IB Bio / Neurobiology and Behavior Unit

“Drugs of Abuse” Chart, Neil 9e KEY  All of these drugs co-opt the brain’s reward pathway, the circuitry normally activated by environmental stimuli having survival value: food, water, mates.  An agonist is a chemical that binds to a receptor and activates the receptor to produce its normal biological response; an antagonist also binds to the receptor, but it inhibits it, blocking the normal response.

Excitatory or Other notes of Drug inhibitory What is the mechanism of action of the drug on the reward circuit? (VTA = ventral tegmental area; NA = nucleus accumbens) interest effect on BRAIN? The other  Increases dopamine synthesis and release from VTA neurons onto NA neurons Nicotine E chemicals in (the addictive component in because nicotine is an acetylcholine agonist. tobacco smoke tobacco, Nicotiana tabacum)  ACh is the NT released from neurons that excite VTA neurons. cause cancer, etc.

Cocaine  Blocks re-uptake of dopamine by the VTA neurons which synapse onto NA neurons, E prolonging dopamine stimulation.  Increase the release of dopamine from VTA neurons & inhibit re-uptake of dopamine Amphetamines E too.  Result: more dopamine stimulation.  Neurons releasing GABA normally inhibit VTA neurons. I  Benzodiazapines stop these neurons from releasing their GABA onto VTA neurons. Benzodiazepines (Valium™, Xanax™)  Inhibiting the release of inhibitor (“disinhibition”) is like taking your foot off the brake, allowing your car to speed.  Result: VTA neurons fire more and release more dopamine. Among its many effects on the brain: I  Like benzodiazepines, ethanol inhibits the release of GABA onto VTA neurons, Ethanol leading to VTA neurons firing more rapidly and releasing more dopamine in the reward system.  High doses of ethanol depress brain regions for coordination, balance and pain There are fewer

CB1 receptors in I  THC is an agonist of naturally occurring endocannabinoids that bind to "CB1 Tetrahydrocannabinol receptors" involved in appetite, pain sensation, mood, and memory. adult brains than those of (THC) in Cannabis sativa,  THC increases extracellular dopamine concentrations in the NA. How this occurs is teens. A.K.A. marijuana unclear. It might be that THC binds to CB1 receptors on neurons that were inhibiting THC dissolves (with GABA) the VTA neurons. Through disinhibition, THC increases dopamine in NA. in myelin.