Scientists at Haifa’s Technion-Israel Institute for Technology have developed for the first time three-dimensional cell networks that can simulate complex aspects of brain activity. These, say the researchers, could provide a better understanding of the physiology of the central nervous system. Called Optonet, the cultures could enable a better understanding of complex activity within neural networks.
Neural cells grown on laboratory plates (two-dimensional neural cultures) constitute a convenient model for many studies in neuroscience and medicine. Their main advantage is the relative simplicity with which they can be used to examine physiological changes in neural cells’ activity patterns caused by changes in the environment. However, the shortcomings of these simple 2D cultures is that they contain only a single layer of cells and do not exhibit the complex three-dimensional network connectivity found in real brains.
Previous attempts to develop 3D models for studying the central nervous system have met with limited success, mainly due to the high complexity of the task of developing a 3D culture capable of simulating brain tissue as well as challenges connected to developing methods for observing network activity in 3D. Technion biomedical engineers led by Prof. Shy Shoham recently reported their discovery in Nature Communications, whose editors commented that 3D neural networks represent a “promising model of complex neural tissue that could lead to a better understanding of the structure and function of the brain. The Technion researchers also present an advanced method for viewing the neural activity of the engineered culture using a fast microscopy system they developed.”
The Israeli team said they grew the advanced culture in a clear gel that supports cellular growth and allows the cells to bind and form neural networks.
“By optimizing the culturing conditions we achieved cellular density and composition similar to those found in the human brain and were able to show the formation of connections between cells and of networks that maintain neural activity. To enable the study of network activity in 3D, optical tools were used: nerve cells in the cultures were genetically altered making it possible to view ongoing network activity through a fluorescence microscope.
RODENTS AFFECTED BY SWEATY MEN Amazingly, results of rodent studies may be skewed if conducted by men as opposed to women, because the former exude pheremones that cause mice and rats undue stress. An international team of pain researchers led by scientists at Montreal’s McGill University discovered that the gender of the experimenters has a big impact on the stress levels of rodents, which are widely used in preclinical studies. Scientists’ inability to replicate research findings using mice and rats has contributed to mounting concern over the reliability of such studies.
In research published online in Nature Methods, the scientists report that the presence of male experimenters produced a stress response in mice and rats equivalent to that caused by restraining the rodents for 15 minutes in a tube or forcing them to swim for three minutes. This stress-induced reaction made mice and rats of both sexes less sensitive to pain. Female experimenters produced no such effects.
“Scientists whisper to each other at conferences that their rodent research subjects appear to be aware of their presence and that this might affect the results of experiments, but this has never been directly demonstrated until now,” says Jeffrey Mogil, a psychology professor at McGill and senior author of the paper.
The research team, which included pain experts from Pennsylvania’s Haverford College and the Karolinska Institute in Sweden and a chemosensory expert from Université de Montreal, found that the effect of male experimenters on the rodents’ stress levels was due to smell. This was shown by placing cotton T-shirts, worn the previous night by male or female experimenters, alongside the mice; the effects were identical to those caused by the presence of the experimenters themselves.
Further experiments proved that the effects were caused by chemosignals, or pheromones, that men secrete from the armpit at higher concentrations than women do. These chemosignals signal to rodents the presence of nearby male animals. (All mammals share the same chemosignals.) These effects are not limited to pain. The researchers found that other behavioral assays sensitive to stress were affected by male but not female experimenters or T-shirts.
“Our findings suggest that one major reason for lack of replication of animal studies is the gender of the experimenter – a factor that’s not currently stated in the methods sections of published papers,” says Robert Sorge, a psychology professor at the University of Alabama, Birmingham.
The good news, Mogil says, is that “the problem is easily solved by simple changes to experimental procedures. For example, since the effect of males’ presence diminishes over time, the male experimenter can stay in the room with the animals before starting testing. At the very least, published papers should state the gender of the experimenter who performed the behavioral testing.”