The Brain’s Reward System: Is Dopamine the Only ‘Feel Good’ Chemical?

Much evidence has associated dopamine with the brain’s reward system. For this reason, dopamine has been called the “feel good” or pleasure chemical. Stimulation of the neurotransmitter, dopamine, makes us feel good.

We like to do things that makes us feel good. Dopamine affects our thoughts and behavior in this way. For example, when we eat, the brain’s reward system tells us to feel good by activating dopamine in the nucleus accumbens or the dopaminergic systems (Wise, 2004). Food is a natural primary reward since it is so crucial for our survival. We are motivated to eat and to survive.

Almost all drugs of abuse activate the reward system in the same way as food does. As a result, these drugs can become highly addictive. This is because the brain’s reward system reinforces behaviors, i.e. the ones that make us feel good.

Many rewards are rendered ineffective in animals that have had their dopamine systems blocked. But is dopamine the only “feel good” chemical? Evidence suggests that it isn’t: The reward circuitry is multisynaptic (Wise & Rompre, 1989).

Dopamine is not required to feel pleasure to natural rewards

In a study by Cannon & Palmiter (2003), the authors compared mice that lacked the ability to produce dopamine (DD mice), and mice that had this ability, to test the hypothesis that dopamine is necessary to feel rewards.

They measured how much time the mice spent eating sugar, as sugar normally activates the brain’s reward system. Interestingly, the DD mice preferred sugar over water. However, compared to the control group, i.e. mice that were able to produce dopamine, the  DD mice initiated eating less frequently and had fewer total licks.

mouse

Food is a natural primary reward.

Dopamine is not required for mice to learn to consume sweets, since  DD mice, without the ability to produce dopamine, preferred to consume sweets over water.  The mice behaved as if they were motivated to consume calories.

So, what was it that motivated the mice to eat, if it was not the effects of dopamine? The answer might be that dopamine is not the only reward chemical, so to speak. Dopamine just plays an important role in the brain’s  reward circuitry.

Indeed, the activity of dopaminergic neurons increases not only in response to rewards but also in response to punishments such as electric shocks (Horvitz, 2002), so it seems that dopamine is more than just a “feel good” chemical and that it is not the only “feel good” chemical. Future research may elucidate this association in greater detail.

Photo: Graeme Lawton (adapted)