Simultaneous depletion of neurokinin A, substance P and calcitonin gene-related peptide from the caudal trigeminal nucleus of the rat during electrical stimulation of the trigeminal ganglion.

The central terminals of the primary sensory trigeminal ganglion (TG) neurons projecting into the caudal trigeminal nucleus (CTN) of the rat exhibit neurokinin A (NKA)-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreactivities (IRs). We stimulated the TG in the rat to induce some of the alterations which might occur during migraine (neurogenic inflammation). Under a stereotaxic apparatus and by means of a bipolar electrode, one-side TG of the animals were electrically stimulated (7.5 Hz, 5 ms, 0.8-1. 4 mA) with square pulses for 5 min. Then, using immunohistochemical methods, the lower medulla of each rat was studied for NKA-, SP- and CGRP-IRs. Light microscopic examination of brain-stem sequencial sections revealed a simultaneous decrease in the immunoreactivities of all neuropeptides (NKA, SP and CGRP) in the CTN ipsilateral to TG stimulation in comparison with the other (not stimulated) side CTN. It is suggested that this decrease in immunoreactivity would be due to the co-release of neuropeptides following noxious stimuli and that NKA, SP and CGRP might therefore act as co-transmitters or co-modulators at the first central synapses of the trigeminal sensory pathway.

Depletion of substance P, neurokinin A and calcitonin gene-related peptide from the contralateral and ipsilateral caudal trigeminal nucleus following unilateral electrical stimulation of the trigeminal ganglion; a possible neurophysiological and neuroanatomical link to generalized head pain.

Primary trigeminal neurons of the trigeminal ganglion (TG) innervate major parts of the face and head, including the dura. Electrical stimulation of the TG at specific parameters, can activate its nociceptive neurons and may serve as an experimental pain model. Markowitz [J. Neurosci. 7 (1987) 4129] reported that electrical stimulation of the trigeminal ganglion (TG) causes extravasation of plasma proteins from venules of the trigeminally innervated domain possibly due to the release of vasoactive substances. Neurogenic inflammation (vasodilatation, plasma protein extravasation, release of vasoactive peptides) in dura may serve as one of the possible pathomechanisms underlying vascular head pain [Moskowitz, Ann. Neurol. 16 (1984) 157]. We performed a unilateral electrical stimulation (7.5 Hz, 5 ms, 0.8-1.4 mA for 5 min) of the TG in rat, to induce a neurogenic inflammation in the peripheral trigeminal domain including the dura, looking for calcitonin gene related peptide (CGRP), substance P (SP) and neurokinin A (NKA) immunoreactivity (IR) in the caudal trigeminal nucleus (CTN) into which massive central trigeminal processes terminate. Here, we show patchy depletion(s) of CGRP-, SP- and NKA-IRs in the contralateral CTN of the rat in addition to their ipsilateral depletion. Such depletion is due to the release of these neuropeptides in the CTN leading to the activation of bilateral trigeminal nociceptive pathway. These data afford the possibility that under specific frequencies (which may roughly correlate to the intensity of the painful stimulus) and/or specific intensities (may correlate to specific areas of the peripheral trigeminal domain) of stimulation, activation of one side of the TG may activate bilateral trigeminal nociceptive pathway leading to the perception of an ill localized/generalized pain or headache rather than a unilateral one.

Alterations in neurokinin A-, substance P- and calcitonin gene-related peptide immunoreactivities in the caudal trigeminal nucleus of the rat following electrical stimulation of the trigeminal ganglion.

We have carried out an immunohistochemical study on the presence of neurokinin A (NKA) and substance P (SP) in the rat caudal trigeminal nucleus (CTN) after electrical stimulation of the trigeminal ganglion (TG), used as an experimental model to induce alterations, some of which may occur during migraine attacks (release of vasoactive peptides from perivascular trigeminal axons and neurogenic inflammation). Both unilateral, 30 min electrical stimulation (5 Hz, 5 ms, 0.1-1 mA) of the TG and 5 min stimulation with a slight increase in the stimulating parameters (7.5 Hz, 5 ms, 1.4 mA) caused a significant depletion of the NKA and SP immunoreactivities (-IR) of the TG nerve central terminals in the ipsilateral CTN. Calcitonin gene-related peptide (CGRP)-IR of the ipsilateral CTN was also studied in the CTN using the increased stimulating parameters and a marked depletion of CGRP-IR was also observed following TG stimulation. Such depletion may be due to the release of neuropeptides from the trigeminal central terminals. These findings suggest that NKA, SP and CGRP could act as neurotransmitters at the first central synapses of the trigeminal nociceptive pathway to transmit the sensory stimuli to the higher brain centers.

[Implication of the neuropeptides methionine enkephalin, neurotensin and somatostatin of the caudal trigeminal nucleus in the experimental migraine]. / Implicación de los neuropéptidos metionina-encefalina, neurotensina y somatostatina del núcleo caudal del trigémino en la migraña experimental.

