5-1-Genes-To-Behavior

Chapter 10: Pathways between Genes and Behavior

From Genes to Behavior

  • External Cues:

    • Environmental triggers that influence behavior.

  • Internal States:

    • Conditions affecting behavioral responses, such as hunger.

  • Neural Networks:

    • Connections among neurons responsible for processing information.

  • Central Decision Making Process:

    • Example: how sleepiness may modulate responses to cues.

  • Epigenetic Control of Gene Expression:

    • The regulatory processes that influence how genes are expressed based on environmental stimuli.

Functional Genomics

  1. Levels of Analysis:

    • Behavioral Level: Observation of individual behaviors.

    • Molecular Level: Study of gene expression and molecular functions.

    • Cellular Level: Examination of neuronal activity and cell function.

    • Systems Level: Interaction of neural circuits that comprise the brain.

    • Individual Behavior: Interaction of genetic and environmental factors affecting a single organism.

    • Social Behavior: Understanding of group dynamics and social networks, linking behavior to evolutionary and societal contexts.

Behavior Modifying Drugs

  • Action of Drugs:

    • Certain drugs can mimic neurotransmitters, either enhancing or inhibiting pathways in the brain.

  • Selected Recreational Drugs:

    • Cocaine, Morphine, and Heroin: Act primarily on endorphin pathways in the hypothalamus.

    • Mescaline and Nicotine: Mimic specific neurotransmitter actions.

    • Amphetamines: Influence dopamine and norepinephrine pathways affecting the reward system and arousal.

  • Brain Chemical Equivalents:

    • Endorphins: Associated with pain relief and stress management.

    • Dopamine: Responsible for motivation and reward pathways.

    • Norepinephrine: Mediates the fight or flight response.

Neuronal Communication

  • Post-Synaptic Action:

    • A receiving neuron determines whether to excite the next neuron based on the signal received.

  • Brain Cells:

    • Neurons: Responsible for transmitting signals.

    • Glial Cells: Support cells constituting 50% of brain mass; their quantity correlates with overall brain size.

Behavioral Genetics Overview

  • Mechanisms of Action:

    • Example: MAOA enzyme's role in neurotransmitter degradation influencing dendrites, vesicle encapsulation, breakdown, release, and receptor activity.

Cell Signaling

  • Three Stages of Cell Signaling:

    1. Ligand-Gated Channel Receptors: Activate in response to specific ligands/ions.

    2. Tyrosine Kinase Receptors: Involved in signaling pathways leading to transcription changes.

    3. G-Protein Coupled Receptors: Involved in a variety of signaling responses by changing conformation and interacting with proteins.

Nerve Impulse

  • Definition:

    • An electrical current leading to signal transmission.

  • Action Potential Process:

    • Voltage-gated channels open/close in response to electric changes:

    • Net positive charge outside and net negative charge inside during depolarization.

    • Potential restoration occurs after signal transmission.

Chemical Synapses

  1. Depolarization: Initiates neurotransmitter release.

  2. Hyperpolarization: Inhibitory signal processing.

  3. Neurotransmitter Activity: Interactions with post-synaptic receptors, leading to excitatory or inhibitory responses.

Gene-Environment Interactions

  • Discussion on MAOA and the 5-HTTLPR polymorphisms affects phenotypes and neurotransmitter systems in monoaminergic synapses.

Vesicular Monoamine Transporter (VMAT)

  • Components of the synapse include:

    • Pre and postsynaptic players, biosynthesis enzymes, monoamine receptors, and metabolizing enzymes such as monoamine oxidase (MAO).

Monoamine Oxidase A (MAOA)

  • Function:

    • Degrades amine neurotransmitters, including dopamine, norepinephrine, and serotonin.

    • Localized to the outer mitochondrial membrane with multiple isoforms identified.

    • Adjacent to MAOB in genetic mapping.

Effects of Psychostimulants

  • Certain drugs, including:

    • Methylphenidate (Ritalin®)/Cocaine: Increases DA at synapses via blocking DAT (reuptake).

    • Amphetamines/Meth: Alter DA levels by enhancing or diminishing proper signaling; block VMAT and decrease synaptic DA, reverse DAT to release into synapse.

Antidepressants and Serotonergic Pathway

  • Antidepressant Mechanisms:

    • Modulation of serotonergic synapses, increasing serotonin uptake, receptor activation, and blocking MAO activity.

5-HTTLPR Gene

  • Function:

    • Encodes the serotonin re-uptake transporter responsible for serotonin availability.

  • Chromosomal Location:

    • Located on Chromosome 17 and features two prominent alleles: S and L alleles affecting brain function significantly.

Circuit Dynamics

  • Excitatory and Inhibitory Interactions:

    • Feedforward Excitation: Initiated by sensory cues, stimulating neurotransmitter release.

    • Feedforward Inhibition: Modulates the reactive pathways by neurotransmitter binding.

Micro Networks

  • A neuron can engage with up to 10,000 presynaptic neurons, and each neuron can connect with up to 10,000 postsynaptic neurons, allowing complex combinatorial neuronal circuit arrangements.

Key Takeaways

  • Remember:

    • Levels of study in behavioral genetics.

    • Drug mechanisms mimicking neurotransmitter actions.

    • Understanding of action potentials and synaptic structures.

    • Impact of MAO-A variants and serotonin transporter gene variations on synaptic function.