) permeability. It is widely used for the treatment of cluster headaches in Europe and is well tolerated in humans. The therapeutic potential for SPG stimulation in other central nervous system (CNS) diseases has yet to be explored. Glioblastoma Multiforme (GBM) remains one of the most difficult primary CNS neoplasms to treat, with an average survival of approximately 18 months at the time of diagnosis. Since 2004, the gold standard of treatment for GBM in the United States includes surgery followed by treatment with temozolomide (TMZ) and radiation. We sought to determine if SPG stimulation could increase chemotherapy concentrations in rodent brains with an intact BBB. Here, we show a statistically significant (p = 0.0006), five-fold upregulation of TMZ crossing the BBB and reaching brain parenchyma in rats receiving low-frequency (LF, 10 Hz) SPG stimulation. All the measurements were performed using a highly sensitive liquid chromatography mass spectrometry (LCMS) method that was developed for quantitation of TMZ in plasma and brain tissue. Our treatment paradigm shows novel delivery route by which we could more effectively and safely deliver TMZ in a targeted manner, to minimize systemic toxicity and maximize action at the target tissue.

Sphenopalatine ganglion stimulation is a reversible and frequency-dependent modulator of the blood-brain barrier

BACKGROUND

The sphenopalatine ganglion (SPG) is a vasoactive mediator of the anterior intracranial circulation in mammals. SPG stimulation has been demonstrated to alter blood-brain barrier (BBB) permeability, although this phenomenon is not well characterized.

OBJECTIVE

To determine the effect of SPG stimulation on the BBB using rat models.

METHODS

Extravasation of fluorescent tracer 70 kDa FITC-dextran into rat brain specimens was measured across a range of stimulation parameters to assess BBB permeability. Tight junction (TJ) morphology was compared by assessing differences in the staining of proteins occludin and ZO-1 and analyzing ultrastructural changes on transmission electron microscopy (TEM) between stimulated and unstimulated specimens.

RESULTS

SPG stimulation at 10 Hz maximally increased BBB permeability, exhibiting a 6-fold increase in fluorescent traceruptake (1.66% vs 0.28%, p < 0.0001). This effect was reversed 4-hours after stimulation (0.36% uptake, p = 0.99). High-frequency stimulation at 20 Hz and 200 Hz did not increase tracer extravasation, (0.26% and 0.28% uptake, p = >0.999 and p = 0.998, respectively). Stimulation was associated a significant decrease in the colocalization of occludin and ZO-1 with endothelial markers in stimulated brains compared to control (74.6% vs. 39.7% and 67.2% vs. 60.4% colocalization, respectively, p < 0.0001), and ultrastructural changes in TJ morphology associated with increased BBB permeability were observed on TEM.

CONCLUSION

This study is the first to show a reversible, frequency-dependent increase in BBB permeability with SPG stimulation and introduces a putative mechanism of action through TJ disruption. Bypassing the BBB with SPG stimulation could enable new paradigms in delivering therapeutics to the CNS. Further study of this technology is needed.

Perivascular neurotransmitters: Regulation of cerebral blood flow and role in primary headaches

In order to understand the nature of the relationship between cerebral blood flow (CBF) and primary headaches, we have conducted a literature review with particular emphasis on the role of perivascular neurotransmitters. Primary headaches are in general considered complex polygenic disorders (genetic and environmental influence) with pathophysiological neurovascular alterations. Identified candidate headache genes are associated with neuro- and gliogenesis, vascular development and diseases, and regulation of vascular tone. These findings support a role for the vasculature in primary headache disorders. Moreover, neuronal hyperexcitability and other abnormalities have been observed in primary headaches and related to changes in hemodynamic factors. In particular, this relates to migraine aura and spreading depression. During headache attacks, ganglia such as trigeminal and sphenopalatine (located outside the blood-brain barrier) are variably activated and sensitized which gives rise to vasoactive neurotransmitter release. Sympathetic, parasympathetic and sensory nerves to the cerebral vasculature are activated. During migraine attacks, altered CBF has been observed in brain regions such as the somatosensory cortex, brainstem and thalamus. In regulation of CBF, the individual roles of neurotransmitters are partly known, but much needs to be unraveled with respect to headache disorders.

Parasympathetic innervation of vertebrobasilar arteries: is this a potential clinical target?

This review aims to summarise the contemporary evidence for the presence and function of the parasympathetic innervation of the cerebral circulation with emphasis on the vertebral and basilar arteries (the posterior cerebral circulation). We consider whether the parasympathetic innervation of blood vessels could be used as a means to increase cerebral blood flow. This may have clinical implications for pathologies associated with cerebral hypoperfusion such as stroke, dementia and hypertension. Relative to the anterior cerebral circulation little is known of the origins and neurochemical phenotypes of the parasympathetic innervation of the vertebrobasilar arteries. These vessels normally provide blood flow to the brainstem and cerebellum but can, via the Circle of Willis upon stenosis of the internal carotid arteries, supply blood to the anterior cerebral circulation too. We review the multiple types of parasympathetic fibres and their distinct transmitter mechanisms and how these vary with age, disease and species. We highlight the importance of parasympathetic fibres for mediating the vasodilatory response to sympathetic activation. Current trials are investigating the possibility of electrically stimulating the postganglionic parasympathetic ganglia to improve cerebal blood flow to reduce the penumbra following stroke. We conclude that although there are substantial gaps in our understanding of the origins of parasympathetic innervation of the vertebrobasilar arteries, activation of this system under some conditions might bring therapeutic benefits.

Changes in number of water-filled vesicles of choroid plexus in early and late phase of experimental rabbit subarachnoid hemorrhage model: the role of petrous ganglion of glossopharyngeal nerve

BACKGROUND

Cerebrospinal fluid (CSF) secretion may be increased in the early phases of subarachnoid hemorrhage (SAH), possibly via ischemic glossopharyngeal nerve discharges, and decreased due to glossopharyngeal nerve degeneration in the late phase of SAH; but this reflex pathway has not been definitively investigated. We studied the relationship between petrous ganglion of the glossopharyngeal nerve (GPN) and water vesicles of the choroid plexus (CP) in the early and late phases of SAH.

METHODS

This study was conducted on 30 rabbits, divided into four groups, with five rabbits in the control group (group I), five rabbits in the sham group (Group II), and 20 rabbits in the SAH group. In the SAH group, five of the animals were decapitated after 4 days of cisternal blood injections (Group III), and the other 15 animals were decapitated after 20 days of injections (Group IV). The Petrous Ganglia and CPs of lateral ventricles were removed and stained for stereological analysis.

