Feature: Investigating Predatory Behavior Using Optogenetics
The latest research related to behavioral optogenetics is a study at Yale University that investigates predatory hunting behavior in mice. The paper, published in the January 12 issue of Cell, describes how the researchers isolated the brain circuitry that coordinates hunting. One set of neurons in the amygdala, the brain's center of emotion and motivation, cues the animal to pursue prey. Another set signals the animal to use its jaw and neck muscles to bite and kill.
The researchers used a blue DPSS 473 nm laser to selectively excite the neurons. They observed that when the laser was off, the mice behaved normally. But when the laser was turned on, they pursued and bit anything in their path - even bottle caps and wood sticks.
The animals did not, however, attack other mice in the cage. Hunger also affected predatory behavior. Hungry mice more aggressively pursued prey during light stimulation than mice that were not hungry. "The system is not just generalized aggression. It seems to be related to the animal's interest in obtaining food," says lead investigator Ivan de Araujo, Associate Professor of Psychiatry at the Yale University School of Medicine and an Associate Fellow at the John B. Pierce Laboratory.
De Araujo's interest in more natural behaviors like feeding pointed him to a study that had mapped brain areas associated with hunting and eating. Many areas were listed, but one responded almost exclusively to hunting and not to eating. That region, the central nucleus of the amygdala, also had projections that were linked to areas that control hunting muscles, such as the jaw and neck. "This area was perfectly compatible with an activation system that drives the motor behavior associated with hunting," he says.
During the investigation, they found that one set of neurons controlled pursuit, and another controlled the kill. The researchers also specifically lesioned each type of neuron. They found that, if they lesioned the neurons associated with biting and killing, the animals would pursue the prey but could not kill. The biting force of the jaw was decreased by 50 percent. "They fail to deliver the killing bite," says de Araujo.
The team is now exploring the sensory input into the amygdala to determine what triggers predatory behaviors and investigating how the two modules--one controlling pursuit and the other controlling the kill--are coordinated.
This work was supported by the National Institutes of Health, the National Natural Science Foundation of China, and the Brazilian government. The full paper may be accessed at: Science Direct
1. Quirks & Quarks, CBC Radio - Saturday, Jan 21, 2017 Laser Mice
Laserglow in Research: Photothermal Therapy of Pancreatic Cancer
A group of researchers associated with the University Health Network (UHN) Canada recently published a paper on the enhanced Photothermal therapy (PTT) of pancreatic cancer using lipid-based nanoparticles. Laserglow's 671 nm LabSpec DPSS laser was used as the light source in the setup.
Localized targeting of tumors is a major problem in the treatment of pancreatic cancer as localized surgery is only possible in a few patients, and radiotherapy doesn't target small areas. PTT for ablation of pancreatic tumors in combination with laser light can result in more efficient conversion of light energy to heat, and confinement of thermal destruction to the tumor, thereby sparing adjacent organs from accidental heat damage.
Porphyrins - a distinct group of organic compounds with four modified sub-units - have been previously employed as photosensitizers for PTT. However their incorporation into 'porphysomes' - lipid-based nanoparticles each containing about 80000 porphyrins - has two advantages. One, it imparts the densely-packed particles with enhanced photonic properties for imaging and phototherapy, and two, the enhanced permeability of porphysomes allows their optimal delivery to the tumor region.
For this study, a patient derived orthotopic pancreas xenograft model was used to evaluate the feasibility of porphysome-enhanced PTT for pancreatic cancer. Bio-distribution and tumor accumulation were evaluated using fluorescence intensity measurements from homogenized tissues and imaging of excised organs. Tumor surface temperature was recorded using IR optical imaging during light irradiation to monitor treatment progress.
For laser irradiation, the emission from a free-space 671 nm laser was adjusted to 750 mW power using a variable ND filter and ~0.7 cm beam diameter spot size at the treatment plane. Histological analyses were conducted to determine the extent of PTT thermal damage.
The researcher's findings show that this treatment method holds promise for further pancreatic cancer studies. They believe that their research may provide insight into the influence of heat-sink effect on thermal therapy dosimetry for well-perfused pancreatic tumors. For the full paper, go to: SPIE Digital Library Full Paper
News: Physicists unveil new form of matter - time crystals
Normal crystals, likes diamond, are an atomic lattice that repeats in space, but physicists recently suggested making materials that repeat in time. Last year, UC Berkeley's Norman Yao sketched out the phases surrounding a time crystal and what to measure in order to confirm that this new material is actually a stable phase of matter. This prompted two teams to build a time crystal, the first examples of a non-equilibrium form of matter.
"Time crystals repeat in time because they are kicked periodically, sort of like tapping Jell-O repeatedly to get it to jiggle," Yao said. The big breakthrough, he argues, is less that these particular crystals repeat in time than that they are the first of a large class of new materials that are intrinsically out of equilibrium, unable to settle down to the motionless equilibrium of, for example, a diamond or ruby.
In a paper published online last week in the journal Physical Review Letters, Yao describes exactly how to make and measure the properties of such a crystal, and even predicts what the various phases surrounding the time crystal should be - similar to the liquid and gas phases of ice. Following this process, 2 teams reported their success at creating the first ever, stable time crystals using two totally different processes.
The time crystal created by Chris Monroe and his colleagues at the University of Maryland employs a line of 10 ytterbium ions whose electron spins interact, similar to the qubit systems being tested as quantum computers. To keep the ions out of equilibrium, the researchers alternately hit them with one laser to create an effective magnetic field and a second laser to partially flip the spins of the atoms, repeating the sequence many times. Because the spins interacted, the atoms settled into a stable, repetitive pattern of spin flipping that defines a crystal. A time crystal breaks time symmetry. In this particular case, the magnetic field and laser periodically driving the ytterbium atoms produce a repetition in the system at twice the period of the drivers, something that would not occur in a normal system. The Harvard team, led by Mikhail Lukin, set up its time crystal using densely packed nitrogen vacancy centers in diamonds.
For a full explanation as well as a discussion of the findings and their impact, go to:
Phys.org full article