Introduction to Psychopharmacology

Psychopharmacology - the study of the effects of drugs on the nervous system and on behaviour

Pharmacotherapy - treatment of illness by drugs - not just psychological

Pharmacokinetics - process by which drugs are absorbed, distributed in the body, metabolised and excreted

Drugs can act at several different sites and have different effect - psychopharmacology looks at effects on CNS

Pharmacodynamics: effects of drugs on target, e.g. 'Therapeutic Index': the ratio between the dose that produces the desired effect in 50% of the animals and the dose that produces toxic effects in 50% of the animals

Repeated drug use usually produces tolerance (reduced effectiveness) and withdrawal effects, but occasionally causes sensitisation

Drug studies need to have a control condition - usually inactive placebo - allows for admin, expection, etc.

 

Influences on Pharmakinetics

1. Mode of administration

How the body eliminates drugs 

- Drugs are broken down in the kidneys, liver, and intestines

- Drugs or metabolites are then executed in urine, faeces, sweat, breast milk, and exhaled air

- Some drugs only become fully active when metabolised to a secondary form

- Some substances that cannot be removed may build up in the body and become toxic

Blood Brain Barrier (BBB)

• Peripherally administered drugs vary in how easily or even if they can enter the brain - due to the BBB
• BBB is formed from tightness of capillary wall cells and also surrounding glial cells or astrocytes
• Fat-soluble drugs pass quite easily through the cell membrane lipid layers
• Many substances need active transport across the cell membranes

Capillaries - capillaries in the brain have tight junctions and are covered with astrocyte feet. These properties prevent materials from moving in and out easily

Areas of the brain known to have weak BBB:

• Pituitary gland
• Pineal gland
• Area postrema

Neurotransmitter receptors

• Receptors are protein complexes which can selectively bind neurotransmitter molecules and send a signal in the target cell
• Surface cell receptors can be divided into two large families:
• receptor-regulated ion channels or ionotropic receptors
• G protein-regulated receptors or metabotropic receptors (slow acting)

Types of Drug action

Agonist - drug that enhances/mimics action of neurotransmitter NT could be excitation or inhibition of postsynaptic cell

Antagonist - drug that block/inhibits action of neurotransmitter

Direct action - binds with receptor and mimics activiation or prevents activation by natural NT

Indirenct action - binds to separate site on receptor that does not interfere directly with natual NT/ligand binding