Age-Dependent Changes in the Occurrence and Segregation of GABA and Acetylcholine in the Rat Superior Cervical Ganglia.

The occurrence, inhibitory modulation, and trophic effects of GABA have been identified in the peripheral sympathetic nervous system. We have demonstrated that GABA and acetylcholine (ACh) may colocalize in the same axonal varicosities or be segregated into separate ones in the rat superior cervical ganglia (SCG). Neurotransmitter segregation varies with age and the presence of neurotrophic factors. Here, we explored age-dependent changes in the occurrence and segregation of GABA and ACh in rats ranging from 2 weeks old (wo) to 12 months old or older. Using immunohistochemistry, we characterized the expression of L-glutamic acid decarboxylase of 67 kDa (GAD67) and vesicular acetylcholine transporter (VAChT) in the rat SCG at 2, 4, 8, 12 wo and 12 months old or older. Our findings revealed that GAD67 was greater at 2 wo compared with the other ages, whereas VAChT levels were greater at 4 wo than at 12 wo and 12 months old or older. The segregation of these neurotransmitters was more pronounced at 2 and 4 wo. We observed a caudo-rostral gradient of segregation degree at 8 and 12 wo. Data point out that the occurrence and segregation of GABA and ACh exhibit developmental adaptative changes throughout the lifetime of rats. We hypothesize that during the early postnatal period, the increase in GABA and GABA-ACh segregation promotes the release of GABA alone which might play a role in trophic actions.

The relevance of the superior cervical ganglion for cardiac autonomic innervation in health and disease: a systematic review.

PURPOSE: The heart receives cervical and thoracic sympathetic contributions. Although the stellate ganglion is considered the main contributor to cardiac sympathetic innervation, the superior cervical ganglia (SCG) is used in many experimental studies. The clinical relevance of the SCG to cardiac innervation is controversial. We investigated current morphological and functional evidence as well as controversies on the contribution of the SCG to cardiac innervation. METHODS: A systematic literature review was conducted in PubMed, Embase, Web of Science, and COCHRANE Library. Included studies received a full/text review and quality appraisal. RESULTS: Seventy-six eligible studies performed between 1976 and 2023 were identified. In all species studied, morphological evidence of direct or indirect SCG contribution to cardiac innervation was found, but its contribution was limited. Morphologically, SCG sidedness may be relevant. There is indirect functional evidence that the SCG contributes to cardiac innervation as shown by its involvement in sympathetic overdrive reactions in cardiac disease states. A direct functional contribution was not found. Functional data on SCG sidedness was largely unavailable. Information about sex differences and pre- and postnatal differences was lacking. CONCLUSION: Current literature mainly supports an indirect involvement of the SCG in cardiac innervation, via other structures and plexuses or via sympathetic overdrive in response to cardiac diseases. Morphological evidence of a direct involvement was found, but its contribution seems limited. The relevance of SCG sidedness, sex, and developmental stage in health and disease remains unclear and warrants further exploration.

P2Y13 receptor involved in HIV-1 gp120 induced neuropathy in superior cervical ganglia through NLRP3 inflammasome activation.

Cardiac autonomic neuropathy resulting from human immunodeficiency virus (HIV) infection is common; however, its mechanism remains unknown. The current work attempted to explore the function and mechanism of the P2Y13 receptor in HIV-glycoprotein 120 (gp120)-induced neuropathy in cervical sympathetic ganglion. The superior cervical ganglion (SCG) of the male SD rat was coated with HIV-gp120 to establish a model of autonomic neuropathy. In each group, we measured heart rate, blood pressure, heart rate variability, sympathetic nerve discharge and cardiac function. The expression of P2Y13 mRNA and protein in the SCG was tested by real-time polymerase chain reaction and western blotting. Additionally, this study focused on identifying the protein levels of NOD-like receptor family pyrin domain-containing 3 (NLRP3), Caspase-1, Gasdermin D (GSDMD), interleukin (IL)-1ß and IL-18 in the SCG using western blotting and immunofluorescence. In gp120 rats, increased blood pressure, heart rate, cardiac sympathetic nerve activity, P2Y13 receptor levels and decreased cardiac function could be found. P2Y13 shRNA or MRS2211 inhibited the above mentioned changes induced by gp120, suggesting that the P2Y13 receptor may be engaged in gp120-induced sympathetic nerve injury. Moreover, the levels of NLRP3, Caspase-1, GSDMD, IL-1ß and IL-18 in the gp120 group were increased, while significantly decreased by P2Y13 shRNA or MRS2211. Therefore, the P2Y13 receptor is involved in gp120-induced sympathetic neuropathy, and its molecular mechanism shows an association with the activation of the NLRP3 inflammasome, followed by GSDMD formation along with the release of inflammatory factors including IL-1ß and IL-18. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Long-term potentiation and its neurotrophin-dependent modulation in the superior cervical ganglion of the rat are influenced by KCNQ channel function.

