Parasympathetic cerebrovasodilator center of the facial nerve

Human Brainstem and Cerebellum Atlas: Chemoarchitecture and Cytoarchitecture Paired to MRI

Lesion localization is the basis for understanding neurologic disease, which is predicated on neuroanatomical knowledge carefully cataloged from histology and imaging atlases. However, it is often difficult to correlate clinical images of brainstem injury obtained by MRI scans with the details of human brainstem neuroanatomy represented in atlases, which are mostly based on cytoarchitecture using Nissl stain or a single histochemical stain, and usually do not include the cerebellum. Here, we report a high-resolution (200 μm) 7T MRI of a cadaveric male human brainstem and cerebellum paired with detailed, coregistered histology (at 2 μm single-cell resolution) of the immunohistochemically stained cholinergic, serotonergic, and catecholaminergic (dopaminergic, noradrenergic, and adrenergic) neurons, in relationship to each other and to the cerebellum. These immunohistochemical findings provide novel insights into the spatial relationships of brainstem cell types and nuclei, including subpopulations of melanin and TH⁺ neurons, and allows for more informed structural annotation of cell groups. Moreover, the coregistered MRI-paired histology helps validate imaging findings. This is useful for interpreting both scans and histology, and to understand the cell types affected by lesions. Our detailed chemoarchitecture and cytoarchitecture with corresponding high-resolution MRI builds on previous atlases of the human brainstem and cerebellum, and makes precise identification of brainstem and cerebellar cell groups involved in clinical lesions accessible for both laboratory scientists and clinicians alike.SIGNIFICANCE STATEMENT Clinicians and neuroscientists frequently use cross-sectional anatomy of the human brainstem from MRI scans for both clinical and laboratory investigations, but they must rely on brain atlases to neuroanatomical structures. Such atlases generally lack both detail of brainstem chemical cell types, and the cerebellum, which provides an important spatial reference. Our current atlas maps the distribution of key brainstem cell types (cholinergic, serotonergic, and catecholaminergic neurons) in relationship to each other and the cerebellum, and pairs this histology with 7T MR images from the identical brain. This atlas allows correlation of the chemoarchitecture with corresponding MRI, and makes the identification of cell groups that are often discussed, but rarely identifiable on MRI scan, accessible to clinicians and clinical researchers.

Regulation of Blood Flow in the Cerebral Posterior Circulation by Parasympathetic Nerve Fibers: Physiological Background and Possible Clinical Implications in Patients With Vertebrobasilar Stroke

Posterior circulation involves the vertebrobasilar arteries, which supply oxygen and glucose to vital human brainstem structures and other areas. This complex circulatory- perfusion system is not homogenous throughout the day; rather, its hemodynamic changes rely on physiological demands, ensuring brainstem perfusion. This dynamic autoregulatory pattern maintains cerebral perfusion during blood pressure changes. Accumulative evidence suggests that activity within the autonomic nervous system is involved in the regulation of cerebral blood flow. Neither the sympathetic nor parasympathetic nervous systems work independently. Functional studies have shown a tight and complicated cross talk between these systems. In pathological processes where sympathetic stimulation is present, systemic vasoconstriction is followed, representing the most important CNS parasympathetic trigger that will promote local vasodilation. Stroke is a clear example of this process. The posterior circulation is affected in 30% of strokes, causing high morbidity and mortality outcomes. Currently, the management of ischemic stroke is focused on thrombolytic treatment and endovascular thrombectomy within an overall tight 4.5 to 6 h ischemic time window. Therefore, the autonomic nervous system could represent a potential therapeutic target to modulate reperfusion after cerebral ischemia through vasodilation, which could potentially decrease infarct size and increase the thrombolytic therapeutic ischemic window. In addition, shifting the autonomic nervous system balance toward its parasympathetic branch has shown to enhance neurogenesis and decrease local inflammation. Regretfully, the vast majority of animal models and human research on neuromodulation during brain ischemia have been focused on anterior circulation with disappointing results. In addition, the source of parasympathetic inputs in the vertebrobasilar system in humans is poorly understood, substantiating a gap and controversy in this area. Here, we reviewed current available literature regarding the parasympathetic vascular function and challenges of its stimulation in the vertebrobasilar system.

Cluster headache pathophysiology - insights from current and emerging treatments

Cluster headache is a debilitating primary headache disorder that affects approximately 0.1% of the population worldwide. Cluster headache attacks involve severe unilateral pain in the trigeminal distribution together with ipsilateral cranial autonomic features and a sense of agitation. Acute treatments are available and are effective in just over half of the patients. Until recently, preventive medications were borrowed from non-headache indications, so management of cluster headache is challenging. However, as our understanding of cluster headache pathophysiology has evolved on the basis of key bench and neuroimaging studies, crucial neuropeptides and brain structures have been identified as emerging treatment targets. In this Review, we provide an overview of what is known about the pathophysiology of cluster headache and discuss the existing treatment options and their mechanisms of action. Existing acute treatments include triptans and high-flow oxygen, interim treatment options include corticosteroids in oral form or for greater occipital nerve block, and preventive treatments include verapamil, lithium, melatonin and topiramate. We also consider emerging treatment options, including calcitonin gene-related peptide antibodies, non-invasive vagus nerve stimulation, sphenopalatine ganglion stimulation and somatostatin receptor agonists, discuss how evidence from trials of these emerging treatments provides insights into the pathophysiology of cluster headache and highlight areas for future research.

