Neurodegenerative actions of interleukin-1 in the rat brain are mediated through increases in seizure activity.

The cytokine interleukin-1 (IL-1) is an established and important mediator of diverse forms of neuronal injury in experimental animals. However, its mechanisms of action remain largely unknown. We have reported previously that IL-1 markedly enhances excitotoxic injury induced in the rat by striatal administration of the excitotoxin alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), leading to widespread neuronal loss throughout the ipsilateral cortex. Here we tested the hypothesis that IL-1 causes this injury through induction and/or enhancement of seizure activity in the rat. Consistently with this hypothesis, intrastriatal injection of AMPA or AMPA with IL-1 in the rat brain increased c-Fos expression in regions similar to those in which c-Fos has been reported previously in response to seizures. A significant increase in cortical neuronal activity (number of c-Fos positive cells) was observed in response to AMPA with IL-1 compared with AMPA (8 hr after injection). Increased seizure duration [3,522 +/- 660 sec (SEM) vs. 1,415 +/- 301 sec; P < 0.001] and cell death volume (140 +/- 20 mm3 vs. 52 +/- 6 mm3; P < 0.001) were seen in response to coinfusion of AMPA with IL-1 vs. AMPA alone. In addition, the anticonvulsant diazepam (intraperitoneal) significantly reduced cell death (P < 0.001) and seizure duration (P < 0.001) induced by AMPA with IL-1, and a significant correlation was found between seizure duration and cell death volume. These findings support our hypothesis that IL-1 enhances excitotoxic injury by enhancement of seizures, which may be of relevance to IL-1 actions in other forms of neuronal injury, including cerebral ischemia.