Effects of ES52, an enkephalinase inhibitor, on responses of ventrobasal thalamic neurons in rat.
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.
D000603:Amino Acids, Sulfur / Q000494:pharmacology*; D000818:Animals; D004594:Electrophysiology; D007031:Hypothalamus / Q000187:drug effects* / Q000502:physiology; D008297:Male; D015260:Neprilysin; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology; D011480:Protease Inhibitors; D051381:Rats; D011919:Rats, Inbred Strains; D015244:Thiorphan / Q000031:analogs & derivatives*; D008625:Tiopronin / Q000031:analogs & derivatives / Q000494:pharmacology*
D000603:Amino Acids, Sulfur; D011480:Protease Inhibitors; C040246:ES 52; D015244:Thiorphan; D008625:Tiopronin; D015260:Neprilysin