Electroacupuncture of the Ophthalmic Branch of the Trigeminal Nerve: Effects on Prefrontal Cortex Blood Flow

Objective: The current authors observed enhanced cerebral blood flow (CBF) in the prefrontal cortex (PFC) in response to 100-Hz electroacupuncture (EA) stimulation of the ophthalmic branch of the trigeminal nerve. However, it is not yet clear if responsiveness to 100-Hz EA depends on stimulus intensity. This study examined the effects of stimulus strength on PFC CBF during 100-Hz EA of the ophthalmic branch of the trigeminal nerve. Materials and Methods: Twelve subjects underwent 3 acupuncture sessions: I, control, no stimulation; II, 0.1 mA EA; and III, 0.2 mA EA). Needles were inserted 1 cm lateral of the head median line; the anterior insertion point was on the front hairline and the posterior insertion point was ∼7 cm behind the hairline. Stimulation frequency was set to 100-Hz. PFC CBF was measured in terms of oxygenated, deoxygenated, and total hemoglobin (OxyHb, DeoxyHb, TotalHb, respectively), using 16-channel (Ch) near-infrared spectroscopy. Results: Stimulation of 0.2 mA was associated with significant elevation of OxyHb levels in the 0.1 mA condition in Chs 6, 10, and 12. Ch 2-6, 10, 12 signals were notably higher than in the control condition. Stimulation of 0.2 mA and 0.1 mA were associated with significant declines in DeoxyHb levels, compared to the control condition in Ch 4. Finally, 0.2 mA stimulation in Chs 12 and 13 was associated with significant elevation of TotalHb levels in the control condition. Conclusions: Using 0.2-mA stimulation, 100-Hz EA of the ophthalmic nerve enhances PFC CBF more strongly than 0.1-mA stimulation.

Neurovascular mechanisms of migraine and cluster headache

Vascular theories of migraine and cluster headache have dominated for many years the pathobiological concept of these disorders. This view is supported by observations that trigeminal activation induces a vascular response and that several vasodilating molecules trigger acute attacks of migraine and cluster headache in susceptible individuals. Over the past 30 years, this rationale has been questioned as it became clear that the actions of some of these molecules, in particular, calcitonin gene-related peptide and pituitary adenylate cyclase-activating peptide, extend far beyond the vasoactive effects, as they possess the ability to modulate nociceptive neuronal activity in several key regions of the trigeminovascular system. These findings have shifted our understanding of these disorders to a primarily neuronal origin with the vascular manifestations being the consequence rather than the origin of trigeminal activation. Nevertheless, the neurovascular component, or coupling, seems to be far more complex than initially thought, being involved in several accompanying features. The review will discuss in detail the anatomical basis and the functional role of the neurovascular mechanisms relevant to migraine and cluster headache.

Brain structure and function related to headache: Brainstem structure and function in headache

OBJECTIVE

To review and discuss the literature relevant to the role of brainstem structure and function in headache.

BACKGROUND

Primary headache disorders, such as migraine and cluster headache, are considered disorders of the brain. As well as head-related pain, these headache disorders are also associated with other neurological symptoms, such as those related to sensory, homeostatic, autonomic, cognitive and affective processing that can all occur before, during or even after headache has ceased. Many imaging studies demonstrate activation in brainstem areas that appear specifically associated with headache disorders, especially migraine, which may be related to the mechanisms of many of these symptoms. This is further supported by preclinical studies, which demonstrate that modulation of specific brainstem nuclei alters sensory processing relevant to these symptoms, including headache, cranial autonomic responses and homeostatic mechanisms.

REVIEW FOCUS

This review will specifically focus on the role of brainstem structures relevant to primary headaches, including medullary, pontine, and midbrain, and describe their functional role and how they relate to mechanisms of primary headaches, especially migraine.

Facial nerve stimulation as a future treatment for ischemic stroke

Stimulation of the autonomic parasympathetic fibers of the facial nerve system (hereafter simply “facial nerve”) rapidly dilates the cerebral arteries and increases cerebral blood flow whether that stimulation is delivered at the facial nerve trunk or at distal points such as the sphenopalatine ganglion. Facial nerve stimulation thus could be used as an emergency treatment of conditions of brain ischemia such as ischemic stroke. A rich history of scientific research has examined this property of the facial nerve, and various means of activating the facial nerve can be employed including noninvasive means. Herein, we review the anatomical and physiological research behind facial nerve stimulation and the facial nerve stimulation devices that are in development for the treatment of ischemic stroke.

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.

Current Understanding on Pain Mechanism in Migraine and Cluster Headache

CONTEXT

Migraine and cluster headache are undoubtedly painful conditions. The respective pathogenesis of these two conditions is incompletely understood. In both cases, the treatments used have largely been empirical and have relied to a much lesser extent on our understanding of the mechanisms causing pain. We hereby review the pain mechanisms in migraine and cluster headache, two of the commonest primary headache disorders.

EVIDENCE ACQUISITION

A review of the English literature was conducted by searching PubMed for studies on pain mechanism in migraine and cluster headache. We entered [migraine] and [pain mechanism] in Pubmed and 488 articles were obtained. Articles were then included according to their relevance to the topic. Similarly, [cluster headache] and [pain mechanism] revealed 79 search results.

RESULTS

There is evidence that the trigeminovascular system and neurogenic inflammation play important roles, together with certain areas of the brain, leading to these conditions being termed 'neurovascular headaches'. Functional imaging findings suggest a possible role of the dorsolateral pons in generating migraine attacks while the role of the hypothalamus in cluster headache is more firmly established.

CONCLUSIONS

Migraine and cluster headache have complex pathophysiologies. The exact mechanism causing pain in both conditions is incompletely understood and more research needs to be undertaken in this area.

