19: Increased cAMP produced in post-synaptic cell
In a closer view, again, show how this affects the function of the post-synaptic cell. Since there is more dopamine released, there is increased activation of dopamine receptors, similar to the effect of cocaine. This causes increased production of cAMP inside the post-synaptic cell, which alters the normal activity of the neuron.

20: Summary: opiate binding in nucleus accumbens and activation of the reward pathway
Show the "big picture." As a result of opiate actions in the nucleus accumbens (point to the sprinkles of opiates in the nuc. acc.), there are increased impulses leaving the nucleus accumbens to activate the reward system (point to the frontal cortex). As with cocaine, continued use of opiates makes the body rely on the presence of the drug to maintain rewarding feelings and other normal behaviors. The person is no longer able to feel the benefits of natural rewards (food, water, sex) and can't function normally without the drug present.

21: Localization of THC binding sites
When a person smokes marijuana, the active ingredient, cannabinoids or THC, travels quickly to the brain. Point to the areas where THC (magenta) concentrates. The VTA, nucleus accumbens, caudate nucleus, hippocampus, and cerebellum are highlighted. THC binds to THC receptors that are concentrated in areas within the reward system as well as these other areas. Indicate that the action of THC in the hippocampus explains its ability to interfere with memory and actions in the cerebellum are responsible for its ability to cause incoordination and loss of balance.

22: THC binding to THC receptors in the nucleus accumbens: increased dopamine release
[Note to scientists - the interaction of THC with the reward system is not fully understood at this point. The following discussion is based on recent data, but additional theories may emerge as we obtain more data.] State that scientists know the least about THC. Over the last few years, there has been intense study to discover where and how THC works. One theory is that it acts in a similar way to opiates. Again use the nucleus accumbens as an example. The same three neurons are probably involved: the dopamine terminal, another terminal (on the right) containing a different neurotransmitter (probably GABA), and the post-synaptic cell containing dopamine receptors. Ask the students if they can tell you how THC might work. THC binds to THC receptors (magenta) on the neighboring terminal and this sends a signal to the dopamine terminal to release more dopamine. [Again, it is probably a presynaptic receptor on GABA interneurons that controls dopamine release.]

23: Increased cAMP produced in post-synaptic cell
In a closer view, show how this affects the function of the post-syanaptic cell. Since there is more dopamine released, there is increased activation of dopamine receptors. This causes increased production of cAMP inside the post-synaptic cell which alters the normal activity of the neuron.

24: Summary: THC binding in nucleus accumbens and activation of the reward pathway
Show the "big picture." As a result of THC actions in the nucleus accumbens (point to the concentration of THC in the nuc. acc.), there are increased impulses leaving the nucleus accumbens to activate the reward system (point to the frontal cortex). Scientists still don't know how the continued use of marijuana alters the reward system. Indicate that this is an area of intense research by neuroscientists.

25: Overall summary: these drugs of abuse all activate the reward system via increasing dopamine neurotransmission
In this last image, the binding of all three drugs is shown in one of the reward areas, the nucleus accumbens. Summarize that each drug increases the activity of the reward pathway by increasing dopamine transmission. This happens even though the drugs act by different mechanisms. Because of the way our brains are designed, and because these drugs activate a particular brain pathway for reward, they have the ability to be abused. Start a discussion; ask the students if they can think of any other drugs that are abused that probably activate the reward system in the same way. Answer: alcohol, nicotine, and amphetamine are good examples.