The neuronal excitability time-dependently changes after lipopolysaccharide administration in mice: possible role of cyclooxygenase-2 induction.

The parameters of pentylenetetrazol (PTZ)-induced seizures have been evaluated at various time intervals after lipopolysaccharide (LPS; Escherichia coli O111:B4, 100 microg/kg, i.p.) administration in mice. A proconvulsant effect occurred 4h after LPS injection with decreased seizure latency and enhanced seizure intensity. In contrast, the incidence of seizures was reduced 18 h after LPS injection. There were no significant alterations on seizure parameters 2, 8, 12, and 24h after LPS treatment. SC-58236, a selective cyclooxygenase (COX)-2 inhibitor (20 or 40 mg/kg, s.c.) treatment alone had no effect on PTZ-induced seizures, but reversed the antiseizure activity observed 18 h after LPS injection. However, SC-58236 treatment partially restored the proconvulsant changes that were observed 4h after LPS administration. On the other hand, COX-1-selective inhibitor valeryl salicylate (20 or 40 mg/kg, s.c.) itself facilitated PTZ-induced seizures. Thus, it was not possible to evaluate the effects of valeryl salicylate on the excitability changes after LPS injection. These results indicate that the parameters of PTZ-induced seizures change time-dependently after LPS treatment, in which proconvulsant and anticonvulsant states could be seen in a sequence. It seems that COX-2 isoenzyme may be involved in the neuronal excitability changes due to LPS.