Motoneurons are known to be vulnerable to the excitotoxic effects of glutamate, both in vivo and in vitro. Caspases have been shown to play a role in this glutamate-mediated death of motoneurons. Here, we examined the effect of treatment with caspase inhibitors on motoneuron survival both in vitro, following exposure to glutamate agonists, and in vivo following peripheral nerve injury.

All animal experiments were carried out humanely and conformed to Home Office Guidelines.

Primary motoneuron cultures were prepared from rat embryos of 14 days gestation. The donor animal was terminally anaesthetised with pentobarbitone (I.P., 140 mg kg^-1), and the embryos removed by hysterectomy, the ventral horns dissected and cultures prepared. At 7 days in vitro the cultures were exposed to AMPA (50 µM) for 48 h. To assess the effect of caspase inhibitors, in parallel cultures the caspase inhibitors BOC-D-FMK or QV-D-FMK (both 25 µM) were co-administered with the AMPA for 48 h. Motoneuron survival was assessed by counting the number of peripherin-positive neurons in each culture.

The effect of caspase inhibition was also assessed in vivo. The sciatic nerve was crushed in 3-day-old rats under halothane anaesthesia. At the same time, a 0.5 mg silicon implant containing either caspase inhibitor or sodium chloride was inserted under the meninges of the spinal cord between levels L1 and L5. Motoneuron survival was assessed 7 days after injury by counting the number of motoneurons in the operated and control ventral horns. The number of motoneurons on the operated side was expressed as a percentage of that on the contralateral control side of each animal.

Following treatment with 50 µM AMPA for 48 h in vitro, 47.4 % (± 3.9 S.E.M., n = 5) of motoneurons survive. When AMPA is co-administered with BOC-D-FMK or QV-D-FMK, motoneuron survival is increased to 82.9 % (± 4.2 S.E.M., n = 5) and 77.8 % (± 5.5 S.E.M., n = 5), respectively.

In vivo, 7 days after nerve crush only 58.2 % (± 2.4 S.E.M., n = 3) of motoneurons in the sciatic motor pool survive. Treatment with BOC-D-FMK improved motoneuron survival so that 73.1 % (± 4.8 S.E.M., n = 3) of motoneurons survive.

Thus treatment with either BOC-D-FMK or QV-D-FMK delays motoneuron cell death, both in in vivo and in vitro models of motoneuron degeneration.

This work was supported by the Brain Research Trust.