Tetrodotoxin-sensitive release of adrenaline, noradrenaline and neuropeptide Y-like immunoreactivity in the pithed guinea-pig in the absence of electrical preganglionic nerve stimulation.
The effect of tetrodotoxin (TTX) on plasma noradrenaline (NA), adrenaline (A) and neuropeptide Y-like immunoreactivity (NPY-LI) levels was evaluated in the pithed guinea pig, in the absence of electrical stimulation and following preganglionic nerve stimulation (PNS). Blood samples for determination of NA, A and NPY-LI were collected 5 min before and 5 min after injection of saline (control group, n = 6) or TTX (13 micrograms/kg, i.v., TTX-treated group, n = 8), respectively. In both groups, blood samples were collected 20 s and 40 s after initiation of PNS. In the absence of electrical stimulation, TTX reduced the plasma NA level by 66%, NPY-LI level by 42%, whereas the plasma A level was not significantly altered by the neurotoxin. In the control group, PNS elicited a 27-fold increase of plasma NA, a 60-fold increase of plasma A and enhanced the NPY-LI levels by 13%. Pretreatment with TTX completely blocked this release of sympathetic transmitters. The present results suggest that a certain degree of spontaneous nerve activity is present in the pithed animal model, also during baseline conditions, since TTX significantly reduced NA and NPY-LI in the absence of electrical stimulation. This spontaneous nerve activity is probably a consequence of local mechanical activity of the pithing rod capable of eliciting action potentials at the preganglionic level of the sympathetic nerve terminals.
Department of Clinical Pharmacology, Sahlgren's Hospital, Gothenburg University, Göteborg, Sweden.
C
C
Dahlöf
P
P
Linton-Dahlöf
J M
JM
Lundberg
D000818:Animals; D001339:Autonomic Fibers, Preganglionic / Q000502:physiology; D003655:Decerebrate State; D004558:Electric Stimulation; D004837:Epinephrine / Q000097:blood*; D006168:Guinea Pigs; D008297:Male; D009478:Neuropeptide Y / Q000097:blood*; D009638:Norepinephrine / Q000097:blood*; D010525:Peripheral Nerves / Q000502:physiology; D011863:Radioimmunoassay; D012016:Reference Values; D009435:Synaptic Transmission; D013779:Tetrodotoxin / Q000494:pharmacology*
D009478:Neuropeptide Y; D013779:Tetrodotoxin; D009638:Norepinephrine; D004837:Epinephrine