Serotonergic, cholinergic and nociceptive inhibition or excitation of raphe magnus neurons in barbiturate-anesthetized rats.
Neurons in the nucleus raphe magnus were recorded extracellularly from barbiturate-anesthetized rats, and were classified by their responses to noxious mechanical stimulation as either pinch-excited, pinch-inhibited or biphasic (inhibited then excited). They were then subjected to iontophoresis of serotonin, some serotonergic agonists and antagonists, acetylcholine, and gamma-amino-n-butyric acid. Serotonin reduced the spontaneous firing of most pinch-inhibited cells (79%). Significantly fewer (P < 0.05) pinch-excited and biphasic cells were inhibited by serotonin (40% and 45%, respectively); in these two cell classes, the observed response was often excitation (30% and 14%), or inhibition for 10-30s followed by excitation for the next 1-2 min (25% and 36%). Acetylcholine showed a similar, statistically significant distribution of effects (P < 0.05), inhibiting all pinch-inhibited neurons (n = 10) but fewer pinch-excited (53%, n = 17) and biphasic neurons (20%, n = 10). Excitation, or excitation then inhibition, was again found frequently among the remaining pinch-excited and biphasic cells. The effect of gamma-amino-n-butyric acid was only inhibitory. In all three nociceptive classes, the serotonin-1A agonist buspirone (n = 15) was inhibitory (87%) and the serotonin-1C/2 antagonist ketanserin (n = 20) was excitatory (35%). The mixed serotonin-1/2 antagonist methysergide (n = 10) was inhibitory (50%) or excitatory (40%). 8-Hydroxy-dipropylaminotetralin (n = 3) was found to increase spontaneous activity (possibly because of partial serotonin-1A agonsim), and +/- propranolol (n = 4) to reduce it (possibly through beta-adrenoceptor antagonism, not serotonin-1A antagonism).(ABSTRACT TRUNCATED AT 250 WORDS)
Hentall
I D
ID
University of Illinois College of Medicine, Rockford 61107-1897.
Andresen
M J
MJ
Taguchi
K
K
D000758:Anesthesia; D000818:Animals; D001463:Barbiturates; D005260:Female; D007478:Iontophoresis; D008845:Microinjections; D009474:Neurons / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D010277:Parasympathomimetics / Q000494:pharmacology; D010812:Physical Stimulation; D011903:Raphe Nuclei / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D001463:Barbiturates; D010277:Parasympathomimetics; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin