The effect of water soluble cyanotoxin(s) produced by two species of Anabaena on the release of acetylcholine from the peripheral cholinergic nervous system of the rat airway

Neurotoxic effects evoked by cyanobacterial extracts suggest multiple receptors involved in electrophysiological responses of molluscan (CNS, heart) models

The responses of the snail central neurons (Helix pomatia, Lymnaea stagnalis) and the isolated Helix heart were characterized evoked by cyanobacterial extracts (Cylindrospermopsis raciborskii ACT strains) isolated from Lake Balaton (Hungary). The nicotinergic acetylcholine (ACh) receptors in the CNS (both excitatory and inhibitory) were blocked by the extracts of ACT 9502 and ACT 9505 strains and the anatoxin- a (homoanatoxin-a) producing reference strain of Oscillatoria sp. (PCC 6506), similar to the inhibitory effects of the pure anatoxin-a. The enhancement of the ACh responses by the ACT 9504 extract suggests additional, probably acetylcholine esterase inhibitory mechanisms. On the isolated Helix heart the crude ACT 9505 and PCC 6506 extracts evoked frequency increase and transient twitch contraction, opposite to the ACh evoked heart relaxation. Anatoxin-a similarly contracted the heart but did not increase its contration frequency. These data suggest the involvement of some non-cholinergic mechanisms, acting very likely by direct modulation of the electrical or contractile system of the isolated heart. Diversity of the effects evoked by the cyanobacterial extracts in the CNS and heart suggest pharmacologically different neuroactive components among the secondary metabolites of the cyanobacteria acting on both (anatoxin-a like) cholinergic and (unidentified) non-cholinergic receptors.

Toxin-Producing Anabaena flos-aquae Induces Settling of Chlamydomonas reinhardtii, a Competing Motile Alga

Toxin production is an adaptation that allows cyanobacteria in resource-limiting environments to ameliorate the effects of herbivory and competition with other phototrophs. We demonstrate that the cyanobacterial toxins anatoxin-a and microcystin-LR paralyze the motile green alga Chlamydomonas reinhardtii. In addition, both purified toxins and cyanobacterial extracellular products containing these toxins cause the alga to settle faster than in nontoxic media. In microcosm experiments, the presence of either the cyanobacterium or its extracellular products induce settling in the alga, similar to the response observed with the addition of both anatoxin-a and microcystin-LR. The cyanobacterial production of paralyzing toxins represents a novel mechanism for phytoplankton settling. This prokaryotic/eukaryotic chemical interaction may create a competitor-free zone for cyanobacteria in lake environments, predicating optimal conditions for a toxic cyanobacterial bloom.