Thyrotropin releasing hormone, cholecystokinin and endogenous opioids in the modulation of spinal reflexes in the rabbit.
Electrical stimulation of the sural nerve of the rabbit evokes reflexes in the ipsilateral ankle extensor gastrocnemius medialis and in the knee flexor semitendinosus which are differentially modulated by endogenous opioids. Intravenous injection of the putative functional opioid antagonist, thyrotropin releasing hormone (TRH) or its analogue RX77368, caused the extensor response to double in size and the flexor reflex to increase to 1.5-1.7 times pre-drug controls. The opioid RX77368 had no effect on the naloxone-reversible inhibition of the gastrocnemius reflex which followed tetanic stimulation of the fine afferent fibres of the common peroneal or sural nerves. The cholecystokinin antagonist proglumide, which has been shown to enhance the actions of endogenous opioids in some species, had no effects on either reflex. It is possible that TRH acts as an excitatory neurotransmitter or modulator in the spinal cord of the rabbit opposing, but not blocking, the actions of endogenous opioids.
Clarke
R W
RW
Department of Physiology and Environmental Science, University of Nottingham, Faculty of Agricultural Science, Loughborough, Leicestershire, U.K.
Ford
T W
TW
Harris
S M
SM
Taylor
J S
JS
D000818:Animals; D002766:Cholecystokinin / Q000494:pharmacology*; D004723:Endorphins / Q000037:antagonists & inhibitors; D005260:Female; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D011817:Rabbits; D012018:Reflex / Q000187:drug effects*; D012844:Sincalide / Q000037:antagonists & inhibitors; D013127:Spinal Nerves / Q000502:physiology*; D013497:Sural Nerve / Q000187:drug effects / Q000502:physiology*; D013973:Thyrotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology*
D004723:Endorphins; D009270:Naloxone; D013973:Thyrotropin-Releasing Hormone; C027979:L-pyroglutamyl-L-histidyl-3,3-dimethylprolinamide; D002766:Cholecystokinin; D012844:Sincalide; D011761:Pyrrolidonecarboxylic Acid