Psychopharmacology: Synaptic Transmission

• Psychopharmacology is the study of how drugs affect the brain and behavior

Drug Action on Synaptic Transmission

• Drugs act as either agonists, enhancing neurotransmitter effects, or antagonists, reducing/blocking them.

Direct Binding Drugs

• Direct agonists mimic neurotransmitters, activating receptors, such as nicotine activating acetylcholine receptors
• Direct antagonists block receptors, preventing neurotransmitter binding; curare blocks acetylcholine receptors

Other Drug Actions

• Synthesis agonists, like L-Dopa, increase neurotransmitter production, used in Parkinson's
• Synthesis antagonists, such as PCPA, block neurotransmitter production
• Storage antagonists, like reserpine, reduce neurotransmitter storage, affecting blood pressure and psychotic symptoms
• Release agonists, such as black widow spider venom, increase neurotransmitter release, causing muscle overstimulation
• Release antagonists, such as Botox, block neurotransmitter release, inducing paralysis
• Reuptake agonists, such as cocaine, block neurotransmitter reuptake, prolonging their action, leading to euphoria and addiction
• Inactivation agonists, like physostigmine, prevent neurotransmitter breakdown, used for memory improvement in Alzheimer's

Dopamine

• Dopamine is a neurotransmitter involved in movement, motivation, and pleasure

Dopamine Synthesis

• Dopamine is synthesized from tyrosine, which converts to L-Dopa, then to dopamine
• Dopamine is produced by dopaminergic neurons

Dopamine Pathways and Functions

• The mesocortical pathway is responsible for focus, decision-making, and impulse control; dysfunction leads to cognitive impairment and lack of motivation, as seen in ADHD and schizophrenia
• The mesolimbic pathway controls pleasure, motivation, and addiction; overactivity leads to schizophrenia symptoms and addiction tendencies
• The nigrostriatal pathway regulates voluntary movement; low dopamine results in Parkinson’s Disease
• The tuberoinfundibular pathway regulates prolactin secretion; its imbalance leads to hormonal issues like infertility and lactation problems

Dopamine Receptors

• D1 and D5 receptors are D1-like and excitatory, stimulating neural activity
• D2, D3, and D4 receptors are D2-like and inhibitory, reducing neural activity

Dopamine-Related Disorders

• Schizophrenia involves excessive dopamine in the mesolimbic pathway
• Schizophrenia symptoms include hallucinations, delusions, disorganized speech (positive), flat affect, lack of motivation, and social withdrawal (negative)
• Schizophrenia phases are prodromal (early, mostly negative symptoms), active (hallucinations, delusions), and residual (fewer psychotic, more negative symptoms)

Parkinson’s Disease

• Parkinson’s Disease involves too little dopamine in the nigrostriatal pathway
• Parkinson's Disease symptoms include tremors, bradykinesia, rigid posture, and difficulty balancing
• Parkinson's Disease treatment uses L-Dopa to increase dopamine production