How drugs work... explain?

[Supaiku]

So a friend of mine has a wack idea about drugs and how they work.

 

So, I have a few questions.

 

First, just how far can the brain go in preventing drugs from working? And creating the effects of drugs on their own? I'm talking any sort of drug, from caffine to morphine to marijunana to heorin.

 

Can anyone give me a semi-detailed version of how drugs work on the brain and body. I know that most (all?) get into your blood and effect your nerves and brain by blocking specific types of transfer but I need the fancy names and a better idea of how exactly it all works and how differnt drugs can work differntly and the like. Semi-technical, maybe slightly above what most highschool biology classes would give?

 

Thanks if anyone can help:D

[Glider]

There are several mechanisms of action for drugs. They act usually at synapses. They can act as an agonist (act on receptor molecules in the same way as a substance) for an endogenous substance, e.g. opiates (opium, morphine, diamorphine etc.) are agonists for enkephalins and endorphins. Or they can act as antagonists (block the action of a substance) e.g. naloxone, (the antagonist for opioids and endorphins).

 

Alternatively, they can alter the concentrations of endogenous transmitters e.g. specific serotonin reuptake inhibitors (SSRIs), or monoamineoxidase inhibitors (MAOIs). Each of these increase the concentrations of serotonin; SSRIs by inhibiting its reuptake by the presynaptic buton, and MAOIs by inhibiting the enzyme that breaks down serotonin.

 

Some drugs used locally work on the axon itself and simply block transmission (e.g. cocaine and its derivitives: Lidocaine, xylocaine, lignocaine etc.). However, the same drug in the central nervous system has the overall effect of increasing dopamine levels (a/w reward).

 

Drugs of abuse all have different effects in many different areas of the brain, but their underlying effect; the reason people take them and get addicted to them is that they share a final common effect, in that they increase activity in dopaminergic systems in the ventral tegmental area, the medial forebrain bundle, the nucleus accumbens and the mesolimbic pathway (essentially, this constitutes the brain reward system).

 

Some do this directly, by stimulating dopamine release and others do it indirectly e.g. barbiturates, benzodiazepines opiates and alcohol. These interact with Gamma Aminobutyric Acid (GABA) receptors, inhibiting the release of GABA onto dopaminergic neurons. GABA is an inhibitory transmitter, and its usual function is to inhibit dopamine release. By inhibiting the inhibitor, you are in effect 'removing the brakes' in the system.

 

The brain can't do anything immediately to prevent drugs from working. It can compensate for their action over time though, often by altering the concentration of receptor molecules in postsynaptic membranes and sometimes by reducing the amount of endogenous transmitter substance it produces.

[Supaiku]

Thanks:D