The effect of naloxone on trigemino-hypoglossal reflex inhibited by periaqueductal central gray stimulation in rats.
The aim of the 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 subsequent series of perfusions of lateral ventricles - cerebellomedullary cistern with Mc Ilwain-Rodnight's solution, Met-enkaphalin (Enk-Met) and naloxone were carried out. 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 Enk-Met (100 nmol/mL) inhibited the trigemino-hypoglossal reflex by 46%, whereas naloxone (100 nmol/mL), added to the solution perfusing the cerebral ventricles system, increased the reflex by 42%. The amplitude of ETJ was significantly reduced during PAG stimulation with a train of electrical impulses. After obtaining a significant 93% - inhibition of ETJ, naloxone (100 nmol/mL) was added to the perfusion fluid. This led to a significant increase of the reflex by 68%. 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.
Zubrzycka
M
M
Department of Physiology, Institute of Physiology and Biochemistry, Medical University of Lodz, Poland. ajanecka@psk2.am.lodz.pl
Janecka
A
A
D000818:Animals; D002552:Cerebral Ventricles / Q000187:drug effects / Q000502:physiology; D003782:Dental Pulp / Q000502:physiology; D004558:Electric Stimulation; D004744:Enkephalin, Methionine / Q000494:pharmacology; D007002:Hypoglossal Nerve / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D012018:Reflex / Q000187:drug effects* / Q000502:physiology; D014059:Tongue / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D014276:Trigeminal Nerve / Q000187:drug effects* / Q000502:physiology
D009292:Narcotic Antagonists; D009270:Naloxone; D004744:Enkephalin, Methionine