The identification and neurochemical characterization of central neurons that target parasympathetic preganglionic neurons involved in the regulation of choroidal blood flow in the rat eye using pseudorabies virus, immunolabeling and conventional pathway tracing methods

The choroidal blood vessels of the eye provide the main vascular support to the outer retina. These blood vessels are under parasympathetic vasodilatory control via input from the pterygopalatine ganglion (PPG), which in turn receives its preganglionic input from the superior salivatory nucleus (SSN) of the hindbrain. The present study characterized the central neurons projecting to the SSN neurons innervating choroidal PPG neurons, using pathway tracing and immunolabeling. In the initial set of studies, minute injections of the Bartha strain of the retrograde transneuronal tracer pseudorabies virus (PRV) were made into choroid in rats in which the superior cervical ganglia had been excised (to prevent labeling of sympathetic circuitry). Diverse neuronal populations beyond the choroidal part of ipsilateral SSN showed transneuronal labeling, which notably included the parvocellular part of the paraventricular nucleus of the hypothalamus (PVN), the periaqueductal gray, the raphe magnus (RaM), the B3 region of the pons, A5, the nucleus of the solitary tract (NTS), the rostral ventrolateral medulla (RVLM), and the intermediate reticular nucleus of the medulla. The PRV+ neurons were located in the parts of these cell groups that are responsive to systemic blood pressure signals and involved in systemic blood pressure regulation by the sympathetic nervous system. In a second set of studies using PRV labeling, conventional pathway tracing, and immunolabeling, we found that PVN neurons projecting to SSN tended to be oxytocinergic and glutamatergic, RaM neurons projecting to SSN were serotonergic, and NTS neurons projecting to SSN were glutamatergic. Our results suggest that blood pressure and volume signals that drive sympathetic constriction of the systemic vasculature may also drive parasympathetic vasodilation of the choroidal vasculature, and may thereby contribute to choroidal baroregulation during low blood pressure.

Autonomic control of the eye

The autonomic nervous system influences numerous ocular functions. It does this by way of parasympathetic innervation from postganglionic fibers that originate from neurons in the ciliary and pterygopalatine ganglia, and by way of sympathetic innervation from postganglionic fibers that originate from neurons in the superior cervical ganglion. Ciliary ganglion neurons project to the ciliary body and the sphincter pupillae muscle of the iris to control ocular accommodation and pupil constriction, respectively. Superior cervical ganglion neurons project to the dilator pupillae muscle of the iris to control pupil dilation. Ocular blood flow is controlled both via direct autonomic influences on the vasculature of the optic nerve, choroid, ciliary body, and iris, as well as via indirect influences on retinal blood flow. In mammals, this vasculature is innervated by vasodilatory fibers from the pterygopalatine ganglion, and by vasoconstrictive fibers from the superior cervical ganglion. Intraocular pressure is regulated primarily through the balance of aqueous humor formation and outflow. Autonomic regulation of ciliary body blood vessels and the ciliary epithelium is an important determinant of aqueous humor formation; autonomic regulation of the trabecular meshwork and episcleral blood vessels is an important determinant of aqueous humor outflow. These tissues are all innervated by fibers from the pterygopalatine and superior cervical ganglia. In addition to these classical autonomic pathways, trigeminal sensory fibers exert local, intrinsic influences on many of these regions of the eye, as well as on some neurons within the ciliary and pterygopalatine ganglia.

Neurochemicals involved in medullary control of common carotid blood flow

The common carotid artery (CCA) supplies intra- and extra-cranial vascular beds. An area in the medulla controlling CCA blood flow is defined as the dorsal facial area (DFA) by Kuo et al. in 1987. In the DFA, presynaptic nitrergic and/or glutamatergic fibers innervate preganglionic nitrergic and/or cholinergic neurons which give rise to the preganglionic fibers of the parasympathetic 7th and 9th cranial nerves. Released glutamate from presynaptic nitrergic and/or glutamatergic fibers can activate N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors on preganglionic nitrergic and/or cholinergic neurons. By modulating this glutamate release, several neurochemicals including serotonin, arginine, nitric oxide, nicotine, choline and ATP in the DFA regulate CCA blood flow. Understanding the neurochemical regulatory mechanisms can provide important insights of the physiological roles of the DFA, and may help develop therapeutic strategies for diseases involving CCA blood flow, such as migraine, hypertensive disease, Alzheimer’s disease and cerebral ischemic stroke.

Vagus nerve stimulation reduces infarct size in rat focal cerebral ischemia: an unlikely role for cerebral blood flow

We sought to investigate the effect of cervical vagus nerve stimulation (VNS) on cerebral blood flow (CBF), infarct volume, and clinical outcome in a model of middle cerebral artery occlusion in rats. Electrical stimulation of the right and left vagus nerves was initiated 30min after the induction of the right-sided ischemia and lasted for 1h. Infarct size measurement revealed that the volume of ischemic damage was 41-45% smaller in animals receiving stimulation as compared with control animals. Both the right and left VNS caused subtle reduction in CBF during each 30-s stimulation period that quickly returned back to the baseline level at the end of each stimulation cycle. There was no significant effect of VNS on CBF during the entire 1-h stimulation period. The effect of VNS on tissue outcome was associated with better neurological outcome at both 1- and 3-day time points after the induction of ischemia. These findings suggest that VNS-induced protection against acute ischemic brain injury is not primarily mediated by changes in CBF, stimulation of both the right and left nerve have comparable effects, and VNS is effective after ipsilateral and contralateral focal ischemia.