Ganglionic long-term potentiation (gLTP) in the rat superior cervical ganglion (SCG) is differentially modulated by neurotrophic factors (Nts): brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF). KCNQ/M channels, key regulators of neuronal excitability, and firing pattern are modulated by Nts; therefore, they might contribute to gLTP expression and to the Nts-dependent modulation of gLTP. In the SCG of rats, we characterized the presence of the KCNQ2 isoform and the effects of opposite KCNQ/M channel modulators on gLTP in control condition and under Nts modulation. Immunohistochemical and reverse transcriptase polymerase chain reaction analyses showed the expression of the KCNQ2 isoform. We found that 1 µmol/L XE991, a channel inhibitor, significantly reduced gLTP (∼50%), whereas 5 µmol/L flupirtine, a channel activator, significantly increased gLTP (1.3- to 1.7-fold). Both modulators counterbalanced the effects of the Nts on gLTP. Data suggest that KCNQ/M channels are likely involved in gLTP expression and in the modulation exerted by BDNF and NGF.

[Characterization of metabotropic glutamate receptor 7 and 8 in rat superior cervical ganglion and their changes following chronic intermittent hypoxia].

OBJECTIVE: To investigate the expression and localization of metabotropic glutamate receptors 7 and 8 (mGluR7/8) in rat superior cervical ganglion (SCG) and their changes in response to chronic intermittent hypoxia (CIH). METHODS: We detected the expressions of mGluR7 and mGluR8 in the SCG of 8-week-old male SD rats using immunohistochemistry and characterized their distribution with immunofluorescence staining. The expression of mGluR7 and mGluR8 in the cytoplasm and nucleus was detected using Western blotting. A 6-week CIH rat model was established by exposure to intermittent hypoxia (6% oxygen for 30 s followed by normoxia for 4 min) for 8 h daily, and the changes in systolic blood pressure, diastolic blood pressure and mean arterial pressure were measured. The effect of CIH on expression levels of mGluR7 and mGluR8 in the SCG was analyzed using Western blotting. RESULTS: Positive expressions of mGluR7 and mGluR8 were detected in rat SCG. mGluR7 was distributed in the neurons and small fluorescent (SIF) cells with positive staining in both the cytoplasm and nuclei, but not expressed in satellite glial cells (SGCs), nerve fibers or blood vessels; mGluR8 was localized in the cytoplasm of neurons and SIF cells, but not expressed in SGCs, nerve fibers, or blood vessels. Western blotting of the nuclear and cytoplasmic fractions of rat SCG further confirmed that mGluR7 was expressed in both the cytoplasm and the nucleus, while mGluR8 exists only in the cytoplasm. Exposure to CIH significantly increased systolic blood pressure, diastolic blood pressure and mean arterial pressure of the rats (all P < 0.001) and augmented the protein expressions of mGluR7 and mGluR8 in the SCG (P < 0.05). CONCLUSION: mGluR7 and mGluR8 are present in rat SCG but with different localization patterns. CIH increases blood pressure of rats and enhanced protein expressions of mGluR7 and mGluR8 in rat SCG.

Immune-mediated denervation of the pineal gland underlies sleep disturbance in cardiac disease.

Disruption of the physiologic sleep-wake cycle and low melatonin levels frequently accompany cardiac disease, yet the underlying mechanism has remained enigmatic. Immunostaining of sympathetic axons in optically cleared pineal glands from humans and mice with cardiac disease revealed their substantial denervation compared with controls. Spatial, single-cell, nuclear, and bulk RNA sequencing traced this defect back to the superior cervical ganglia (SCG), which responded to cardiac disease with accumulation of inflammatory macrophages, fibrosis, and the selective loss of pineal gland-innervating neurons. Depletion of macrophages in the SCG prevented disease-associated denervation of the pineal gland and restored physiological melatonin secretion. Our data identify the mechanism by which diurnal rhythmicity in cardiac disease is disturbed and suggest a target for therapeutic intervention.

Regulation of Tau Expression in Superior Cervical Ganglion (SCG) Neurons In Vivo and In Vitro.

