title: Microinjections of glutamate or morphine at coincident midbrain sites have different effects on nociceptive dorsal horn neurons in the rat.
abstract: Responses of single lumbar spinal neurons to noxious skin heating (50 degrees C, 10 s) were electrophysiologically recorded in barbiturate-anesthetized rats. Responses of all neurons were suppressed by electrical stimulation in the midbrain periaqueductal gray (PAG) or lateral reticular formation (LRF). Microinjection of glutamate (GLU, 0.1-0.3 microliter, 0.5 M) into the PAG rapidly (within 15 s) suppressed (to 13-55% of control) the responses of 6/16 neurons with recovery within 8 min. The remainder were affected less at even higher doses (0.5-1 microliter). Responses of 4/10 neurons were suppressed following GLU microinjected into the LRF. We also tested effects of microinjection of morphine (MOR, 5 micrograms/0.5 microliter) into GLU-sensitive and insensitive PAG sites. Responses of 4 neurons were unaffected, 4 were enhanced (to 130-155%), and 2 suppressed (to 43 and 57%) following MOR in PAG, with enhancement or suppression beginning within 12-20 min and lasting 40 to over 70 min. The differing effects of GLU and MOR may reflect different mechanisms for the descending modulation of spinal nociceptive transmission.
authors.affiliation: II. Physiologisches Institut, Universität Heidelberg, F.R.G.
authors.forename: E
authors.initials: E
authors.lastname: Carstens
authors.forename: B
authors.initials: B
authors.lastname: Stelzer
authors.forename: M
authors.initials: M
authors.lastname: Zimmermann
mesh_terms: D000818:Animals; D004525:Efferent Pathways / Q000502:physiology; D004558:Electric Stimulation; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D008636:Mesencephalon / Q000187:drug effects / Q000503:physiopathology*; D008845:Microinjections; D009020:Morphine / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects*; D010146:Pain / Q000503:physiopathology*; D010487:Periaqueductal Gray / Q000187:drug effects / Q000503:physiopathology; D051381:Rats; D011919:Rats, Inbred Strains; D012154:Reticular Formation / Q000187:drug effects / Q000503:physiopathology; D013116:Spinal Cord / Q000187:drug effects / Q000503:physiopathology*
chemical_list: D005971:Glutamates; D018698:Glutamic Acid; D009020:Morphine