Amitriptyline converts non-responders into responders to low-frequency electroacupuncture-induced analgesia in rats.
OBJECTIVE
The purpose of this study was to examine whether the use of intraperitoneal or intrathecal amitriptyline combined with electroacupuncture modifies the tail-flick reflex and incision pain in rats that normally do not have analgesia to electroacupuncture in the tail-flick test (non-responder rats).


METHODS
Changes in the nociceptive threshold of intraperitoneal or intrathecal saline- or amitriptyline-treated non-responder rats were evaluated using the tail-flick or incision pain tests before, during and after a 20-min period of electroacupuncture, applied at 2 Hz to the Zusanli and Sanynjiao acupoints. Amitriptyline was used at doses of 0.8 mg/kg or 30 μg/kg by intraperitoneal or intrathecal route, respectively. At these doses, amitriptyline has no effect against thermal or incision pain in rats.


RESULTS
Rats selected as non-responders to the analgesic effect of electroacupuncture 2 Hz in tail-flick and incision pain tests become responders after an intraperitoneal or intrathecal injection of amitriptyline.


CONCLUSIONS
Amitriptyline converts non-responder rats to rats that respond to electroacupuncture with analgesia in a model of thermal phasic pain and anti-hyperalgesia in a model of incision pain.
Department of Pharmacology, Faculty of Medicine of Ribeirão Preto, Brazil.
Rafael S
RS
Fais
G M
GM
Reis
A C
AC
Rossaneis
J W S
JW
Silveira
Q M
QM
Dias
W A
WA
Prado
D000639:Amitriptyline / Q000627:therapeutic use*; D018712:Analgesics, Non-Narcotic / Q000627:therapeutic use; D000818:Animals; D003131:Combined Modality Therapy; D015671:Electroacupuncture; D007263:Infusions, Parenteral; D007278:Injections, Spinal; D008297:Male; D059226:Nociceptive Pain / Q000628:therapy*; D017288:Pain Threshold / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar
D018712:Analgesics, Non-Narcotic; D000639:Amitriptyline