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Mechanisms of trigeminal pain


The main objectives of this project will be the understanding of the mechanisms underlying pain in the trigeminal territory, and the setting up of techniques aimed at relieving it. The 2 objectives are strongly interrelated, as the pursuance of the latter will be exploited to acquire knowledge useful to the former.

Specific Objectives:

- study of physiology of nociception within the trigeminal system
- study of pathophysiology of trigeminal pain syndromes
- development and improvement of surgical techniques for the treatment of trigeminal neuralgia
- study of mechanisms of the trigemino-vascular system in humans and in animals
- development of equipment and computer software

Investigation of the trigeminal system and the related pain has been so far hampered by the difficulties of using the neurophysiological techniques otherwise commonly employed for the other nerves. This is due to the fact that the trigeminal nerve lies mainly within the skull, in an unaccessible position, and only its far field activity may be recorded from the scalp of the intact subject. Also, stimulation of the trigeminal afferents gives rise to many reflexes, some of them possibly still unknown, whose electrical activity spreads also to the scalp and interferes with the activity coming from the stimulated trigeminal pathway. Attempts at using the evoked potentials technique, theoretically very reliable, had ended in failure, because of intrinsic drawbacks in the techniques used, and consequent misinterpretation of the recordings obtained. The recent discovery of a new type of trigeminal evoked potential, performed in 1985-86 by the team in Genova, working together with those in Liverpool and Northampton, has opened up new possibilities in the functional exploration of the trigeminal system. This has been very successfully applied to patients suffering from trigeminal pathology, allowing precise identification of the lesion in many cases. Within the proposed project this technique will be employed to clarify the origin of trigeminal neuralgia, to screen patients for the micro-vascular-decompression (MVD) operation, to monitor trigeminal activity during MVD, and to set up a new, very accurate technique for radiofrequency thermorhizotomy aimed at relieving trigeminal pain. Further important results are expected by the use of trigeminal reflexes in order to explore possible functional abnormalities of the trigeminal sensory and motor nuclei. So far the use of trigeminal reflexes has been aimed at assessing the integrity of the peripheral part of the nerve, and little attention has been paid to the central circuitry. As the peripheral part of the nerve will now be explored by means of the trigeminal evoked potentials, the study of trigeminal reflexes will provide far more accurate information about the reflex centres under normal and pathological conditions. The teams in Paris and Roma are the leaders in this.
The importance of opioid and non-opioid peptide systems within the central nervous system has been widely assessed in the last 20 years, but their relevance to trigeminal pain has not been fully investigated. We do not actually know what part these systems may play in trigeminal neuralgia, or in cluster headaches. But the alternate phases of worsening and spontaneous remission of these two syndromes may well be connected with some disturbance in the biochemistry of the central pain control. The laboratories in Liverpool and Roma will seek evidence of changes in neuropeptides at various stages of these syndromes.
A further peculiarity of the trigeminal system is its key role in regulation of blood flow both intra and extra-cranially. This has led to the wording of the new term "trigemino-vascular" system, to which much attention has recently been devoted, because of its great potential relevance. The trigemino-vascular system is strongly interrelated with pain transmission within the nerve. Most of the experimental evidence so far collected on this matter has been derived from animal studies. It will be the aim of the laboratories in Torino and Genova to make a comparison between findings in animal and human studies; the Torino laboratory will also investigate the effect of the sympathetic activity on the cerebral blood flow. Traditional and new techniques for very reliable evaluation of cerebral blood flow and for stimulation of the peripheral trigeminal afferents developed in Genova will be used for these experiments.

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Università degli Studi di Genova
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Via Dodecaneso 35
16146 Genova

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