Effects of ES52, an enkephalinase inhibitor, on responses of ventrobasal thalamic neurons in rat |
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Authors: | Valrie Kayser Jean-Michel Benoist Michle Gautron Gisle Guilbaud |
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Institution: | Unité de Recherches de Neurophysiologie Pharmacologique de l'I.N.S.E.RM. (Unité 161), 2 rue d'Alésia 75014, Paris, France |
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Abstract: | The effects of ES52, a highly potent derivative of Thiorphan, an inhibitor of enkephalinase, at doses of 5 and 10 mg/kg IV were studied on the responses to cutaneous stimuli of 18 “nociceptive” (N), 10 “convergent” (NNn) and 4 “non-nociceptive” (Nn) neurons recorded in the ventrobasal (VB) complex of the rat. The responses of neurons exclusively driven by noxious mechanical and thermal stimuli (N neurons) were depressed by 56% by ES52 15 min after the injection of 5 or 10 mg/kg IV. This depressive effect was reversed by naloxone for half the neurons. For the ten neurons driven by both noxious and non-noxious stimuli (convergent NNn neurons), the responses to noxious heat were decreased by 42% at 15 min. By contrast, there was a marked enlargement of their receptive fields to light tactile stimuli, which was not naloxone-reversible. The receptive fields of neurons exclusively driven by non-noxious stimuli (Nn neurons) were also greatly expanded by ES52. These results show that ES52 can depress the responses of VB thalamic neurons to noxious stimuli; the effects on receptive field size underlines the complexity of the endogenous opiate systems. |
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Keywords: | Enkephalinase inhibitor Ventrobasal thalamic neurons Noxious and non-noxious stimuli |
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