Final answer:
The effect of nicotine to indirectly inhibit CB1 receptors may explain the weight gain associated with smokers who quit.
Step-by-step explanation:
Nicotine affects the body through the activation of nicotinic acetylcholine receptors, leading to various downstream effects, including the release of dopamine, which is linked to the reward system in the brain. Withdrawal from nicotine can lead to several symptoms such as cravings, irritability, and anxiety. One of the effects of smoking cessation is weight gain, which might be explained by the influence of nicotine or the absence thereof on certain regulatory systems that control appetite and metabolism.
Option 2) CB1 receptors - smokers who quit is the most accurate completion of the statement. When individuals quit smoking, they often experience an increase in appetite and weight gain. The CB1 receptors, part of the endocannabinoid system, are implicated in the regulation of feeding behavior and energy balance. Nicotine use is thought to indirectly inhibit these receptors, and thus inhibiting them may contribute to decreased appetite while smoking. Once smoking is stopped, the inhibition on these receptors is lifted, potentially leading to an increase in appetite and associated weight gain.