Acute phenobarbital administration induces hyperalgesia: pharmacological evidence for the involvement of supraspinal GABA-A receptors.
The aim of the present study was to determine if phenobarbital affects the nociception threshold. Systemic (1-20 mg/kg) phenobarbital administration dose dependently induced hyperalgesia in the tail-flick, hot-plate and formalin tests in rats and in the abdominal constriction test in mice. Formalin and abdominal constriction tests were the most sensitive procedures for the detection of hyperalgesia in response to phenobarbital compared with the tail-flick and hot-plate tests. The hyperalgesia induced by systemic phenobarbital was blocked by previous administration of 1 mg/kg ip picrotoxin or either 1-2 mg/kg sc or 10 ng icv bicuculline. Intracerebroventricular phenobarbital administration (5 microg) induced hyperalgesia in the tail-flick test. In contrast, intrathecal phenobarbital administration (5 microg) induced antinociception and blocked systemic-induced hyperalgesia in this test. We suggest that phenobarbital may mediate hyperalgesia through GABA-A receptors at supraspinal levels and antinociception through the same kind of receptors at spinal levels.
Departamento de Farmacologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil.
C M
CM
Yokoro
S M
SM
Pesquero
R M
RM
Turchetti-Maia
J N
JN
Francischi
M A
MA
Tatsuo
D000704:Analysis of Variance; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D018756:GABA Antagonists / Q000494:pharmacology; D006930:Hyperalgesia / Q000139:chemically induced / Q000503:physiopathology*; D006993:Hypnotics and Sedatives / Q000008:administration & dosage*; D008297:Male; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D010634:Phenobarbital / Q000008:administration & dosage*; D010852:Picrotoxin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects*
D001640:Bicuculline; D018756:GABA Antagonists; D006993:Hypnotics and Sedatives; D010634:Phenobarbital; D010852:Picrotoxin; D011963:Receptors, GABA-A