Medullary control of the pontine swallowing neurones in sheep

Summary The origin of the inputs from the medullary swallowing centre (dorsal region including the nucleus of the solitary tract, or ventral region corresponding to the reticular formation surrounding the nucleus ambigous) to the pontine swallowing neurones (PSNs) was studied in sheep anaesthetized with halothane.Out of 101 PSNs located in the posterior part of the trigeminal (Vth) motor nucleus, 46 were activated by stimulating either the dorsal (21 neurones) or the ventral (25 neurones) region of the ipsilateral medullary swallowing centre, 3–4 mm rostral from the obex. Thirty-one neurones out of the 46 were identified as a motoneurones supplying swallowing muscles (mylohyoïd, anterior body of digastric and medial pterygoïd). Their average activation latency through stimulation of the dorsal medullary region was about 1 ms longer than through stimulation of the ventral region (3.63 ms±0.81 versus 2.72 ms±0.32).To determine the origin of the medullary input to the PSNs, we tried to activate the medullary swallowing neurones (MSNs) antidromically through stimulating the posterior part of the Vth motor nucleus, which contains the swallowing motoneurones. Seventy-three MSNs were tested (25 located in the dorsal and 48 in the ventral region). None of the dorsal neurones tested could be antidromically activated by pontine stimulation: 15 ventral neurones showed a clear antidromic response (collision test) with an average latency of 2.5 ms±0.73. These neurones, which send their axons into the pons, were all located in the reticular formation, above the nucleus ambiguus, 3–4 mm rostral from the obex.These results suggest that MSNs in the ventral reticular formation connect the medullary swallowing centre to the Vth motor nucleus. They also suggest that during swallowing, inputs originating from the dorsal region of the medullary centre (interneurones programming the motor sequence) are relayed in the ventral region (reticular formation adjacent to the nucleus ambiguus) before reaching the PSNs.This work was supported, in part, by grants from CNRS (LA 205), INRA and M.R.I. (82 E 0685)     

Conditioning of heteronymous H reflex in human temporalis muscle by stimulation of perioral afferents

A heteronymous H reflex in the temporalis muscle can be elicited by selective stimulation of the masseteric nerve. The present study aimed at defining the optimal amplitude of the H reflex to detect inhibitory changes induced by stimulation of the perioral afferents and at providing new information on the control of masticatory muscles. Sixteen healthy volunteers participated in the experiment. A conditioning stimulus (CS) to the perioral skin was applied at various delays before an ipsilateral selective masseteric nerve stimulation (test stimulus: TS) while the subject was clenching the teeth at 25% of the maximal voluntary contraction. Two intensities of CS and TS were employed, high and low. The peak-to-peak amplitude of the H reflex (TS) and the root-mean-square value of the preceding electromyography were measured and the data analyzed by three-way analysis of variance and Tukey's posthoc tests. For both intensities used the heteronymous H reflex in the temporalis muscle was significantly decreased by prior activation of perioral afferents for delays from 5 to 60 ms. With a delay of 5 and 35 ms the preceding EMG level was not changed, while it was reduced at 20 and 60 ms delay. The intensities used to elicit the heteronymous H reflex of the temporalis muscle were appropriate to detect a reduction in motoneuron excitability. The reduction in the H reflex without a change in the preceding EMG at 5 and 35 ms delays could be due to presynaptic inhibition of the masseteric afferents exerted by the ipsilateral perioral afferents.     

腓浅神经痛诊治的解剖学基础(系列介绍之十五)

目的 介绍腓浅神经痛的诊断与局部注射的治疗方法。方法 选择门诊确诊为腓浅神经痛的患者18例，采用强的松龙混悬液加麻药局部注射神经穿出小腿深筋膜的部分的治疗方法。结果 所有病例皆在注射后短时完全止痛，多数病例一周后痊愈，少数病例经1～3次注射后痊愈。结论 对诊断明确的病例，采取强的松龙局部注射法，可以获得满意的疗效。     

Compensation of labyrinthine lesions: effects of trigeminal neurotomy on vestibular field potentials

The aim of the research was to analyse the vestibular nuclear activity before and after the section of the 5th cranial nerve in chronically hemilabyrinthectomized guinea pigs during the stage of compensation. The animals were hemilabyrinthectomized (chloroform and vaselin oil into the right middle ear) and upon compensation (24–45 days), field potentials were recorded from the vestibular nuclei of the intact side following electrical stimulation of the ipsilateral labyrinthine receptors. Then the left trigeminal trunk was sectioned ventrally through the foramen lacerum and ovale which are fused in the guinea pig and the vestibular field potentials were again recorded for a period of 120 min. Trigeminal neurotomy modified the vestibular field potentials determining an increment in amplitude of 30–50% of N₁ and N₂ waves, configuration and latency remained unaltered. The dependence of vestibular compensation on trigeminal afferents is discussed on the light of reported results.     

