Electrical stimulation of the stellate ganglion and the vertebral nerve

The vertebral nerve: A comprehensive review of its form and function

The literature is littered with variable and scant reports of the vertebral nerve. The present paper reviews the literature regarding this nervous structure of the neck and attempts to clarify a number of issues surrounding its form, function, and implications of surgical manipulation. The nerve may arise from the stellate ganglion or the ansa subclavia, amongst a number of other structures. Additionally, the terminal insertion of the vertebral nerve varies in the reported literature, with authors observing various terminations. Animal models of the vertebral nerve have limited value, as variations between species and with species have been observed. This review also indicates that contradictory evidence exists regarding the clinical implications of vertebral nerve damage. Although irritation may result in ocular disturbance, hearing loss, headaches, and dizziness, a high degree of incongruity exists around whether or not any clinical findings will actually be observed. Based on our review of the available literature and recent cadaveric research, it appears it may be more logical to classify the vertebral nerve as a variable ramus communicans that connects the stellate or inferior cervical ganglia to the lower cervical spinal nerves and not a structure that ascends entirely with the vertebral artery to enter the cranium.

The vertebral nerve revisited

There is significant paucity in the literature regarding the vertebral nerve. Moreover, descriptions of this structure are conflicting. To evaluate further the anatomy and potential clinical significance of this structure, 10 fresh adult cadavers (20 sides) underwent dissection and macroscopic observation of this structure. All specimens were found to have a vertebral nerve that originated from the stellate ganglion with the exception of two left sides (10%) in which this nerve arose from the inferior cervical ganglion. This nerve ascended posteromedial to the vertebral artery. The vertebral nerve was found to be, in essence, a long and deep gray ramus communicans that connected most commonly the stellate ganglia to C6 or C7 spinal nerves by passing through the C6 and C7 transverse foramina. Fifteen percent of sides were found to have a vertebral nerve that was plexiform in its configuration. Fifty percent were found to have very small branches that entered the fibrous capsule of adjacent zygapophyseal and intervertebral joints. Some specimens were noted to have meningeal branches of the vertebral nerve. Based on our observations, the vertebral nerve is simply a deep ramus communicans, which often provides articular and meningeal branches to the adjacent spine. As neck pain is a significant reason for physician office visits, additional knowledge of the nerves innervating the joints and adjacent meninges of the neck could be important for both surgical and medical blockade of nerve fibers.

Involvement of non-NMDA and NMDA receptors in glutamate-induced pressor or depressor responses of the pons and medulla

1. Fifty-five intact and six baroreceptor denervated and vagotomized cats of either sex were anaesthetized intraperitoneally with urethane (400 mg/kg) and alpha-chloralose (40 mg/kg). Responses of the systemic arterial pressure (SAP), mean SAP (MSAP) and sympathetic vertebral nerve (VNA) and renal nerve activities (RNA) were recorded. 2. In intact animals, monosodium L-glutamate (Glu, 0.1 mol/L, 50 nL) was microinjected into pressor areas of the locus coeruleus (LC), gigantocellular tegmental field (GTF), rostral ventrolateral medulla (RVLM) and dorsomedial medulla (DM), and the depressor areas of caudal ventrolateral medulla (CVLM). The induced actions were compared before and after microinjection of either glutamate antagonists, glutamate diethylester (GDEE, 0.5 mol/L, 50-100 nL), a competitive AMPA receptor blocker, or 2-amino-5-phosphonovaleric acid (D-AP5, 0.025 mol/L, 50-100 nL), a competitive N-methyl-D-aspartate (NMDA) receptor blocker. GDEE completely blocked the increases of SAP and VNA elicited from all pressor areas. D-AP5 only partially blocked the pressor but slightly blocked VNA and RNA responses from LC, GTF and DM, particularly those from RVLM. Neither GDEE nor D-AP5 blocked the depressor responses of SAP and two nerve activities elicited from CVLM. 3. In baroreceptor denervated animals, NMDA (2 mmol/L, 50-100 nL) and AMPA (0.2 mmol/L, 50-100 nL) were micro-injected into the same pressor areas of GTF, RVLM and DM and the depressor area of CVLM responsive to Glu activation (0.1 mol/L, 30 nL). In RVLM, DM and CVLM, the results of either NMDA or AMPA were similar to those induced by Glu. However, in GTF, microinjection of either NMDA or AMPA did not induce similar responses to Glu. This suggests that the nature of GTF may differ from RVLM and DM. 4. The above results suggest that the Glu-induced pressor responses from LC, GTF, DM and especially RVLM, are primarily mediated through AMPA receptors. The Glu-induced depressor responses from CVLM may not be predominantly mediated by either AMPA or NMDA receptors. 5. In both baroreceptor-intact and -denervated cats stimulation of the pressor areas often produced an increase of VNA and a decrease of RNA, while in the depressor CVLM decreased both VNA and RNA. The VNA, but not RNA were positively correlated with the pressor responses, while both VNA and RNA were positively correlated with the depressor responses. This may suggest that neurons of the sympathetic vertebral and renal nerves are topographically organized in the brain.

