Abstract. The discovery, about forty years ago, of a -bungarotoxin, a three-finger a -neurotoxin from Bungarus multicinctus venom, enabled the isolation of the nicotinic acetylcholine receptor (nAChR), making it one of the most thoroughly characterized receptors today. Since then, the sites of interaction between a -neurotoxins and nAChRs have largely been delineated, revealing the remarkable plasticity of the three-finger toxin fold that has optimally evolved to utilize different combinations of functional groups to generate a panoply of target specificities to discern subtle differences between nAChR subtypes. New facets in toxinology have now broadened the scope for the use of a-neurotoxins in scientific discovery. For instance, the development of short, combinatorial library-derived, synthetic peptides that bind with subnanomolar affinity to a -bungarotoxin and prevent its interaction with muscle nAChRs has led to the in vivo neutralization of experimental a -bungarotoxin envenomation, while the successful introduction of pharmatopes bearing "a -bungarotoxin-sensitive sites" into toxin-insensitive nAChRs has permitted the use of various a -neurotoxin tags to localize and characterize new receptor subtypes. More ambitious strategies can now be envisaged for engineering rationally designed novel activities on three-finger toxin scaffolds to generate lead peptides of therapeutic value that target the nicotinic pharmacopoeia. This review details the progress made towards achieving this goal.

In contrast to most short and long chain curaremimetic neurotoxins that produce virtually irreversible neuromuscular blockade in isolated nerve-muscle preparations, candoxin, a novel three-finger toxin from the Malayan krait Bungarus candidus, produced postjunctional neuromuscular blockade that was readily and completely reversible. Nanomolar concentrations of candoxin (IC 50 ‫؍‬ ϳ10 nM) also blocked acetylcholineevoked currents in oocyte-expressed rat muscle (␣␤␥␦) nicotinic acetylcholine receptors in a reversible manner. In contrast, it produced a poorly reversible block (IC 50 ‫؍‬ ϳ50 nM) of rat neuronal ␣7 receptors, clearly showing diverse functional profiles for the two nicotinic receptor subsets. Interestingly, candoxin lacks the helix-like segment cyclized by the fifth disulfide bridge at the tip of the middle loop of long chain neurotoxins, reported to be critical for binding to ␣7 receptors. However, its solution NMR structure showed the presence of some functionally invariant residues involved in the interaction of both short and long chain neurotoxins to muscle (␣␤␥␦) and long chain neurotoxins to ␣7 receptors. Candoxin is therefore a novel toxin that shares a common scaffold with long chain ␣-neurotoxins but possibly utilizes additional functional determinants that assist in recognizing neuronal ␣7 receptors.Curaremimetic or ␣-neurotoxins from snake venoms are well known to bind with high affinity and selectivity and in most instances, almost irreversibly to Torpedo and muscle (␣␤␥␦) nicotinic acetylcholine receptors (nAChR), 1 thereby affecting synaptic neurotransmission and producing flaccid paralysis (1, 2). They belong to a family of proteins called "three-finger toxins," which adopt a flat, leaf-like shape formed by three adjacent loops that emerge from a small globular core, which is the location of the four conserved disulfide bridges (3-9). Other members of this family include -bungarotoxins, which recognize neuronal nicotinic receptors (10), muscarinic toxins with selectivity toward distinct types of muscarinic receptors (11), fasciculins that inhibit acetylcholinesterase (12), calciseptins that block the L-type calcium channels (13,14), cardiotoxins (cytotoxins) that exert their toxicity by forming pores in cell membranes (15), and dendroaspins, which are antagonists of various cell adhesion processes (16). Despite their common structural fold and comparable affinity for the Torpedo and muscle (␣␤␥␦) nAChRs, ␣-neurotoxins are classified as short chain neurotoxins (e.g. erabutoxin-b (Laticauda semifasciata)) that have 60 -62 residues and four conserved disulfide bonds and long chain neurotoxins (e.g. ␣-bungarotoxin (Bungarus multicinctus); ␣-cobratoxin (Naja kaouthia)) with 66 -75 residues and five disulfide bonds (3). The additional disulfide bridge in long chain ␣-neurotoxins, as well in the neuronal -bungarotoxin (B. multicinctus) is located in the middle loop (loop II) (3,8,9). This fifth bridge, which cyclizes a helix-like conformation at the tip of loop II, has been reported to be cru...

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Problem-based learning (PBL) was first implemented by McMaster University medical school in 1969 as a radical, innovative, and alternative pathway to learning in medical education, thus setting a new educational trend. PBL has now spread widely across the globe and beyond the healthcare disciplines, and has prevailed for almost four decades. PBL is essentially a strategic learning system design, which combines several complementary educational principles for the delivery of instruction. PBL is specifically aimed at enhancing and optimizing the educational outcomes of learner-centered, collaborative, contextual, integrated, self-directed, and reflective learning. The design and delivery of instruction in PBL involve peer teaching and learning in small groups through the social construction of knowledge using a real-life problem case to trigger the learning process. Therefore, PBL represents a major shift in the educational paradigm from the traditional teacher-directed (teacher-centered) instruction to student-centered (learner-centered) learning. PBL is firmly underpinned by several educational theories, but problems are often encountered in practice that can affect learning outcomes. Educators contemplating implementing PBL in their institutions should have a clear understanding of its basic tenets, its practice and its philosophy, as well as the issues, challenges, and opportunities associated with its implementation. Special attention should be paid to the training and selection of PBL tutors who have a critical role in the PBL process. Furthermore, a significant change in the mindsets of both students and teachers are required for the successful implementation of PBL. Thus, effective training programs for students and teachers must precede its implementation. PBL is a highly resource-intensive learning strategy and the returns on investment (i.e. the actual versus expected learning outcomes) should be carefully and critically appraised in the decision-making process. Implementation of PBL can be a daunting task and will require detailed and careful planning, together with a significant commitment on the part of educators given the responsibility to implement PBL in an institution. PBL can offer a more holistic, value-added, and quality education to energize student learning in the healthcare professions in the 21st century. Successful implementation of PBL can therefore help to nurture in students the development of desired "habits of mind, behavior, and action" to become the competent, caring, and ethical healthcare professionals of the 21st century. Thus, PBL can contribute to the improvement of the healthcare of a nation by healthcare professionals, but we need to do it right.

5. Our studies confirmed that the rat anococcygeus muscle is an excellent nerve-smooth muscle preparation for investigating the effects of bioactive agents on noradrenergic and nitrergic transmission, as well as the direct agonist actions of these agents on post-synaptic ␣-adrenoceptors and M3 muscarinic cholinoceptors. Although many studies, including our own, have documented that scorpion venoms and toxins mediate their primary effects via a prejunctional mechanism that leads to the marked release of various autonomic neurotransmitters, our studies have shown that there are exceptions to this generally accepted phenomenon. In particular, we have provided firm evidence to show that the venoms from H. longimanus and H. spinifer do not have such a prejunctional site of action but, instead, the venoms mediate their autonomic effects through direct agonist actions on post-junctional muscarinic M3 cholinoceptors and ␣-adrenoceptors.