ATP P2x receptors and sensory synaptic transmission between primary afferent fibers and spinal dorsal horn neurons in rats. J. Neurophysiol. 80: 3356-3360, 1998.
Glutamate is a major fast transmitter between primary afferent fibers and dorsal horn neurons in the spinal cord. Recent evidence indicates that
ATP acts as another fast transmitter at the rat cervical spinal cord and is proposed to serve as a transmitter for nociception and
pain. Sensory synaptic transmission between dorsal root afferent fibers and neurons in the superficial dorsal horn of the lumbar spinal cord were examined by whole cell patch-clamp recording techniques. Experiments were designed to test if
ATP could serve as a transmitter at the lumbar spinal cord. Monosynaptic excitatory postsynaptic currents (EPSCs) were completely abolished after the blockade of both glutamatergic
alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/
kainate and N-methyl--
aspartate receptors. No residual current was detected, indicating that
glutamate but not
ATP is a fast transmitter at the dorsal horn of the lumbar spinal cord. Pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic
acid (
PPADS), a selective P2x receptor antagonist, produced an inhibitory modulatory effect on fast EPSCs and altered responses to paired-pulse stimulation, suggesting the involvement of a presynaptic mechanism. Intrathecal administration of
PPADS did not produce any antinociceptive effect in two different types of behavioral nociceptive tests. The present results suggest that
ATP P2x2 receptors modulate excitatory synaptic transmission in the superficial dorsal horn of the lumbar spinal cord by a presynaptic mechanism, and such a mechanism does not play an important role in behavioral responses to noxious heating. The involvement of other P2x subtype receptors, which is are less sensitive to
PPADS, in acute nociceptive modulation and persistent
pain remains to be investigated.