Projections from the hypothalamic paraventricular nucleus and the nucleus of the solitary tract to prechoroidal neurons in the superior salivatory nucleus: Pathways controlling rodent choroidal blood flow

Using intrachoroidal injection of the transneuronal retrograde tracer pseudorabies virus (PRV) in rats, we previously localized preganglionic neurons in the superior salivatory nucleus (SSN) that regulate choroidal blood flow (ChBF) via projections to the pterygopalatine ganglion (PPG). In the present study, we used higher-order transneuronal retrograde labeling following intrachoroidal PRV injection to identify central neuronal cell groups involved in parasympathetic regulation of ChBF via input to the SSN. These prominently included the hypothalamic paraventricular nucleus (PVN) and the nucleus of the solitary tract (NTS), both of which are responsive to systemic BP and are involved in systemic sympathetic vasoconstriction. Conventional pathway tracing methods were then used to determine if the PVN and/or NTS project directly to the choroidal subdivision of the SSN. Following retrograde tracer injection into SSN (biotinylated dextran amine 3K or Fluorogold), labeled perikarya were found in PVN and NTS. Injection of the anterograde tracer, biotinylated dextran amine 10K (BDA10K), into PVN or NTS resulted in densely packed BDA10K+terminals in prechoroidal SSN (as defined by its enrichment in nitric oxide synthase-containing perikarya). Double-label studies showed these inputs ended directly on prechoroidal nitric oxide synthase-containing neurons of SSN. Our study thus establishes that PVN and NTS project directly to the part of SSN involved in parasympathetic vasodilatory control of the choroid via the PPG. These results suggest that control of ChBF may be linked to systemic blood pressure and central control of the systemic vasculature.

Animal models of headache: from bedside to bench and back to bedside

In recent years bench-based studies have greatly enhanced our understanding of headache pathophysiology, while facilitating the development of new headache medicines. At present, established animal models of headache utilize activation of pain-producing cranial structures, which for a complex syndrome, such as migraine, leaves many dimensions of the syndrome unstudied. The focus on modeling the central nociceptive mechanisms and the complexity of sensory phenomena that accompany migraine may offer new approaches for the development of new therapeutics. Given the complexity of the primary headaches, multiple approaches and techniques need to be employed. As an example, recently a model for trigeminal autonomic cephalalgias has been tested successfully, while by contrast, a satisfactory model of tension-type headache has been elusive. Moreover, although useful in many regards, migraine models are yet to provide a more complete picture of the disorder.

Paraventricular hypothalamic nucleus: axonal projections to the brainstem

The paraventricular hypothalamic nucleus (PVH) contains many neurons that innervate the brainstem, but information regarding their target sites remains incomplete. Here we labeled neurons in the rat PVH with an anterograde axonal tracer, Phaseolus vulgaris leucoagglutinin (PHAL), and studied their descending projections in reference to specific neuronal subpopulations throughout the brainstem. While many of their target sites were identified previously, numerous new observations were made. Major findings include: 1) In the midbrain, the PVH projects lightly to the ventral tegmental area, Edinger-Westphal nucleus, ventrolateral periaqueductal gray matter, reticular formation, pedunculopontine tegmental nucleus, and dorsal raphe nucleus. 2) In the dorsal pons, the PVH projects heavily to the pre-locus coeruleus, yet very little to the catecholamine neurons in the locus coeruleus, and selectively targets the viscerosensory subregions of the parabrachial nucleus. 3) In the ventral medulla, the superior salivatory nucleus, retrotrapezoid nucleus, compact and external formations of the nucleus ambiguous, A1 and caudal C1 catecholamine neurons, and caudal pressor area receive dense axonal projections, generally exceeding the PVH projection to the rostral C1 region. 4) The medial nucleus of the solitary tract (including A2 noradrenergic and aldosterone-sensitive neurons) receives the most extensive projections of the PVH, substantially more than the dorsal vagal nucleus or area postrema. Our findings suggest that the PVH may modulate a range of homeostatic functions, including cerebral and ocular blood flow, corneal and nasal hydration, ingestive behavior, sodium intake, and glucose metabolism, as well as cardiovascular, gastrointestinal, and respiratory activities.

Glutamate release upon purinergic action in the dorsal facial area of the medulla increases blood flow in the common carotid artery in cats

Interactions of glutamatergic and purinergic actions in the medulla regulate important cardiovascular functions. The glutamatergic action in dorsal facial area (DFA) of the medulla increases blood flow of common carotid artery (CCA) in cats. We hypothesized that interactions of glutamatergic and purinergic actions in the DFA may regulate the CCA blood flow. Purinergic and glutamatergic agonists and antagonists were microinjected into the DFA through a four-barrel tubing in anesthetized cats. Drug effects were evaluated by changes in the CCA blood flow. Microinjection with 20 nmol ATP or alpha,beta-methyleneATP (alpha,beta-MeATP, a P2 purinergic receptor agonist) induced an increase of the CCA blood flow. This increase was dose-dependently reduced by prior administration with 1,3-dipropyl-8-p-sulfophenylxanthine (DPSPX, a specific P1 purinergic receptor antagonist), or pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS, a selective P2 purinergic receptor antagonist) as well as with MK-801 (a non-competitive NMDA receptor antagonist) or glutamate diethyl ester (GDEE, a competitive AMPA/kainate receptor antagonist). It was almost completely blocked by administrations with combined maximal doses of P1 and P2 receptor antagonists as well as NMDA and AMPA receptor antagonists. Nevertheless, P1 receptor agonist induced only mild and poorly reproducible increase in the CCA blood flow. In conclusion, prominent P2 and minor P1 purinergic receptors appear to be present in the DFA; the purinergic activation can mediate a release of glutamate that stimulates NMDA and AMPA to induce the increase of the CCA blood flows. These findings may provide important information for developing therapeutic strategy for diseases involving the CCA blood flow, such as hypertensive disease and cerebral ischemia.

Neuromodulatory approaches to the treatment of trigeminal autonomic cephalalgias

The trigeminal autonomic cephalalgias (TACs) are a group of primary headache syndromes characterised by intense pain and associated activation of cranial parasympathetic autonomic outflow pathways out of proportion to the pain. The TACs include cluster headache, paroxysmal hemicrania and SUNCT (short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing). The pathophysiology of these syndromes involves activation of the trigeminal-autonomic reflex, whose afferent limb projects into the trigeminocervical complex in the caudal brainstem and upper cervical spinal cord. Functional brain imaging has shown activations in the posterior hypothalamic grey matter in TACs. This paper reviews the anatomy and physiology of these conditions and the brain imaging findings. Current treatments are summarised and the role of neuromodulation procedures, such as occipital nerve stimulation and deep brain stimulation in the posterior hypothalamus are reviewed. Neuromodulatory procedures are a promising avenue for these highly disabled patients with treatment refractory TACs.

