Detailed Notes on Neuropsychopharmacology of Drug Addiction – Part 2

Neuropsychopharmacology of Drug Addiction – Part 2

Overview

  • This lecture focuses on the neuropsychopharmacology of drug addiction.
Stained Neurons and Visualization
  • Introduction to stained neurons: Used to visualize projections in the brain.
    • Features visible include neuron cell body and axons.
    • Importance of visuals in understanding neural structures.

Resources and Reminders

  • Student Wellness Center: Available for assistance with alcohol, tobacco, or other drugs.
  • Project One: Create a piece of art reflecting your perception of addiction (due date: January 28th, 11:59 PM EST).
  • Reading Expectation: Completing assigned readings and watching videos is essential for understanding upcoming quizzes and exams.

Recap of Previous Lecture

  • Discussed the basic structure and function of neurons.
    • Neurons convert chemical signals to electrical signals.
    • Neurotransmitter release occurs at axon terminals triggered by electrical impulses.
  • Key neurotransmitters discussed:
    • Dopamine
    • Glutamate
    • Gamma-Aminobutyric Acid (GABA)
  • Areas of focus for addiction and reward include:
    • Ventral tegmental area
    • Nucleus accumbens
    • Prefrontal cortex
    • Striatum
  • Importance of understanding neuronal communication for substance use disorder.

Neurotransmitter Functions

  • Neurotransmitter as Agonists:
    • Neurotransmitters bind to receptors, causing effects (depolarization/hyperpolarization).
    • Antagonists: Bind to receptors but do not induce a conformational change, preventing signaling.
    • Higher concentrations of agonists may be needed to overcome antagonists.
  • Drugs function similarly to neurotransmitters as agonists influencing signal transduction.
Electrical Signaling in Neurons
  • Sequence of signaling initiated by neurotransmitters leading to neurotransmitter release in the synaptic cleft.
  • Overview of neurotransmitter degradation and recycling promoting neurotransmission adequacy:
    • Degradation and metabolism decrease neurotransmitter concentration.
Interaction of Drugs and Electrical Pulses
  • Drugs can either increase or decrease neuronal electrical pulses altering how signals are relayed.
  • Importance of understanding how signals are converted from chemical to electrical in the presence of drugs.

Mechanisms of Action of Neurotransmitters

  • Dendritic Trees: Key function in neurotransmitter signaling; rich in receptors for chemical signals.
  • Depolarization and Hyperpolarization:
    • Depolarization: Involves sodium channels opening when glutamate binds, facilitating an action potential.
    • Hyperpolarization: GABA opens chloride channels, making it harder for neurons to fire an action potential,
  • Axon Hillock: Site where signals summate to determine if an action potential occurs based on overall input from excitatory and inhibitory signals.
  • Action Potential: Waves of depolarization propagating down the axon, allowing neurotransmitter release.

Distinction of Glutamate and GABA Functions

  • Glutamate: Main excitatory neurotransmitter, induces depolarization and action potentials.
  • GABA: Main inhibitory neurotransmitter, causes hyperpolarization, reducing firing rates.

Neurotransmitter Receptors

  • AMPA Receptors for Glutamate:
    • Binding causes a conformational change, allowing ion flow (specifically sodium).
  • Importance of glutamate: Regulates learning and memory through synaptic plasticity, including Long-Term Potentiation (LTP).

Role of Glutamate in Addiction

  • Glutamate's involvement in addiction through:
    • Modulation of excitability of neural circuits.
    • Influence on memory and behavioral responses.

Neuroplasticity and Addiction

  • Neuroplasticity refers to the brain's ability to adapt to environmental changes; beneficial in learning but potentially harmful in substance use disorders.
  • Reward Pathways and Dopaminergic Neurons:
    • Stimulation of reward areas (e.g., nucleus accumbens) affects behavioral responses.

Structural Changes in Addiction

  • Changes in neuron structure (e.g., smaller dendrites) noted in individuals with substance use disorder reduce reward experiences.
  • In contrast, increased branching noted in the nucleus accumbens correlates with addiction behaviors.

Brain Areas and Addiction System

  • Ventral Tegmental Area: Origin of dopaminergic signaling to the prefrontal cortex and nucleus accumbens.
  • Amygdala's Role: Mediates stress and anxiety, triggering withdrawal symptoms in absence of drugs.
The Addiction Cycle
  1. Binge and Intoxication Stage: Characterized by substance use and resulting pleasure/reward.
    • Reward is linked to dopamine and opioid systems in the nucleus accumbens.
  2. Withdrawal Stage: Occurs during absence of substances and features negative emotional states.
  3. Preoccupation and Anticipation Stage: Urges to seek substances following periods of abstinence, driven by environmental cues.

Cue and Trigger Influence

  • Recognition of cues, previous substance-associated contexts can trigger cravings, reinforcing the addiction cycle.
  • Incentive Salience: A classification for cues that recall the reward associated with drug use leading to seeking behavior.

Conclusion of Addiction Mechanisms

  • Role of the Prefrontal Cortex:
    • Involved in executive function necessitating control over substance-seeking behavior.
    • Impairment in this area leads to challenges in decision-making and the potential for substance misuse.
Summary
  • Overall, addiction results in long-term neurobiological changes in the reward system, impacting emotion and behavior control leading to sustained substance use disorders.