Author: Julie Pryor

In the Chinese calendar, 2013 is the Year of the Snake, and to celebrate we’ve compiled a list of interesting facts about how snakes have contributed to brain research. [Click for Chinese version of graphic.]

Snake venom

Snake venom has been a rich source of reagents for neuroscience research. Venom from the many-banded krait, a species found in Taiwan and Southern China, led to the identification of the first neurotransmitter receptor. In 1963 Chang and Lee at the National Taiwan University isolated a toxin, known as alpha-bungarotoxin, that binds strongly to the receptor for acetylcholine, the main neurotransmitter at neuromuscular synapses. This toxin, used by snakes to paralyze their victims’ muscles, was used by researchers to purify the acetylcholine receptor, and is still widely used today to study the biology of synapses.

Snake venom played central role in the identification of nerve growth factor (NGF) by Stanley Cohen and Rita Levi-Montalcini, who shared the 1986 Nobel Prize for their work. They discovered that the venom of the moccasin snake (a species of pit viper from the Southeastern US) was a rich source of a factor that could induce outgrowth of fibers from cultured neurons. This enabled them to characterize and eventually purify NGF, the first growth factor to be identified and the prototype for a large family of signaling molecules.

Snake venom has also led to several important advances in pain research, an area of great therapeutic interest. A protein complex isolated from the Texas coral snake has recently been shown to activate acid-sensitive ion channels (ASICs) in pain neurons, which is why bites from these snakes are so painful.  A peptide from the venom of a different species (the black mamba of East Africa, among the most venomous of all snakes) blocks the same channels and shows powerful analgesic effects – suggesting a promising new direction for drug development.

There are hundreds of species of venomous snakes, whose venoms contain a rich diversity of substances that have evolved specifically to interfere with the nervous systems of their victims and predators – a diversity that has only begun to be explored.

Snake evolution and behavior

Several families of snakes, including pit vipers, boas and pythons, can hunt at night using infrared (IR) radiation emitted by their warm-blooded prey. This ability arises from pit organs below the eyes, which allow these snakes to locate IR sources, sometimes with great accuracy. The molecular basis of IR detection was recently identified, and found to be an ion channel of the TRP family that is highly sensitive to warmth. The corresponding channel in other species is not strongly temperature-sensitive and is used mainly to detect chemical irritants (in humans it responds to wasabi and mustard).  During snake evolution the same channel appears to have been co-opted for IR detection on several independent occasions in different snake families.

Another example of the evolutionary flexibility of brain and behavior comes from the tentacled snake of South-East Asia. This species hunts underwater, lying in wait for fish and detecting their location through a combination of vision and vibration. The snake captures a fish by exploiting its startle reflex – by making a feint with its body, the snake induces the fish to make a stereotypical escape response, directly toward the snake’s jaws. The snake can predict the fish’s behavior and makes a lunge to swallow it, all within about 25ms, or 1/40th second [video]. Remarkably a naïve snake, raised in captivity with no prior experience of fish, can do the same. Thus, the snake’s brain has been pre-wired by evolution to perform this behavior without the need for learning.

Snake phobia

Some people have a phobia for snakes, as do some animals, providing a useful model for understanding the neural basis of fear and anxiety. In one study, researchers even scanned volunteer subjects as they confronted a live snake inside the MRI scanner. These phobic responses are at least partly innate; monkeys, for example, will respond fearfully to a snake-like object even if they have never encountered one before. This raises interesting questions about how our brains are pre-wired to recognize specific stimuli, and also provides an opportunity to study how innate and leaned responses interact to control behavior.

These days snakes have more to fear from humans than vice versa, and many species around the world are now endangered. Awareness of their biology and potential for neuroscience discovery may strengthen efforts to conserve these remarkable creatures.

We are pleased to announce the appointment of Gloria Choi as a new McGovern Investigator, starting in summer 2013. She will also be an assistant professor in the MIT Department of Brain and Cognitive Sciences. Choi’s research addresses the mechanisms by which the brain learns to recognize olfactory stimuli and to associate them with appropriate behavioral responses.