The superior cervical ganglion (SCG) is part of the autonomic nervous system providing sympathetic innervation to the head and neck, and has been regularly used to prepare postnatal neuronal cultures for cell biological studies. We found that during development these neurons change tau expression from the low molecular weight (LMW) isoforms to Big tau, with the potential to affect functions associated with tau such as microtubule dynamic and axonal transport. Big tau contains the large 4a exon that transforms tau from LMW isoforms of 45-60 kDa to 110 kDa. We describe tau expression during postnatal development reporting that the transition from LMW tau to Big tau which started at late embryonic stages is completed by about 4-5 weeks postnatally. We confirmed the presence of Big tau in dissociated postnatal SCG neurons making them an ideal system to study the function of Big tau in neurons. We used SCG explants to examine the response of SCG neurons to lesion and found that Big tau expression returned gradually along the regrowing neurites suggesting that it does not drives regeneration, but facilitates the structure/function of mature SCG neurons. The structural/functional roles of Big tau remain unknown, but it is intriguing that neurons that express Big tau appear less vulnerable to tauopathies.

Schisandrin B Alleviates Diabetic Cardiac Autonomic neuropathy Induced by P2X7 Receptor in Superior Cervical Ganglion via NLRP3.

Diabetic cardiovascular autonomic neuropathy (DCAN) is a common complication of diabetes mellitus which brings about high mortality, high morbidity, and large economic burden to the society. Compensatory tachycardia after myocardial ischemia caused by DCAN can increase myocardial injury and result in more damage to the cardiac function. The inflammation induced by hyperglycemia can increase P2X7 receptor expression in the superior cervical ganglion (SCG), resulting in nerve damage. It is proved that inhibiting the expression of P2X7 receptor at the superior cervical ganglion can ameliorate the nociceptive signaling dysregulation induced by DCAN. However, the effective drug used for decreasing P2X7 receptor expression has not been found. Schisandrin B is a traditional Chinese medicine, which has anti-inflammatory and antioxidant effects. Whether Schisandrin B can decrease the expression of P2X7 receptor in diabetic rats to protect the cardiovascular system was investigated in this study. After diabetic model rats were made, Schisandrin B and shRNA of P2X7 receptor were given to different groups to verify the impact of Schisandrin B on the expression of P2X7 receptor. Pathological blood pressure, heart rate, heart rate variability, and sympathetic nerve discharge were ameliorated after administration of Schisandrin B. Moreover, the upregulated protein level of P2X7 receptor, NLRP3 inflammasomes, and interleukin-1ß in diabetic rats were decreased after treatment, which indicates that Schisandrin B can alleviate the chronic inflammation caused by diabetes and decrease the expression levels of P2X7 via NLRP3. These findings suggest that Schisandrin B can be a potential therapeutical agent for DCAN.

Expression of group II metabotropic glutamate receptors in rat superior cervical ganglion.

BACKGROUND: The superior cervical ganglion (SCG) plays critical roles in the regulation of blood pressure and cardiac output. Metabotropic glutamate receptors (mGluRs) in the SCG are not clearly elucidated yet. Most studies on the expression and functions of mGluRs in the SCG focused on the cultured SCG neurons, and yet little information has been reported in the SCG tissue. Chronic intermittent hypoxia (CIH), one of the major clinical features of obstructive sleep apnea (OSA) patients, is a critical pathological cause of secondary hypertension in OSA patients, but its impact on the level of mGluRs in the SCG is unknown. OBJECTIVE: To explore the expression and localization of mGluR2/3 and the effect of CIH on mGluR2/3 level in rat SCG tissue. METHODS: RT-PCR and immunostaining were conducted to examine the mRNA and protein expression of mGluR2/3 in rat SCG. Immunofluorescence staining was conducted to examine the distribution of mGluR2/3. Rats were divided into control and CIH group which the rats were exposed to CIH for 6 weeks. Western blots were performed to examine the level of mGluR2/3 in rat SCG. RESULTS: mRNAs of mGluR2/3 expressed in rat SCG. mGluR2 distributed in principal neurons and small intensely fluorescent cells but not in satellite glial cells, nerve fibers, and vascular endothelial cells; mGluR3 was detected in nerve fibers rather than in the cells mentioned above. CIH exposure reduced the protein level of mGluR2/3 in rat SCG. CONCLUSION: mGluR2/3 exists in rat SCG with diverse distribution patterns, and may be involved in CIH-induced hypertension.

