Assessment of the mutagenic and genotoxic activity of cyanobacterial toxin beta-N-methyl-amino-L-alanine in Salmonella typhimurium.

A neurotoxin ß-N-methylamino-L-alanine (L-BMAA) is a non-protein amino acid produced by most cyanobacteria ubiquitously present in aquatic and terrestrial environments. Due to its global presence in surface waters, a widespread human exposure is possible and therefore this toxin represents a health risk for humans and animals. L-BMAA has been linked to the development of a variety of neurodegenerative diseases. Its neurotoxic activity has been extensively studied, while nothing is known on its genotoxic properties. In the present study we evaluated for the first time L-BMAA mutagenic potential using Ames assay on several Salmonella typhimurium strains (TA97a, TA98, TA100, TA102 and TA1535). The results showed that the toxin (up to 0.9 mg/plate) did not induce mutations without or with S9 metabolic activation. Its genotoxic activity was further studied with the SOS/umuC assay on S. typhimurium TA1535/pSK1002 and the results showed that it was not cytotoxic nor genotoxic for bacteria. The present study represents the first evidence that L-BMAA is not mutagenic nor genotoxic for bacteria even at concentrations much higher than those typically found in the environment. However, as most of the cyanobacterial toxins are not bacterial mutagens it is very important to further elucidate its genotoxic activity in eukaryotic cells.

Costs of venom production in the common death adder (Acanthophis antarcticus).

The utilization of venom in predatory and defensive contexts is associated with benefits regarding minimization of energetic expenditure on hunting, maximization of success in prey acquisition and avoidance of injury from dangerous prey and aggressors. Multiple characteristics suggest that venom is quite expensive to produce, thereby creating a tradeoff between advantages and disadvantages associated with its possession. The metabolic costs of venom production have rarely been studied and no information on the detailed metabolic processes during venom replenishment exists. Where costs of venom production have been studied they are often not in context with other components of the energy budget of the study organism. Using flow-through respirometry, we examined changes in metabolic rate in the Australian elapid Acanthophis antarcticus after venom expenditure and feeding as well as during preparation for shedding to establish a comparison of the magnitude of energetic expenditure during venom replenishment and other common physiological processes. We also defined the temporal pattern of metabolic processes during venom replenishment at a higher resolution than has previously been attempted in snakes. Our results suggest that total costs of venom replenishment are relatively small when compared to costs of digestion and shedding. We conclude that, in spite of the manifold factors suggesting a high cost of venom in snakes, its production is less energetically costly than often assumed. Until further research can clarify the reasons for this more caution should therefore be applied when assuming that costs of venom production exert strong selection pressures on the ecology, behavior and evolution of venomous taxa.

Exocytotic dynamics and calcium cooperativity effects in the calyx of Held synapse: a modelling study.

A stochastic computational approach to the study of secretory processes at the calyx of Held synapse is presented in this paper. The calyx of Held is a giant synapse located in the brainstem which is widely used for experimental recording of neurotransmitter release. We focus on the study of the exocytotic dynamics for a pool of readily releasable vesicles using a Monte Carlo simulation scheme that includes models for the P-type calcium channels, the kinetic reactions of endogenous and exogenous (mobile) buffers, the kinetic reactions for the secretory vesicles, as well as the microscopic diffusion of mobile buffers and calcium ions. The simulations are performed in a 3-D orthogonal grid which approximates a cylindrical domain representing an active zone of the presynaptic terminal of the calyx. For this domain, we quantify the release rates related to calcium currents in response to depolarizing voltage pulses. The influence on simulated pulse/action potential depolarization protocols of the kinetic scheme for the calcium sensor of vesicles and the geometry of calcium channels for the kinetic cooperativity for release, is analyzed at a microdomain level. Among other aspects, our results suggest that the spatial organization of Ca2+ channels could have measurable effects in the kinetic cooperativity which could reflect developing changes in the calyx of Held synapse.

Assessment of cyanobacteria toxins in freshwater fish: a case study of Murchison Bay (Lake Victoria) and Lake Mburo, Uganda.

There is little information on the distribution of microcystins (MCs) in Oreochromis niloticus (ON) and Lates niloticus (LN) obtained from L. Mburo and Murchison Bay of L. Victoria. These fishes are harvested and sold both for local human consumption and for export. The presence of MC-RR, MC-LR and MC-YR in different organs (gut, muscle and liver) was determined using Liquid Chromatography coupled with a Mass Spectrometry Detector (LC/MS/MS). The total MCs in ON gut, muscle and liver were 1312.08, 208.65 and 73.10 ng g(-1) from L. Mburo and 1479.24, 9.65 and 48.07 ng g(-1) from Murchison Bay, respectively, while for LN from Murchison Bay they were 27.78, 1.86 and 3.74 ng g(-1). Generally, in both lakes, MC-RR was the most dominant followed by MC-YR and MC-LR, respectively. Gut showed a high MC content, followed by liver and muscle, in that order. The presence of MCs in muscle indicated possible fish contamination, which implied that it was possible to transfer the toxins to humans who are at the end of the food chain. This poses a risk to them since the MCs are heat stable. The local authorities should warn the public of the risk of possible poisoning by eating the contaminated fish.

Quantitative assessment of AMPA receptor mRNA in human spinal motor neurons isolated by laser capture microdissection.

Disturbance of glutamate neurotransmission may contribute to the motor neuron injury seen in amyotrophic lateral sclerosis. Previous studies have suggested that human spinal motor neurons express a specific profile of the AMPA subtype of glutamate receptor with low mRNA expression for the GluR2 AMPA receptor subunit but other studies have contested this finding. The present study uses laser capture microdissection to isolate specifically identified neurons coupled with quantitative RT-PCR to demonstrate that the level of expression of the GluR2 subunit is lower in spinal motor neurons than in dorsal horn neurons from the same spinal cord region. Thus, it is likely that human spinal motor neurons express a proportion of Ca2+-permeable AMPA receptors which may contribute to the selective vulnerability of these cells in amyotrophic lateral sclerosis.