5-HT-immunoreactive fibers in the trigeminal nuclear complex of the rat

Summary The distribution of serotonin immunoreactive (5-HT-IR) fibers in the trigeminal nuclear complex of the rat was mapped. In the sensory nuclei, innervation appeared to be dense in areas primarily related to nociceptive afferent activity, and sparse in areas primarily related to nonnociceptive afferent activity. Specifically, the marginal and gelatinosa layers of the spinal subnucleus caudalis contained many 5-HT-IR fibers while few labeled fibers were seen in the magnocellular portion of subnucleus caudalis or in the principal sensory nucleus. The spinal subnuclei oralis and interpolaris were sparsely innervated except for a few areas which contained more 5-HT-IR fibers. The motor nucleus contained as many immunoreactive fibers as the subnucleus caudalis, although fibers in the motor nucleus were thicker and varicosities more irregularly spaced than in caudalis.This research was supported by grant BNS-79-06474 from the National Science Foundation awarded to Efrain Azmitia     

细胞外信号调节激酶在三叉神经痛动物模型中的表达

为了研究细胞外信号调节激酶(ERK)信号转导通路在三叉神经痛动物模型中的表达,将24只雄性SD大鼠分为三叉神经痛模型组和对照组两组,模型组大鼠以铬制羊肠线疏松结扎大鼠一侧眶下神经,对照组大鼠眶下神经不结扎。应用免疫组化和免疫荧光染色方法,分别检测大鼠三叉神经节(TG)和三叉神经脊束核尾侧亚核(Vc)中磷酸化ERK(p-ERK)的表达。本研究发现p-ERK在模型组和对照组大鼠的TG和Vc中均有不同程度的表达,但模型组大鼠中p-ERK表达明显高于对照组(P<0.05)。提示ERK可能参与了三叉神经痛(TGN)痛觉信号的传导,在三叉神经痛的发病机制中发挥重要的作用。     

Depletion of calcitonin gene-related peptide from the caudal trigeminal nucleus of the rat after electrical stimulation of the Gasserian ganglion

Electrical stimulation of the Gasserian ganglion resulted in partial depletion of calcitonin gene-related peptide (CGRP) from ipsilateral central terminals of pseudounipolar primary sensory ganglion cells. Affected terminals exhibit decreased CGRP immunoreactivity as shown by cytophotometric densitomery of the caudal trigeminal nucleus. The decrease in CGRP immunoreactivity is statistically significant only in the medial one-third of the caudal trigeminal nucleus. Since earlier studies have shown that electrical stimulation of the Gasserian ganglion induces first accumulation then depletion of CGRP from perivascular sensory terminals in the dura mater, the present experiments suggest that CGRP is depleted also from central terminals of primary sensory trigeminal neurons, which might be of importance in the pathogenesis of migraine headache. Received: 18 December 1996 / Accepted: 26 June 1997     

Somatosensory properties of globus pallidus neurons in awake cats

Summary The somatosensory properties of globus pallidus (GP) neurons were assessed in awake restrained cats. Forty-two percent of GP units responded to stimulation of the face. Receptive fields were typically bilateral (49%) or contralateral and 75% included perioral tissue.Responsive units showed little ability to encode force. In contrast, cells were sensitive to changes in stimulus location within the receptive zone. The majority of cells so tested showed enhanced responding to stimuli applied within the perioral zone.Many (42%) of the cells which responded to brushing of the guard hairs or vibrissa were directionally sensitive. Of those, 89% showed enhanced responding to stimuli which moved toward the front of the mouth.These data were discussed in relation to a role of the GP in feedback regulated head positioning movements.Supported by N.I.N.C.D.S. grant NS 16054     

Mechanoreceptor activity from the human face and oral mucosa

Summary The feasibility of adopting the microneurography technique (Vallbo and Hagbarth 1968) as a tool to investigate the mechanoreceptive innervation of peri- and intra-oral tissues was explored. Multi-unit activity and impulses in single nerve fibers were recorded from the infraorbital nerve in healthy volunteers. The innervation territories of individual nerve fascicles were mapped. These varied considerably but most fascicle fields comprised the corner of the mouth. Twenty-four single mechanoreceptive units were recorded. Eighteen innervated the skin of the face, and six innervated the mucous membranes of the lips or cheeks. A majority of the mechanoreceptive afferent units were slowly adapting with small and well defined receptive fields. It is suggested that the various slowly adapting responses may originate from two different types of afferent units. No afferents showed response properties similar to typical Pacinian-corpuscle afferents.     

