Effect of excitatory and inhibitory agents and a glial inhibitor on optically-recorded primary-afferent excitation.
The effects of GABA, excitatory amino-acid receptors antagonists and a glial metabolism inhibitor on primary-afferent excitation in the spinal dorsal horn were studied by imaging the presynaptic excitation of high-threshold afferents in cord slices from young rats with a voltage-sensitive dye. Primary afferent fibers and terminals were anterogradely labeled with a voltage-sensitive dye from the dorsal root attached to the spinal cord slice. Single-pulse stimulation of C fiber-activating strength to the dorsal root elicited compound action potential-like optical responses in the superficial dorsal horn. The evoked presynaptic excitation was increased by the GABAA receptor antagonists picrotoxin and bicuculline, by glutamate receptor antagonists D-AP5 and CNQX, and by the glial metabolism inhibitor mono-fluoroacetic acid (MFA). The increase in presynaptic excitation by picrotoxin was inhibited in the presence of D-AP5, CNQX and MFA. Presynaptic modulation in the central terminal of fine primary afferents by excitatory and inhibitory amino acids may represent a mechanism that regulates the transmission of pain.
Ikeda
Hiroshi
H
Department of Human and Artificial Intelligence Systems, Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan. ikeda@synapse.his.fukui-u.ac.jp
Kiritoshi
Takaki
T
Murase
Kazuyuki
K
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D005463:Fluoroacetates / Q000494:pharmacology*; D018756:GABA Antagonists / Q000494:pharmacology*; D009457:Neuroglia / Q000187:drug effects / Q000502:physiology; D010852:Picrotoxin / Q000494:pharmacology*; D020671:Posterior Horn Cells / Q000187:drug effects; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000378:metabolism
D002211:Capsaicin; D018691:Excitatory Amino Acid Antagonists; D005463:Fluoroacetates; D018756:GABA Antagonists; D010852:Picrotoxin; D017470:Receptors, Glutamate; C014815:fluoroacetic acid