Afferent projections of the rat major occipital nerve studied by transganglionic transport of HRP

Involvement of the Ipsilateral Tongue, an Intraoral Structure of Referred Pain due to Entrapment of the Greater Occipital Nerve

This study reports a rare case of referred pain in the trigeminal nerve distribution caused by entrapment of the greater occipital nerve (GON). Notably, the pain extended to the ipsilateral tongue, an unusual intraoral involvement. GON entrapment can lead to sensitization in secondary nociceptive neurons within the trigeminocervical complex (TCC), which receives signals from both trigeminal and occipital nerves, causing referred facial pain. A 55-year-old female presented with chronic left temporo-occipital pain, along with pain in her left periorbital area, ear canal, gum, and a 20-year history of atypical facial pain on her left tongue and lower lip. Following GON decompression, her temporo-occipital pain and facial symptoms improved, with a significant reduction in burning pain on her tongue and resolution of lip tingling. The TCC, comprising convergent inputs from trigeminal and occipital nerves, is the anatomical basis of referred craniofacial pain. Chronic GON entrapment can sensitize second-order neurons in the TCC and medullary dorsal horn, explaining this unusual referred pain to the intraoral structures.

Ipsilateral Limb Extension of Referred Trigeminal Facial Pain due to Greater Occipital Nerve Entrapment: A Case Report

We report a very rare case of referred pain associated with entrapment of the greater occipital nerve (GON) occurring not only in the ipsilateral hemiface but also in the ipsilateral limb. There is an extensive convergence of cutaneous, tooth pulp, visceral, neck, and muscle afferents onto nociceptive and nonnociceptive neurons in the trigeminal nucleus caudalis (medullary dorsal horn). In addition, nociceptive input from trigeminal, meningeal afferents projects into trigeminal nucleus caudalis and dorsal horn of C1 and C2. Together, they form a functional unit, the trigeminocervical complex (TCC). The nociceptive inflow from suboccipital and high cervical structures is mediated with small-diameter afferent fibers in the upper cervical roots terminating in the dorsal horn of the cervical cord extending from the C2 segment up to the medullary dorsal horn. The major afferent contribution is mediated by the spinal root C2 that is peripherally represented by the greater occipital nerve (GON). Convergence of afferent signals from the trigeminal nerve and the GON onto the TCC is regarded as an anatomical basis of pain referral in craniofacial pain and primary headache syndrome. Ipsilateral limb pain occurs long before the onset of the referred facial pain. The subsequent severe hemifacial pain suggested GON entrapment. The occipital nerve block provided temporary relief from facial and extremity pain. Imaging studies found a benign osteoma in the ipsilateral suboccipital bone, but no direct contact with GON was identified. During GON decompression, severe entrapment of the GON was observed by the tendinous aponeurotic edge of the trapezius muscle, but the osteoma had no contact with the nerve. Following GON decompression, the referred trigeminal and extremity pain completely disappeared. The pain referral from GON entrapment seems to be attributed to the sensitization and hypersensitivity of the trigeminocervical complex (TCC). The clinical manifestations of TCC hypersensitivity induced by chronic entrapment of GONs are diverse when considering the occurrence of extremity pain as well as facial pain.

Feasibility study of greater occipital nerve blocks by focused ultrasound - an animal study

OBJECTIVE

Greater occipital nerve (GON) block may provide substantial relief for headache in the occipital location. This study tested the feasibility of focused ultrasound (FUS) to induce the conduction block of GONs in rats.

APPROACH

For in vitro experiments, the nerve was dissected and cut from C2 to the site near the ear of the rats and preserved in Ringer's solution. Pulsed FUS was used for the block, and sensory action potentials were recorded in the GON. For in vivo experiments, the GONs of the rats were surgically exposed for precise ultrasonic treatment. All data are expressed as the mean ± the standard deviation.

MAIN RESULTS

A single ultrasonic treatment temporarily suppressed the amplitude of action potentials of the in vitro nerves to 42 ± 14% of the baseline values, and the time to recovery was 55 min. The in vivo results showed that FUS acutely inhibited the amplitude of action potentials to 41 ± 8% of the baseline value in rat GONs, and the time to recovery was 67 min. Histological examination revealed no appreciable changes in the nerve morphology caused by FUS. Therefore, FUS reversibly blocked the conduction of the rat GON when the sonication parameters were appropriate.

SIGNIFICANCE

Noninvasive FUS may be a novel treatment paradigm for occipital headache by blocking the occipital nerve, and the procedure is repeatable if indicated.

