Central Nervous System Pharmacology

Overview

• Focus on CNS drugs vs. autonomic nervous system drugs.
• CNS drugs target receptors in the brain and spinal cord, not peripheral receptors.
• Understanding of receptors is essential for grasping drug effects.
• CNS excitability continuum: from no energy to excessive energy.
  • Dopamine and serotonin receptors: Increase CNS excitability when activated.
  • GABA receptors: Decrease CNS excitability when activated.

Categories of CNS Drugs

1. Antipsychotics

• Purpose: Treat schizophrenia, a disorder with excessive brain activity.

• Key receptors: Dopamine (D2) and serotonin (5-HT) receptors.

• First-generation antipsychotics:

  • Block D2 receptors.
  • Examples: Haloperidol, phenothiazines.
  • Side effects: Anticholinergic effects, tardive dyskinesia (involuntary movements).

• Second-generation antipsychotics:

  • Block both dopamine and serotonin receptors.
  • Fewer side effects than first-generation.

• Additional uses: Sometimes act as antiemetic drugs (prevent nausea/vomiting).

2. Antidepressants

• Purpose: Treat depression by increasing CNS activity.
• Mechanism: Increase monoamines (e.g., dopamine, norepinephrine, serotonin).
• Categories:
  • SSRIs (Selective Serotonin Reuptake Inhibitors):
    • Block reuptake of serotonin.
    • More serotonin available in the synapse.
  • SNRIs (Serotonin-Norepinephrine Reuptake Inhibitors) and Tricyclic Antidepressants:
    • Block reuptake of serotonin and norepinephrine.
  • Monoamine Oxidase Inhibitors (MAOIs):
    • Inhibit the enzyme that degrades neurotransmitters, increasing their levels.
• Side effects: Anticholinergic effects due to increased monoamines.

3. Sedatives and Anxiolytics

• Types: Benzodiazepines and barbiturates.
• Benzodiazepines:
  • Bind to GABA-A receptor.
  • Increase GABA activity, promoting chloride influx, and slowing CNS activity.
  • Safer for sedation (e.g., Diazepam/Valium).
• Barbiturates:
  • Similar mechanism as benzodiazepines but with more side effects.
  • Contraindicated in patients with intermittent porphyria.

4. General Anesthetics

• Purpose: Induce medically controlled coma for surgeries.
• Onset: Inversely proportional to blood solubility of the anesthetic.
• Stages of General Anesthesia:
  • Analgesia (pain relief)
  • Delirium
  • Surgical anesthesia (desirable stage)
  • Overdose and medullary paralysis
• Example: Halothane (associated with hepatotoxicity).

5. Treatment for Parkinson's Disease

• Cause: Dopamine deficiency in the brain.
• Treatment: Increase dopamine using levodopa (crosses the blood-brain barrier) and carbidopa (blocks levodopa conversion to dopamine before it reaches the brain).
• Note: Levodopa is a sympathomimetic, which can stimulate peripheral sympathetic activity.

Conclusion

• Understanding CNS pharmacology is essential for various medical and dental practices.
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