Much recent work has been devoted to the question of how the binding of odorant molecules to their receptors in the olfactory epithelium leads to the perception of odors. In other sensory modalities such as vision, touch or hearing, the primary sensory cortex shows a topographical organization in which stimulus features are systematically mapped on the cortical surface. In the piriform cortex, however, no such order has been found; while individual inputs to the cortex are tuned to specific odorants, their projections within the piriform cortex appears topographically random. Consistent with this, olfactory stimuli typically activate sparse ensembles of piriform cells, with no obvious spatial pattern. Yet somehow the brain must learn to recognize these apparently arbitrary spatial patterns of activity and to endow them with behavioral significance.

Choi uses the power of rodent molecular genetics to study how this happens. Using the optogenetic molecule Channelrhodopsin2, she has been able to activate sparse arbitrarily-chosen populations of neurons within the piriform cortex using direct light stimulation. She has shown that animals can learn to recognize and distinguish these artificial “smell-like” cues, which can be flexibly associated with either rewarding or aversive stimuli to drive the appropriate behavioral responses.

In her own lab at MIT, Choi plans to dissect the brain circuits underlying this behavior, to understand how sensory representations in piriform cortex can drive downstream targets to generate learned behavioral responses. She also plans to extend her approach to study social behavior, which in rodents is strongly affected by olfactory cues. One important modulator of social behavior is the hormone oxytocin, and Choi plans to study how oxytocin may control the mechanisms by which animals learn to attribute social significance to olfactory stimuli.

Olfactory learning also provides an opportunity to study more general questions about how the brain learns to categorize sensory stimuli and to associate them with complex rule-based behaviors. Such cognitive processes have been linked to the prefrontal cortex in humans and other species, and olfactory behavior in mice may offer a new and genetically tractable system for exploring these issues.

Choi received her bachelor’s degree from University of California, Berkeley, and her Ph.D. from Caltech, where she studied with David Anderson. She is currently a postdoctoral research scientist in the laboratory of Richard Axel at Columbia University.

Neurons in the brain of a transgenic mouse engineered to express a protein that emits light when neurons become active. Image: Qian Chen, Guoping Feng

Satra Ghosh is a research scientist in John Gabrieli’s lab at the McGovern Institute for Brain Research at MIT. In this video, Satra talks about his research on mild traumatic brain injury in U.S. soldiers.

[Stock footage/music: U.S. Department of Defense, Satra Ghosh, shockwave-sound.com]

Warmest wishes this holiday season from your friends at the McGovern Institute for Brain Research at MIT.

Our researchers and staff are an amazing bunch of individuals. To thank them for their efforts this past year, we gave them “magic mugs” — they’re quite a hit.

Feng Zhang, a member of the McGovern Institute for Brain Research at MIT, is designing new molecular tools for manipulating the living brain. As a student, he played a major role in the development of optogenetics, a technology by which the brain’s electrical activity can be controlled with light-sensitive proteins. He is now working to extend this molecular engineering approach to other aspects of brain function such as gene expression, and to develop new approaches to understanding and eventually treating brain diseases.

Warmest wishes this holiday season from your friends at the McGovern Institute for Brain Research at MIT.

John Gabrieli, a member of the McGovern Institute for Brain Research, uses brain imaging and behavioral tests to understand the organization of memory, thought, and emotion in the human brain. [Stock footage: pond5, Elekta Instrument AB]

Read more about John Gabrieli here.

 

Guoping Feng, an investigator at the McGovern Institute for Brain Research at MIT, studies the development and function of synapses and their disruption in brain disorders.  He uses molecular genetics combined with behavioral and electrophysiological methods to study the molecular components of the synapse and to understand how disruptions in these components can lead to diseases like autism  and OCD. [“The Synapse Revealed” illustrated by Graham Johnson of grahamj.com for HHMI ©2004.]

Read more about Guoping Feng here.