The greater occipital nerve and its spinal and brainstem afferent projections: A stereological and tract-tracing study in the rat

The neuromodulation of the greater occipital nerve (GON) has proved effective to treat chronic refractory neurovascular headaches, in particular migraine and cluster headache. Moreover, animal studies have shown convergence of cervical and trigeminal afferents on the same territories of the upper cervical and lower medullary dorsal horn (DH), the so-called trigeminocervical complex (TCC), and recent studies in rat models of migraine and craniofacial neuropathy have shown that GON block or stimulation alter nociceptive processing in TCC. The present study examines in detail the anatomy of GON and its central projections in the rat applying different tracers to the nerve and quantifying its ultrastructure, the ganglion neurons subserving GON, and their innervation territories in the spinal cord and brainstem. With considerable intersubject variability in size, GON contains on average 900 myelinated and 3,300 unmyelinated axons, more than 90% of which emerge from C₂ ganglion neurons. Unmyelinated afferents from GON innervates exclusively laminae I-II of the lateral DH, mostly extending along segments C_2-3 . Myelinated fibers distribute mainly in laminae I and III-V of the lateral DH between C₁ and C₆ and, with different terminal patterns, in medial parts of the DH at upper cervical segments, and ventrolateral rostral cuneate, paratrigeminal, and marginal part of the spinal caudal and interpolar nuclei. Sparse projections also appear in other locations nearby. These findings will help to better understand the bases of sensory convergence on spinomedullary systems, a critical pathophysiological factor for pain referral and spread in severe painful craniofacial disorders.

Hemifacial Pain and Hemisensory Disturbance Referred from Occipital Neuralgia Caused by Pathological Vascular Contact of the Greater Occipital Nerve

Here we report a unique case of chronic occipital neuralgia caused by pathological vascular contact of the left greater occipital nerve. After 12 months of left-sided, unremitting occipital neuralgia, a hypesthesia and facial pain developed in the left hemiface. The decompression of the left greater occipital nerve from pathological contacts with the occipital artery resulted in immediate relief for hemifacial sensory change and facial pain, as well as chronic occipital neuralgia. Although referral of pain from the stimulation of occipital and cervical structures innervated by upper cervical nerves to the frontal head of V1 trigeminal distribution has been reported, the development of hemifacial sensory change associated with referred trigeminal pain from chronic occipital neuralgia is extremely rare. Chronic continuous and strong afferent input of occipital neuralgia caused by pathological vascular contact with the greater occipital nerve seemed to be associated with sensitization and hypersensitivity of the second-order neurons in the trigeminocervical complex, a population of neurons in the C2 dorsal horn characterized by receiving convergent input from dural and cervical structures.

Brainstem and Cervical Spinal Cord Fos Immunoreactivity Evoked by Nerve Growth Factor Injection into Neck Muscles in Mice

Although myofascial tenderness is thought to play a key role in the pathophysiology of tension-type headache, very few studies have addressed neck muscle nociception. The neuronal activation pattern following local nerve growth factor (NGF) administration into semispinal neck muscles in anaesthetized mice was investigated using Fos protein immunohistochemistry. In order to differentiate between the effects of NGF administration on c-fos expression and the effects of surgical preparation, needle insertion and intramuscular injection, the experiments were conducted in three groups. In the sham group ( n = 7) cannula needles were only inserted without any injection. In the saline ( n = 7) and NGF groups ( n = 7) 0.9% physiological saline solution or 0.8 µM NGF solution were injected in both muscles, respectively. In comparison with sham and saline conditions, NGF administration induced significantly stronger Fos immunoreactivity in the mesencephalic periaqueductal grey (PAG), the medullary lateral reticular nucleus (LRN), and superficial layers I and II of cervical spinal dorsal horns C1, C2 and C3. This activation pattern corresponds very well to central nervous system processing of deep noxious input. A knowledge of the central anatomical representation of neck muscle pain is an essential prerequisite for the investigation of neck muscle nociception in order to develop a future model of tension-type headache.

The Role of the Craniospinal Nerves in Mediating the Antinociceptive Effect of Transcranial Electrostimulation in the Rat

Transcranial electrostimulation (TES) has been reported to elicit significant analgesia, but its mechanism of action has not been elucidated. In a recently introduced clinically relevant rat model of TES we have validated and characterized the TES antinociceptive effect, suggesting involvement of the sensory nerves of the rat's scalp in mediating that effect. In this study, we have further investigated the role of the craniospinal nerves by attempting to block the TES antinociceptive effect with local anesthetic injected under the TES electrodes. We also applied different transcutaneous electrical nerve stimulation modalities through the TES electrodes and compared the elicited antinociceptive effect to that of TES. The antinociceptive effect was assessed by measuring nociceptive thresholds in the tail-flick latency test in awake, unrestrained male rats. Data were analyzed by one-way analysis of variance followed by the Bonferroni t-test. The TES antinociceptive effect was significantly reduced after local anesthetic injection, and administration of 100 Hz transcutaneous electrical nerve stimulation was, over time, capable of eliciting the same degree of antinociceptive effect as TES. We conclude that sensory craniospinal nerves play a critical role in mediating the TES antinociceptive action and offer a hypothesis on the underlying mechanism(s) responsible for this action.

