Substance P and NMDA receptor-mediated slow potentials in neonatal rat spinal cord: age-related changes.
Slow ventral root potentials (slow VRP's) recorded from 1- to 5-day-old rat spinal cords are implicated in nociception, but there is controversy over their origin and persistence in the adult. The present study investigated changes in the role of substance P and NMDA receptors in slow VRP generation during the postnatal period (1-21 days). Through 9 days, dorsal root stimulation elicits slow VRP's with typical peak amplitudes at 3-4 s, decay time constants of 18-20 s, and durations > 20 s. After 11 days, peak amplitude shortens to < 1 s, decay time constant 4-5 s, and duration < 10 s. At 1-6 days, slow VRP's are sensitive to the NMDA receptor antagonist APV and the substance P antagonists spantide and CP 96,345. After 11 days, APV sensitivity is retained, but spantide and ability of substance P to evoke a response are diminished. Abbreviated slow VRP's in post-11-day spinal cords appear to correspond to the early APV-sensitive component of long-duration slow VRP's in younger animals. Attempts to restore long-duration slow VRP's in 12- to 14-day-old rat cords by blocking various inhibitory mechanisms were not successful. The results suggest that a substance P response, some of which is mediated by NK1 receptors, is lost with maturation of the cord. Either a developmental role played by substance P changes with maturity, or the motor neurons of the isolated post-11-day cord lose the capacity to sustain large long-duration plateau potentials.
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D015761:4-Aminopyridine / Q000494:pharmacology; D000375:Aging / Q000378:metabolism*; D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*; D013126:Spinal Nerve Roots / Q000502:physiology; D013373:Substance P / Q000031:analogs & derivatives / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000502:physiology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D000700:Analgesics; D016194:Receptors, N-Methyl-D-Aspartate; D013757:Tetraethylammonium Compounds; D013373:Substance P; D015763:2-Amino-5-phosphonovalerate; C042867:spantide; D015761:4-Aminopyridine