Spontaneous and evoked release of methionine-enkephalin-like material from the rat spinal cord in vivo.
In vivo perfusion of the subarachnoid space with an artificial cerebrospinal fluid (CSF) in paralyzed halothane-anesthetized rats allowed the collection of methionine-enkephalin (Met-Enk)-like material (MELM) released from the spinal cord. Bio-Gel P2 chromatography and high-performance liquid chromatography showed that 65% of this material corresponded to authentic Met-Enk. Under resting conditions, about 1 pg of MELM per minute was regularly released for at least 3 h; for Met-Enk, this value corresponded to a fractional rate constant of 0.002% (i.e. tissue content of the pentapeptide which was released per minute from the whole spinal cord). Perfusion with K+-enriched (40-60 mM) CSF resulted in a marked enhancement (+ 150-200%) of spinal MELM release. Similarly, calibrated pinches of the muzzle and i.p. administration of acetic acid, two strong noxious stimuli in awake animals, induced a significant increase (+ 75-150%) in spinal MELM release. In contrast, pinches applied to the tail did not enhance but instead slightly reduced (-35%) MELM release from the rat spinal cord. These data suggest that mechanisms other than segmental controls could be involved in the activation of spinal enkephalinergic neurons by some nociceptive stimuli.
Cesselin
F
F
Le Bars
D
D
Bourgoin
S
S
Artaud
F
F
Gozlan
H
H
Clot
A M
AM
Besson
J M
JM
Hamon
M
M
D000818:Animals; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D004744:Enkephalin, Methionine / Q000032:analysis / Q000378:metabolism*; D008297:Male; D010146:Pain / Q000503:physiopathology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000378:metabolism* / Q000503:physiopathology; D009435:Synaptic Transmission
D004744:Enkephalin, Methionine; D011188:Potassium