Repeated tail pinch leads to desensitization of postsynaptic α2-adrenoceptors which modulate the jaw-opening reflex in the rat

• Published in: Psychopharmacologia 1998-07, Vol.138 (1), p.96-101
• Main Authors: GOMEZ, F. M, GARCIA-VALLEJO, P, INFANTE, C, MAGDALENO, F, ARESO, P
• Format: Article
• Language: English
• Subjects: Adrenergic receptors; Agonists; Biological and medical sciences; Clonidine; Electrical stimuli; Electromyography; Fundamental and applied biological sciences. Psychology; Personality. Affectivity; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Stress; Tails
• ISSN: 0033-3158; 1432-2072
• DOI: 10.1007/s002130050650

There are few in vivo studies which have investigated the modulation of central postsynaptic α2-adrenoceptors functionality provoked by stress. We assessed in the rat the effects of either single or repeated tail pinch on clonidine-induced inhibition of the jaw-opening reflex (JOR) via activation of postsynaptic central α2-adrenoceptors. At the end of each experimental period, the progressive inhibition of the digastric electromyographic responses elicited by orofacial electrical stimulation after the IV administration of cumulative doses (× 3.3) of clonidine (0.1–10 000 μg/kg) was recorded. Single tail pinch did not significantly modify the ability of the agonist to inhibit the JOR, although there was a tendency to decrease the basal amplitude of the reflex (a 40% reduction) immediately after exposure to the single stressor. However, the dose-response curve for clonidine-induced inhibition of the JOR was clearly shifted to the right in rats exposed to repeated tail pinch (ED50 was increased by 152%, P