The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 19 No. 6 • July 2016


FOOD ADDICTION, a TRUE Addiction

The basis for addiction is REWARD. All addictive substances are rewarding. The frantic bar pressing of a rat is a good example of how important reward can be in focusing the attention of an animal. In the case of food, unlike addictive drugs, the pleasure of its consumption is important for survival. From an evolutionary perspective, it would have been highly adaptive for the consumption of food to be rewarding, especially in the case of foods rich in fat and sugar, since they can be rapidly converted into energy.

Interestingly, in the case of cocaine addiction, a decreased number of D2 receptors are available to provide the motivation to obtain and use cocaine. The form of the D2 receptor known as the TaqA1 variant that is associated with a lower release of dopamine in humans is a fairly common version of the D2 receptor in Caucasians. (Reuter, 2013) Possessing it causes individuals to be susceptible to risky behavior, including the use of addictive drugs, but also for less extreme sorts of risky activity, such as auto racing, skydiving, mountain climbing, gambling, promiscuous sexuality, and even risky trading at the stock market. Activating the D2 receptors at medium spiny neurons that express the dopamine D2 receptors has been shown in mice to suppress cocaine self-administration. (Bock, 2013) The way this works is that the D2 receptor signals reward (or the prediction of reward) and when the numbers of these receptors are reduced, dopamine release is lower, and this induces behavior to increase dopaminergic release. One way people do this is by engaging in “thrill-seeking.”

References

Reuter et al. The influence of dopaminergic gene variants on decision making in the ultimatum game. Front Hum Neurosci. 4;7:242. doi: 10.3389/fnhum.2013.00242. (June 2013).

Bock, Shin, et al. Strengthening the accumbal indirect pathway promotes resilience to compulsive cocaine use. Nat Neurosci. 16(5):632-8 (2013).

How is Food Intake Regulated?

A host of molecules are involved in the process of addiction. It is because an overpowering desire to consume opiates and an obvious withdrawal syndrome is easier to distinguish than an overpowering desire to eat certain kinds of food followed by its own form of the withdrawal syndrome that the label “addiction” is easy to apply to opiate addiction but is less readily recognized in the eating of food. The molecules regulating the processes tell the story.

A mechanism has been identified to explain in part how these molecules foster addiction: they activate the vitally important reward system in which the cholinergic and dopaminergic nervous systems interact. In fact, a study (Joshua, 2008) reports that midbrain dopaminergic neurons and striatal cholinergic interneurons distinguish between rewarding and aversive stimuli. Importantly, the interaction between the dopaminergic and cholinergic nervous systems links these neurotransmitters to experimental findings that show that eating is initiated by a cholinergic signal and is terminated by a dopaminergic signal. (Rada, 2000) (Other studies have reported initiation by a dopaminergic signal and termination by a cholinergic signal; thus, the evidence is inconsistent.) This hub in which the neurotransmitter systems interact is a target for the complex process of food and perhaps other addictions.

References

Joshua et al. Midbrain dopaminergic neurons and striated cholinergic interneurons encode the difference between reward and aversive events at different epochs of probabilistic classical conditioning trials. J Neurosci. 28(45):11673-84 (2008).

Rada et al. Acetylcholine release in ventral tegmental area by hypothalamic self-stimulation, eating, and drinking. Pharmacol Biochem Behav. 65(3):375-39 (2000).

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