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Opioidergic inhibition of flexor and extensor reflexes in the rabbit.
Author(s) -
Clarke R W,
Galloway F J,
Harris J,
Taylor J S,
Ford T W
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019098
Subject(s) - stimulation , reflex , (+) naloxone , medicine , opioidergic , endogenous opioid , heel , opioid antagonist , antagonist , withdrawal reflex , anatomy , opioid , anesthesia , chemistry , endocrinology , receptor
1. Recordings were made from gastrocnemius medialis (GM), semitendinosus (ST) and tibialis anterior/extensor digitorum longus (TA/EDL) motor nerves during mechanical and electrical stimulation of the skin of the foot in decerebrated and spinalized rabbits. 2. GM motoneurones were excited from the heel and not from the toes, whereas TA/EDL responded to stimulation at the toes but not at the heel. ST also responded to electrical and mechanical stimulation at the toes, but there was a disparity between the effects of the two types of stimuli when they were applied at the heel: ST motoneurones fired in response to electrical stimulation of the heel but showed only an ‘off’ response to mechanical stimulation at this site. 3. The opioid antagonist naloxone caused a dose‐dependent increase in all reflexes evoked by electrical stimulation of the skin. The heel‐GM, toes‐ST and toes‐TA/EDL reflexes all increased to more than 3 times control levels with naloxone, which also caused significant decreases in the latencies of these reflex responses. On the other hand, the heel‐ST response increased to just 1.4 times control levels and showed no decrease in latency with the opioid antagonist. 4. These data suggest that segmental withdrawal reflex pathways in the rabbit are suppressed by endogenous opioid peptides. This opioid‐mediated inhibition seems to operate non‐selectively on reflex pathways between cutaneous afferents and motoneurones.