Angiotensin II activates pressor and depressor sites of the pontomedulla that react to glutamate

1. In cats anaesthetized with a mixture of alpha-chloralose (40 mg/kg) and urethane (400 mg/kg) and in rats anaesthetized with a mixture of alpha-chloralose (60 mg/kg) and urethane (800 mg/kg), changes in systemic arterial pressure (SAP), heart rate (HR) and sympathetic activities of vertebral (VNA) and renal (RNA) nerves were determined following the microinjection of angiotensin II (AngII; 0.16 mmol/L; 50 nL) into the pressor and depressor sites of the pontomedulla previously reacted to a microinjection of monosodium L-glutamate (Glu; 0.1 mol/L; 50 nL). Pressor sites included gigantocellular tegmental field (FTG) and dorsal medulla (DM) and rostral ventrolateral medulla (VLM). The depressor site was the caudal VLM (CVLM). The effects of losartan (1 mmol/L; 50 nL), a specific AT1 receptor non-peptide antagonist for AngII, on responses induced by AngII in the VLM, DM and CVLM were also determined. 2. In 30% of pressor sites in the FTG, 55% in the VLM and 67% in the DM and in 76% of depressor sites in the CVLM previously exposed to Glu, microinjection of AngII to the same site produced pressor or depressor responses similar to that of Glu, but smaller in magnitude, particularly in the pressor VLM. Changes in both VNA and RNA induced by AngII were also smaller than those induced by Glu, particularly RNA from DM activation. 3. In the dorsal motor nucleus of the vagus, AngII, as Glu, produced marked bradycardia, but again this was smaller in magnitude than the bradycardia produced by Glu. 4. In rats, in the DM near or around the nucleus of the solitary tract where Glu increased SAP, microinjection of AngII (0.8 mmol/L; 60 nL) produced a depressor response, while the microinjection of 1.6 mmol/L (60 nL) AngII produced a pressor response. 5. Losartan blocked the increase in SAP induced by AngII in the VLM and DM. Decreases in SAP induced by AngII in the CVLM, however, were only slightly decreased by losartan. 6. Our data suggest that a significant portion of pressor and depressor sites of the pontomedulla contain neurons responsive to both AngII and Glu. In neurons in the VLM and DM, AngII produced pressor responses that were primarily mediated through AT1 receptors, while the depressor actions of AngII in the CVLM were not mediated by AT1 receptors.

Differential effects on sympathetic nerve activities elicited by activation of neurons in the pressor areas of dorsal and rostral ventrolateral medulla in cats

Changes of the nerve activity of the sympathetic renal and vertebral nerves were elicited by microinjection of sodium glutamate (50 nmol/100 nl) into the pressor areas of the dorsal (DM) and rostral ventrolateral medulla (RVLM) in cats under urethane-chloralose anesthesia. Animals were bilaterally vagotomized, artificially ventilated, and paralyzed with gallamine triethiodide. The vertebral nerve activity always increased when pressor responses were induced by DM or RVLM stimulation. However, the effects of medullary stimulation on the renal nerve activity were variable. Three types of renal nerve responses concomitant with the pressor responses were observed in either baroreceptor-intact or baroreceptor-denervated cats. They were: (1) augmentation (type I); (2) attenuation (type II); and (3) insignificant change (type III). Type I responses were often elicited by RVLM stimulation whereas type II responses were often elicited by DM stimulation. Findings suggested that neurons integrating these sympathetic nerve activities were not equally distributed in the pressor areas of DM and RVLM. This result supports the notion that neurons located in different pressor areas of the brainstem exert differential effects over different sympathetic nerve activities.