Regulation of common carotid arterial blood flow by nitrergic neurons in the medulla of cats

Glutamate stimulation of the dorsal facial area, an area located dorsal to the facial nucleus, increases common carotid arterial blood flow. Nitrergic neurons are important in cardiovascular regulatory areas. We investigated whether the nitrergic neurons might be present and play a role in the dorsal facial area to regulate the arterial blood flow. Injections of L-arginine (an NO precursor) and sodium nitroprusside (an NO donor) into the area caused dose-dependent increases in the arterial blood flow. Injection of N(G)-nitro-arginine methyl ester (L-NAME, an NO synthase inhibitor) or methylene blue (a guanylate cyclase inhibitor) decreased the arterial blood flow. Nitrergic neurons and fibers were found in the dorsal facial area by histochemical staining of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase, a maker of NO synthase. In conclusion, nitrergic neurons are present in the dorsal facial area and appear to release NO tonically in stimulating the area to cause increase in common carotid arterial blood flow.

Regulation of the common carotid arterial blood flow by nicotinic receptors in the medulla of cats

BACKGROUND AND PURPOSE

Actions of glutamate and serotonin on their respective receptors in the dorsal facial area (DFA) of the medulla are known to regulate common carotid arterial (CCA) blood flow in cats. Less is known about acetylcholine action on its nicotinic receptor (nAChR) subtypes in the DFA for regulation of CCA blood flow and this aspect was investigated.

EXPERIMENTAL APPROACH

Nicotinic and muscarinic agonists and antagonists were microinjected into the DFA through a three-barrel tubing in anesthetized cats.

RESULTS

CCA blood flow was dose-dependently increased by nicotine (a non-selective nAChR agonist) and choline (a selective alpha7-nAChR agonist). These effects of nicotine were attenuated by alpha-bungarotoxin (an alpha7-nAChR antagonist), methyllycaconitine (an alpha7-nAChR antagonist), mecamylamine (a relatively selective alpha3beta4-nAChR antagonist) and dihydro-beta-erythroidine (a relatively selective alpha4beta2-nAChR antagonist). The choline-induced flow increase was attenuated by alpha-bungarotoxin and mecamylamine, but not by dihydro-beta-erythroidine. Muscarinic agonists (muscarine and methacholine) and antagonist (atropine) affected neither the basal nor the nicotine-induced increase in the CCA blood flow.

CONCLUSIONS AND IMPLICATIONS

Functional alpha7, alpha4beta2, and alpha3beta4 subunits of the nAChR appear to be present on the DFA neurons. Activations of these receptors increase the CCA blood flow. The present findings do not preclude the presence of other nAChRs subunits. Muscarinic receptors, if any, on the DFA are not involved in regulation of the CCA blood flow. Various subtypes of nAChRs in the DFA may mediate regulation of the CCA and cerebral blood flows.

The role of CGRP and nicotinic receptors in centrally evoked facial blood flow changes

The release of CGRP in humans is associated with the occurrence of migraine headaches. The vasoactive neuropeptide is released by afferent neurones originating in the peripherally located trigeminal ganglion supplying the dura mater. The role of CGRP in migraine is further supported by recently released data showing that the CGRP-antagonist BIBN4096BS is clinically effective for the treatment of migraine headaches. Yet, the trigger for CGRP release during migraine attacks is not identified. It is suggested that the peripheral CGRP release during a migraine attack might be either triggered by direct activation of afferent dural neurones, or, by indirect activation via the central nervous system. Recently, we were able to show that the CGRP-antagonist BIBN4096BS is able to inhibit vasodilation induced by trigeminal ganglion stimulation. Now, we extend our studies to the investigation of facial blood flow changes induced by electrical stimulation of the brainstem trigeminal nucleus caudalis (TNC). Here, we show that stimulation of the TNC leads to a pronounced increase of facial blood flow. The nicotinic antagonist Hexamethonium reduced the evoked flow by approximately 50% (30 mg/kg), while the muscarinic antagonist Atropin did not influence the stimulation evoked blood flow. Application of BIBN4096BS (0.3 mg/kg, i.v.) diminished the evoked flow almost completely. Therefore, we conclude that CGRP represents the key player in TNC-induced facial vasodilation, while activation of nicotinic receptors modulates centrally induced peripheral neurogenic vasodilation.

Patterns of fos expression in the rostral medulla and caudal pons evoked by noxious craniovascular stimulation and periaqueductal gray stimulation in the cat

Functional imaging studies and clinical evidence suggest that structures in the brainstem contribute to migraine pathophysiology with a strong association between the brainstem areas, such as periaqueductal gray (PAG), and the headache phase of migraine. Stimulation of the superior sagittal sinus (SSS) in humans evokes head pain. Second-order neurons in the trigeminal nucleus that are activated by SSS stimulation can be inhibited by PAG stimulation. The present study was undertaken to identify pontine and medullary structures that respond to noxious stimulation of the superior sagittal sinus or to ventrolateral PAG stimulation. The distribution of neurons expressing the protein product (fos) of the c-fos immediate early gene were examined in the rostral medulla and caudal pons of the cat after (i) sham, (ii) stimulation of the superior sagittal sinus, (iii) stimulation of the superior sagittal sinus with PAG stimulation, or (iv) stimulation of the PAG alone. The structures examined for fos were the trigeminal nucleus, infratrigeminal nucleus, reticular nuclei, nucleus raphe magnus, pontine blink premotor area, and superior salivatory nucleus. Compared with all other interventions, fos expression was significantly greater in the trigeminal nucleus and superior salivatory nucleus after SSS stimulation. After PAG with SSS stimulation, on the side ipsilateral to the site of PAG stimulation, fos was significantly greater in the nucleus raphe magnus. These structures are likely to be involved in the neurobiology of migraine.

