Waglerin-1 inhibits GABA(A) current of neurons in the nucleus accumbens of neonatal rats

What Are the Neurotoxins in Hemotoxic Snake Venoms?

Snake venoms as tools for hunting are primarily aimed at the most vital systems of the prey, especially the nervous and circulatory systems. In general, snakes of the Elapidae family produce neurotoxic venoms comprising of toxins targeting the nervous system, while snakes of the Viperidae family and most rear-fanged snakes produce hemotoxic venoms directed mainly on blood coagulation. However, it is not all so clear. Some bites by viperids results in neurotoxic signs and it is now known that hemotoxic venoms do contain neurotoxic components. For example, viperid phospholipases A₂ may manifest pre- or/and postsynaptic activity and be involved in pain and analgesia. There are other neurotoxins belonging to diverse families ranging from large multi-subunit proteins (e.g., C-type lectin-like proteins) to short peptide neurotoxins (e.g., waglerins and azemiopsin), which are found in hemotoxic venoms. Other neurotoxins from hemotoxic venoms include baptides, crotamine, cysteine-rich secretory proteins, Kunitz-type protease inhibitors, sarafotoxins and three-finger toxins. Some of these toxins exhibit postsynaptic activity, while others affect the functioning of voltage-dependent ion channels. This review represents the first attempt to systematize data on the neurotoxins from "non-neurotoxic" snake venom. The structural and functional characteristic of these neurotoxins affecting diverse targets in the nervous system are considered.

Animal toxins for channelopathy treatment

Ion channels are transmembrane proteins that allow passive flow of ions inside and/or outside of cells or cell organelles. Except mutations lead to nonfunctional protein production or abolished receptor entrance on the membrane surface an altered channel may have two principal conditions that can be corrected. The channel may conduct fewer ions through (loss-of-function mutations) or too many ions (gain-of-function mutations) compared to a normal channel. Toxins from animal venoms are specialised molecules that are generally oriented toward interactions with ion channels. This is a result of long coevolution between predators and their prey. On the molecular level, toxins activate or inhibit ion channels, so they are ideal molecules for restoring conductance in mutated channels. Another aspect of this long coevolution is that a broad variety of toxins have been fine tuned to recognize the channels of different species, keeping many amino acids substitution among sequences. Many peptide ligands with high selectivity to specific receptor subtypes have been isolated from animal venoms, some of which are absolutely non-toxic to humans and mammalians. It is expected that molecules that are selective to each known receptor can be found in animal venoms, but the pool of toxins currently does not override all receptors described as being involved in channelopathies. Modern investigating methods have enhanced the search process for selective ligands. One prominent method is a site-directed mutagenesis of existing toxins to change the selectivity or/and affinity to the selected receptor, which has shown positive results. This article is part of the Special Issue entitled 'Channelopathies.'

Neurotoxicity in snakebite--the limits of our knowledge

Snakebite is classified by the WHO as a neglected tropical disease. Envenoming is a significant public health problem in tropical and subtropical regions. Neurotoxicity is a key feature of some envenomings, and there are many unanswered questions regarding this manifestation. Acute neuromuscular weakness with respiratory involvement is the most clinically important neurotoxic effect. Data is limited on the many other acute neurotoxic manifestations, and especially delayed neurotoxicity. Symptom evolution and recovery, patterns of weakness, respiratory involvement, and response to antivenom and acetyl cholinesterase inhibitors are variable, and seem to depend on the snake species, type of neurotoxicity, and geographical variations. Recent data have challenged the traditional concepts of neurotoxicity in snake envenoming, and highlight the rich diversity of snake neurotoxins. A uniform system of classification of the pattern of neuromuscular weakness and models for predicting type of toxicity and development of respiratory weakness are still lacking, and would greatly aid clinical decision making and future research. This review attempts to update the reader on the current state of knowledge regarding this important issue.

Taurine activates strychnine-sensitive glycine receptors in neurons freshly isolated from nucleus accumbens of young rats

Although functional glycine receptors (GlyRs) are present in the mature nucleus accumbens (NAcc), an important area of the mesolimbic dopamine system involved in drug addiction, their role has been unclear because the NAcc contains little glycine. However, taurine, an agonist of GlyRs, is abundant throughout the brain, especially during early development. In the present study on freshly dissociated NAcc neurons from young Sprague-Dawley rats (12- to 21-day old), we found that both glycine and taurine can strongly depolarize NAcc neurons and modulate their excitability. In voltage-clamped NAcc neurons, glycine and taurine elicited chloride currents (IGly and ITau) with an EC50 of 0.12 and 1.25 mM, respectively. The reversal potential of IGly or ITau was 0 mV in conventional whole cell mode and -30 mV in gramicidin-perforated mode. At concentrations <1 mM, both glycine and taurine were very effectively antagonized by strychnine and by picrotoxin (with an IC50 of 60 nM and 36.5 microM for IGly, and 40 nM and 42.2 microM for ITau) but were insensitive to 10 microM bicuculline. The currents elicited by taurine (< or =1 mM) showed complete cross-desensitization with IGly, but none with gamma-aminobutyric acid (GABA)-induced currents (IGABA). However, ITau elicited by very concentrated taurine (10 mM) showed partial cross-desensitization with IGABA, and it was substantially antagonized by 10 microM bicuculline. These results indicate that taurine binds mainly to GlyRs in NAcc, but it could be a partial agonist of GABAA receptors. By activating GlyRs, taurine may play an important physiological role in the control of NAcc function, especially during development.

Genistein directly blocks glycine receptors of rat neurons freshly isolated from the ventral tegmental area

The effects of tyrosine kinase inhibitors on the glycine-induced current (I(Gly)) were studied in rat neurons freshly isolated from the ventral tegmental area (VTA). Genistein reversibly and concentration-dependently depressed I(Gly), with an IC(50) of 13 microM. Preincubation with genistein had no effect on I(Gly), indicating that genistein is effective only when glycine is bound to the receptor and channels are most likely open. Genistein depressed maximum I(Gly) without significantly changing the EC(50) for glycine. Genistein-induced inhibition of I(Gly) was sensitive to membrane voltage, being greater at positive membrane potentials. A kinetic analysis indicated that genistein lengthens the time constant of I(Gly) activation, but has no effect on deactivation or desensitization. When genistein was rapidly washed out, a transient rebound current probably reflected a faster dissociation of genistein, with respect to glycine. Results of competition experiments suggest that genistein acts on the same region of the glycine receptor as picrotoxin. Daidzein, an analog of genistein that does not act on protein kinases, also inhibited I(Gly). Co-application of lavendustin A, a specific inhibitor of tyrosine kinase, had no effect on I(Gly). Our results extend to neurons isolated from the VTA, the previous finding that genistein directly inhibits glycine receptors of hypothalamic brain slices.