Histogram showing the effect of analgesic and sedative dose on paw movements of rats during the second phase i.e. 30 to 50 minutes after an injection of 1.5% Formalin solution into a hind paw
Control rats (given formalin but no pre-treatment drugs) spent about 1000 seconds lifting and licking the paw, this reduced to about 810 sec when pre treated with 1.25 mg/kg morphine, about 350 sec at 2.5 mg/kg and 50 seconds at 5.0 mg/kg Morphine. Equivalent values for Amphetamine were 700 sec at 0.37 mg/kg; 300 sec at 0.75 mg/kg and less than 30 sec at 1.5 mg/kg. When the sedative, Pentobarbital, was given pre-treatment the rats spent about 900 seconds paw lifting and licking - not significantly different to values in control rats (given formalin but no pre-treatment). The correlation between the behaviour and the analgesic dose were similar in value (but negative) to the correlations found by increasing the formalin concentration.