A novel central pathway links arterial baroreceptors and pontine parasympathetic neurons in cerebrovascular control

1. We tested the hypothesis that arterial baroreceptor reflexes modulate cerebrovascular tone through a pathway that connects the cardiovascular nucleus tractus solitarii with parasympathetic preganglionic neurons in the pons. 2. Anesthetized rats were used in all studies. Laser flowmetry was used to measure cerebral blood flow. We assessed cerebrovascular responses to increases in arterial blood pressure in animals with lesions of baroreceptor nerves, the nucleus tractus solitarii itself, the pontine preganglionic parasympathetic neurons, or the parasympathetic ganglionic nerves to the cerebral vessels. Similar assessments were made in animals after blockade of synthesis of nitric oxide, which is released by the parasympathetic nerves from the pterygopalatine ganglia. Finally the effects on cerebral blood flow of glutamate stimulation of pontine preganglionic parasympathetic neurons were evaluated. 3. We found that lesions at any one of the sites in the putative pathway or interruption of nitric oxide synthesis led to prolongation of autoregulation as mean arterial pressure was increased to levels as high as 200 mmHg. Conversely, stimulation of pontine parasympathetic preganglionic neurons led to cerebral vasodilatation. The second series of studies utilized classic anatomical tracing methods to determine at the light and electron microscopic level whether neurons in the cardiovascular nucleus tractus solitarii, the site of termination of baroreceptor afferents, projected to the pontine preganglionic neurons. Fibers were traced with anterograde tracer from the nucleus tractus solitarii to the pons and with retrograde tracer from the pons to the nucleus tractus solitarii. Using double labeling techniques we further studied synapses made between labeled projections from the nucleus tractus solitarii and preganglionic neurons that were themselves labeled with retrograde tracer placed into the pterygopalatine ganglion. 4. These anatomical studies showed that the nucleus tractus solitarii directly projects to pontine preganglionic neurons and makes asymmetric, seemingly excitatory, synapses with those neurons. These studies provide strong evidence that arterial baroreceptors may modulate cerebral blood flow through direct connections with pontine parasympathetic neurons. Further study is needed to clarify the role this pathway plays in integrative physiology.

Noxious chemical stimulation of rat facial mucosa increases intracranial blood flow through a trigemino-parasympathetic reflex--an experimental model for vascular dysfunctions in cluster headache

Cluster headache is characterized by typical autonomic dysfunctions including facial and intracranial vascular disturbances. Both the trigeminal and the cranial parasympathetic systems may be involved in mediating these dysfunctions. An experimental model was developed in the rat to measure changes in lacrimation and intracranial blood flow following noxious chemical stimulation of facial mucosa. Blood flow was monitored in arteries of the exposed cranial dura mater and the parietal cortex using laser Doppler flowmetry. Capsaicin (0.01-1 mm) applied to oral or nasal mucosa induced increases in dural and cortical blood flow and provoked lacrimation. These responses were blocked by systemic pre-administration of hexamethonium chloride (20 mg/kg). The evoked increases in dural blood flow were also abolished by topical pre-administration of atropine (1 mm) and [Lys1, Pro2,5, Arg3,4, Tyr6]-VIP (0.1 mm), a vasoactive intestinal polypeptide (VIP) antagonist, onto the exposed dura mater. We conclude that noxious stimulation of facial mucosa increases intracranial blood flow and lacrimation via a trigemino-parasympathetic reflex. The blood flow responses seem to be mediated by the release of acetylcholine and VIP within the meninges. Similar mechanisms may be involved in the pathogenesis of cluster headache.

Ionotropic NMDA receptor evokes an excitatory response in superior salivatory nucleus neurons in anaesthetized rats

Extracellular recordings were taken from preganglionic superior salivatory nucleus (SSN) neurons projecting to submandibular and intra-lingual ganglia, in order to study the action of SSN neurons resulting from ionophoretic application of ionotropic NMDA receptor agonist in urethane-chloralose anaesthetized rats. Single SSN neurons were identified by their antidromic spike responses following stimulation of the chorda-lingual nerve (CLN), chorda tympani branches (CTBs) and the lingual nerve (LN). About one-third (33%, 10/30) of the identified SSN neurons were induced to fire by ionophoretic application of the NMDA receptor agonists used, dl-homocysteic acid (DLH) and N-methyl-D-aspartic acid (NMDA). More than half exhibited firing at high frequencies, often exceeding 40 Hz. About one-fifth (20%; 6/30) of the identified SSN neurons exhibited orthodromic spike responses to the combination of NMDA receptor agonist application and sensory nerve (CLN or LN) stimulus. These excitatory responses evoked by application of NMDA receptor agonist were attenuated (n = 4) by ionophoretic application of DL-2-amino-5-phosphonovaleric acid (AP5; NMDA receptor antagonist). About half (47%) of the neurons did not respond to any combination of NMDA receptor agonist and sensory nerve stimuli. No differences were observed between SSN neurons with B fibre axons and those with C fibre axons in response to ionophoresis of the NMDA receptor agonists. The NMDA-sensitive neurons, which exhibited high frequency firing, were predominantly found in the rostral part of the SSN. In summary, activation of ionotropic NMDA receptors exerts an excitatory effect on about half of the SSN neurons. These data support the view that NMDA receptors are involved in information processing and transmission on SSN neurons.

