4. Drugs Flashcards
4 Methods of Administration
Ingestion
Absorption
Inhalation
Injection
Ingestion
- Goes through the digestive system into the intestines, where they are absorbed into the blood
- Relatively safe & easy but unpredictable (food intake and other factors affect rate)
Absorption
Through mucus membranes
Inhalation
- e.g. smoking
- Cannot regulate dose
- Damage to lungs if done incorrectly
- Absorbed into the blood from the lungs
Injection
- Into muscles, fatty tissue or veins
- Intravenous - blood stream takes them straight to the brain
- Little to no opportunity to counteract an overdose or allergic reaction
- Scar tissue, collapsed veins and infections are also a risk
Drug penetration of the CNS
- Travel through the bloodstream to blood vessels of the CNS
- Blood-brain barrier makes it difficult for drugs to get past into the “extracellular” space surrounding the neurons and glia of the CNS
- Drugs like alcohol & many general anesthetics diffuse across neural membranes (nerve cells)
Drug metabolism
Enzymes in the liver convert active drugs to non-active forms
Most cases: inhibits the drugs ability to pass through lipid membranes, meaning it can no longer get past the blood-brain barrier
Agonists
Drugs that facilitate the effects of a specific neurotransmitter e.g. a dopamine agonist
Activate certain receptors
Antagonists
Drugs that inhibit the effects of a specific neurotransmitter e.g. a dopamine antagonist
Block certain receptors
Affinity & Efficacy
Affinity - tendency to bind to a receptor
Efficacy - tendency to activate a receptor
A drug that binds easily but does not stimulate would be high in affinity and low in efficacy
This would also be an antagonistic effect
Mesocorticolimbic System
a component of the mesotelencephalic dopamine system which play an important part in mediating ICSS (Intracranial self-stimulation)
- Self-stimulation occurs at many brain sites that are part of the mesocorticolimbic system
- ICSS is associated with spikes in dopamine release in the mesocorticolimbic system
- Dopamine agonists increase ICSS and dopamine antagonists decrease ICSS
- ICSS is disrupted when there are lesions (abnormal tissue growth) in the mesocorticolimbic system
Intracranial self-stimulation
self-administration of weak electrical stimulation to the brain
- Think rats and levers
Ventral Tegmental Area (VTA)
The cell bodies of the neurons composing the MDS (Mesotelencephalic Dopamine System) are contained here and in the substantia nigra
- Axons of the neurons in the VTA mostly project into many cortical and limbic sites
- This section of the MDS is called the Mesocorticolimbic system
Nucleus Accumbens
‘Reward centre’
Motivation (anticipation of reward) and reward
‘Dopaminergic’ input is sent from the VTA to the nucleus accumbens - strongest, clearest relation to reward and pleasure
- Lesions in this area stopped rats administering drugs to themselves
Subcutaneous Injection
Into fatty tissue
Intramuscular Injection
Into large muscles
Intravenous Injection
Into veins
Amphetamine
Blocks reuptake of dopamine & several other transmitters
Cocaine
Blocks reuptake of dopamine + others
Stimulant