Do opioid peptides mediate a presynaptic control of C-fibre transmission in the rat spinal cord?
A presynaptic inhibitory role for opioid peptides in the control of C-fibre-evoked activity in the dorsal horn has been investigated. The excitability of C-fibre terminals in the dorsal horn of decerebrate spinal rats was tested using intraspinal terminal stimulation and recording the size of the antidromic C wave from the dorsal roots. Naloxone (1-2 mg/kg) failed to alter the baseline terminal excitability of the C-fibres, but reduced the increase in terminal excitability produced by A-fibre afferent conditioning stimuli. The inhibition of postsynaptic C-evoked activity in lamina 5 cells produced by A-afferent fibre conditioning stimuli was also reduced by naloxone. This effect may reflect the reversal of an opioid-mediated presynaptic inhibition, although blockade of a direct postsynaptic inhibitory action could also be involved.
D000818:Animals; D004056:Differential Threshold; D004723:Endorphins / Q000502:physiology*; D005071:Evoked Potentials; D009270:Naloxone / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects; D009412:Nerve Fibers / Q000502:physiology*; D051381:Rats; D013116:Spinal Cord / Q000033:anatomy & histology / Q000502:physiology*; D013376:Substantia Gelatinosa / Q000502:physiology; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission
D004723:Endorphins; D009270:Naloxone