Spinothalamic and propriospinal neurones in the upper cervical cord of the rat: terminations of primary afferent fibres on soma and primary dendrites

Summary Experiments were performed on rats to determine whether primary afferents from the upper cervical region terminate directly on Spinothalamic and propriospinal neurones. The central terminations of primary afferents from the upper cervical region were identified by diffusely filling their axons with horseradish peroxidase. Spinothalamic neurones or propriospinal neurones were identified in the same experimental animals by using retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. Approximately 3–11 % of Spinothalamic cells in laminae 4–6 of spinal segments C2–4 received apparent synaptic contacts from primary afferents on the soma or primary dendrites. Approximately 18–36% of propriospinal neurones with axons descending to lower thoracic or lumbar levels received apparent synaptic contacts on the soma or primary dendrites. These data provide anatomical evidence that Spinothalamic and long propriospinal neurones in the upper cervical cord are excited directly by primary afferents. The data also help to clarify the neural circuitry underlying somatic sensation and reflex movements evoked by neck receptors.     

Neonatal damage to the rat's infraorbital nerve upregulates both galanin and neuropeptide Y in individual vibrissae-related primary afferent axons

Previous studies in adult animals have suggested that the peptides galanin and neuropeptide Y (NPY) may be upregulated in the same primary afferent neurons after peripheral axotomy. The present study was undertaken to determine whether such upregulation occurred in vibrissae-related primary afferent neurons and their axons after damage to the infraorbital nerve [ION; the trigeminal (V) branch that innervates the vibrissae follicles]. Double-labelling experiments demonstrated that approximately 75% of axotomized V ganglion cells and the central arbors of vibrissae-related primary afferents expressed both galanin and NPY after perinatal, but not adult, nerve damage. However, additional experiments demonstrated that the sensitive periods for lesion-induced upregulation of the two peptides and the period over which they were expressed after neonatal ION transection differed substantially. Staining for both peptides was increased after ION damage on P-0 through P-14, but only galanin staining was increased in vibrissae-related primary afferents after lesions on P-21. Galanin expression was elevated in vibrissae-related primary afferents in rats killed 3,8, and 15 days after neonatal ION transection, while increased NPY was observed at only the middle time point. The lesion-induced increases in galanin and NPY in vibrissae-related ION primary afferents suggest that these peptides may modulate central V reorganization after such damage.     

Synaptic organization of damaged infraorbital nerve axons in perinatal rats: demonstration by galanin immunocytochemistry

Neonatal transection of the infraorbital nerve (ION; the trigeminal, V, branch that supplies the mystacial vibrissae follicles) results in an upregulation of galanin in the central arbors of primary afferent axons. The present study was undertaken to evaluate the synaptic organization of these galanin-positive primary afferents and compare it with that of normal neurobiotin/biocytin-labeled primary afferent axons from animals of the same age. Examination of 1200 neurobiotin/biocytin-labeled profiles in V nucleus principalis (PrV) of rats killed on postnatal day (P-) 7 indicated that 23.3% (n=279) of these profiles made synaptic contacts: 87.4% were axodendritic, 8.9% were axoaxonic, 2.8% were axosomatic, and 0.7% were axospinous. Evaluation of 1200 galanin-positive profiles in PrV from rats that sustained transection of the ION on P-0 and were killed on P-7 indicated that only 64 (5.3%) of these profiles made synaptic contacts (P<0.05 compared with the intact animals). Of the galanin-positive profiles that did make synapses in PrV, 81.2% (n=52) were axodendritic and 18.8% (n=12) were axoaxonic. These results indicate that galanin released by damaged ION primary afferents in PrV is likely to affect the activity of second-order V neurons by a paracrine action rather than by acting at specific synapses.     

