Indian red scorpion venom depresses spinal synaptic transmission without involving NMDA receptors

Stings of Indian red scorpion (Mesobuthus tamulus, MBT) produce neurological abnormalities such as convulsions and paralysis. These parameters indicate the activity at α-motoneuron. The present study was therefore, undertaken to evaluate the effect of MBT-venom on spinal reflexes and the involvement of N-methyl-d-aspartate (NMDA) receptors. The experiments were performed on isolated hemisected spinal cords from 4 to 6 days old rats. Stimulation of a dorsal root with supramaximal strength at 0.1 Hz evoked monosynaptic (MSR) and polysynaptic reflex (PSR) potentials in the corresponding segmental ventral root. Superfusion of MBT-venom depressed the spinal reflexes in a time- and a concentration-dependent (0.1–1 μg/ml) manner. MBT-venom at 0.1, 0.3 and 1.0 μg/ml produced maximal depression of 55, 75 and 90% at 30, 10 and 7 min, respectively. The time required to produce 50% depression (T-50) of MSR was 19.0, 8.0, and 3.6 min and for PSR was 15.0, 5.6, and 2.9 min at 0.1, 0.3 and 1 μg/ml of venom, respectively. Pre-treatment with DL-α-2-amino-5-phosphonovaleric acid (APV) decreased MSR by 26% and abolished PSR. In the presence of APV, the MBT-venom-induced depression of MSR was not different from the venom only group. The results indicate that venom-induced depression of spinal reflexes did not involve NMDA receptors.