Effects of adenosine 5'-monophosphate and adenosine 5'-triphosphate on functionally identified units in the cat spinal dorsal horn. Evidence for a differential effect of adenosine 5'-triphosphate on nociceptive vs non-nociceptive units.
A study was done of the effects of iontophoretic application of adenosine 5'-monophosphate (AMP) and adenosine 5'-triphosphate (ATP) on functionally identified neurones in the spinal dorsal horn of the cat. AMP depressed nearly two-thirds of the 32 neurones tested regardless of functional type; the remainder were unaffected. ATP, on the other hand, had three types of effect: depression, excitation and a biphasic effect which consisted of excitation followed by depression. A significant difference was found when a comparison was made of the frequency of occurrence of each of these three types of effect in the samples of non-nociceptive (n = 18) and of wide dynamic range neurones (n = 42): of non-nociceptive neurones 61% were excited, 11% were depressed, 6% had a biphasic response and 22% were unaffected; of wide dynamic range neurones 45% had a biphasic response, 19% were depressed, 14% were excited and 21% were unaffected (chi 2 = 16.2, P less than 0.005). The depressant effects of both AMP and ATP and the depressant phase of the biphasic effect of ATP seem to be mediated through activation of P1-purinergic receptors because these effects were blocked by theophylline, a P1-purinergic antagonist [Burnstock (1978) In Cell Membrane Receptors for Drugs and Hormones: A Multidisciplinary Approach, pp. 107-118]. Thus the biphasic effect appears to consist of excitatory and depressant responses in the same neurone. The differential effects of ATP on non-nociceptive vs wide dynamic-range neurones are similar to the differential effects on these neurones observed during activation of low-threshold primary afferents. This similarity, together with evidence that ATP can be released from primary afferent neurones [Holton and Holton (1954) J. Physiol., Lond. 126, 124-140; Holton (1959) J. Physiol., Lond. 145, 494-504], prompts us to suggest that ATP may be a chemical mediator of effects of low-threshold primary afferent inputs in the spinal dorsal horn.
D000249:Adenosine Monophosphate / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology* / Q000502:physiology; D000818:Animals; D002415:Cats; D002951:Citrates / Q000494:pharmacology; D019343:Citric Acid; D009475:Neurons, Afferent / Q000187:drug effects; D009619:Nociceptors / Q000187:drug effects*; D010146:Pain / Q000503:physiopathology; D013116:Spinal Cord / Q000187:drug effects* / Q000503:physiopathology; D009435:Synaptic Transmission; D013806:Theophylline / Q000494:pharmacology
D002951:Citrates; D019343:Citric Acid; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D013806:Theophylline