INTRODUCTION: Primary peptidergic sensory neurons of the trigeminal ganglion that innervate the cerebral dura have been involved in the pathogenesis of headache, including the migraine. In addition, it is known that nociceptive central processes of the trigeminal neurons terminate in the caudal trigeminal nucleus. Moreover, the electrical stimulation of the trigeminal ganglion has been used as an experimental model in order to study the vascular headache, including the migraine. AIM: To study whether there is or not a decrease of the immunoreactivity for methionine enkephalin, somatostatin and neurotensin in the caudal trigeminal nucleus after electrical stimulation of the trigeminal ganglion. MATERIAL AND METHODS: The trigeminal ganglia of Wistar albino rats of both sexes were electrically stimulated (frequency, 5 Hz; duration, 5 ms; intensity, 0,8 1.4 mA) and unilaterally for five minutes. Sections of the medulla oblongata containing the caudal trigeminal nucleus were obtained and processed for immunocytochemistry, in which specific antibodies were used against methionine enkephalin, neurotensin and somatostatin 28. RESULTS: In stimulated animals, we observed a decrease in the immunoreactivity for the three neuropeptides studied in the stimulated (ipsilateral) side, in comparison with the not stimulated side (contralateral). In control animals (not stimulated) the degree of the immunoreactivity was the same on both sides. CONCLUSIONS: 1. The decrease of the immunoreactivity in the ipsilateral side (stimulated) suggests that methionine enkephalin, neurotensin and somatostatin 28 are released in the caudal trigeminal nucleus after electrical stimulation of the trigeminal ganglion; 2. Methionine enkephalin and somatostatin 28 could act in the caudal trigeminal nucleus as inhibitors (with antinociceptive action) of another released exciters neuropeptides (with nociceptive action); and 3. These data will allow in the future to try new therapeutic strategies (e.g., the inhibition of the receptors implicated.), in order to alleviate certain headaches.

Impaired sensory function in heterozygous P0 knockout mice is associated with nodal changes in sensory nerves.

Mice heterozygously deficient in the major myelin component P0 are an established model of an inherited neuropathy and show signs of myelin degeneration in motor nerves. Unlike the case in patients, the sensory nerves are only mildly affected in the mouse mutants and do not show features indicative of myelin degeneration. Unexpectedly, by applying established behavioral tests, we found sensory deficits, as reflected by raised withdrawal thresholds to mechanical and thermal stimuli, whereas behavioral signs of a painful neuropathy were not detectable. By electron microscopy of longitudinal sections of sensory nerves, we found abnormalities in nodes of Ranvier comprising enlarged nodal gaps and poorly developed nodal Schwann cell microvilli. These alterations might be causally linked to the sensory deficits in the absence of profound myelin degeneration in the sensory nerves of the mutants.

Effect of a serotonin agonist (sumatriptan) on the peptidergic innervation of the rat cerebral dura mater and on the expression of c-fos in the caudal trigeminal nucleus in an experimental migraine model.

The supratentorial cerebral dura of the albino rat is equipped with a rich sensory innervation including nociceptive axons and their terminals, which display intense calcitonin gene-related peptide (CGRP) immunoreactivity both in the connective tissue and around blood vessels. Stereotactic electrical stimulation of the trigeminal (Gasserian) ganglion, regarded as an experimental migraine model, induces marked increase and disintegration of club-like perivascular CGRP-immunopositive nerve endings in the dura. Intravenous administration of sumatriptan, prior to electrical stimulation, prevents disintegration of perivascular terminals and induces accumulation of CGRP in terminal and preterminal portions of peripheral sensory axons. Consequently, immunopositive terminals and varicosities increase in size; accumulation of axoplasmic organelles results in a "hollow" appearance of many varicosities. Since sumatriptan exerts its anti-migraine effect by virtue of its agonist action on 5-HT1D receptors, we suggest that sumatriptan prevents the release of CGRP from dural perivascular terminals by an action at 5-HT1D receptors. In the caudal trigeminal nucleus electrical stimulation of the trigeminal ganglion induces, in interneurons, increased expression of the oncoprotein c-fos which is not prevented by intravenous application of sumatriptan. Disparate findings regarding this effect are partly due to the fact that sumatriptan very poorly passes the blood-brain barrier and partly to different experimental paradigms used by different authors.

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 densitometry 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.

Preserved myelin integrity and reduced axonopathy in connexin32-deficient mice lacking the recombination activating gene-1.

Mice heterozygously deficient for myelin protein zero (P0) mimicking human Charcot-Marie-Tooth (CMT) disease 1B show T-lymphocyte and macrophage upregulation in peripheral nerves, which aggravates and modulates the genetically mediated demyelinating neuropathy. In connexin32 (cx32)-deficient (cx32(def)) mice, which mimic the X-linked dominant form of CMT (CMTX), T-lymphocyte and macrophage numbers are also significantly elevated in peripheral nerves. To test the hypothesis that immune cells are indeed pathogenic in this model, we cross-bred cx32(def) mice with recombination activating gene-1 (RAG-1)-deficient mice, which lack mature T- and B-lymphocytes. In these immunoincompetent double mutants, the number of endoneurial macrophages was reduced. Furthermore, features indicative of myelin degeneration and axonopathic changes were mitigated in the RAG-1-deficient double mutants, whereas enlarged periaxonal Schwann cell collars, a hallmark specific for cx32-mutants, were not reduced. Since both cx32- and P0 deficiency lead to similar immunopathogenic processes, we conclude that immune-mediated demyelination may be a feature common to many CMT-like neuropathies independent of the genetic origin.