title: The effects of strychnine, bicuculline, and ketamine on 'immersion-inhibited' dorsal horn convergent neurons in intact and spinalized rats.
abstract: In both intact and spinalized rats, this study examined the effects of strychnine (a glycine antagonist), bicuculline (a GABAA antagonist), and ketamine (a non-competitive NMDA receptor antagonist) on one particular class of lumbar dorsal horn convergent neurons. This group of convergent neurons are inhibited when a rat's entire ipsilateral hindpaw is immersed in 50 degrees C water and has a strong afterdischarge as soon as the paw is removed from the water. Strychnine (2 mg/kg, iv) increased ongoing activity and blocked the 'inhibition phase' in both intact and spinalized rats demonstrating that a spinal-related glycine mechanism was involved in the inhibition. However, only in intact rats did the firing rate of the 'afterdischarge phase' increase significantly from pre-drug levels, suggesting that supraspinal sites may be involved in modulating this phase. Ketamine (15 mg/kg, iv) depressed ongoing activity and the firing rate in the afterdischarge phase of these neurons. Additionally, ketamine reversed the strychnine-induced increase in ongoing activity. Bicuculline (2 mg/kg, iv) had no effect on the activity of this cell class. As shown previously, and replicated here, these 'immersion-inhibited' neurons invariably have both inhibitory and excitatory mechano-receptive fields on the ipsilateral hindpaw. Thus, the response of this class of convergent neurons to noxious stimulation may be a function of relative inputs of glycine and EAA's, each possibly triggered by the stimulation of different receptive fields/regions on the same paw. Furthermore, when both fields are co-stimulated during noxious immersion of the entire paw, glycine has a stronger influence on activity than does the EAA's.
authors.affiliation: Departments of Physiology and Psychiatry, McGill University, 3655 Drummond St., Montreal, Que., Canada.
authors.forename: S
authors.initials: S
authors.lastname: McGaraughty
authors.forename: J L
authors.initials: JL
authors.lastname: Henry
mesh_terms: D000818:Animals; D001640:Bicuculline / Q000494:pharmacology*; D003655:Decerebrate State / Q000473:pathology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D005110:Extracellular Space / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology*; D058787:GABA-A Receptor Antagonists; D018684:Glycine Agents / Q000494:pharmacology*; D007649:Ketamine / Q000494:pharmacology*; D008297:Male; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors; D013331:Strychnine / Q000494:pharmacology*
chemical_list: D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D058787:GABA-A Receptor Antagonists; D018684:Glycine Agents; D016194:Receptors, N-Methyl-D-Aspartate; D007649:Ketamine; D013331:Strychnine; D001640:Bicuculline