III. Psychopharmacology

Psychopharmacology is the study of drugs that influence the brain and thereby behavior.  The typical way that drugs influence brain is by impacting the normal function of neurochemicals.  Neurochemicals act as chemical messengers and when released they produce a reaction in a target cell.   The communication process is called synaptic transmission and it is both a chemical and an electrical event.

1. Types of known neurochemicals

2.  Action sites of Neurotransmission

 Neurochemicals  are classified as neurotransmitters, neuromodulators and neurohormones. Neuortransmitters generally act at the synapse.

3. Drug Actions at the Synapse

Most psychoactive drugs produce their effects by acting at the synapse, including at the action sites of the above illustration. Drugs that enhance the activity of a neurochemical from the target cell are known as agonists.  Drugs that reduce the activity are known as antagonists.  Actions of an agonists and antagonists link a particular drug to a specific neurochemical and often to a specific receptor type of that chemical.  Because neurochemicals are associated with certain brain areas, the drug action can be specifically targeted to a brain region and therefore to a particular behavior. However, no drugs acts at only one place, so there are always other drug actions or side-effects.

Review the Gross Anatomy page to link the areas in blue to their neurochemical.

•Cocaine, Amphetamines  ventral tegmental area DA,NE

•Cannabis sativa, hashish basal ganglia Anandamide

Narcotic opium, Morphine Descending analgesic circuit Spinal Column Endogenous Opioids or Peptides

Alcohol All over the brain  GABA

Peyote, PCP, LSD reticular activating system 5-HT

Nicotine  Neuromuscular junction  Ach

4. Basic Principles of Pharmacology

In order for drugs to reach the synapse, they must first enter the brain.  This process depends on how the drug is administered.

•Pharmacokinetcis = Movement of drug in and out of the body.

•Drug Dose   Ratio of mg/kg =concentration of drug.

•You must be given two of the three numbers to compute a drug dose mg/kg.

•“mg”= amount of drug given

• “kg” = weight of person (convert from pounds)

•  “concentration” = unit of dose.

•Routes of Administration

•Oral

•Injection (subcutaneous, intramuscular, intravenous)

•Inhalation

•Others: intranasal, sublingual and transdermal

•Drug Absorption

•Bioavailability

•Factors that influence absorption

•Membrane barriers, drug form, size of surface

•Drug Distribution

•Blood flow, diffusibility, fat solubility, affinity

•Drug Elimination

•Zero-order kinetics, first-order kinetics, half-life

•Routes of elimination

•Drug testing and metabolic byproducts