RESULTS

The mean number of follicles per cubic millimeter was 5.3 ± 1.2 the in control group (Group I), 4.5 ± 0.9 in the sham group (Group II), 16.60 ± 3.77 the in early decapitated group (Group III), and 4.30 ± 0.84 in the late decapitated group (Group IV). The mean number of degenerated neuron density of petrous ganglions was 6 ± 2, 50 ± 6, 742 ± 96, and 2.420 ± 350 in the control (Group I), sham (Group II), early decapitated (Group III), and late decapitated group (Group IV), respectively. The mean number of water vesicles was statistically different after SAH between the early decapitated group (group III) and the late decapitated group (group IV) (P < 0.05).

CONCLUSIONS

We studied the relationship between petrous ganglion cells of the GPN and water vesicles of CP in the early and late phases of SAH, and found that CP vesicles are increased in the early phase of SAH due to irritation of GPN, and decreased in the late phase due to ischemic insult of the petrous ganglion and parasympathetic innervation of the CP.

The role of sympathectomy on the regulation of basilar artery volume changes in stenoocclusive carotid artery modeling after bilateral common carotid artery ligation: an animal model

BACKGROUND

Stenoocclusive carotid artery disease causes important histomorphologic changes in all craniocervical vasculatures, such as luminal enlargement, vascular wall thinning, elongation, convolutions, and aneurysm formation in the posterior circulation. Although increased pressure, retrograde blood flow, and biochemical factors are described in the pathogenesis of vascular remodelisation, the vasoregulatory role of the autonomic nervous system has not been investigated thus far. We investigated the relationship between the sympathetic nervous system and the severity of histomorphologic alterations of basilar arteries after bilateral common carotid artery ligation (BCCAL).

MATERIAL AND METHODS

This study was conducted on 21 rabbits. The rabbits were randomly divided into three groups: baseline group (n = 5), sympathectomy non-applied group (SHAM; n = 8), and sympathectomy applied group (n = 8) before bilateral common carotid artery ligation. Permanent ligation of the prebifurcations of the common carotid arteries was performed to replicate stenoocclusive caroid artery disease. Basilar artery volumes were measured after ligation. Volumes of the basilar arteries were estimated by stereologic methods and compared between groups.

RESULTS

Luminal enlargement, wall thinning, elongation, convolutions, and doligoectatic configurations were detected in the majority of basilar arteries. The mean basilar arterial volume was 4.27 ± 0.22 mm3 in the baseline group; 5.28 ± 0.67 mm(3) in the SHAM group, and 8.84 ± 0.78 mm3 in the study group. The severity of basilar enlargement was significantly higher in the study group compared with the SHAM (p < 0.005) and baseline groups (p < 0.001).

CONCLUSIONS

Sympathectomy causes basilar artery enlargment, which is beneficial for maintaining cerebral blood flow; however, it also causes wall thinning, elongation, convolution, and aneurysm formation, which may be hazardous in stenoocclusive carotid artery disease. Sympathectomy can prevent new vessel formation and hyperthyrophic changes at the posterior circulation. Neovascularisation is not detected adequately in sympathectomised animals.

Nitric oxide and cerebrovascular regulation

The cerebrovascular regulation involves highly complex mechanisms to assure that the brain is perfused at all times. These mechanisms depend on all components of the neurovascular units: neurons, glia, and vascular cells. All these cell types can produce nitric oxide (NO), a powerful vasodilator through different NO synthases. Many studies underlined the key role of NO in the maintenance of resting cerebral blood flow (CBF) as well as in the mechanisms that control cerebrovascular tone: autoregulation and neurovascular coupling. However, although the role of NO in the control of CBF has been largely investigated, the complexity of the NO system and the lack of specific NO synthase inhibitors led to still unresolved questions such as the origin of NO and the pathways by which it controls the vascular tone. In this chapter, the role of NO in the regulation of CBF is critically reviewed and discussed in the context of the neurovascular unit and the general principles of cerebrovascular regulation.

Effects of ischemic phrenic nerve root ganglion injury on respiratory disturbances in subarachnoid hemorrhage: an experimental study

INTRODUCTION

Phrenic nerves have important roles on the management of respiration rhythm. Diaphragm paralysis is possible in phrenic nerve roots ischemia in subarachnoid hemorrhage (SAH). We examined whether there is a relationship between phrenic nerve root ischemia and respiratory disturbances in SAH.

MATERIAL AND METHODS

This study was conducted on 5 healthy control and 14 rabbits with experimentally induced SAH by injecting autologous blood into their cisterna magna. Animals were followed up via monitors for detecting the heart and respiration rhythms for 20 days and then decapitaed by humanely. Normal and degenerated neuron densities of phrenic nerve root at the level of C4 dorsal root ganglia (C4DRG) were estimated by Stereological methods. Between the mean numerical density of degenerated neurons of C4DRG and respiratory rate/minute of groups were compared statistically.

RESULTS

Phrenic nerve roots, artery and diaphragm muscles degeneration was detected in respiratory arrest developed animals. The mean neuronal density of C4DRG was 13272 ±1201/mm3 with a mean respiration rate of 23 ±4/min in the control group. The mean degenerated neuron density was 2.240 ±450/mm(3) and respiration rhythm was 31 ±6/min in survivors. But, the mean degenerated neuron density was 5850 ±650/mm(3) and mean respiration rhythm was 34 ±7/min in respiratory arrest developed animals (n = 7). A linear relationship was noticed between the degenerated neuron density of C4DRG and respiraton rate (r = -0.758; p < 0.001).

CONCLUSIONS

Phrenic nerve root ischemia may be an important factor in respiration rhythms deteriorations in SAH which has not been mentioned in the literature.

Sphenopalatine ganglion neuromodulation in migraine: what is the rationale?

OBJECTIVE

The objective of this article is to review the prospect of treating migraine with sphenopalatine ganglion (SPG) neurostimulation.

BACKGROUND

Fuelled by preliminary studies showing a beneficial effect in cluster headache patients, the potential of treating migraine with neurostimulation has gained increasing interest within recent years, as current treatment strategies often fail to provide adequate relief from this debilitating headache. Common migraine symptoms include lacrimation, nasal congestion, and conjunctival injection, all parasympathetic manifestations. In addition, studies have suggested that parasympathetic activity may also contribute to the pain of migraineurs. The SPG is the largest extracranial parasympathetic ganglion of the head, innervating the meninges, lacrimal gland, nasal mucosa, and conjunctiva, all structures involved in migraine with cephalic autonomic symptoms.

CONCLUSION

We propose two possible mechanisms of action: 1) interrupting the post-ganglionic parasympathetic outflow to inhibit the pain and cephalic autonomic symptoms, and 2) modulating the sensory processing in the trigeminal nucleus caudalis. To further explore SPG stimulation in migraineurs as regards therapeutic potential and mode of action, randomized clinical trials are warranted.

