Opponent Process Theory and Addiction

Opponent Process Theory

• Explains how responses to a stimulus (A process) trigger an opposing process (B process).
• The B process increases in magnitude and duration with repeated exposure.
• A process weakens, and B process strengthens.

Opponent Process Theory Applied to Addiction

• Tolerance develops as the A process adapts (metabolic, pharmacodynamic, or behavioral).
• Withdrawal arises from a stronger B process.
• A process effects are the opposite of B process effects.
• Example: Alcohol's A process (relaxation/anxiety relief) and B process (anxiety).

The Brain Disease Model of Addiction: Stages & Circuitry

• Binge/Intoxication Stage:

  • Basal Ganglia (striatum) and reward pathway are activated.
  • Drug exposure initially releases dopamine in the reward pathway.
  • Reward deficiency hypothesis: Individuals with fewer D2 receptors may experience more pleasure from stimulants.
  • Incentive salience: Drug/cue associations form, leading to habit formation in the basal ganglia.
  • Dopamine is released in response to cues, not the drug itself.

• Withdrawal/Negative Affect Stage:

  • Limbic system (amygdala) and stress system (HPA axis) activated.
  • "Anti-reward" or "Dark Side" develops.
  • The reward pathway becomes desensitized to natural rewards.
  • Brain stress systems and amygdala cause negative mood.

• Preoccupation/Anticipation Stage:

  • Prefrontal cortex (PFC), stress system (HPA axis), basal ganglia, and insula involved.
  • Executive function impairment due to hypofrontality.
  • PFC experiences desensitization to natural rewards but sensitization to drug cues.
  • Insula sensitive to cravings (interoception).
  • Stress system and basal ganglia habit formation remain active.

Pharmacotherapy of Addiction

• Agonist Treatments: Replace the addictive drug with a similar-acting drug.
  • Examples: Methadone for heroin, nicotine patch for cigarettes.
• Partial Agonist Treatments: Prevent withdrawal and cravings with a drug offering a partial effect.
  • Example: Varenicline (Chantix) for nicotine addiction (partial nAch receptor agonist).
• Antagonist Treatments: Block the effects of the addictive drug.
  • Example: Naloxone for heroin (competitive mu receptor agonist).
• Aversive Treatments: Induce a negative reaction when the addictive drug is taken.
  • Example: Disulfiram (Antabuse) for alcohol.
  • Example: Suboxone (buprenorphine + naloxone) for opioids.
• Antidrug Vaccines: Inject synthetic molecules similar to the drug.
  • Immune system creates antibodies to decrease drug brain absorption.

This quiz explores the Opponent Process Theory and its application to addiction, detailing how stimulus responses trigger opposing processes. It also examines the brain circuitry involved in addiction, specifically during the binge/intoxication stage and the effects of dopamine release.