Direct excitation of deep dorsal horn neurones in the rat spinal cord by the activation of postsynaptic P2X receptors

• Published in: The Journal of physiology Vol. 573; no. 3; pp. 753 - 763
• Main Authors: Shiokawa, Hiroaki, Nakatsuka, Terumasa, Furue, Hidemasa, Tsuda, Makoto, Katafuchi, Toshihiko, Inoue, Kazuhide, Yoshimura, Megumu
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 15.06.2006; Blackwell Publishing Ltd; Blackwell Science Inc
• Subjects: Adenosine Triphosphate - analogs & derivatives; Adenosine Triphosphate - pharmacology; Animals; Animals, Newborn; Dose-Response Relationship, Drug; Excitatory Postsynaptic Potentials; In Vitro Techniques; Neuroscience; Patch-Clamp Techniques; Posterior Horn Cells - drug effects; Posterior Horn Cells - growth & development; Posterior Horn Cells - metabolism; Presynaptic Terminals - drug effects; Presynaptic Terminals - metabolism; Purinergic P2 Receptor Agonists; Pyridoxal Phosphate - analogs & derivatives; Pyridoxal Phosphate - pharmacology; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P2 - drug effects; Receptors, Purinergic P2 - metabolism; Receptors, Purinergic P2X; Receptors, Purinergic P2Y2; Spinal Cord - drug effects; Spinal Cord - growth & development; Spinal Cord - metabolism; Synaptic Transmission; Uridine Triphosphate - pharmacology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2006.108613

ATP mediates somatosensory transmission in the spinal cord through the activation of P2X receptors. Nonetheless, the functional significance of postsynaptic P2X receptors in spinal deep dorsal horn neurones is still not yet well understood. Using the whole-cell patch-clamp technique, we investigated whether the activation of postsynaptic P2X receptors can modulate the synaptic transmission in lamina V neurones of postnatal day (P) 9–12 spinal cord slices. At a holding potential of −70 mV, ATPγS (100 μ m ), a nonhydrolysable ATP analogue, generated an inward current, which was resistant to tetrodotoxin (1 μ m ) in 61% of the lamina V neurones. The ATPγS-induced inward current was accompanied by a significant increase in the frequency of glutamatergic miniature excitatory postsynaptic currents (mEPSCs) in the majority of lamina V neurones. The ATPγS-induced inward current was not reproduced by P2Y receptor agonists, UTP (100 μ m ), UDP (100 μ m ), and 2-methylthio ADP (100 μ m ), and it was also not affected by the addition of guanosine-5′- O- (2-thiodiphosphate) (GDPβS) into the pipette solution, thus suggesting that ionotropic P2X receptors were activated by ATPγS instead of metabotropic P2Y receptors. On the other hand, α,β-methylene ATP (100 μ m ) did not change any membrane current, but instead increased the mEPSC frequency in the majority of lamina V neurones. The ATPγS-induced inward current was suppressed by pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) (10 μ m ), but not by trinitrophenyl-ATP (TNP-ATP) (1 μ m ). Furthermore, we found that ATPγS (100 μ m ) produced a clear inward current which was observed in all lamina V neurones over P16 spinal cord slices, in contrast to P9–12. These results indicate that distinct subtypes of P2X receptors were functionally expressed at the post- and presynaptic sites in lamina V neurones, both of which may contribute to the hyperexcitability of lamina V in a different manner. In addition, the data relating to the developmental increase in the functional P2X receptors suggest that purinergic signalling may thus be more common in somatosensory transmission with maturation.