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Venoms are a rich source of highly specific toxins, which allow the identification of novel therapeutic targets. We have now applied high content screening (HCS) microscopy to identify toxins that modulate pain sensitization signaling in primary sensory neurons of rat and elucidated the underlying mechanism. A set of venoms and fractions thereof were analyzed for their ability to activate type II protein kinase A (PKA‐II) and extracellular signal‐regulated kinases (ERK1/2). We identified MeuNaTxα‐1, a sodium channel‐selective scorpion α‐toxin from Mesobuthus eupeus, which affected both PKA‐II and ERK1/2. Recombinant MeuNaTxα‐1 showed identical activity to the native toxin on mammalian voltage‐gated sodium channels expressed in Xenopus laevis oocytes and induced thermal hyperalgesia in adult mice. The effect of MeuNaTxα‐1 on sensory neurons was dose‐dependent and tetrodotoxin‐sensitive. Application of inhibitors and toxin mutants with altered sodium channel selectivity demonstrated that signaling activation in sensory neurons depends on NaV1.2 isoform. Accordingly, the toxin was more potent in neurons from newborn rats, where NaV1.2 is expressed at a higher level. Our results demonstrate that HCS microscopy‐based monitoring of intracellular signaling is a novel and powerful tool to identify and characterize venoms and their toxins affecting sensory neurons. [ABSTRACT FROM AUTHOR]

Lynx1 is a GPI‐tethered protein colocalized with nicotinic acetylcholine receptors (nAChRs) in the brain areas important for learning and memory. Previously, we demonstrated that at low micromolar concentrations the water‐soluble Lynx1 variant lacking GPI‐anchor (ws‐Lynx1) acts on α7‐nAChRs as a positive allosteric modulator. We hypothesized that ws‐Lynx1 could be used for improvement of cognitive processes dependent on nAChRs. Here we showed that 2 µM ws‐Lynx1 increased the acetylcholine‐evoked current at α7‐nAChRs in the rat primary visual cortex L1 interneurons. At higher concentrations ws‐Lynx1 inhibits α7‐nAChRs expressed in Xenopus laevis oocytes with IC50 ~ 50 µM. In mice, ws‐Lynx1 penetrated the blood‐brain barrier upon intranasal administration and accumulated in the cortex, hippocampus, and cerebellum. Chronic ws‐Lynx1 treatment prevented the olfactory memory and motor learning impairment induced by the α7‐nAChRs inhibitor methyllycaconitine (MLA). Enhanced long‐term potentiation and increased paired‐pulse facilitation ratio were observed in the hippocampal slices incubated with ws‐Lynx1 and in the slices from ws‐Lynx1‐treated mice. Long‐term potentiation blockade observed in MLA‐treated mice was abolished by ws‐Lynx1 co‐administration. To understand the mechanism of ws‐Lynx1 action, we studied the interaction of ws‐Lynx1 and MLA at α7‐nAChRs, measured the basal concentrations of endogenous Lynx1 and the α7 nAChR subunit and their association in the mouse brain. Our findings suggest that endogenous Lynx1 limits α7‐nAChRs activation in the adult brain. Ws‐Lynx1 partially displaces Lynx1 causing positive modulation of α7‐nAChRs and enhancement of synaptic plasticity. Ws‐Lynx1 and similar compounds may constitute useful hits for treatment of cognitive deficits associated with the cholinergic system dysfunction. [ABSTRACT FROM AUTHOR]