On 2014 May 06, Serge Ahmed commented:

This study is outstanding. Together with other studies, it confirms that sugar is a double reward. Sugar activates brain dopamine (DA) neurons twice: once during sweet tasting (via an initial polysynaptic brainstem pathway) and once after blood glucose absorption (via an activation of MCH neurons). The latter delayed activation of DA neurons plays a critical role in learned food preferences and may also contribute to maintain the ability of sweet taste to activate DA neurons.

Rather surprisingly, this study also shows that concurrent optogenetic activation of hypothalamic MCH neurons during access to water sweetened with sucralose (a non-caloric sweetener) increases consumption of sweet water and also DA levels in the striatum. The time course of this effect is somewhat paradoxical, however, if one supposes that it mimics activation of MCH neurons by post-absorptive glucose. In fact, this effect is more consistent with a direct modulation of sweet palatability by MCH neurons. It would be interesting to know how glucose activation of MCH neurons during access to sweet water would affect consumption.

On 2014 May 06, Serge Ahmed commented:

This study is outstanding. Together with other studies, it confirms that sugar is a double reward. Sugar activates brain dopamine (DA) neurons twice: once during sweet tasting (via an initial polysynaptic brainstem pathway) and once after blood glucose absorption (via an activation of MCH neurons). The latter delayed activation of DA neurons plays a critical role in learned food preferences and may also contribute to maintain the ability of sweet taste to activate DA neurons.

Rather surprisingly, this study also shows that concurrent optogenetic activation of hypothalamic MCH neurons during access to water sweetened with sucralose (a non-caloric sweetener) increases consumption of sweet water and also DA levels in the striatum. The time course of this effect is somewhat paradoxical, however, if one supposes that it mimics activation of MCH neurons by post-absorptive glucose. In fact, this effect is more consistent with a direct modulation of sweet palatability by MCH neurons. It would be interesting to know how glucose activation of MCH neurons during access to sweet water would affect consumption.