Original Article

Validation of a simple automated movement detection system for formalin test in rats1

Yu-feng XIE, Jing WANG, Fu-quan HUO, Hong JIA, Jing-shi TANG


Aim: 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
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 μL).
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.
These data suggest that this automated movement detection system for formalin
test is a simple, validated measure with good pharmacological sensitivity suitable