Convergence of cervical and trigeminal sensory afferents

Cranial nociceptive perception shows a distinct topographic distribution, with the trigeminal nerve receiving sensory information from the anterior portions of the head, the greater occipital nerve, and branches of the upper cervical roots in the posterior regions. However, this distribution is not respected during headache attacks, even if the etiology of the headache is specific for only one nerve. Nociceptive information from the trigeminal and cervical territories activates the neurons in the trigeminal nucleus caudalis that extend to the C2 spinal segment and lateral cervical nucleus in the dorsolateral cervical area. These neurons are classified as multimodal because they receive sensory information from more than one afferent type. Clinically, trigeminal activation produces symptoms in the trigeminal and cervical territory and cervical activation produces symptoms in the cervical and trigeminal territory. The overlap between the trigeminal nerve and cervical is known as a convergence mechanism. For some time, convergence mechanisms were thought to be secondary to clinical observations. However, animal studies and clinical evidence have expanded our knowledge of convergence mechanisms. In this paper, the role of convergence mechanisms in nociceptive physiology, physiopathology of the headaches, clinical diagnosis, and therapeutic conduct are reviewed.

The trigeminocervical complex and migraine: current concepts and synthesis

Neurones in the trigeminocervical complex are the major relay neurones for nociceptive afferent input from the meninges and cervical structures; therefore, they are the neural substrates of head pain. This review highlights the importance of two basic mechanisms in headache physiology: convergence of nociceptive afferents and sensitization of trigeminocervical neurones. These physiologic findings have clinical correlates such as hypersensitivity and spread and referral of pain frequently seen in patients with primary headache, such as migraine. Special reference is made to the influence of structures from the upper cervical spine in generating and contributing to migraine headaches. The pathophysiology and functional relevance of these basic mechanisms to headaches is discussed in the context of recent experimental findings with regard to pain processing.

Central projections of C4-C8 dorsal root ganglia in the rat studied by anterograde transport of WGA-HRP

Injections of WGA-HRP were made in the rat C4-C8 dorsal root ganglia (DRGs) individually to study the central projections and their relations to each other. The main dorsal horn projections from these DRGs to the dorsal horn lamina II extended for about two segments rostrally and caudally to the injected DRG, whereas the projections to laminae I, III, and IV were less restricted rostrocaudally. Comparisons of the dorsal horn projections from the DRGs investigated indicated a tendency for a somatotopic organization, which was most prominent in lamina II. Labeled central branches from the C4-8 DRGs could be traced in the dorsal column as far caudally as 12-17 segments caudal to the level of entrance. Most of these fibers appeared to end in the medial dorsal horn base, including the column of Clarke. Labeling of primary afferents in the ventral horn generally extended for at least 3-4 segments rostral and caudal to the level of the injected DRG. Projections to the central cervical nucleus were most prominent from the C4 DRG and gradually became less prominent from the more caudal DRGs. Heavy projections to the cuneate nucleus (Cun) originated from the C7 and C8 DRG, whereas those from the C4-C6 DRGs were less extensive. The Cun projections from the different DRGs appeared to overlap, and the same was true for the projections to the external cuneate nucleus. Projections to the gracile nucleus, the vestibular nuclear complex, including nucleus X, and to trigeminal sensory nuclei were seen from all DRGs investigated.

Central distribution of cervical primary afferents in the rat, with emphasis on proprioceptive projections to vestibular, perihypoglossal, and upper thoracic spinal nuclei