Experimental activation of the sphenopalatine ganglion provokes cluster-like attacks in humans

Background

High frequency (HF) stimulation of the sphenopalatine ganglion (SPG) is an emerging abortive treatment for cluster headache (CH) attacks. HF SPG stimulation is thought to exert its effect by physiologically blocking parasympathetic outflow. We hypothesized that low frequency (LF) SPG stimulation may activate the SPG, causing increased parasympathetic outflow and thereby provoking cluster attacks in CH patients.

Methods

In a double-blind randomized cross-over study, seven CH patients implanted with an SPG neurostimulator were randomly allocated to receive HF or LF stimulation for 3 min on 2 separate days. We recorded headache characteristics and autonomic symptoms during and after stimulation.

Results

Six patients completed the study. Three out of six patients (50%) reported ipsilateral cluster-like attacks during or within 30 min of LF SPG stimulation. These cluster-like attacks were all successfully treated with the therapeutic HF SPG stimulation. One out of six reported a cluster-like attack with 3 min HF SPG stimulation, which was also successfully treated with continued HF therapeutic SPG stimulation.

Discussion

LF SPG stimulation may induce cluster-like attacks with autonomic features, which can subsequently be treated by HF SPG stimulation. Efferent parasympathetic outflow from the SPG may initiate autonomic symptoms and activate trigeminovascular sensory afferents, which may initiate the onset of pain associated with CH.

5-HT(1D) receptor immunoreactivity in the sphenopalatine ganglion: implications for the efficacy of triptans in the treatment of autonomic signs associated with cluster headache

OBJECTIVE

To determine if 5-HT(1D) receptors are located in the sphenopalatine ganglion.

BACKGROUND

While the 5-HT(1D) receptor has been described in sensory and sympathetic ganglia in the head, it was not known whether they were also located in parasympathetic ganglia.

METHODS

We used retrograde labeling combined with immunohistochemistry to examine 5-HT(1D) receptor immunoreactivity in rat sphenopalatine ganglion neurons that project to the lacrimal gland, nasal mucosa, cerebral vasculature, and trigeminal ganglion.

RESULTS

We found 5-HT(1D) receptor immunoreactivity in nerve terminals around postganglionic cell bodies within the sphenopalatine ganglion. All 5-HT(1D) -immunoreactive terminals were also immunoreactive for calcitonin gene-related peptide but not vesicular acetylcholine transporter, suggesting that they were sensory and not preganglionic parasympathetic fibers. Our retrograde labeling studies showed that approximately 30% of sphenopalatine ganglion neurons innervating the lacrimal gland, 23% innervating the nasal mucosa, and 39% innervating the trigeminal ganglion were in apparent contact with 5-HT(1D) receptor containing nerve terminals.

CONCLUSION

These data suggest that 5-HT(1D) receptors within primary afferent neurons that innervate the sphenopalatine ganglion are in a position to modulate the excitability of postganglionic parasympathetic neurons that innervate the lacrimal gland and nasal mucosa, as well as the trigeminal ganglion. This has implications for triptan (5-HT(1D) receptor agonist) actions on parasympathetic symptoms in cluster headache.

Trigeminal ganglion neuron density and regulation of anterior choroid artery vasospasm: In a rabbit model of subarachnoid hemorrhage

Background:

Subarachnoid hemorrhage (SAH) is associated with severe vasospasm caused by a variety of neurochemical mechanisms. The anterior choroid arteries (AChAs) are innervated by vasodilated fibers of the trigeminal ganglion (TGG). The goal of this study was to determine whether there is a relationship between the neuron density of the TGG and the severity of AChAs vasospasm with SAH.

Methods:

Thirty-two rabbits were used for the study; eight served as the baseline control group, seven as a SHAM group, with injections of 1 cc of isotonic saline solution, and 17 rabbits were included in the experimental SAH group, with injection of homologous blood into the cisterna magna. After 10 days, the histopathology of the AChAs and TGGs were examined. The AChAs vasospasm index (VSI) of the external/internal diameter and the neuron density of the ophthalmic root of the TGGs were evaluated stereologically. The AChAs VSI was preferred -- a measure of the degree of vasospasm. As the VSI increased, the degree of arterial vasospasm increased. The results were statistically analyzed.

Results:

The mean AChAs VSI was significantly higher and the mean neuronal density of the ophthalmic root of the TGG was significantly lower in the group with severe vasospasm associated with SAH compared to the controls, SHAM, and the group with mild vasospasm associated with SAH (P< 0.05). The ophthalmic root of the TGG neuron density in the 7 rabbits that developed severe vasospasm was statistically less than that observed in the 10 rabbits with mild vasospasm. There was a linear relationship between the low neuronal density in the ophthalmic root of the TGG and the severity of the AChA vasospasm.

Conclusions:

The trigeminal ganglion neuron density may be an important factor in the regulation of AChAs diameter and cerebral blood flow. Low neuron density of the ophthalmic root of the TGG may play a role in the pathogenesis of AChAs vasospasm associated with SAH.

The parasympathetic nervous system in the quest for stroke therapeutics

Stroke is a devastating neurovascular disease with limited therapeutic options. The pathogenesis of stroke involves complex interrelated molecular mechanisms including excitotoxicity, oxidative and nitrosative stress, cortical spreading depolarizations, inflammation, necrosis, and apoptosis. Successful development of stroke therapeutics depends on understanding these molecular mechanisms and how to counteract them to limit tissue damage during stroke. Activation of the parasympathetic nervous system (PNS) has been shown to antagonize a multiplicity of pathologic mechanisms. Elements of parasympathetic activation such as vagus nerve stimulation have already been used successfully in treating brain disorders such as epilepsy and depression. This review discusses the anatomical basis and molecular mechanisms involved in activation of the PNS, and assesses the strength of available evidence for the further development of this modality into a stroke therapy.

Role of degenerated neuron density of dorsal root ganglion on anterior spinal artery vasospasm in subarachnoid hemorrhage: experimental study

BACKGROUND

The spinal arteries are innervated by several systems that contribute to the control of spinal cord blood flow. The sensory fibers of upper cervical nerves have vasodilatatory effect on the anterior spinal arteries (ASA). Subarachnoid hemorrhage (SAH) causes severe vasospasm by various neurochemical mechanisms. We examined whether there is a relationship between the neuron density of the C3 dorsal root ganglion and the severity of ASA vasospasm in SAH.

METHODS

This study was conducted on 20 rabbits. Four of them were used as baseline group. Experimental SAH has been applied to all of 16 animals by injecting homologous blood into cisterna magna. After 20 days of injection, ASA and C3 dorsal root ganglia (C3DRG) were examined histopathologically. ASA volume values and normal and degenerated neuron densities of C3DRG were estimated stereologically and the results were analyzed statistically.

