GOLLYGEE! – Page 33 – a science blog

Page 33 of 111

03.27.2013

bees, socialization and electric fields

Here at GOLLYGEE! we’ve been following the news on bees and electric fields.

We learned last month that flowers use electric fields to guide bees their way. Bees pick up a positive charge from the static they encounter while flying through the air. Flowers, like most plants, conduct electricity toward the ground and have a negative charge at their surfaces. When bees encounter a flower, the negatively charged pollen is attracted to their positive charge. And when they leave, other bees can tell the flower was just visited because of the reduced electric field.

Yesterday, Ed Yong at Not Exactly Rocket Science reported that bees also use electric fields to facilitate social interaction:

Greggers created Pavlov’s bees. He exposed them to artificial electric fields that mimicking those found in the hive, before giving them a rewarding sip of nectar. Soon, he found that the field alone was enough to make them extend their tongues in anticipation of a tasty treat, just like Pavlov’s dogs salivating at a the sound of a bell.

Greggers found that the bees detect these fields with their flagella—the very tips of their antennae. Picture a bee, dancing away in a tightly packed hive with many neighbours in close proximity. As it waggles, it also vibrates its wings. As the dancer’s positively-charged wing get closer to a neighbour’s positively-charged antenna, it produces a force that physically repels the antenna. As the dancer’s wing swings back to its original position, the neighbour’s antenna bounces back too. With their electric fields, the bees can move each other’s body parts without ever making contact. (Sure, the beating wing also pushes air past a neighbour’s antenna, but Greggers found that the force produced by the incoming electric field is ten times stronger.)

The bee detects these forces with small touch-sensitive fibres in the joints of their antennae, which send electrical signals towards the insect’s brain. If Greggers immobilised the joints by covering the antennal joints with wax, the bees couldn’t learn to associate electric fields with nectar rewards.

These signals from the fibres are intercepted and processed by a structure called Johnston’s organ within the antennae. By recording the activity of neurons in this organ, Greggers showed that it does indeed fire when an electrically charged object—like a Styrofoam ball—is brought close to the flagellum.

Head over to Not Exactly Rocket Science for more. Or read the research paper here.

03.26.2013

lithium and bipolar

Lithium has been used for over 60 years as a treatment for manic depressive or bipolar disorder. The treatment is one of the most effective for the disorder as well as one of the most inexpensive. Bethany Halford surveys the current research on the drugs mechanism of action in this week’s C&EN:

Lithium has a reputation for being moderately effective at treating or preventing bipolar depression. Scientists know that lithium displaces magnesium ions and inhibits at least 10 cellular targets. They have been able to narrow that range on the basis of what lithium inhibits at therapeutically relevant concentrations, roughly 0.6 to 1 mM.

One putative lithium target researchers have been pursuing for decades is inositol monophosphatase, or IMPase. The enzyme is part of the phosphatidylinositol signaling pathway. It strips the phosphate off of inositol phosphate to produce inositol, a key substance in the biosynthesis of compounds that trigger cellular responses.

There is some evidence that in bipolar patients the phosphatidylinositol signaling pathway becomes hyperactive. Inhibiting IMPase halts the pathway and depletes inositol. Adding credence to this theory, researchers have fingered inositol depletion in the mechanisms of two other bipolar medications—carbamazepine (Tegretol) and divalproex (Depakote), also called valproic acid.

Click the link for much much more.

03.22.2013

a death receptor crystal structure

Illustrations of the binding pockets of 5-HT1B and 5-HT2b Serotonin receptors. Image from Science via C&EN.

Receptors for the neurotransmitter serotonin are popular drug targets. Drugs that target these receptors are used to treat problems like depression and migraine headaches. Serotonin receptors are also the targets of some psychedelic drugs like LSD and mescaline.

There are at least 14 subtypes of serotonin receptors known. Most of the drugs that target one subtype of serotonin receptor will also target the others. This is usually not a problem except in the case of one type called 5-HT2B. This receptor is called the death receptor because activating it can cause heart problems that will lead to death. This receptor is to be avoided.

Chemical & Engineering News brings word of two crystal structures that might help drug developers better avoid activating the 5-HT2B subtype of receptors:

Help will come from new crystal structures of 5-HT_1B and of 5-HT_2B, each bound to the migraine drugs ergotamine and dihydroergotamine (Science,DOI: 10.1126/science.1232807 and DOI: 10.1126/science.1232808). The findings provide a blueprint for designing more selective 5-HT inhibitors.

The team behind the structures includes Raymond C. Stevens, a chemistry and molecular biology professor at Scripps Research Institute, La Jolla, Calif.; Bryan L. Roth, a pharmacology professor at the University of North Carolina; H. Eric Xu, director of the Center for Structural Biology & Drug Discovery at Van Andel Research Institute in Grand Rapids, Mich., and Hualiang Jiang, a professor at the Shanghai Institute of Materia Medica.

This is major news for our field,” adds Kathryn A. Cunningham, a professor in the pharmacology and toxicology department at the University of Texas Medical Branch. “The structures were solved for the receptor-ligand cocrystals, which provides important insights into how the receptors work.”

The importance of selectivity was most infamously illustrated in the 1990s by the obesity treatment Fen-Phen (fenfluramine-phentermine). Both molecules targeted 5-HT receptors, but they weren’t selective enough. Unbeknown to scientists, they also bound to the death receptor, 5-HT2B, triggering sometimes-fatal cardiovascular side-effects. Fen-Phen’s withdrawal from the market was the largest in history and cost its manufacturer, Wyeth, billions of dollars in damages.

Check out the original research here and here.