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

Abstract: 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 0.1Hz 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 (0.1–1μg/ml) manner. MBT-venom at 0.1, 0.3 and 1.0μg/ml produced maximal depression of 55, 75 and 90% at 30, 10 and 7min, respectively. The time required to produce 50% depression (T-50) of MSR was 19.0, 8.0, and 3.6min and for PSR was 15.0, 5.6, and 2.9min at 0.1, 0.3 and 1μg/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. [Copyright &y& Elsevier]