RESULTS

The mean ASA volume was 1.050±0.450 mm³, [corrected] and the mean neuronal density of C3DRG was 10,500 ± 850 in all animals. The mean volume value of ASA was 0.970±0.150 [corrected] mm³, and the normal neuron density of C3DRG fell to 8,600 ± 400/mm³ in slight vasospasm group. In severe vasospasm-developed animals, mean volume value of ASA was 0.540±0.90 [corrected]mm³ and the normal neuron density of C3DRG fell to 5,500 ± 360/mm³. An inverse relationship between the degenerated neuronal density of the C3DRG and ASA volume values may indicate the severity of ASA vasospasm.

CONCLUSION

The neuron density of C3DRG may be an important factor on the regulation of ASA volume values and the continuation of spinal cord blood flow. Low neuron density of C3DRG may be considered as an important factor in the pathogenesis of severe ASA vasospasm in SAH.

Biological sciences related to headache

Headache can occur as a result of activation of pain-sensitive cranial structures, such as the dura mater, vasculature, and the cranial and cervical muscles and ligaments, which are innervated by primary afferent neurons originating from the trigeminal and dorsal root ganglia of the upper cervical spinal nerves. Similar to general nociceptive sensation, C fibers and Adelta fibers are known to play an important role in headache perception. Findings from nerve stimulation studies indicate that C fibers transmit aching, throbbing, or burning pain that builds up slowly, whereas the Adelta fibers conduct sharper initial pain sensation. These primary afferent nerve fibers transmit nociceptive information from the pain-sensitive endings in the cranial structures through the trigeminal and first and second spinal dorsal root ganglia to the brainstem at the pontine level. The nociceptive fibers then project to the central pain-conducting pathways at the spinal trigeminal nucleus. In this chapter, we discuss the anatomy in relation to headache, including the meninges, dural sinuses, blood vessels, sensory ganglia, cranial and neck muscles, and the central pain-conducting pathways.

Effect of nitric oxide synthase inhibitor on increase in nasal mucosal blood flow induced by sensory and parasympathetic nerve stimulation in rats

OBJECTIVES

Neural control of nasal blood flow (NBF) has not been systematically investigated. The aim of the present study was to evaluate the effect of electrical stimulation of both sensory and parasympathetic nerves innervating the nasal mucosal arteries on NBF in rats.

METHODS

In anesthetized rats, nasociliary (sensory) nerves and postganglionic (parasympathetic) nerves derived from the right sphenopalatine ganglion were electrically stimulated. We measured NBF with a laser-Doppler flowmeter.

RESULTS

The nerve stimulation increased NBF on both sides and increased the mean arterial blood pressure. The increase in NBF was larger on the ipsilateral side than on the contralateral side. Hexamethonium bromide, a ganglion blocker, abolished the stimulation-induced pressure effect and the increase in NBF on the contralateral side, but did not abolish the increase in NBF on the ipsilateral side. The remaining increase in NBF was abolished by N(G)-nitro-L-arginine, a nitric oxide synthase inhibitor. Histochemical analysis with nicotinamide adenine dinucleotide phosphate-diaphorase showed neuronal nitric oxide synthase-containing nerves that innervate nasal mucosal arteries.

CONCLUSIONS

Nitric oxide released from parasympathetic nitrergic nerves may contribute to an increase in NBF in rats. The afferent impulses induced by sensory nerve stimulation may lead to an increase in mean arterial blood pressure that is partly responsible for the increase in NBF.

Muscarinic acetylcholine receptor modulation of mu (mu) opioid receptors in adult rat sphenopalatine ganglion neurons

The sphenopalatine ganglion (SPG) neurons represent the parasympathetic branch of the autonomic nervous system involved in controlling cerebral blood flow. In the present study, we examined the coupling mechanism between mu (mu) opioid receptors (MOR) and muscarinic acetylcholine receptors (mAChR) with Ca(2+) channels in acutely dissociated adult rat SPG neurons. Successful MOR activation was recorded in approximately 40-45% of SPG neurons employing the whole cell variant of the patch-clamp technique. In addition, immunofluorescence assays indicated that MOR are not expressed in all SPG neurons while M(2) mAChR staining was evident in all neurons. The concentration-response relationships generated with morphine and [d-Ala2-N-Me-Phe4-Glycol5]-enkephalin (DAMGO) showed IC(50) values of 15.2 and 56.1 nM and maximal Ca(2+) current inhibition of 26.0 and 38.7%, respectively. Activation of MOR or M(2) mAChR with morphine or oxotremorine-methiodide (Oxo-M), respectively, resulted in voltage-dependent inhibition of Ca(2+) currents via coupling with Galpha(i/o) protein subunits. The acute prolonged exposure (10 min) of neurons to morphine or Oxo-M led to the homologous desensitization of MOR and M(2) mAChR, respectively. The prolonged stimulation of M(2) mAChR with Oxo-M resulted in heterologous desensitization of morphine-mediated Ca(2+) current inhibition, and was sensitive to the M(2) mAChR blocker methoctramine. On the other hand, when the neurons were exposed to morphine or DAMGO for 10 min, heterologous desensitization of M(2) mAChR was not observed. These results suggest that in rat SPG neurons activation of M(2) mAChR likely modulates opioid transmission in the brain vasculature to adequately maintain cerebral blood flow.

Cholinergic signal transduction in the mouse sphenopalatine ganglion

The sphenopalatine ganglia (SPG) receive their preganglionic innervation from the ventro-lateral reticular formation and nuclei of the caudal pons, and are involved in parasympathetic control of cranial glandular and vascular components including the blood supply to specific brain areas. In 53% of all SPG neurons, a particular member (MOL2.3) of the odorant receptor superfamily is co-expressed with green fluorescent protein (GFP) in MOL2.3 transgenic mouse pups. Choline acetyltransferase and vesicular acetylcholine transporter (VAChT) could be demonstrated in 90% of the GFP-positive, and 60% of the GFP-negative cells, these cells thus representing cholinergic neurons. Some 50% of all SPG neurons were nitrergic at a high rate of VAChT co-expression, the majority of them being GFP-positive. Most SPG neurons received cholinergic innervation as demonstrated by perineuronal VAChT immunoreactive nerve terminals. To characterize cholinergic signal transduction in SPG neurons, calcium imaging experiments were performed in a SPG primary culture system containing GFP-positive and -negative neurons. Ganglionic neurons could repeatedly be activated by cholinergic stimulation in a dose-dependent manner, with calcium entering all cells from the extracellular compartment. Stimulation with specific agonists supported prevalence of nicotinic cholinergic receptors (nAChRs). Inhibition of cholinergically induced intracellular calcium signalling by various omega-conotoxins indicated functional expression of alpha 3 beta 4 and alpha 7 nAChR subtypes in murine SPG cells, which could be supported by RT-PCR analysis of the neonatal mouse SPG. With regard to secondary cholinergic activation, L- but not N-subtype voltage-gated calcium channels might represent a prime target. Nicotinic signal transduction did not prove to be different in GFP-positive as compared to-negative murine SPG neurons.