Evidence for a glutamatergic input to pontine preganglionic neurons of the superior salivatory nucleus in rat

Parasympathetic preganglionic neurons of the superior salivatory nucleus (SSN), which projects to the pterygopalatine ganglion (PPG), modulate salivation, lacrimation, and cerebrovascular tone. Our previous studies suggest that excitatory projections from the nucleus tractus solitarii modulate cerebrovascular tone by actions on SSN neurons. In this study we sought to test the hypothesis that N-methyl-D-aspartate (NMDA) type glutamate receptors and vesicular glutamate transporters (VGLUT) are present in the SSN and that SSN neurons receive glutamatergic input. In six rats we injected tetramethylrhodamine dextran (TRD), a fluorescent tracer, unilaterally into the PPG to label SSN neurons. Four days later, rats were perfused and brain stem sections containing the SSN were processed for fluorescent immunohistochemistry for N-methyl-D-aspartate receptor subunit 1 (NMDAR1) and vesicular glutamate transporters (VGLUT1 and VGLUT2). Confocal laser scanning microscopy showed that 88+/-3% of TRD-labeled SSN neurons contained NMDAR1-immunoreactivity (IR). The surrounding neuropil contained numerous fibers labeled for VGLUT2-IR, but not VGLUT1-IR. Double fluorescent immunohistochemistry for NMDAR1 and VGLUT2 revealed that fibers containing VGLUT2-IR were often in close proximity to cell bodies or proximal dendrites of TRD-labeled SSN neurons that were positive for NMDAR1-IR. These studies support our hypothesis that NMDA receptors and VGLUT are present in the SSN. They further provide support for the suggestion that there are glutamatergic inputs to SSN neurons and would be consistent with an excitatory input that could regulate cerebrovascular tone.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Glutamatergic and serotonergic mechanisms in the dorsal facial area for common carotid artery blood flow control in the cat

This study explored which subtyes of glutamate receptors in the dorsal facial area are involved in the interaction between glutamatergic and serotonergic actions in controlling common carotid arterial blood flow. Microinjection of glutamate (25-100 nmol), N-methyl-D-aspartate (NMDA; 1-4 nmol), or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 0.5-2 nmol) into the dorsal facial area dose-dependently increased common carotid arterial blood flow. The potency order was AMPA>NMDA>glutamate. The glutamate-induced increase in common carotid arterial blood flow was reduced by pretreatment with either D-2-amino-5-phosphonopentanoate (D-AP5; 2.5-5.0 nmol), or glutamate diethylester (25-50 nmol). The common carotid arterial blood flow was increased by ketanserin (1.0 nmol) and decreased by (+/-)-1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (1.0 nmol). Both effects were attenuated by pretreatment with either D-AP5 or glutamate diethylester. We conclude that activation of both NMDA and AMPA receptors in dorsal facial area is responsible for the increase in common carotid arterial blood flow, and AMPA receptor may play a greater role. Such response may be suppressed by 5-HT2 action.

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.

Inhibiting the nucleus tractus solitarii extends cerebrovascular autoregulation during hypertension

Autoregulation maintains cerebral blood flow near basal levels as blood pressure increases, but vasodilation, breakthrough, occurs when hypertension exceeds the autoregulatory range. Loss of breakthrough after transection of baroreceptor nerves suggests that breakthrough is neurally mediated. We hypothesize that central baroreflex interruption will likewise prevent breakthrough. In treated rats, injections of lidocaine into the nucleus tractus solitarii blocked breakthrough and the baroreflex. Therefore, central, like peripheral, baroreflex interruption extends autoregulation during hypertension.

Neurons of nucleus of the solitary tract synchronize the EEG and elevate cerebral blood flow via a novel medullary area

In anesthetized spinalized rat, electrical stimulation of the nucleus tractus solitarius (NTS) synchronizes the EEG by increasing the power of 4-6-Hz waves (>100%; P<0.01), and elevates cerebral blood flow (rCBF) by 18+/-5% (P<0.05). The coordinated response appears within seconds, is global, reversible, graded, evoked from the commissural sub-nucleus, and replicated by L-glutamate. The responses are markedly reduced by bilateral lesions or muscimol microinjections restricted to a region of ventral medullary reticular formation, the medullary cerebral vasodilator area (MCVA), a region from which stimulation elicits identical responses and mediates the comparable responses to hypoxic/ischemic excitation of sympathoexcitatory neurons of rostral ventrolateral medulla (RVLM). We conclude that: (a) excitation of intrinsic neurons of commissural NTS synchronizes the EEG and coordinately elevates rCBF; (b) the responses are mediated by excitation of neurons in MCVA; (c) the MCVA may be a common final pathway mediating cerebrovascular and EEG responses from multiple areas of CNS; and (d) the NTS-MCVA pathway may be a part of the anatomical substrate for behaviors, including slow-wave sleep and seizure suppression evoked by stimulation of visceral afferents terminating in NTS.

A brainstem area mediating cerebrovascular and EEG responses to hypoxic excitation of rostral ventrolateral medulla in rat

We sought to identify the medullary relay area mediating the elevations of regional cerebral blood flow (rCBF) and synchronization of the electroencephalogram (EEG) in the rat cerebral cortex elicited by hypoxic excitation of reticulospinal sympathoexcitatory neurons of the rostral ventrolateral medulla (RVLM ). In anaesthetized spinalized rats electrical stimulation of RVLM elevated rCBF (laser-Doppler flowmetry) by 31 +/- 6 %, reduced cerebrovascular resistance (CVR) by 26 +/- 8 %, and synchronized the EEG, increasing the power of the 5-6 Hz band by 98 +/- 25 %. Stimulation of a contiguous caudal region, the medullary cerebral vasodilator area (MCVA), had comparable effects which, like responses of RVLM, were replicated by microinjection of L-glutamate (5 nmol, 20 nl). Microinjection of NaCN (300 pmol in 20 nl) elevated rCBF (17 +/- 5 %) and synchronized the EEG from RVLM, but not MCVA, while nicotine (1.2 nmol in 40 nl) increased rCBF by 13 +/- 5 % and synchronized the EEG from MCVA. In intact rats nicotine lowered arterial pressure only from MCVA (101 +/- 3 to 52 +/- 9 mmHg). Bilateral electrolytic lesions of MCVA significantly reduced, by over 59 %, elevations in rCBF and, by 78 %, changes in EEG evoked from RVLM. Bilateral electrolytic lesions of RVLM did not affect responses from MCVA. Anterograde tracing with BDA demonstrated that RVLM and MCVA are interconnected. The MCVA is a nicotine-sensitive region of the medulla that relays signals elicited by excitation of oxygen-sensitive reticulospinal neurons in RVLM to reflexively elevate rCBF and slow the EEG as part of the oxygen-conserving (diving) reflex initiated in these neurons by hypoxia or ischaemia.

