The enigma of site of action of migraine preventives: no effect of metoprolol on trigeminal pain processing in patients and healthy controls.

BACKGROUND: Beta-blockers are a first choice migraine preventive medication. So far it is unknown how they exert their therapeutic effect in migraine. To this end we examined the neural effect of metoprolol on trigeminal pain processing in 19 migraine patients and 26 healthy controls. All participants underwent functional magnetic resonance imaging (fMRI) during trigeminal pain twice: Healthy subjects took part in a placebo-controlled, randomized and double-blind study, receiving a single dose of metoprolol and placebo. Patients were examined with a baseline scan before starting the preventive medication and 3 months later whilst treated with metoprolol. RESULTS: Mean pain intensity ratings were not significantly altered under metoprolol. Functional imaging revealed no significant differences in nociceptive processing in both groups. Contrary to earlier findings from animal studies, we did not find an effect of metoprolol on the thalamus in either group. However, using a more liberal and exploratory threshold, hypothalamic activity was slightly increased under metoprolol in patients and migraineurs. CONCLUSIONS: No significant effect of metoprolol on trigeminal pain processing was observed, suggesting a peripheral effect of metoprolol. Exploratory analyses revealed slightly enhanced hypothalamic activity under metoprolol in both groups. Given the emerging role of the hypothalamus in migraine attack generation, these data need further examination.

Descripción de las propiedades funcionales del sistema nociceptivo trigeminal en relación con el dolor pulpar / Description of the functional properties of the nociceptive trigeminal system in relation to pulpal pain

El sistema trigeminal nociceptivo es un componente del sistema sensorial somestésico que tiene la capacidad de discriminar cuatro variables básicas de los estímulos que provocan daño tisular, ellas son: cualidad, curso temporal, localización e intensidad. Las fibras A delta y C, vinculadas a la nocicepción están presentes en la pulpa dental. Se utilizan varias clasificaciones del dolor, atendiendo a diversos criterios: calidad de la sensación, velocidad de transmisión por las fibras, en relación con el lugar del cuerpo donde se exprese, y a la ubicación del nociceptor. La evolución de las condiciones pulpares se clasifican como: pulpitis reversible, pulpitis transicional, pulpitis irreversible y pulpa necrótica.Según su cualidad, el dolor pulpar puede ser punzante o continuo; atendiendo a su aparición, provocado o espontáneo; por su curso, intermitente o continuo; por su localización puede ser limitado a una región, irradiado y referido; y en relación con su intensidad se considera leve, moderado o severo. La capacidad del sistema sensorial nociceptivo en cuanto a discriminar la modalidad, curso temporal, localización e intensidad del estímulo, permite conocer las diferentes etapas de un proceso inflamatorio pulpar(AU)

The nociceptive trigeminal system is a component of the somatosensory system capable of distinguishing four basic variables of stimuli causing tissue damage: quality, time course, location and intensity. A-delta and C fibers, which are related to nociception, are present in dental pulp. Several classifications of pain are used, based on various criteria: quality of the sensation, transmission velocity along fibers, body part where it is expressed, and location of the nociceptor. According to their evolution, pulpal conditions are classified into reversible pulpitis, transitional pulpitis, irreversible pulpitis and necrotic pulp. Pulpal pain has been classified according to the following variables: quality: sharp or continuous; cause: provoked or spontaneous; course: intermittent or continuous; location: limited to a region, radiating or referred; and intensity: mild, moderate or severe. The capacity of the nociceptive sensory system to distinguish the mode, time course, location and intensity of the stimulus makes it possible to recognize the different stages of a pulpal inflammatory process(AU)