The projections of primary afferents from rostral cervical segments to the brainstem and the spinal cord of the rat were investigated by using anterograde and transganglionic transport techniques. Projections from whole spinal ganglia were compared with those from single nerves carrying only exteroceptive or proprioceptive fibers. Injections of horseradish peroxidase (HRP) or wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) were performed into dorsal root ganglia C2, C3, and C4. Free HRP was applied to the cut dorsal rami C2 and C3, greater occipital nerve, sternomastoid nerve, and to the C1/2 anastomosis, which contains afferents from suboccipital muscles and the atlanto-occipital joint. WGA-HRP injections into ganglia C7 and L5 were performed for comparative purposes. Injections of WGA-HRP or free HRP into rostral cervical dorsal root ganglia and HRP application to C2 and C3 dorsal rami produced labeling in dorsal and ventral horns at the level of entrance, the central cervical nucleus, and in external and main cuneate nuclei. From axons ascending to pontine and descending to upper thoracic spinal levels, medial collaterals were distributed to medial and descending vestibular, perihypoglossal and solitary nuclei, and the intermediate zone and Clarke's nucleus dorsalis in the spinal cord. Lateral collaterals projected mainly to the trigeminal subnucleus interpolaris and to lateral spinal laminae IV and V. Results from HRP application to single peripheral nerves indicated that medial collaterals were almost exclusively proprioceptive, whereas lateral collaterals were largely exteroceptive with a contribution from suboccipital proprioceptive fibers. WGA-HRP injections into dorsal root ganglia C7 and L5 failed to produce significant labeling within vestibular and periphypoglossal nuclei, although they demonstrated classical projection sites within the brainstem and spinal cord. The consistent collateralisation pattern of rostral cervical afferents along their whole rostrocaudal course enables them to contact a variety of precerebellar, vestibulospinal, and preoculomotor neurons. These connections reflect the well-known significance of proprioceptive neck afferents for the control of posture, head position, and eye movements.

Afferent projections from forelimb muscles to the external and main cuneate nuclei in the cat. A study with transganglionic transport of horseradish peroxidase

Muscular and cutaneous afferents from distal forelimb distributed to the cuneate and external cuneate nuclei have been demonstrated in cat with the method of transganglionic transport of horseradish peroxidase. Injections of the same tracer were also done in ganglia C7 to T6 to demonstrate the afferents to these two nuclei. It is concluded that only muscle afferents terminate in the external cuneate nucleus. Afferents from paw and forearm occupy sequential territories in the medial part of the nucleus, which are only partly exclusive. Afferents from individual flexor muscles of forearm occupy distinct sites but their distributions overlap with those of forearm extensor muscles. In the external cuneate nucleus, the distributions of afferents from individual muscles constitute integral parts of a segmental representation. In the cuneate nucleus, cutaneous afferents are located dorsally and terminate over cells of the "clusters". Muscle afferents are distributed in ventral regions and are topographically arranged. They terminate over "reticular" regions.

The splenius capitis muscle of the rat, architecture and histochemistry, afferent and efferent innervation as compared with that of the quadriceps muscle

The splenius muscle of the rat was investigated with regard to its structure and innervation. The latter was compared with that of the quadriceps muscle. The results can be summarized as follows: The splenius muscles of both sides form a bipennate muscle plate connecting the occipital bone with the spinous process of the second thoracic vertebra. The lateral parts of both muscles are attached directly to this prominent bony process, whereas the medial parts end in a median raphe which forms a tendinous cranial extension of the second thoracic vertebra. This tendinous extension, showing no connection to the cervical vertebrae, serves also for the attachment of acromio-trapezius muscle fibers. The lateral part of the splenius muscle is divided into two parts by a tendinous intersection. The splenius muscle consists mainly of fast twitch fibers: 55% were characterized as IIB and 40% as IIA fibers by histochemical demonstration of myosin ATPase-activity. A high content of muscle spindles--57 spindles per gram of muscle tissue--was found. Comparing several aspects of the innervation of the splenius to that of the quadriceps muscle, the following results could be obtained: The ratio of motor end plate size to muscle fiber volume is significantly higher in the splenius than in the quadriceps muscle. As demonstrated by transganglionary HRP-transport, the main part of labeled splenius afferents to the spinal cord terminates in the central cervical nucleus. Quadriceps afferents, entering the lower thoracic and upper lumbar segments, mainly end in the area of Clarke's column. Several labeled fibers descend to the sixth lumbar and first sacral segments, where they terminate in the area of Stilling's nucleus. A group of primary afferents from both muscles--most probably III- and IV-afferents--projects to the dorsal laminae of the dorsal horn; terminals from the splenius are accumulated in the lateral parts of these laminae, whereas those of the quadriceps are more concentrated in the medial areas. Within the brain stem, most afferents from the splenius terminate in the external cuneate nucleus. Most of the quadriceps afferents course to the gracile nucleus. Terminals from both muscle nerves were found in the area of the spinal vestibular nucleus. In conclusion, the most conspicuous results were: 1) Besides the segmental projection to the dorsal horn there is an almost exclusive projection of splenius primary afferents to relay nuclei to the cerebellum. 2) The relatively high ratio: end plate size/muscle fiber volume, which is characteristic of finely adjusting muscles.(ABSTRACT TRUNCATED AT 400 WORDS)