Sympathoinhibitory action of nociceptin in the rat spinal cord.
1. Whole-cell patch recordings were made from antidromically identified sympathetic preganglionic neurons (SPN) of immature rat spinal cord slices. Bath application of nociceptin (0.1-1 micromol/L) suppressed excitatory postsynaptic potentials (EPSP) and hyperpolarized a population of SPN; these effects were naloxone (1 micromol/L) insensitive. 2. Nociceptin suppressed the amplitude of EPSP without causing a concomitant change in glutamate-induced depolarizations, suggesting a presynaptic inhibitory action. 3. Analysis of current-voltage relationships showed that nociceptin hyperpolarized SPN by increasing an inwardly rectifying K+ current. 4. Intrathecal injection of nociceptin (3, 10 and 30 nmol) to urethane-anaesthetized rats dose-dependently reduced the mean arterial pressure and heart rate; these effects were not prevented by prior intravenous injection of naloxone (1 mg/kg). 5. Results from our in vitro and in vivo experiments suggest that nociceptin suppresses spinal sympathetic outflow either by attenuating excitatory synaptic responses or hyperpolarizing SPN.
Brailoiu
G C
GC
Department of Pharmacology, James H Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614, USA.
Lai
C C
CC
Chen
C T
CT
Hwang
L L
LL
Lin
H H
HH
Dun
N J
NJ
D000320:Adrenergic Fibers / Q000187:drug effects* / Q000502:physiology*; D000818:Animals; D001339:Autonomic Fibers, Preganglionic / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D007278:Injections, Spinal; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D018847:Opioid Peptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology; D000097629:Nociceptin
D018847:Opioid Peptides; D014665:Vasodilator Agents; D000097629:Nociceptin