neurotransmitters and psychopharmacology

PS4721 Neurotransmitters & Drug Effects

  • Instructor: Dr. Aoife McLoughlin

  • Overview: Understanding the role of chemicals in shaping behavior and the ways drugs affect neurotransmission.

Recap from Last Session

  • Neurons communicate via:

    • Electrical signals → initiate the release of neurotransmitters

    • Neurotransmitter release → activates specific receptors on target neurons

  • Key Inquiry: What happens when external factors interrupt this neurochemical communication?

Today's Big Questions

  • Common Neurotransmitters: What are they?

  • Impact of Drugs: How do drugs affect neurotransmission?

  • Tolerance & Withdrawal / Addiction: Why does the body develop tolerance and experience withdrawal, leading to addiction?

Key Neurotransmitters

  • Dopamine (DA):

    • Functions: Movement, attention, learning, reward, and addiction

  • Serotonin (5-HT):

    • Functions: Pain regulation, sleep, eating, arousal, and mood regulation

  • Acetylcholine (ACh):

    • Functions: Controls muscular tissue in the peripheral nervous system, regulates heart contractions and organ functions

  • Glutamate (glutamic acid):

    • Role: Main excitatory neurotransmitter in the central nervous system, critical for memory formation

    • Opposing neurotransmitter: GABA acts as the main inhibitory neurotransmitter, regulating neuron activation spread

  • Norepinephrine (noradrenaline):

    • Function: Integral to the 'Fight or Flight' response, primary neurotransmitter of the sympathetic nervous system

    • Effects: Increases alertness and blood pressure, links to attention and focus

Neurotransmitter Mechanism and Drug Interaction

  • Storage: Neurotransmitters are stored in vesicles within the neuron.

  • Synthesis: Neurotransmitters are made from chemical building blocks termed precursors.

  • Release Mechanism:

    • Action Potentials: Trigger vesicles to merge with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.

    • Post-Release Actions: Released neurotransmitters bind to postsynaptic receptors for signaling relay.

  • Termination of Neurotransmission:

    • Processes include:

    • Reuptake: Neurotransmitters are reabsorbed back into the presynaptic neuron.

    • Enzymatic Deactivation: Breakdown of neurotransmitters by specific enzymes.

    • Autoreception: Regulation of neurotransmitter release via receptors on the presynaptic neuron itself.

  • Types of Drug Action:

    • Agonist: Enhances neurotransmitter action (e.g., mimics natural neurotransmitters).

    • Antagonist: Blocks or dampens neurotransmitter action (e.g., prevents binding).

Homeostasis: The Balancing Act

  • Definition: The body's processes strive to maintain internal equilibrium, balancing the effects of neurotransmitters and drugs.

Tolerance

  • Definition: The phenomenon where the body requires increased doses of a drug to achieve the same physiological effect.

  • Example: Increased coffee consumption over time as acclimatization occurs.

Withdrawal Symptoms

  • Typical Symptoms Include:

    • Cold shakes, chills, and sweating

    • Fever-like symptoms

    • Mood swings, anxiety, and depression

    • Bone pain, vomiting, insomnia, and diarrhea

    • Symptoms often mirror the opposite effects of the drug itself (e.g., alcohol withdrawal leading to hyperarousal and seizures).

Addiction, Tolerance, and Withdrawal

  • Key Topic: The science of addiction includes understanding how these phenomena interact and affect behavior over time.

Case Examples of Drug Effects

  • Alcohol:

    • Mechanism: GABA agonist and glutamate antagonist

    • Effects: Slows CNS, leading to relaxation and impaired motor functions

    • Tolerance Development: Brain responds by increasing excitatory activity

    • Withdrawal Symptoms: Shakes, anxiety, seizures.

  • Cocaine:

    • Mechanism: Blocks dopamine reuptake

    • Effects: Causes euphoria and increased energy

    • Body Response: Downregulation of dopamine receptors

    • Withdrawal Symptoms: Low mood and fatigue.

  • Nicotine:

    • Mechanism: Acts as an acetylcholine agonist

    • Effects: Increases alertness and focus, mild euphoria

    • Addictive Nature: Highly addictive due to dopamine release in the reward pathway

    • Withdrawal Symptoms: Irritability, cravings, and difficulty in concentration.

Quick Poll Question

  • Which neurotransmitter system does MDMA primarily affect?

    • A. Dopamine

    • B. Serotonin

    • C. GABA

Summary and Conclusion

  • Key Takeaways:

    • Drugs modify neurotransmission by acting as agonists or antagonists.

    • The body’s compensatory mechanisms are vital in maintaining homeostasis, leading to tolerance and withdrawal.

    • Neurotransmitters play crucial roles in our emotions, thoughts, and behaviors.

  • Philosophical Question: Considering the body’s resistance to foreign substances, what drives individuals to continue substance use despite adverse effects?