Week 4: Leptin and Development

The importance of leptin, continued…

Hey all, Josiah here to give y’all a sense of what we learned and discussed during this week (week 4). We continued our discussion of leptin and complicated its role in feeding to include functions important for development and reproduction.

As a recap from last week, leptin is released primarily by adipocytes, circulates through the blood stream, and crosses the blood brain barrier to bind primarily to sites on the hypothalamus. These sites, located at the arcuate nucleus, signal downstream to the nucleus tractus solitarius, where the behavioral responses regulating energy expenditure begin to take place. High levels of leptin lead to a negative energy balance of decreased food intake and increased energy expenditure, while low leptin levels lead to the opposite effect.

Leptin and Sex

Considering the hypothalamus to have direct effects toward the 4 F’s (feeding, fighting, fleeing, and mating), it is necessary to consider leptin’s role toward the other F’s as well. We explored the role of leptin in reproductive disorders. Leptin, while being an indicator of the body’s long-term energy stores, is also an initiator of puberty.

In normal reproductive development, leptin concentrations actually rise in both boys and girls before the transition into puberty. This then leads to the release of hormones responsible for the growth and maturation of sex organs. In fact, the neural mechanism by which leptin mediates this function is through similar circuitry that mediates energy balance. The POMC neurons that signal to the NTS also signal to what are known as Kiss1 neurons. These Kiss1 neurons, located in the ARC, then signal to gonadotropin-releasing hormones to stimulate sex organ maturation.

Developmental Importance of Leptin

Leptin is also shown to be important during prenatal and postnatal development, where genetic and environmental factors can lead to long-lasting effects and outcomes once adult age is reached. For example, restricting maternal food intake during pregnancy can lead to increased eating behaviors in the offspring, along with restructured brain feeding circuitry. The opposite situation of high-fat diets during pregnancy can lead to higher rates of obesity in the offspring.

There is so much more to discuss, but hopefully these examples are enough to show that leptin is a lot more than just an indicator of stored energy in the body. Without the normal function of leptin during important developmental time periods, the brain can remain underdeveloped, sexual maturation may be hindered, and unhealthy eating habits may dominate. Hopefully, these understandings will allow people to take nutrition a little more seriously.