The lack of effect of baclofen on action potentials of spinal motor axon collateral terminations in vivo.
In the lumbar ventral horn of pentobarbitone-anaesthetised cats, (-)-baclofen reduces both the synaptic release of excitatory transmitter from muscle group Ia afferent terminations and the duration of the presynaptic action potentials of these terminations, presumably by interfering with the influx of calcium ions through voltage-activated channels. Baclofen, however, has little or no effect on cholinergic excitation at motor axon collateral synapses on spinal Renshaw cells and, in the present study, was found not to reduce the duration of the action potential of axon collateral terminations located in the vicinity of Renshaw cells in pentobarbitone-anaesthetised cats. Furthermore, in contrast to group Ia terminations, a 4-aminopyridine-sensitive potassium conductance could not be detected as contributing to axon collateral termination action potentials. These results suggest that there may be differences in presynaptic ion fluxes associated with transmitter release at the intraspinal terminations of group Ia afferent fibres and motor axon collaterals in the cat spinal cord.
Curtis
D R
DR
Division of Neuroscience, John Curtin School of Medical Research, Canberra, Australia.
Lacey
G
G
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D001418:Baclofen / Q000494:pharmacology*; D002415:Cats; D005260:Female; D008297:Male; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology*; D011930:Reaction Time / Q000187:drug effects; D013116:Spinal Cord / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects
D015761:4-Aminopyridine; D001418:Baclofen