External Signal Response - Cori Bargmann (Rockefeller/HHMI)

TL;DR

G-protein-coupled receptors link genes to behavior via neuronal signaling.

Transcript

so I will talk about three different topics today using examples from animals to illustrate how this framework for Behavior can be used to understand how genes affect neurons which affect brains which affect Behavior and the three examples will be one example on the left side moving from Sensation to action in the response the innate responses to e... Read More

Key Insights

• G-protein-coupled receptors are crucial for translating external stimuli into neuronal signals, affecting behavior through their presence on sensory neurons.
• These receptors detect environmental cues like odors, tastes, and light, initiating behavioral responses such as attraction or repulsion.
• Internal signals, like adrenaline and dopamine, are also mediated by G-protein-coupled receptors, influencing physiological and behavioral changes.
• The nematode C. elegans serves as a model organism for studying innate behaviors through genetic manipulation of receptors like odor 10.
• Experiments show that the location of receptor expression in neurons determines whether a response is attractive or repulsive.
• The principles of receptor-mediated behavior in simple organisms like worms extend to more complex systems, including mammals.
• Mammalian taste responses are hardwired, with specific neurons encoding responses to sweet and bitter compounds via G-protein-coupled receptors.
• The concept of innate behavioral pathways was historically acknowledged, illustrating the deep-rooted nature of these mechanisms in biology.

Questions & Answers

Q: How do G-protein-coupled receptors influence behavior?

G-protein-coupled receptors influence behavior by acting as molecular sensors on the surface of neurons. They detect external stimuli like odors and tastes, as well as internal signals such as hormones. Upon activation, they initiate intracellular signaling cascades, leading to changes in neuronal activity and, consequently, behavioral responses. This receptor-mediated signaling is crucial for translating sensory inputs into appropriate actions, such as attraction, repulsion, or physiological adjustments.

Q: What role do G-protein-coupled receptors play in olfaction?

In olfaction, G-protein-coupled receptors are essential for detecting odor molecules in the environment. They are expressed on olfactory neurons in the nasal epithelium, where they bind specific odorants. This binding triggers signal transduction pathways, resulting in neuronal activation and the perception of smell. Different receptors are tuned to different odorants, allowing organisms to distinguish a wide range of smells, which can drive behaviors like food-seeking or avoiding harmful substances.

Q: How do experiments with C. elegans illustrate the function of G-protein-coupled receptors?

Experiments with C. elegans illustrate the function of G-protein-coupled receptors by demonstrating how these receptors mediate innate behavioral responses to odors. By manipulating the expression of the odor 10 receptor, researchers showed that its presence in specific neurons dictates whether the worm is attracted to or repelled by certain smells. These findings underscore the importance of receptor location in neuronal circuits for determining behavioral outcomes, providing insights into the genetic basis of behavior.

Q: What is the significance of receptor location in neurons for behavior?

The location of receptors in neurons is significant for behavior because it determines the nature of the response to a stimulus. For example, in C. elegans, expressing the odor 10 receptor in neurons associated with attraction results in the worm approaching the odor. Conversely, expressing the same receptor in neurons linked to avoidance leads to repulsion. This demonstrates that the neuronal context in which a receptor is expressed is crucial for the behavioral output, highlighting the intricate wiring of neural circuits.

Q: How do mammalian taste responses relate to G-protein-coupled receptors?

Mammalian taste responses are closely linked to G-protein-coupled receptors, which are responsible for detecting sweet and bitter compounds in food. These receptors are expressed on specific taste cells in the tongue, with different types of cells dedicated to attractive or aversive tastes. Experiments have shown that the expression of engineered receptors on these cells can alter taste perception, reinforcing the idea that taste preferences are hardwired through specific receptor-mediated pathways.

Q: What experiment demonstrated the hardwiring of taste preferences in mammals?

An experiment demonstrating the hardwiring of taste preferences in mammals involved expressing an engineered receptor, the racol receptor, on either sweet-sensing or bitter-sensing taste cells in mice. Mice with the receptor on bitter cells rejected the racol ligand, perceiving it as bitter, while those with the receptor on sweet cells consumed it, perceiving it as sweet. This experiment showed that the neural circuitry of taste is preconfigured to drive innate acceptance or rejection of certain tastes based on receptor expression.

Q: How do G-protein-coupled receptors mediate internal signals?

G-protein-coupled receptors mediate internal signals by detecting hormones and neurotransmitters within the body. For example, receptors for adrenaline trigger responses such as increased heart rate and sweating, while dopamine receptors are involved in reward signaling and addiction. These receptors translate chemical signals into cellular responses, affecting various physiological and behavioral processes. This signaling mechanism is crucial for maintaining homeostasis and adapting to internal changes.

Q: What historical perspective supports the concept of innate behavioral pathways?

The concept of innate behavioral pathways is historically supported by the ideas of René Descartes, who illustrated reflexive responses to stimuli as automatic and not requiring conscious thought. His depiction of a person withdrawing their foot from a fire due to a nerve signal reflects the modern understanding of hardwired neural circuits that drive instinctive behaviors. This perspective highlights the deep-rooted nature of these pathways in biological systems, emphasizing their evolutionary significance.

Summary & Key Takeaways

• Dr. Cori Bargmann's talk emphasizes the role of G-protein-coupled receptors in connecting genes to behavior through neuronal pathways. These receptors are pivotal in detecting both environmental and internal stimuli, leading to physiological and behavioral changes. The discussion includes examples from both simple organisms like nematodes and complex mammals.

• The talk explores how specific genes, particularly those encoding G-protein-coupled receptors, influence behavior by mediating sensory inputs. Through experiments on C. elegans, it is demonstrated that the expression of these receptors in different neurons can transform behavioral responses from attraction to repulsion, highlighting the importance of neuronal context.

• In mammals, similar principles apply where taste preferences for sweet and bitter are hardwired through specific neural pathways. These insights underscore the evolutionary conservation of receptor-mediated behaviors and their foundational role in an organism's interaction with its environment from birth.