Neuroprotective effects of tetrodotoxin as a Na+ channel modulator and glutamate release inhibitor in cultured rat cerebellar neurons and in gerbil global brain ischemia.

Abstract

Background and Purpose Studies examining the role of tetrodotoxin-sensitive ion channels in hypoxic-ischemic neuronal damage have concluded that sodium influx is an important initiating event. We examined the neuroprotectant effect of tetrodotoxin on both cultured cerebellar neurons and on CA1 hippocampal neurons of gerbils exposed to brain ischemia.Methods We studied neuroprotective mechanisms using cultured rat cerebellar granule cells exposed to veratridine, which induced cytotoxicity, neurotransmitter release, and calcium influx. Survival of gerbil CA1 neurons was examined by direct neuron counts 7 days after 6 minutes of global ischemia with reperfusion.Results Tetrodotoxin protected cultured neurons in a dosedependent manner from veratridine-induced toxicity (protective concentration [PC 50 ]=22 nmol/L). Veratridine induced [ 3 H]aspartate efflux that was sodium dependent, only 25% calcium dependent, and was inhibited by tetrodotoxin (inhib-

Mechanism of the persistent sodium current activator veratridine‐evoked Ca2+ elevation: implication for epilepsy

“…The biphasic [Ca 2+ ] i elevation, evoked by veratridineinduced persistent Na + influx was extracellular [Ca 2+ ]-and VGSC-dependent, as we (Zelles et al 2001) and others (Mulkey and Zucker 1992;Lysko et al 1994) have previously shown. Veratridine exerted its excitatory action directly on the examined neurons, as its effect was not influenced by the inhibition of ionotropic glutamate receptors.…”

“…Veratridine has also been used as a cellular model for epileptiform activity in acute brain slices (Otoom et al 1998;Otoom and Alkadhi 2000). The TTX-sensitive I Na,P may have relevance in the ischemic/hypoxic cascade, as well (Lysko et al 1994;Gage 1998, 2002;Banasiak et al 2004).…”

Local Blockade of Sodium Channels by Tetrodotoxin Ameliorates Tissue Loss and Long-Term Functional Deficits Resulting from Experimental Spinal Cord Injury

“…An alternative explanation could be based on reports showing that Na ϩ channel blockers such as TTX can rescue neuronal cell bodies from anoxic insult through reducing release of glutamate and aspartate: in other words, by preventing excitotoxicity (Leach et al, 1993;Lysko et al, 1994;Lynch et al, 1995;Okiyama et al, 1995). This alternative hypothesis, however, cannot adequately explain our results.…”

“…(Wrathall et al, 1994), there was a relatively greater effect of TTX in sparing WM and a lesser effect in sparing GM. Thus, although TTX may also reduce neuronal loss by blocking excitotoxicity, as has been postulated for TTX and other Na ϩ channel blockers used in studies of experimental brain injury (Leach et al, 1993;Lysko et al, 1994;Sun and Faden, 1995), we postulate that the main effect of the use of TTX in SCI is through a direct reduction of WM pathology. Ultrastructural studies are in progress to further investigate this hypothesis, and preliminary results indicate a reduction in acute axonal pathology with TTX (Rosenberg et al, 1996).…”

Cellular Protection Mechanisms against Extracellular Heme

“…In stroke, reperfusion injury is considered to be due to the toxic effects of heme (45) and to cascades from calcium channels and glutamate receptors (46,47). Hemopexin has both extra-and intra-cellular protective roles and the present research begins to define the responses of cells to high concentrations (2-10 M) of heme-hemopexin as a model for a physiological, cellular heme "load" and to determine at the molecular level some of the initial hemopexin receptor-activated and heme-related events in hemolysis, trauma, and ischemia reperfusion.…”