Roles of dorsal column pathway and transient receptor potential vanilloid type 1 in augmentation of cerebral blood flow by upper cervical spinal cord stimulation in rats

Clinical and basic studies have indicated that upper cervical spinal cord stimulation (cSCS) significantly increases cerebral blood flow (CBF), but the mechanisms are incompletely understood. This investigation was conducted to differentiate between stimulation of dorsal column fibers and upper cervical spinal cord cell bodies in cSCS-induced increases in CBF and decreases in cerebrovascular resistance (CVR). cSCS (50 Hz, 0.2 ms, 1 min) was applied on the left C1-C2 dorsal column of pentobarbital anesthetized, ventilated and paralyzed male rats. Laser Doppler flowmetry probes were placed bilaterally over the parietal cortex, and arterial pressure was monitored. cSCS at 30%, 60%, and 90% of motor threshold (MT) produced vasodilation bilaterally in cerebral cortices. Subsequently, cSCS was applied at 90% MT, and ipsilateral responses were recorded. Ibotenic acid (0.3 mg/ml, 0.1 ml) placed on dorsal surface of C1-C2 (n=7) to suppress cell body activity, did not affect cSCS-induced %DeltaCBF (42.5+/-8.1% vs. 36.8+/-7.1%, P>0.05) and %DeltaCVR (-19.4+/-4.2% vs. -15.2+/-5.6%, P>0.05). However, bilateral transection of the dorsal column at rostral C1 (n=8) abolished cSCS-induced changes in CBF and CVR. Also, rostral C1 transection (n=7) abolished cSCS-induced changes in CBF and CVR. Resinferatoxin (RTX), an ultrapotent transient receptor potential vanilloid type 1 (TRPV1) agonist, was used to inactivate TRPV1 containing nerve fibers/cell bodies. RTX (2 microg/ml, 0.1 ml) placed on the C1-C2 spinal cord (n=7) did not affect cSCS-induced %DeltaCBF (60.2+/-8.1% vs. 46.3+/-7.7%, P>0.05) and %DeltaCVR (-25.5+/-3.5% vs. -21.4+/-8.9%, P>0.05). However, i.v. RTX (2 microg/kg, n=9) decreased cSCS-induced %DeltaCBF from 65.0+/-9.5% to 27.4+/-7.2% (P<0.05) and %DeltaCVR from -28.0+/-7.6% to -14.8+/-4.2% (P<0.05). These results indicated that cSCS-increases in CBF and decreases in CVR occurred via rostral spinal dorsal column fibers and did not depend upon C1-C2 cell bodies. Also, our results suggested that cerebral but not spinal TRPV1 was involved in cSCS-induced cerebral vasodilation.

Parasympathetic stimulation elicits cerebral vasodilatation in rat

Forebrain arteries receive nitroxidergic input from parasympathetic ganglionic fibers that arise from the pterygopalatine ganglia. Previous studies have shown that ganglionic stimulation in some species led to cerebral vasodilatation while interruption of those fibers interfered with vasodilatation seen during acute hypertension. Because the ganglionic fibers are quite delicate and are easily damaged when the ganglia are approached with published techniques we sought to develop a method that allowed clear exposure of the ganglia and permitted demonstration of cerebral vasodilatation with electrical stimulation of the ganglia in the rat. We had found that an orbital approach during which the eye was retracted for visualization of the ganglion precluded eliciting vasodilatation with ganglionic stimulation. In the current study approaching the ganglion through an incision over the zygomatic arch provided clear exposure of the ganglion and stimulation of the ganglion with that approach led to vasodilatation.

Neuronal nitric oxide mediates cerebral vasodilatation during acute hypertension

Parasympathetic nerves from the pterygopalatine ganglia provide nitroxidergic innervation to forebrain cerebral blood vessels. Disruption of that innervation attenuates cerebral vasodilatation seen during acute hypertension as does systemic administration of a non-selective nitric oxide synthase (NOS) inhibitor. Although such studies suggest that nitric oxide (NO) released from parasympathetic nerves participates in vasodilatation of cerebral vessels during hypertension, that hypothesis has not been tested with selective local inhibition of neuronal NOS (nNOS). We tested that hypothesis through these studies performed in anesthetized rats instrumented for continuous measurement of blood pressure, heart rate and pial arterial diameter through a cranial window. We sought to determine if the nNOS inhibitor propyl-L-arginine delivered directly to the outer surface of a pial artery would (1) attenuate changes in pial arterial diameter during acute hypertension and (2) block nNOS-mediated dilator effects of N-methyl-D-aspartate (NMDA) delivered into the window but (3) not block vasodilatation elicited by acetylcholine (ACh) and mediated by endothelial NOS dilator. Without the nNOS inhibitor arterial diameter abruptly increased 70+/-15% when mean arterial pressure (MAP) reached 183+/-3 mm Hg while with nNOS inhibition diameter increased only 13+/-10% (p<0.05) even when MAP reached 191+/-4 mm Hg (p>0.05). The nNOS inhibitor significantly attenuated vasodilatation induced by NMDA but not ACh delivered into the window. Thus, local nNOS inhibition attenuates breakthrough from autoregulation during hypertension as does complete interruption of the parasympathetic innervation of cerebral vessels. These findings further support the hypothesis that NO released from parasympathetic fibers contributes to cerebral vasodilatation during acute hypertension.

Increased BBB permeability by parasympathetic sphenopalatine ganglion stimulation in dogs

The blood-brain barrier (BBB) is a major obstacle for movement of large molecules to and from the brain. Stimulation of the sphenopalatine ganglion (SPG), the major source of parasympathetic innervation to brain vasculature, is known to vasodilate brain vessels, and has recently been shown to also increase the permeability of the BBB in the rat. In this work, we studied the effect of SPG stimulation on BBB permeability in larger animals--Beagle dogs. Left SPG was exposed by lateral approach in five Beagle dogs, and stimulated at 10 Hz. FITC labeled 10 kDa dextran was continuously infused to the left atrium during stimulation, and cerebral angiography was periodically obtained via the vertebral artery. Three control dogs received labeled dextran, without SPG exposure or stimulation. Brains were perfused with saline thoroughly at the end of stimulation, and samples from various regions were taken for fluorescence reading of tissue homogenates. Cerebral vasodilatation was evidenced in all but one dog, whose fluorescence results were consequently excluded from analysis, assuming that its SPG had been damaged by surgery. Fluorescence was significantly higher in the four stimulated compared to the three non-stimulated animals; e.g. mean FITC-dextran concentration in the anterior brain regions was 0.98+/-0.12 ug (mean+/-S.D.) FITC/g brain for experimental animals, and 0.40+/-0.02 for controls (p<0.01). No effect was seen in the pons and cerebellum (0.68+/-0.22 vs. 0.60+/-0.03, NS) whose vascular innervation is supplied by the otic rather than the SPG ganglion. SPG stimulation appears to be an effective way to increase BBB permeability, allowing introduction of large molecules to the brain. This could be a therapeutic method for a wide variety of brain disorders, including tumors and neurodegenerative diseases.

