brain plasticity: changing synapse activity (Introduction)

by David Turell , Friday, December 04, 2015, 15:30 (3068 days ago) @ David Turell
edited by David Turell, Friday, December 04, 2015, 15:48

Brain plasticity depends on new neurons, new axon branch connections and synapse strength. This study in fruit flies shows synapse changes while learning:-http://www.sciencedaily.com/releases/2015/12/151202132749.htm-"The researchers exposed fruit flies to a specific test odor and a very short time later subjected them to an artificial aversive cue. To do so they fired tiny beams of laser light at dopamine-releasing neurons in the mushroom body that were genetically engineered to become active in response to the light. Just like our own neurons, dopamine-releasing neurons in the fly are involved in reward and punishment." Presenting the smell of cherries, for example, which is normally an attractive odor to flies, while at the same time stimulating a particular dopamine neuron, trains the fly to avoid cherry odor," Turner explains.-"In addition to the dopamine neurons, the team identified neurons that represented the test odor and neurons that represented the flies' behavioral response to that odor. These neurons are connected to each other, while the dopamine neurons, which represent the punishment signal, modulate that connection. The team then made recordings of the neurons representing the behavior. This enabled them to discover any changes to the synaptic inputs those neurons received from the odor-representing neurons before and after learning.-"Strikingly, the team found a dramatic reduction in the synaptic inputs upon subsequent presentations of the test odor, but not control odors. This drop reflected the decrease in the attractiveness of the odor that resulted from the learning. "The average drop in synaptic strength was around 80 percent -- that's huge," says Turner."-Comment: With several ways to change structure and function, the brain is very pliable in response to what the organism is doing.-In a related study how to follow synapse function is described:-http://medicalxpress.com/news/2015-12-neuroscientists-mind.html-"By reading fluorescent signals, the researchers could tell if a fly had been in either heat or cold for 10 minutes an entire hour after the sensory event had happened, for example. They also could see that exposure to the scent of a banana activated neural connections in the olfactory system that were different from those activated when the fly smelled jasmine.-***-"Different synapses are active during different behaviors, and we can see that in the same animal with our three distinct labels," said Gallio, the paper's corresponding author.-"The fluorescent green, yellow and blue signals enabled the researchers to label different synapses activated by the sensory experience in different colors in the same animal. The fluorescent signals persisted and could later be viewed under a relatively simple microscope.-"The researchers studied the fruit fly Drosophila melanogaster, a model animal for learning about the brain and its communication channels. They tested their newly engineered fluorescent molecules by applying them to the neural connections of the most prominent sensory systems in the fly: its sense of smell, sophisticated visual system and highly tuned thermosensory system.-"They exposed the animals to different sensory experiences, such as heat or light exposure and smelling bananas or jasmine, to see what was happening in the brain during the experience.-"To create the labels, the scientists split a fluorescent molecule in half, one half for the talking neuron and one half for the listening neuron. If those neurons talked to each other when a fly was exposed to the banana smell or heat, the two halves came together and lit up. This only happened at the site of active synaptic transmission.-"'Our results show we can detect a specific pattern of activity between neurons in the brain, recording instantaneous exchanges between them as persistent signals that can later be visualized under a microscope," Gallio said."-Comment: These synaptic changes require changes in production of acetylcholine and dopamine by a series of molecular action triggers.