title: Subarachnoid serotonergic and noradrenergic antagonists increase the pain response in rats.
abstract: OBJECTIVE
  There is evidence that the passage of nociceptive information through the posterior horn of the spinal cord (PHSC) on its way to rostral levels of the central nervous system undergoes profound excitatory and inhibitory influences. The objective of the present study was to compare the effects of the subarachnoid administration of methysergide, phentolamine, and phentolamine associated with methysergide on phases I, intermediate, and II of the modified formalin test in rats.
  
  
  METHODS
  Twenty-eight male Wistar rats distributed randomly in four groups (n=7) to received subarachnoid saline solution (GC), phentolamine (GF), methysergide (GM), or phentolamine associated with methysergide (GFM). Pain was induced by the administration of formalin in the dorsal region of the right hind paw. The test was divided in three phases: phase I, intermediate, and phase II. Statistical analysis of the results was performed using the software SPSS (Statistical Package for Social Sciences), adopting a level of significance of 5%.
  
  
  RESULTS
  In the intermediate phase the number of paw elevations was significantly higher in GF, GM, and GFM groups when compared to the GC group.
  
  
  CONCLUSIONS
  The results suggest the existence of a noradrenergic and serotonergic effect in the inhibitory descending system of acute pain, with the possibility of using serotonergic and α1-adrenergic antagonists to control acute pain.
authors.affiliation: Instituto Básico de Biociências-Universidade de Taubaté (UNITAU), Taubaté, São Paulo, Brazil. ocpires@uol.com.br
authors.forename: Oscar César
authors.initials: OC
authors.lastname: Pires
authors.forename: Hazem Adel
authors.initials: HA
authors.lastname: Ashmawi
authors.forename: Elton
authors.initials: E
authors.lastname: Constantino
authors.forename: Naira Correa Cusma
authors.initials: NC
authors.lastname: Pelogia
authors.forename: Irimar de Paula
authors.initials: Ide P
authors.lastname: Posso
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D008297:Male; D008784:Methysergide / Q000008:administration & dosage / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010646:Phentolamine / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D012702:Serotonin Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D013346:Subarachnoid Space
chemical_list: D000317:Adrenergic alpha-Antagonists; D012702:Serotonin Antagonists; D008784:Methysergide; D010646:Phentolamine