Blood-brain barrier opened by stimulation of the parasympathetic sphenopalatine ganglion: a new method for macromolecule delivery to the brain

OBJECT

Drug delivery across the blood-brain barrier remains a significant challenge. Based on earlier findings, the authors hypothesized that parasympathetic innervation of the brain vasculature could be used to augment drug delivery to the brain.

METHODS

Using a craniotomy-cerebrospinal fluid superfusate paradigm in rats with an intravenous injection of tracer the authors demonstrated that stimulation of the postganglionic parasympathetic fibers of the sphenopalatine ganglion (SPG) increased the concentration of fluorescein isothiocyanate-dextran (4-250 kD) in the superfusate by two- to sixfold. A histological examination indicated the presence of dextran in the parenchyma. In another experiment the amount of Evans blue dye in the brain following SPG activation was similarly significantly elevated. The chemotherapeutic agents anti-HER2 monoclonal antibody and etoposide were also delivered to the brain and reached therapeutic concentrations. Brain homeostasis was not disturbed by this procedure; a measurement of nicotinamide adenine dinucleotide reduction did not show a decrease in the tissue metabolic state and brain water content did not increase significantly.

CONCLUSIONS

Sphenopalatine ganglion activation demonstrates a promising potential for clinical use in the delivery of small and large molecules to the brain.

Origin of PACAP-immunoreactive nerve fibers innervating the subarachnoidal blood vessels of the rat brain

The subarachnoidal cerebral blood vessels of the rat are innervated by nerve fibers containing different neuropeptides, e.g. pituitary adenylatecyclase activating polypeptide (PACAP). PACAP dilates brain arterioles and immunohistochemical studies of the rat have indicated that PACAP binds to a VPAC1-receptor in the cerebral vasculature of this species. We have investigated the perikaryal origin of the nerve fibers innervating the subarachnoidal blood vessels of the rat by combined retrograde tracing with Fluorogold and immunohistochemistry. The in vivo neuronal retrograde tracings were done by injection of 2% Fluorogold in water into the subarachnoidal space in the area of the middle cerebral artery. The retrograde transported tracer was detected by use of an antibody against Fluorogold. One week after the injections, the animals were vascularly perfused with Stephanini's fixative and labeled perikarya were found bilaterally in the trigeminal, sphenopalatine, and otic ganglia. The retrograde Fluorogold tracings were combined with immunohistochemistry for PACAP using a mouse monoclonal antibody and the biotinylated tyramide amplification system. Double labeled perikarya containing both Fluoro-gold and PACAP were found predominantly in the trigeminal ganglion, and only rarely in the otic and sphenopalatine ganglion. Summarizing, our retrograde tracings combined with immunohistochemistry indicate that the perikarya in the trigeminal ganglion are the main origin of PACAPergic nerve fibers projecting to the cerebral vasculature of the rat.

Direct projections from the cardiovascular nucleus tractus solitarii to pontine preganglionic parasympathetic neurons: a link to cerebrovascular regulation

Peripheral or central interruption of the baroreflex or the parasympathetic innervation of cerebral vessels leads to similar changes in regulation of cerebral blood flow. Therefore, we sought to test the hypothesis that the cardiovascular nucleus tractus solitarii, the site of termination of arterial baroreceptor nerves, projects to pontine preganglionic neurons whose stimulation elicits cerebral vasodilatation. The current study utilized both light and electron microscopic techniques to analyze anterograde tracing from the cardiovascular nucleus tractus solitarii to preganglionic parasympathetic neurons in the pons. We further used retrograde tracing from that same pontine region to the cardiovascular nucleus tractus solitarii and evaluated the confluence of tracing from the cardiovascular nucleus tractus solitarii to pontine preganglionic neurons labeled retrogradely from the pterygopalatine ganglia. The cardiovascular nucleus tractus solitarii projected to pontine preganglionic parasympathetic neurons, but more rostral and caudal regions of nucleus tractus solitarii did not. In contrast, all three regions of nucleus tractus solitarii projected to the nucleus ambiguus and dorsal motor nucleus of the vagus. Although not projecting to pontine preganglionic parasympathetic neurons, regions lateral, rostral, and caudal to cardiovascular nucleus tractus solitarii sent projections through the pons medial to the preganglionics. The study establishes the presence of a direct monosynaptic pathway from neurons in the cardiovascular nucleus tractus solitarii to pontine preganglionic parasympathetic neurons that project to the pterygopalatine ganglia, the source of nitroxidergic vasodilatory innervation of cerebral blood vessels. It provides evidence that activation of those preganglionic neurons can cause cerebral vasodilatation and increased cerebral blood flow. Finally, it demonstrates differential innervation of medullary and pontine preganglionic parasympathetic neurons by different regions of the nucleus tractus solitarii.

Innervation of cerebral blood vessels: morphology, plasticity, age-related, and Alzheimer's disease-related neurodegeneration

The light microscopical and ultrastructural morphology of the innervation of the major cerebral arteries and pial vessels is described, including the origins of the different groups of nerve fibres and their characteristic neurotransmitter phenotype. Species and region specific variations are described and novel data regarding the parasympathetic innervation of cerebral vessels are presented. The dynamic nature, or plasticity, of cerebrovascular innervation is emphasized in describing changes affecting particular subpopulations of neurons during normal ageing and in Alzheimer's disease. The molecular controls on plasticity are discussed with particular reference to target-associated factors such as the neurotrophins and their neuronal receptors, as well as extracellular matrix related factors such as laminin. Hypotheses are presented regarding the principal extrinsic and intrinsic influences on plasticity of the cerebrovascular innervation.

Cavernous sinus ganglia are sources for parasympathetic innervation of cerebral arteries in rat

Retrograde tracing and immunohistochemistry was used in rats to investigate whether the ganglia in the cavernous sinus contribute to cerebrovascular innervation. The cavernous sinus ganglia in rat include the cavernous part of the pterygopalatine ganglion (PGC) and small cavernous ganglia (CG). The tracers, fluorogold and fast blue, were applied to the middle cerebral artery in eight rats. After 1 to 4 days, the cavernous sinuses were dissected out and studied as whole mount preparations and sections. A moderate number of labeled neurons were visible in the ipsilateral PGC and CG. Furthermore, fibers in the cavernous nerve plexus and abducens nerve were labeled, suggesting that the pathway from the cavernous sinus ganglia to the cerebral arteries runs through the cavernous plexus and then retrogradely along the abducens nerve to the internal carotid artery. Selected sections were immunohistochemically stained for the cholinergic marker, vesicular acetylcholine transporter (VAChT). Most cells in the PGC and CG were VAChT-immunoreactive, some of which also contained tracer. It is concluded that in rat, the cavernous sinus ganglia, consisting of the PGC and small CG, contribute to parasympathetic cerebrovascular innervation and that the cavernous nerve plexus and abducens nerve are involved in the pathway from these ganglia to the cerebral arteries.

