SECOND HELPING

What makes us feel hungry? Scientists have 
identified proteins that do the trick, writes Biplab Das

In these calorie-conscious days, it's only too common to come across people who want to lose weight. But there are just as many people who are concerned about their lack of appetite. Studies conducted at the University of Texas Southwestern Medical Centre may pave the way for new medicines that help such patients.

Scientists at the Centre have identified certain peptides, which enhance appetite. The findings of the research team, led by Masashi Tanagisama, could help design drugs that either mimic or block these proteins, which have been named orexins. 

The researchers already knew the identity of the receptors through which orexins work. They began their research with efforts to find peptides that could activate the receptors.

After discovering the relationship between two peptides and two receptors, Tanagisama's team injected the peptides directly into rat brains. This caused the animals to eat from three to six times more than rats in a control group, which did not receive peptides.

The researchers studied the effect of starvation on brain levels of orexins. They found that starvation caused a rise in orexin levels in the brain. The team reported their findings in the journal Cell earlier this year. 

The findings take the researchers one step closer to understanding how the brain controls appetite. "Every new discovery (like the orexins) add to an understanding of how the system works," Science quoted physiologist Larry Bellinger as saying. Bellinger studies feeding behaviour at the Baylor College of Dentistry in Dallas, US. 

The striking feature of orexins is that they reside in an area of the brain called the lateral hypothalamus, LH for short. Until recently, scientists believed the ventro medial hypothalamus (VMH), a neighbouring area of LH, was the main region of the brain controlling appetite. The VMH was described as satiety centre because destroying this region turned animals into overeaters. 

According to Bellinger, the hypothalamus is criss-crossed by an intricate network of neurons, which control chemical communication within the body. For instance, low blood sugar levels provide the wake-up call to neurons in the LH. These, in turn, could trigger the release of orexins and enhance appetite. With this discovery, researchers think they are close to developing appetite-controlling drugs. But before reaching that goal, they need to completely understand the neuronal network in the hypothalamus.