Validation of a simple automated movement detection system for formalin test in rats.
OBJECTIVE
To investigate the validity and sensitivity of an automatic movement detection system developed by our laboratory for the formalin test in rats.


METHODS
The effects of systemic morphine and local anesthetic lidocaine on the nociceptive behaviors induced by formalin subcutaneously injected into the hindpaw were examined by using an automated movement detection system and manual measuring methods.


RESULTS
Formalin subcutaneously injected into the hindpaw produced typical biphasic nociceptive behaviors (agitation). The mean agitation event rate during a 60-min observation period increased linearly following increases in the formalin concentration (0.0%, 0.5%, 1.5%, 2.5%, and 5%, 50 microL). Systemic application of morphine of different doses (1, 2, and 5 mg/kg) 10-min prior to formalin injection depressed the agitation responses induced by formalin injection in a dose-dependent manner, and the antinociceptive effect induced by the largest dose (5 mg/kg) of morphine was significantly antagonized by systemic application of the opioid receptor antagonist naloxone (1.25 mg/kg). Local anesthetic lidocaine (20 mg/kg) injected into the ipsilateral ankle subskin 5-min prior to formalin completely blocked the agitation response to formalin injection. These results were comparable to those obtained from manual measure of the incidence of flinching or the duration time of licking/biting of the injected paw.


CONCLUSIONS
These data suggest that this automated movement detection system for formalin test is a simple, validated measure with good pharmacological sensitivity suitable for discovering novel analgesics or investigating central pain mechanisms.
Xie
Yu-feng
YF
Department of Physiology, School of Medicine, Xi'an Jiaotong University, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an 710061, China.
Wang
Jing
J
Huo
Fu-quan
FQ
Jia
Hong
H
Tang
Jing-shi
JS
D000701:Analgesics, Opioid / Q000494:pharmacology; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005557:Formaldehyde / Q000008:administration & dosage / Q000037:antagonists & inhibitors*; D007279:Injections, Subcutaneous; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects*; D010147:Pain Measurement / Q000295:instrumentation*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results
D000701:Analgesics, Opioid; D000779:Anesthetics, Local; D005557:Formaldehyde; D009020:Morphine; D008012:Lidocaine