Characterization of metabotropic glutamate receptor 7 and 8 in rat superior cervical ganglion and their changes following chronic intermittent hypoxia / 南方医科大学学报

OBJECTIVE@#To investigate the expression and localization of metabotropic glutamate receptors 7 and 8 (mGluR7/8) in rat superior cervical ganglion (SCG) and their changes in response to chronic intermittent hypoxia (CIH).@*METHODS@#We detected the expressions of mGluR7 and mGluR8 in the SCG of 8-week-old male SD rats using immunohistochemistry and characterized their distribution with immunofluorescence staining. The expression of mGluR7 and mGluR8 in the cytoplasm and nucleus was detected using Western blotting. A 6-week CIH rat model was established by exposure to intermittent hypoxia (6% oxygen for 30 s followed by normoxia for 4 min) for 8 h daily, and the changes in systolic blood pressure, diastolic blood pressure and mean arterial pressure were measured. The effect of CIH on expression levels of mGluR7 and mGluR8 in the SCG was analyzed using Western blotting.@*RESULTS@#Positive expressions of mGluR7 and mGluR8 were detected in rat SCG. mGluR7 was distributed in the neurons and small fluorescent (SIF) cells with positive staining in both the cytoplasm and nuclei, but not expressed in satellite glial cells (SGCs), nerve fibers or blood vessels; mGluR8 was localized in the cytoplasm of neurons and SIF cells, but not expressed in SGCs, nerve fibers, or blood vessels. Western blotting of the nuclear and cytoplasmic fractions of rat SCG further confirmed that mGluR7 was expressed in both the cytoplasm and the nucleus, while mGluR8 exists only in the cytoplasm. Exposure to CIH significantly increased systolic blood pressure, diastolic blood pressure and mean arterial pressure of the rats (all P < 0.001) and augmented the protein expressions of mGluR7 and mGluR8 in the SCG (P < 0.05).@*CONCLUSION@#mGluR7 and mGluR8 are present in rat SCG but with different localization patterns. CIH increases blood pressure of rats and enhanced protein expressions of mGluR7 and mGluR8 in rat SCG.

Surgical Technique for Superior Cervical Ganglionectomy in a Murine Model.

Growing evidence suggests that the sympathetic nervous system plays an important role in cancer progression. Adrenergic innervation regulates salivary gland secretion, circadian rhythm, macular degeneration, immune function, and cardiac physiology. Murine surgical sympathectomy is a method for studying the effects of adrenergic innervation by allowing for complete, unilateral adrenergic ablation while avoiding the need for repeated pharmacologic intervention and the associated side effects. However, surgical sympathectomy in mice is technically challenging because of the small size of the superior cervical ganglion. This study describes a surgical technique for reliably identifying and resecting the superior cervical ganglion to ablate the sympathetic nervous system. The successful identification and removal of the ganglion are validated by imaging the fluorescent sympathetic ganglia using a transgenic mouse, identifying post-resection Horner's syndrome, staining for adrenergic markers in the resected ganglia, and observing diminished adrenergic immunofluorescence in the target organs following sympathectomy. This model enables future studies of cancer progression as well as other physiological processes regulated by the sympathetic nervous system.

Immunohistochemical localization of vesicular nucleotide transporter in small intensely fluorescent (SIF) cells of the rat superior cervical ganglion.

Our previous study reported that a part of small intensely fluorescent (SIF) cells in the rat superior cervical ganglion were innervated by P2X3 purinoceptor-expressing glossopharyngeal sensory nerve endings, suggesting the occurrence of adenosine 5'-triphosphate (ATP)-mediated transmission between them. The present study investigated the immunolocalization of vesicular nucleotide transporter (VNUT) in SIF cells of the superior cervical ganglion in male Wistar rats. VNUT was immunohistochemically localized in tyrosine hydroxylase-immunoreactive SIF cells and sympathetic postganglionic neurons, but not in a few SIF cells with immunoreactivity for dopamine beta-hydroxylase. P2X3-immunoreactive ramified nerve endings formed flat leaf-like or spherical terminal parts to surround some VNUT-immunoreactive SIF cells, but not other VNUT-immunoreactive SIF cells attached to ganglionic neurons. VNUT-immunoreactive SIF cells contained bassoon-immunoreactive products at the contacting surface of P2X3-immunoreactive nerve endings. Immunoreactivity for ectonucleoside triphosphate diphosphohydrolase 2, which hydrolyzes extracellular ATP, was observed in S100B-immunoreactive satellite glial cells surrounding VNUT-immunoreactive SIF cells, but not in the attachment surfaces between SIF cells and nerve endings with P2X3 immunoreactivity. The present results suggest that SIF cells release ATP by exocytosis to modulate the excitability of sensory nerve endings and postganglionic neurons in the superior cervical ganglion.

