Browsing by Author "S. Das Gupta"

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Ptychodiscus brevis toxin enhances the frequency-dependent depression of the monosynaptic reflex in neonatal rat spinal cord in vitro
(Elsevier Ireland Ltd, 2003) S.B. Deshpande; J.N. Singh; S. Das Gupta
The involvement of frequency-dependent depression (FDD) of synaptic transmission for the depressant action of the Ptychodiscus brevis toxin (PbTx) was investigated in neonatal rat spinal cord in vitro. The stimulation of a dorsal root by train of pulses (five stimuli) at different frequencies evoked potentials in the ventral root (monosynaptic reflex, MSR). Amplitude of the fifth response as percent of first response at 0.1, 0.2, 0.5, 1.0 and 2.0Hz were 90, 80, 75, 70 and 50%, respectively. In Mg2+-free medium, PbTx depressed the MSR and also enhanced the FDD in a concentration-dependent manner. Further, the PbTx-induced depression can well be correlated with the enhancement of FDD (r=0.98). In the presence of Mg2+ (1.3mM), the FDD was greater than that in the absence of Mg2+. But in the presence of Mg2+ PbTx did not alter FDD, eventhough there was 25% depression at 28μM (significantly lesser than in Mg2+-free medium). The results indicate that the Mg2+-sensitive component of PbTx-induced depression of MSR is mediated via the neuronal systems involving FDD. © 2003 Elsevier Ireland Ltd. All rights reserved.
Relative potency of synthetic analogs of Ptychodiscus brevis toxin in depressing synaptic transmission evoked in neonatal rat spinal cord in vitro
(2002) J.N. Singh; S. Das Gupta; A.K. Gupta; S.N. Dube; S.B. Deshpande
Effects of Ptychodiscus brevis toxin (PbTx) analogs on the spinal synaptic transmission in neonatal rats in vitro were evaluated. PbTx1/PbTx2 had aromatic groups and PbTx3/PbTx4 had aliphatic groups. All the analogs depressed monosynaptic reflex (MSR) and polysynaptic reflex (PSR) in a concentration-dependent manner. The maximal depression of MSR (75% from initial) and PSR (96%) was at 84 μM for PbTx1. Concentration to produce 25% inhibition from initial (IC25) by PbTx1 for MSR and PSR was ≤2.8 μM. The maximal depression of MSR (80%) was at 96 μM and PSR (100%) was at 32 μM by PbTx2. IC25 for MSR and PSR were 5.5 μM and <3.2 μM, respectively. PbTx3 decreased MSR by 25% maximally (=IC25) at 36 μM. The depression of PSR fluctuated and was maximal (75%) at 108 μM and IC25 was 6.2 μM. PbTx4 depressed MSR and PSR at the maximum of 35% at 32 μM and IC25 for MSR was 8.3 μM and for PSR was 35 μM. Rank order of potency of toxins for depressing MSR was PbTx1>PbTx2≫PbTx4>PbTx3; and for PSR it was PbTx2>PbTx1>PbTx3≫PbTx4. Results indicate that the toxins having aromatic groups exhibited greater neurotoxicity. © 2002 Elsevier Science Ireland Ltd. All rights reserved.