Neurogram recording during acute inflammation in the rat hind paw

Electrophysiological recording was conducted using the intact tibiotarsal nerve of the left hind leg of adult male rats before and after subplantar injections of three different phlogistic agents or saline vehicle in the left hind paw. In three-hour recordings, peak neural activity as activated by 5 g of pressure to the injected paw was reached in 90 min (dextran), 120 min (brewer's yeast) and 150 min (carrageenan). The least neural hyperactivity was seen with dextran, while yeast and carrageenan produced comparably high degrees of hyperactivity. Neurograms were also studied in rats receiving orally administered prototype anti-inflammatory agents or chlorpromazine 1 hr before carrageenan was injected pedally. Chlorpromazine HCl pretreatment (100 mg/kg) exerted the greatest protective effect with the nadir of neural activity seen at 90-120 min. The nadir for phenylbutazone (100 mg/kg) was at 60-120 min, indomethacin (10 mg/kg) at 60-90 min and aspirin (300 mg/kg) at 45-90 min. Despite these temporal differences, the protective effects of these three anti-inflammatory agents were statistically equivalent at the doses tested. Hydrocortisone alcohol (20 mg/kg) provided a significant reduction in hyperactivity at 30-60 min but the duration was much shorter than the other agents which showed protective effects through to the end of the 180-min observation period.