Anatomically and physiologically based guidelines for use of the sphenopalatine ganglion block versus the stellate ganglion block to reduce atypical facial pain

This literature review is designed to develop guidelines needed for the use of a sphenopalatine ganglion block versus a stellate ganglion block to reduce atypical facial pain. We have reviewed the basic anatomy of both ganglia and the physiological responses usually associated with each, and have given an opinion on appropriate use of these therapeutic modalities.

Calbindin-D28k in cerebrovascular extrinsic innervation system of the rat

Calbindin-D28k, one of the calcium-binding proteins, belongs to the EF hand family and is commonly found in neurons. It serves as a representative neuronal marker for neuroanatomical investigations. The authors' knowledge of its precise function, however, is yet very limited. In this study, we examined the existence of nerve fibers with calbindin-D28k immunoreactivity in the cerebral blood vessels and ganglia that innervate the cerebral blood vessels in the rat. Numerous nerve fibers with calbindin-D28k immunoreactivity were observed on the walls of the major extracerebral arteries forming the circle of Willis and its branches. Calbindin-D28k immunoreactivity was seen in many neurons of the trigeminal, dorsal root and jugular ganglia. A small number of neurons showed calbindin-D28k immunoreactivity in the otic and superior cervical ganglia. Calbindin-D28k immunoreactivity was not detected in the sphenopalatine or internal carotid ganglia. Pericellular basket-like formations of nerve terminals with calbindin-D28k immunoreactivity were observed in the sphenopalatine, otic, internal carotid and superior cervical ganglia. The present study demonstrated calbindin-D28k immunoreactivity in the cerebrovascular nerve fibers as well as in their origins--the cranial ganglia. These findings are significant in understanding the calcium-mediated mechanism of the neural control of the cerebral blood vessels.

N-type Ca2+ channels in cultured rat sphenopalatine ganglion neurons: an immunohistochemical and electrophysiological study

Results from pharmacological studies have suggested that presynaptic N-type Ca2+ channels play an important role in regulating neuronal Ca2+ influx and transmitter nitric oxide (NO) release in isolated cerebral arteries. However, the presence of N-type Ca2+ channels in cerebral perivascular nerves has not been directly demonstrated. As a major source of cerebral perivascular NOergic innervation is the sphenopalatine ganglion (SPG), adult rat SPGs were cultured and examined by whole-cell patch-clamp technique. One week after growing in the culture medium, significant neurite outgrowth from the SPG neuronal cells was observed. Both soma and neurites of these cells were immunoreactive for N-type Ca2+ channels, transmitter-synthesizing enzymes (choline acetyltransferase and NO synthase), and several neuropeptides (vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, substance P, and pituitary adenylate cyclase-activating peptide-38) that had been found in cerebral perivascular nerves in whole-mount vascular preparations. In current-clamp recordings, injection of a small depolarizing current caused action potential firing. In voltage-clamp recordings, the fast inward currents were blocked by tetrodotoxin and outward currents by tetraethylammonium, which is typical for neurons. Most Ca2+ currents isolated by blockade of sodium and potassium currents were blocked by omega-conotoxin, indicating that N-type Ca2+ channels are the dominant voltage-dependent Ca2+ channels regulating Ca2+ influx during membrane depolarization of SPG neurons. The ability to culture postganglionic SPG neurons provides an opportunity to directly study the electrophysiological and pharmacological properties of these neurons.

Occurrence and distribution of substance P receptors in the cerebral blood vessels of the rat

The distribution of immunoreactivity to the receptor for substance P was examined in the cerebral blood vessels of the rat. Substance P immunoreactivity has been demonstrated in the nerve fibers of the cerebral blood vessels. Recently, the production of substance P receptor specific antibody has enabled the detection of localization of the substance P receptor in the central nervous system. In this study, we examined the existence of nerve fibers with substance P receptor immunoreactivity in the cerebral blood vessels and the cranial ganglia innervating the cerebral blood vessels. Sprague-Dawley rats were perfused with fixative and the pial arteries and the cranial ganglia known to innervate the cerebral blood vessels, i.e., trigeminal, sphenopalatine, internal carotid, otic and superior cervical ganglia, were dissected. All specimens were incubated with anti-substance P receptor IgG, then stained by the avidin-biotin-peroxidase complex method. Numerous nerve fibers with varicosities forming plexuses, with substance P receptor immunoreactivity were observed on the walls of the major extracerebral arteries forming the circle of Willis and its branches. Substance P receptor immunoreactivity was also detected in the endothelium of the cerebral arteries. Substance P receptor immunoreactivity was positive in many neurons of the sphenopalatine ganglion, otic ganglion, trigeminal ganglion, superior cervical ganglion and internal carotid ganglion. The present study demonstrated the existence of nerve fibers with substance P receptor immunoreactivity in the cerebral blood vessels and the cranial ganglia that innervate the cerebral blood vessels. These findings are important in understanding the responsiveness of the cerebral blood vessels to substance P.

Parasympathetic innervation of cephalic arteries in rabbits: comparison with sympathetic and sensory innervation

We investigated the distribution of parasympathetic, sympathetic, and sensory perivascular nerve fibers in rabbit cephalic arteries supplying the brain, exocrine glands, nasal mucosa, masseter muscles, tongue, and skin in the face and also examined cranial autonomic and sensory ganglia. NADPH diaphorase (NADPHd)-positive and vasoactive intestinal peptide-like immunoreactive (VIP-LI) neurons were located in the cranial parasympathetic ganglia. Neuropeptide Y (NPY)-LI neurons occurred mainly, and dopamine beta-hydroxylase (DBH)-LI neurons occurred exclusively, in the superior cervical (sympathetic) ganglion. Substance P (SP)-LI and calcitonin gene-related peptide (CGRP)-LI neurons occurred only in the trigeminal (sensory) ganglion. Therefore, it was assumed that NADPHd-positive and VIP-LI perivascular nerve fibers in cephalic arteries were parasympathetic, all DBH-LI and most NPY-LI fibers were sympathetic, and SP-LI and CGRP-LI fibers were sensory in nature. In the cerebral arteries, NADPHd-positive and VIP-LI varicose fibers were more numerous in the rostral than in the caudal half of the Circle of Willis. In the extracranial arteries, NADPHd-positive and VIP-LI fibers were most abundant in the lingual, lacrimal, and supraorbital arteries; sparse in the parotid and submandibular arteries; and absent in the ear artery. There was an obvious proximal-to-distal density gradient along individual cephalic arterial trees. In contrast, DBH-LI, NPY-LI, SP-LI, and CGRP-LI varicose nerve fibers were similar in density in all cephalic arteries and their branches. These neuroanatomical findings suggest that differential parasympathetic innervation in cephalic arteries may play a role in the partitioning of blood flow between different cephalic tissues.

