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Oenanthotoxin (OETX) and dihydro-OETX are polyacetylenic diols occurring in Oenanthe crocata and are known to exert proconvulsant effects. We have recently demonstrated that these compounds downregulated GABAergic currents (Appendino et al., 2009) and that OETX induced open channel block and allosterically modulated GABA(A) receptors (Wyrembek et al., 2010). O. crocata also contains several minor OETX analogues and in the present study we tested whether their effect on GABA(A) receptors depends on the compounds' polarity. We investigated a series of five polyacetylenes characterized by a higher lipophylicity than OETX, (1-acetyl-2,3-dihydrooenanthotoxin - X1, 14-acetyloenanthotoxin-X2, 1-deoxyoenanthotoxin - X3, 14-deoxyoenanthotoxin - X4, 14-dehydro-1-deoxyOETX - X5, polarity sequence: X1>X2>X3>X4>X5). Their effects were tested first on miniature inhibitory postsynaptic currents (mIPSCs). All but X3, significantly decreased the mIPSC amplitudes while X1, X2, X4 decreased, and X3 and X5 increased the mIPSC frequency. The lack of a clear correlation between the compounds' polarity and their effect on mIPSCs might result from their presynaptic effects. We thus considered their impact on current responses to exogenous GABA applications. Amplitude reduction of current responses was most prominent for X1 and virtually absent for X5 indicating a dependence on the compound's polarity. Only X1 and X2 showed open channel block, while the kinetics of currents were affected only by X1 which further supports a dependence of the drug's effects on their polarity. In conclusion, GABA(A) receptors are inhibited and allosterically modulated by naturally occurring OETX analogues (except X5) and these effects are positively correlated with the compounds' polarity., (Copyright © 2012. Published by Elsevier B.V.)

An increasing body of data has shown that matrix metalloproteinase-9 (MMP-9), an extracellularly acting, Zn(2+)-dependent endopeptidase, is important not only for pathologies of the central nervous system but also for neuronal plasticity. Here, we use three independent experimental models to show that enzymatic activity of MMP-9 causes elongation and thinning of dendritic spines in the hippocampal neurons. These models are: a recently developed transgenic rat overexpressing autoactivating MMP-9, dissociated neuronal cultures, and organotypic neuronal cultures treated with recombinant autoactivating MMP-9. This dendritic effect is mediated by integrin β1 signalling. MMP-9 treatment also produces a change in the decay time of miniature synaptic currents; however, it does not change the abundance and localization of synaptic markers in dendritic protrusions. Our results, considered together with several recent studies, strongly imply that MMP-9 is functionally involved in synaptic remodelling., (@ 2011. Published by The Company of Biologists Ltd)

Matrix Metalloproteinase 9 (MMP-9) has been demonstrated to play a crucial role in maintenance of NMDA receptor-dependent LTP and in lateral mobility of these receptors. However, the effect of MMP-9 on NMDA receptor (NMDAR) functional properties is unknown. For this purpose we have investigated the impact of recombinant MMP-9 on the whole-cell NMDAR-mediated current responses in cultured hippocampal neurons. Treatment with MMP-9 induced a reversible acceleration of desensitization and deactivation kinetics but had no effect on current amplitude. Interestingly, phorbol ester, a PKC activator known to enhance NMDAR lateral mobility, induced kinetic changes of currents similar to those produced by MMP-9. In conclusion, our results show that MMP-9 reversibly modulates the NMDAR kinetics and raise a possibility that this modulation could be related to the lateral mobility of these receptors., (© 2009 Wiley-Liss, Inc.)

Background and Purpose: Oenanthotoxin (OETX), a polyacetylenic alcohol from plants of the genus Oenanthe, has recently been identified as potent inhibitor of GABA-evoked currents. However, the effects of OETX on the inhibitory postsynaptic currents (IPSCs), as well as the pharmacological mechanism(s) underlying its effects on GABA(A) receptors, remain unknown. The purpose of this study was to elucidate the mechanism underlying the inhibition of GABAergic currents by OETX., Experimental Approach: Effects of OETX on GABAergic currents were studied using the patch clamp technique on rat cultured hippocampal neurons. Miniature IPSCs (mIPSCs) were recorded in the whole-cell configuration, while the current responses were elicited by ultrafast GABA applications onto the excised patches., Key Results: OETX potently inhibited both mIPSCs and current responses, but its effect was much stronger on synaptic currents. Analysis of the effects of OETX on mIPSCs and evoked currents disclosed a complex mechanism: allosteric modulation of both GABA(A) receptor binding and gating properties and a non-competitive, probably open channel block mechanism. In particular, OETX reduced the binding rate and nearly abolished receptor desensitization. A combination of rapid clearance of synaptic GABA and OETX-induced slowing of binding kinetics is proposed to underlie the potent action of OETX on mIPSCs., Conclusions and Implications: OETX shows a complex blocking mechanism of GABA(A) receptors, and the impact of this toxin is more potent on mIPSCs than on currents evoked by exogenous GABA. Such effects on GABAergic currents are compatible with the convulsions and epileptic-like activity reported for OETX.

Benzodiazepines (BDZs) are known to increase the amplitude and duration of IPSCs. Moreover, at low [GABA], BDZs strongly enhance GABAergic currents suggesting the up-regulation of agonist binding while their action on gating remains a matter of debate. In the present study we have examined the impact of flurazepam and zolpidem on mIPSCs by investigating their effects on GABA(A)R binding and gating and by considering dynamic conditions of synaptic receptor activation. Flurazepam and zolpidem enhanced the amplitude and prolonged decay of mIPSCs. Both compounds strongly enhanced responses to low [GABA] but, surprisingly, decreased the currents evoked by saturating or half-saturating [GABA]. Analysis of current responses to ultrafast GABA applications indicated that these compounds enhanced binding and desensitization of GABA(A) receptors. Flurazepam and zolpidem markedly prolonged deactivation of responses to low [GABA] but had almost no effect on deactivation at saturating or half-saturating [GABA]. Moreover, at low [GABA], flurazepam enhanced desensitization-deactivation coupling but zolpidem did not. Recordings of responses to half-saturating [GABA] applications revealed that appropriate timing of agonist exposure was sufficient to reproduce either a decrease or enhancement of currents by flurazepam or zolpidem. Recordings of currents mediated by recombinant ('synaptic') alpha1beta2gamma2 receptors reproduced all major findings observed for neuronal GABA(A)Rs. We conclude that an extremely brief agonist transient renders IPSCs particularly sensitive to the up-regulation of agonist binding by BDZs.