A transient calcium increase triggers nuclear envelope breakdown (mitosis entry) in sea urchin embryos. Cdk1/cyclin B kinase activation is also known to be required for mitosis entry. More recently, MAP kinase activity has also been shown to increase during mitosis. In sea urchin embryos, both kinases show a similar activation profile, peaking at the time of mitosis entry. We tested whether the activity of both kinases is required for mitosis entry and whether either kinase controls mitotic calcium signals. We found that reducing the activity of either mitotic kinase prevents nuclear envelope breakdown, despite the presence of a calcium transient, when cdk1/cyclin B kinase activity is alone inhibited. When MAP kinase activity alone was inhibited, the calcium signal was absent, suggesting that MAP kinase activity is required to generate the calcium transient that triggers nuclear envelope breakdown. However, increasing intracellular free calcium by microinjection of calcium buffers or InsP 3 while MAP kinase was inhibited did not itself induce nuclear envelope breakdown, indicating that additional MAP kinase-regulated events are necessary. After MAP kinase inhibition early in the cell cycle, the early events of the cell cycle (pronuclear migration/fusion and DNA synthesis) were unaffected, but chromosome condensation and spindle assembly are prevented. These data indicate that in sea urchin embryos, MAP kinase activity is part of a signaling complex alongside two components previously shown to be essential for entry into mitosis: the calcium transient and the increase in cdk1/cyclinB kinase activity.

Extracellular recording techniques have been used in the guinea pig hippocampal slice preparation to investigate the electrophysiological actions of the organophosphate (OP) anticholinesterase soman. When applied at a concentration of 100 nM, soman induced epileptiform activity in the CA1 region in approximately 75% of slices. This effect was mimicked by the anticholinesterases paraoxon (1 and 3 M), physostigmine (30 M), and neostigmine (30 M), thus providing indirect evidence that the epileptiform response was mediated by elevated acetylcholine levels. Soman-induced bursting was inhibited by the muscarinic receptor antagonists atropine (concentrations tested, 0

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The enzyme atropinesterase (EC 3.1.1.10) causes the rapid hydrolysis of tropane alkaloids such as atropine and scopolamine. This enzyme is known to occur in a certain proportion of rabbits and some plants, although its presence in other animal species remains controversial. The potential presence in some animals but not others of an enzyme which can rapidly hydrolyse compounds such as atropine is a potential unwanted experimental variable in many experiments. Because of the uncertainty surrounding the enzyme and the paucity of data, it was decided to examine whether we could detect and characterise atropinesterase activity in the plasma of dogs, goats, guinea-pigs, humans, pigs, rabbits and rhesus by separating and quantitating the substrate (atropine) and one of the products (tropic acid) by high performance liquid chromatography (HPLC). It was found that plasma from some but not all rabbits possessed a capacity to breakdown large quantities of atropine; an effect that was apparently enantiomer-specific. Plasma from other rabbits, and plasma from all other species investigated, proved capable of hydrolysing atropine at a rate exceeding that of non-specific breakdown. It remains to be determined whether this effect is due to a low expression of atropinesterase or an alternative hydrolysing enzyme.

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