Elevated nociceptive thresholds in rats with multifocal brain damage induced with single subcutaneous injections of lithium and pilocarpine.

To quantify the variability in thermal pain perception of rats with chemically induced brain injury following subcutaneous lithium and pilocarpine administration, 9 female Wistar rats were subjected to a nociceptive (hotplate) paradigm. At approximately 200 days of age, subjects were injected subcutaneously with 3 mEq/kg of lithium chloride followed 4 hr. later by 30 mg/kg of the cholinergic agonist pilocarpine to generate lesions that mimic human temporal lobe (limbic) epilepsy. Over 2 trials 4 of 9 subjects exhibited thermal latencies that exceeded 60 sec. while the remaining subjects obtained mean latencies of 13.40 sec. before demonstrating the criterion nociceptive response. These findings suggest that the multifocal neuronal necrosis subsequent to single peripheral injections of lithium and pilocarpine, followed by the neuroleptic, acepromazine, may significantly augment pain thresholds in certain rats within experimentally epileptic populations.