Surgical Techniques and Nuances for Superior Cervical Ganglionectomy and Decentralization in Rats.

The sympathetic nervous system has been implicated in various physiological and pathological processes, including regulation of homeostatic functions, maintenance of the circadian rhythms, and neuronal disruption and recovery after injury. Of special interest is focus on the role of the superior cervical ganglion (SCG) in regulating the daily changes in pineal function. Removal of the superior cervical ganglion (SCGx) and decentralization have served as valuable microsurgical models to investigate the effects of surgical denervation on this gland or organ. In this chapter, we offer information about methodologies for performing SCGx along with decentralization and denervation procedures, including details about recommended equipment as well as tips that can improve these techniques.

Implication of P2Y12 receptor in uc.48+-mediated abnormal sympathoexcitatory reflex via superior cervical ganglia in myocardial ischemic rats.

Purinergic 2Y12 (P2Y12) receptor antagonists are used as platelet aggregation inhibitors. Long non-coding RNAs (lncRNAs) play an important role in neuropathological events. Satellite glial cells (SGCs) in the superior cervical ganglia (SCGs) encircle the somata of neurons. This study explored if the upregulated P2Y12 receptor in SCGs was relevant to lncRNA uc.48+ during myocardial ischemia (MI). The results showed that upregulation of P2Y12 receptor was accompanied by increased expression of uc.48+ in the SCGs of MI rats which displayed abnormal changes in cervical sympathetic nerve activity, blood pressure, heart rate, electrocardiograms and cardiac tissue structure. The P2Y12 antagonist clopidogrel improved abnormal alterations in cardiac function and tissue structure in MI rats. Short hairpin RNA (shRNA) against uc.48+ significantly inhibited P2Y12 receptor upregulation and its co-expression with glial fibrillary acidic protein (GFAP) in SCGs, and ameliorated the cardiac dysfunction in MI rats. By contrast, overexpression of uc.48+ increased the expression of P2Y12 in SCGs and enhanced cervical sympathetic nerve activity in control rats. Direct interaction between uc.48+ and the P2Y12 receptor was predicted using the bioinformatic tool CatRAPID and confirmed by RNA immunoprecipitation. Moreover, overexpression of the P2Y12 receptor reversed the protective effect of uc.48+ shRNA on cardiac dysfunction in MI rats. Uc.48 shRNA treatment also inhibited the enhanced rise of intracellular free Ca2+ level ([Ca2+]i) evoked by the P2Y12 agonist 2-methylthio-adenosine-5'-diphosphate (2-MeSADP) in SGCs of SCGs after oxygen-glucose deprivation (OGD) treatment. These data demonstrated that uc.48+ shRNA could counteract the P2Y12 upregulation and improve P2Y12-implicated cardiac dysfunction due to MI.

Sympathetic nervous system hyperactivity results in potent cerebral hypoperfusion in swine.

INTRODUCTION: Cerebral vasospasm is a complex disease resulting in reversible narrowing of blood vessels, stroke, and poor patient outcomes. Sympathetic perivascular nerve fibers originate from the superior cervical ganglion (SCG) to innervate the cerebral vasculature, with activation resulting in vasoconstriction. Sympathetic pathways are thought to be a significant contributor to cerebral vasospasm. OBJECTIVE: We sought to demonstrate that stimulation of SCG in swine can cause ipsilateral cerebral perfusion deficit similar to that of significant human cerebral vasospasm. Furthermore, we aimed to show that inhibition of SCG can block the effects of sympathetic-mediated cerebral hypoperfusion. METHODS: SCG were surgically identified in 15 swine and were electrically stimulated to achieve sympathetic activation. CT perfusion scans were performed to assess for changes in cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT) and time-to-maximum (TMax). Syngo.via software was used to determine regions of interest and quantify perfusion measures. RESULTS: SCG stimulation resulted in 20-30% reduction in mean ipsilateral CBF compared to its contralateral unaffected side (p < 0.001). Similar results of hypoperfusion were seen with CBV, MTT and TMax with SCG stimulation. Prior injection of lidocaine to SCG inhibited the effects of SCG stimulation and restored perfusion comparable to baseline (p > 0.05). CONCLUSION: In swine, SCG stimulation resulted in significant cerebral perfusion deficit, and this was inhibited by prior local anesthetic injection into the SCG. Inhibiting sympathetic activation by targeting the SCG may be an effective treatment for sympathetic mediated cerebral hypoperfusion.