Parasympathetic nerves influence cerebral blood flow during hypertension in rat

This study tested the hypothesis that cerebral vasodilatation during marked acute hypertension is mediated in part through the influence of parasympathetic nerves from the pterygopalatine ganglia. Blood pressure was increased slowly in anesthetized rats after bilateral transection of the parasympathetic nerves. Cerebral blood flow was measured by laser flowmetry. Acutely hypertensive denervated animals developed significantly less cerebral vasodilatation than did control animals with intact nerves. Thus, parasympathetic vasodilator nerves contribute to vasodilatation seen with acute hypertension.

Preganglionic and postganglionic neurons responsible for cerebral vasodilation mediated by nitric oxide in anesthetized dogs

The authors performed investigations to functionally determine the route of efferent innervation in vivo responsible for cerebral vasodilation mediated by nitric oxide (NO). In anesthetized beagles, electrical stimulation of the pterygopalatine ganglion vasodilated ipsilateral cerebral arteries such as the middle cerebral and posterior communicating arteries. Intravenous injections of NG-nitro-L-arginine (L-NA) markedly inhibited the response to nerve stimulation, and the effect was reversed by L-arginine. Stimulation of the proximal portion of the greater superficial petrosal nerve, upstream of the pterygopalatine ganglion, also produced cerebral vasodilation, which was abolished by L-NA and restored by L-arginine. Treatment with hexamethonium abolished the response to stimulation of the petrosal nerve but did not affect the response to pterygopalatine ganglion stimulation. Destruction of the pterygopalatine ganglion by cauterization constricted the cerebral arteries. Postganglionic denervation abolished the vasodilation, lacrimation, and nasal secretion induced on the ipsilateral side by stimulation of the pterygopalatine ganglion and petrosal nerve. The vasodilator response was suppressed by L-NA but unaffected by atropine, whereas lacrimation and nasal secretion were abolished solely by atropine. It is concluded that postganglionic neurons from the pterygopalatine ganglion play crucial roles in cerebral vasodilation mediated by NO from the nerve, and preganglionic neurons, possibly from the superior salivatory nucleus through the greater superficial petrosal nerve, innervate the pterygopalatine ganglion. Tonic discharges from the vasomotor center participate significantly in the maintenance of cerebral vasodilation.

Dorsal facial area of cat medulla; 5-HT2 action on glutamate release in regulating common carotid blood flow

Serotonin (5-HT) may inhibit glutamate release in the dorsal facial area (DFA) of the medulla and decrease common carotid arterial (CCA) blood flow. We attempted to clarify which subtype(s) of 5-HT receptor was involved. A microdialysis probe was inserted in DFA. The concentration of glutamate in dialysates were determined by chromatography. Glutamate concentration was dose-dependently decreased by perfusion of 5-HT or DOI, a 5-HT2 agonist, but not by 5-CT, a 5-HT1 agonist. The 5-HT-induced decrease in glutamate was reversed by co-perfusion of ketanserin, a 5-HT2 antagonist, but not by propranolol, a 5-HT1 antagonist. CCA blood flow was decreased when 5-HT or DOI was perfused, and was reversed by co-perfusing ketanserin. In conclusion, 5-HT may inhibit glutamate release via 5-HT2 receptor in DFA, resulting in the reduction of CCA blood flow.

Origin of sensory and autonomic innervation of the rat temporomandibular joint: a retrograde axonal tracing study with the fluorescent dye fast blue

Previous studies that have used retrograde axonal tracers (horseradish peroxidase alone or conjugated with wheat germ agglutinin) have shown that the temporomandibular joint (TMJ) is supplied with nerve fibers originating mainly from the trigeminal ganglion, in addition to other sensory and sympathetic ganglia. The existence of nerve fibers in the TMJ originating from the trigeminal mesencephalic nucleus is unclear, and the possible innervation by parasympathetic nerve fibers has not been determined. In the present work, the retrograde axonal tracer, fast blue, was used to elucidate these questions and re-evaluated the literature data. The tracer was deposited in the supradiscal articular space of the rat TMJ, and an extensive morphometric analysis was performed of the labeled perikaryal profiles located in sensory and autonomic ganglia. This methodology permitted us to observe labeled small perikaryal profiles in the trigeminal ganglion, clustered mainly in the posterior-lateral region of the dorsal, medial, and ventral thirds of horizontal sections, with some located in the anterior-lateral region of the ventral third. Sensory perikarya were also labeled in the dorsal root ganglia from C2 to C5. No labeled perikaryal profiles were found in the trigeminal mesencephalic nucleus. On the other hand, autonomic labeled perikaryal profiles were distributed in the sympathetic superior cervical and stellate ganglia, and parasympathetic otic ganglion. Our results confirmed those of previous studies and also demonstrated that: (i) there is a distribution pattern of labeled perikaryal profiles in the trigeminal ganglion; (ii) some perikaryal profiles located in the otic ganglion were labeled; and (iii) the trigeminal mesencephalic nucleus did not show any retrogradely labeled perikaryal profiles.