The medullary projection from the mesencephalic trigeminal nucleus. An experimental study with comments on the intrinsic trigeminal connections

Summary The medullary projection from the mesencephalic trigeminal nucleus has been studied in cats where the wheat germ agglutinin-horseradish peroxidase complex has been used as a retrograde and anterograde tracer. All injections were made at the level of the caudal pole of the inferior olive and show that it is especially the lateral part of nucleus parvicellularis of the reticular formation which is the main area for termination of the fibres. In addition, it can not be excluded that the descending fibres also reach the medialmost part of the spinal trigeminal sensory nucleus (pars magnocellularis and the adjoining pars gelatinosa). All three cell types of the mesencephalic trigeminal nucleus are labelled, the large globular, the small globular and the polygonal cells. Some of these cells are only faintly labelled. The observations confirm previous studies of the intrinsic trigeminal connections, but show that when the wheat germ agglutinin-horseradish peroxidase complex is used as a tracer, the origin as well as the termination for the intrinsic fibres (also the commissural) can be studied in the same section. The use of this sensitive tracer also shows new details within the intrinsic connections. The findings are discussed with special reference to the recent observations by Ruggiero et al. (1982). These authors found that in rabbit and rat there is a more restricted termination for the descending mesencephalic trigeminal fibres. The discrepancies between the observations seem to indicate that there are species differences as regards the connections between the mesencephalic trigeminal nucleus and the nuclei in the lower part of the brain stem.     

Localization of evoked potentials in the digastric,masseteric, supra- and intertrigeminal subnuclei of the cat

Summary Extracellular focal potentials were evoked and mapped in the trigeminal motor nucleus and its surrounding borderzone in the cat. Graded electrical stimulation was used for orthodromic and antidromic excitation of the masseteric and digastric motoneurones and for orthodromic stimulation of the lingual and inferior alveolar nerves. The method of referring Horsley Clarke coordinates of microelectrode recording positions to their location of the actual histological section was studied and the total error affecting the method was calculated for the H, AP and L axes. The characteristics and the distribution of the evoked focal potentials were described and related to the histological section from the actual experiment. A phase reversal of the negative focal potential evoked by the lingual and inferior alveolar nerves in the main sensory nucleus and in the intertrigeminal nucleus was observed to indicate the dorso-lateral border of the motor nucleus. Other borders were given by the antidromic potentials evoked in the nucleus. Digastric motoneurones were found medially in the caudal third and ventro-medially in the middle third of the motor nucleus. The masseteric motoneurones were located laterally in the middle and rostral thirds of the nucleus. Potentials evoked in the supratrigeminal and intertrigeminal subnuclei, adjacent to the motor nucleus, were considered and discussed in relation to the available evidence of interneurones subserving trigeminal reflex arcs.     

大白鼠三叉神经核至小脑核的纤维投射

本实验用微电泳方法将HRP分别导入20只大白鼠的小脑核,研究三叉神经各核至小脑核的纤维投射。结果表明,三叉神经各核均向小脑核发出纤维投射。其中以三叉神经脊束核极间亚核和吻侧亚核最多,三叉神经脊束核尾侧亚核和三叉神经感觉主核次之,三叉神经中脑核和三叉神经运动核最少。此外,在三叉神经运动核的腹外侧和三叉神经根内也有向小脑核投射的起源细胞。来自中脑核的纤维多终于顶核和间位核前部,来自脊束核和感觉主核的纤维较多地终止于间位核后部和齿状核。运动核的纤维终止于顶核、间位核前部和齿状核。起源于三叉神经运动核腹外侧,三叉神经根内细胞群的纤维,在小脑核中有和三叉神经感觉核簇相似的终止。三叉—小脑核的纤维投射是双侧性的,但以同侧为主。     

Short-latency trigemino-cervical ref

We describe a reflex evoked in neck muscles by stimulation of afferent fibres in the trigeminal nerve. The clearest responses were seen in averaged, unrectified, monopolar surface electromyographic (EMG) recordings from active sternocleidomastoid muscles after stimulation of the infraorbital nerve. They consisted of a bilateral positive/negative (p19, n31) wave with a mean onset latency of 12.9 ms which corresponded to a period of inhibition in the underlying motor unit activity. Responses also could be seen in splenius and trapezius, but not in arm muscles. Stimuli to other branches of the trigeminal nerve (supraorbital or mental) did not produce such clear effects. The threshold for the reflex was relatively low (2–4 times perceptual threshold) and its size scaled with the level of background EMG in an approximately linear fashion. Responses to infraorbital stimulation did not interact with other short-latency inhibitory responses in the sternocleidomastoid muscle evoked by loud acoustic clicks or stimulation of the median nerve at the wrist. We suggest that the infraorbital response is part of a head withdrawal reflex involving an oligosynaptic trigemino-cervical system similar to that described in the cat.     

Modulation of stretch-evoked reflexes in single motor units in human masseter muscle by experimental pain

The interaction between muscle pain and motor function of the jaw has been examined in recent years, but the nature of the modulation of the short-latency stretch reflex by pain is not fully understood. In this study, the reflex responses to stretch were measured in single low-threshold motor units that were kept discharging at a constant frequency, before, during and after the induction of experimental pain in one masseter muscle by controlled infusion of hypertonic saline. The probability of evoking a reflex response in individual motor units in the painful muscle at near-monosynaptic latency was reduced by a mean of about 20%. However, the overall reflex response in the surface electromyogram of both the ipsi- and contralateral masseter muscles was greater during pain. This was apparently a secondary response to the pain-induced increase in pre-stimulus activity in the motoneurone pools of both muscles, because increased motoneurone excitability may facilitate stretch reflexes. It is concluded that the most likely explanation for the reduced reflex response of low-threshold masseter motor units during experimental pain is a tonic reduction in the fusimotor drive to the masseter spindles.