Protective Felix Culpa Effect of Superior Sympathetic Cervical Ganglion Degenerations on Prevention of Basilar Artery Spasm After Subarachnoid Hemorrhage: A Preliminary Experimental Study.

BACKGROUND: Posterior cerebral blood flow is regulated by the basilar arteries (BAs). Vasospasm of BAs can occur after subarachnoid hemorrhage (SAH). Superior cervical sympathetic ganglia (SCG) fibers have a vasoconstrictor effect on the BA. We aimed to investigate the relationship between the degenerated neuron density of the SCG and the severity of BA vasospasm after experimental SAH. METHODS: Twenty-four rabbits were used. Five were used as the control group, and 5 were used as the sham group. Experimental SAHs were performed in the remaining 14 animals (study group) by injecting homologous blood into the cisterna magna. After 3 weeks of injection, neuron densities of SCG and the severity of BA vasospasm index values (VSI) were examined histopathologically and compared statistically. RESULTS: The mean VSI was 0.669 ± 0.1129 in the control group, 0.981 ± 0.159 in the sham group, and 1.512 ± 0.298 in the study group. The mean degenerated neuronal density of SCG was 436 ± 79/mm3 in severe vasospasm (n = 3), 841 ± 101/mm3 in moderate vasospasm (n = 4), and 1.921 ± 849/mm3 in the less vasospasm detected animals (n = 6). CONCLUSIONS: This study shows an inverse relationship between the degenerated neuronal density in the SCG and VSI values. This finding indicates a diminished sympathetic input from the SCG, resulting in a beneficial effect (the felix culpa) by dilating the lumen diameter of the BA, so SCG degeneration after SAH protects the BA spasm.

Pulsed radiofrequency of superior cervical ganglion for treatment of painful post-traumatic trigeminal neuropathy (PTTN): A case series report.

Objective: Painful post-traumatic trigeminal neuropathy (PTTN) is a clinical pain syndrome that occurs due to injuries to the peripheral branches of the trigeminal nerve and is characterized by a deep burning pain and accompanied by positive and negative neurological signs. In patients with recalcitrant PTTN, the sympathetic nervous system is a potential therapeutic target. The aim of this study was to investigate the therapeutic response of PTTN patients to pulsed radiofrequency treatment (PRF) of the superior cervical sympathetic ganglion (SCG).Methods: Thirty-five patients with PTTN who had a history of severe disabling facial neuropathic pain underwent PRF of the SCG under a new lateral fluoroscopic approach.Results: The patients' pain intensity post-PRF was 3.94 (± 3.11), compared with 8.82 (± 1.27) pre-PRF (p < 0.001).Conclusion: PRF of the SCG could be an effective method to treat chronic PTTN.

The jugular nerve: A review of this enigmatic structure.

The jugular nerve (JN) is described as joining the superior cervical ganglion to the vagus nerve. It has been studied extensively in many different animal species; however, there is very limited literature about humans. This review delves into various descriptions of this nerve's anatomy and animal studies aimed at deciphering its function. The goal is to shed more light on this understudied structure in humans.

Regulatory effects of nicotine on neurite outgrowth in rat superior cervical ganglia cells.

We have reported that nicotine has a neurotrophic action on peripheral adrenergic nerves in vivo, which is mediated by α7 nicotinic acetylcholine receptors (nAChRs). To clarify the possible mechanisms, the present study further investigated the effect of nicotine on neurite outgrowth in tyrosine hydroxylase (TH)-positive superior cervical ganglia (SCG) cells isolated from neonatal rats in vitro. Nicotine at low concentrations (0.01-0.3 mM) increased the number of neurite outgrowths in TH-immunopositive SCG cells, while high concentrations of nicotine (1-10 mM) gradually reduced it, and only 10 mM nicotine was markedly inhibited compared to the control. A 100 µM of nicotine-induced increase in neurite numbers depended on the exposure time and was inhibited by treatment with the nAChR antagonist hexamethonium (Hex) and α7 nAChR antagonist α-bungarotoxin (α-Bgtx). The nicotine (10 mM)-induced a significant decrease in neurite outgrowth in SCG, which was perfectly canceled by Hex to the control level but not by α-Bgtx. These results suggest that nicotine has a regulatory neurotrophic action mediated by both α7 nAChR and other subtypes in TH-positive SCG cells of rats.