Preganglionic parasympathetic neurons projecting to the sphenopalatine ganglion contain nitric oxide synthase in the rabbit

We have investigated the possible presence of nitric oxide synthase (NOS) and choline acetyltransferase (ChAT) in brainstem preganglionic parasympathetic neurons projecting to the sphenopalatine ganglion in rabbits, using combined retrograde axonal tracing and immunohistochemistry. Retrogradely labeled neurons were observed in the ipsilateral rostral medulla and caudal pons, in a region laterodorsal to the facial motor nucleus. Double-labeling experiments demonstrated that 75 +/- 5% of retrogradely labeled neurons contained NOS immunoreactivity, while all of retrogradely labeled neurons contained ChAT immunoreactivity. These observations suggest that nitric oxide could influence cholinergic transmission from preganglionic endings in the sphenopalatine ganglion.

Neural connections in and around the cavernous sinus in rat, with special reference to cerebrovascular innervation

There is a confluence in and around the cavernous sinus of neural pathways innervating the intracranial structures. To determine the patterns of innervation, particularly of the cerebral arteries, we stained whole-mount preparations of the cavernous sinus and adjacent regions of the rat for acetylcholinesterase. The cavernous nerve plexus, with several small ganglia, mainly occupied the lateral wall of the sinus and extended laterally above the ophthalmic and maxillary divisions of the trigeminal nerve, in relation to the oculomotor and trochlear nerves. The cavernous plexus was connected to the pterygopalatine ganglion, the trigeminal ganglion, and the abducens nerve. The elongated pterygopalatine ganglion consisted of an orbital part, from which parasympathetic fibers ran to the cerebral arteries, and a cavernous part. Nerves from the lateral extension of the cavernous plexus ran rostrally into the orbit along the oculomotor, trochlear, and ophthalmic nerves, and caudally to the pineal gland along the trochlear nerve. Several branches also ran over the dura mater. Caudal to the cavernous sinus, we found two large nerves and a number of small nerves that ran between the nerves surrounding the internal carotid artery and the abducens nerve. These nerves may represent additional parasympathetic and/or sensory pathways to the cerebral arteries.

Origins of nitric oxide synthase-containing nerve fibers in the rat basilar artery with reference to the fine structure of the nerve fibers

The origins of nitric oxide synthase (NOS)-containing nerve fibers in the rat basilar artery were studied by a combination of Fluoro-Gold retrograde tracing and immunohistochemistry. After application of Fluoro-Gold onto the middle part of the basilar artery, the dye accumulated in the sphenopalatine, otic, trigeminal, superior cervical, nodose ganglia and in the spinal ganglia at level C2 and C3. Nerve cells with NOS-like immunoreactivity were detected in the above ganglia, except for the superior cervical ganglion. Neurons that showed both NOS-like immunoreactivity and Fluoro-Gold fluorescence were numerous in the sphenopalatine and otic ganglia, and less numerous in the trigeminal, nodose and spinal ganglia. Under electron microscopy, a number of unmyelinated nerve terminals with neuronal NOS-like immunoreactivity was seen in proximity to smooth muscle cells in the tunica media of the basilar artery. These findings provide morphological evidence that NOS-containing nerve fibers in the rat basilar artery have multiple origins, and suggest that the control of posterior cerebral circulation by the parasympathetic and sensory ganglia are more complex than previously considered.

Distribution and pathway of the cerebrovascular nerve fibers from the otic ganglion in the rat: anterograde tracing study

The distribution and pathway of cerebrovascular nerve fibers from the otic ganglion were studied by an anterograde tracing technique in the rat. Wheat germ agglutinin-horseradish peroxidase was injected as an anterograde axonal tracer into the otic ganglion on one side. Forty-eight hours later, the animals were killed and specimens were reacted with tetramethylbenzidine. Wheat germ agglutinin-horseradish peroxidase positive fine nerve fibers were observed in the circle of Willis and its branches, i.e., anterior cerebral artery, middle cerebral artery, internal ethmoidal artery and posterior cerebral artery, while no positive fiber could be detected in the vertebrobasilar artery. A positive reaction with tetramethylbenzidine was also observed in the lesser superficial petrosal nerve, the greater superficial petrosal nerve, the vidian nerve, the greater deep petrosal nerve, the internal carotid ganglion and the trigeminal ganglion. The sphenopalatine ganglion, however, failed to reveal any positive neurons or nerve fibers. It is concluded that the cerebrovascular nerve fibers originating from the otic ganglion run along the lesser superficial petrosal nerve to join the greater superficial petrosal nerve. They then reach the greater deep petrosal nerve and ascend along the internal carotid artery to distribute themselves to the cerebral blood vessels. This study demonstrated, for the first time, that the otic ganglion innervates the cerebral vessels and elucidated the pathway from the otic ganglion to the cerebral vessels directly by means of an anterograde axonal tracing technique.

Density of peptide histidine-isoleucine- and vasoactive intestinal peptide-immunoreactive nerve fibers in the sheep pineal gland is not affected by superior cervical ganglionectomy

Peptide histidine-isoleucine (PHI) is a regulatory peptide, synthesized as part of the same propeptide that includes also vasoactive intestinal peptide (VIP). The present study describes the distribution of PHI-immunoreactive nerve fibers in the sheep pineal organ and compares their location with the distribution of VIP-immunoreactive fibers in both normal and superior cervical ganglionectomized sheep in order to elucidate the origin of the PHI/VIP immunoreactive nerve fibers. Several PHI-immunoreactive nerve fibers were present in the meninges and in the pineal capsule. Numerous positive nerve fibers entered the pineal gland and travelled within connective tissue spaces. Individual PHI-positive nerve fibers were either smooth, without specialization, or varicose. Generally VIP- and PHI-immunoreactive fibers were located close to connective septa and blood vessels. However, many PHIergic and VIPergic fibers possessing varicosities of variable sizes were also dispersed between pinealocytes. The distribution, density, and morphology of PHI- and VIP-immunoreactive fibers in the sheep pineal gland were similar. In superior cervical ganglionectomized animals, intrapineal VIP- and PHI-immunoreactive nerve fibers were present with the same density as in control animals. In agreement, the concentration of immunoreactive VIP and PHI did not change after ganglionectomy. No VIP- and PHI-immunoreactive cell bodies were observed in the superior cervical ganglia. Thus this study shows that the intrapineal VIP- and PHI-immunoreactive nerve fibers do not originate from the sympathetic superior cervical ganglion.