Sensory and autonomic innervation of the rat eyelid: Neuronal origins and peptide phenotypes

Neuronal origins, peptide phenotypes and target distributions were determined for sensory and autonomic nerves projecting to the eyelid. The retrograde tracer, Fluoro-Ruby, was injected into the superior tarsal muscle and meibomian gland of Sprague-Dawley rats. Labelled neurons were observed within the pterygopalatine (31 ± 6 of a total of 8238 ± 1610 ganglion neurons), trigeminal (173 ± 43 of 62 082 ± 5869) and superior cervical ganglia (184 ± 35 of 21 900 ± 1741). Immunostaining revealed vasoactive intestinal polypeptide immunoreactivity (VIP-ir) in nearly all Fluoro-Ruby-labelled pterygopalatine ganglion neurons (86 ± 5%) but only rarely in trigeminal (0.3 ± 0.3%) or superior cervical (1.4 ± 1.4%) ganglion neurons. Calcitonin gene-related peptide (CGRP)-ir was not observed in pterygopalatine or superior cervical ganglion somata, but was present in 24 ± 4% of trigeminal neurons. Bright dopamine β-hydroxylase (DBH) immunofluorescence was observed in the majority of eyelid-projecting neurons within the superior cervical ganglia (65 ± 5%) and lighter staining was detected in pterygopalatine neurons (63 ± 3%), but no DBH-ir was observed in trigeminal neurons. Examination of eyelid sections revealed dense VIP-ir innervation of meibomian gland acini and vasculature and modest distribution within tarsal muscle. CGRP-ir fibers surrounded ductal and vascular elements of the meibomian gland and the perimeter of tarsal muscle. DBH-ir fibers were associated with meibomian gland blood vessels and acini, and were more densely distributed within tarsal muscle. This study provides evidence for prominent meibomian gland innervation by parasympathetic pterygopalatine ganglion VIP-ir neurons, with more restricted innervation by sensory trigeminal CGRP-ir and sympathetic neurons. Tarsal muscle receives abundant sympathetic innervation, as well as moderate parasympathetic and sensory CGRP-ir projections. The eyelid contains substantial non-CGRP-ir sensory innervation, the targets of which remain undetermined. The distribution of identified autonomic and sensory fibers is consistent with the idea that meibomian gland function, as well as that of the tarsal muscle, is regulated by peripheral innervation.     

Local immune responses and systemic cytokine responses in zoster: relationship to the development of postherpetic neuralgia

Varicella zoster virus (VZV) causes varicella (chickenpox) as the primary infection and zoster (shingles) on reactivation from latency, often many years later. One of the most common and most severe sequela of zoster is postherpetic neuralgia (PHN). Apart from age, factors which predispose towards PHN are unknown. In the present study, the concentration of a variety of Th1 and Th2 cytokines in the serum of 30 zoster patients at the time of the acute disease were correlated with the subsequent development of PHN in nine of these patients, but no association was found. In addition, although some cytokines such as IFN-gamma, IL-6 and IL-8 were slightly raised in the zoster group compared with a group of normal healthy subjects of a similar age distribution, these differences only verged on significance. Antibody titres to VZV were raised in the zoster group compared with the controls but these did not differ between the patients who developed PHN and those who did not. Biopsies of zoster lesions were collected from nine patients. There were significantly fewer infiltrating lymphocytes in the lesions of the three patients who subsequently developed PHN compared with the six who did not, although the expression of the neuropeptide, substance P, did not differ between the two groups. It is possible that the poor inflammatory response at the time of the acute zoster may result in less effective containment of the VZV and more damage in the dermatome, thus contributing to the persistence of the neuralgia.     

The medullary relay from neck receptors to somatosensory thalamus in the rat: a neuroanatomical study

Summary Experiments were performed on rats to determine the location of thalamic projecting neurones in the medulla which receive direct contacts from neck primary afferents. The medullary terminations of primary afferents from the cervical region were identified by silver staining their degenerating terminals, diffusely filling their axons with horseradish peroxidase (HRP), or reacting for transganglionically transported HRP applied to muscle or cutaneous nerves. Neurones projecting to the ventrobasal thalamus were identified in the same experimental animals by using retrograde transport of HRP or Fluoro-Gold. En passant swellings or terminals of neck primary afferents were found in the vicinity of neurones projecting to the thalamus in the dorsolateral part of the rostral cuneate nucleus, the ventral aspect of the external cuneate nucleus, and the border zone between the two. Terminals of neck afferents and retrogradely labelled cells also coincided in nucleus x. Putative synaptic contacts were found in the region between the dorsolateral part of the rostral cuneate nucleus and ventromedial external cuneate nucleus. Cutaneous afferents from the neck were associated with thalamic projecting cells located along the dorsolateral border of the rostral cuneate nucleus, and afferents from neck muscles were associated with thalamic projecting cells in the caudal third of the external cuneate nucleus and in nucleus x.