Effect of cerebral ventricles perfusion with naloxone on trigemino-hypoglossal reflex in rats

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The goal of this study was to determine whether opioid receptor antagonist naloxone abolishes the influence of periaqueductal central gray (PAG) on nociceptive evoked tongue jerks (ETJ) – a trigemino-hypoglossal reflex induced by tooth pulp stimulation. In rats under chloralose anesthesia three series of experiments were performed. In the first two groups perfusions of lateral ventricles–cerebellomedullary cistern with McIlwain–Rodnight’s solution and naloxone were carried out. In group 3 naloxone was infused through a catheter through the jugular vein. The amplitudes of tongue jerks induced by tooth pulp stimulation were recorded during subsequent 10 min perfusions. Mean amplitude of tongue movements induced by tooth pulp stimulation was regarded as the indicator of the magnitude of trigemino-hypoglossal reflex. We observed that perfusion of the cerebral ventricles with naloxone (100 nmol/ml) increased the trigemino-hypoglossal reflex up to 143%. The amplitude of ETJ was significantly reduced during PAG stimulation with a train of electrical impulses. After obtaining a significant – 93% – inhibition of ETJ (7% of the control), naloxone (100 nmol/ml) was added to the perfusion fluid. This led to a significant increase of the reflex up to 68%. Infusion of naloxone through the jugular vein did not affect the reflex. The above results suggest that the inhibition of ETJ due to PAG stimulation is partially reversed by naloxone and mediated via interactions with endogenous opioid systems involved in modulation of nociception.