Whats the connection between Dopamine and bodyfat? The answer seems to be the sympathetic nervous system.
The receptors that dopamine acts on in the brain sends a signal down the nervous system much like electricity down a copper wire to the targeted group of fat cells, whereby some triglyceride is subsequently kicked out of the central lipid droplet and is then chopped up by lipases in the cytoplasm, breaking it down to fatty acids + glycerol.
Much attention is often paid to the circulating factors in the blood that influence fat cell size, like insulin, acylation stimulating protein, epinephrine etc etc. But the connection of fat cells directly to the brain by the nervous system is often overlooked, And this connection is also reported to be a major source of lipolysis.
This paper talks about the Siberian Hamster that is seasonally obese, it is fat in the summer when the days are long and lean in the winter when the days are short. The brain is able to keep track of this seasonality by the duration of the nocturnal secretion of melatonin. However, melatonin itself does not stimulate lipolysis when cultured with fat cells.
Despite much investigation into the blood circulating hormones that where known to affect fat cell size, none of them were able to account for the dramatic change in bodyfat seen in the Hamster in response to season changes. The logical conclusion from this was that seasonal obesity was almost completely controlled by nervous system lipolysis.
It seems that in addition to dopamine, the nervous system wires coming from fat cells and ending in the brain also express melatonin receptors, and melatonin hitting these receptors triggers additional lipolysis. This is actually surprising to me, as when I was supplementing melatonin to help cope with shift work I could swear I was gaining bodyfat. I will admit though at the time that I was still eating a junk food diet, that was very insulinogenic.
Insulin really is the daddy you know.
I think this also explains why reduced sleep is linked to obesity, less melatonin reduces lipolysis, giving the chance for fat cells to increase in size the next day when you eat normally. Could it be the same principle for why dopamine blocking drugs cause weight gain? Its not that blocking dopamine causes fat storage, but rather, it greatly inihibits fat break down. The paper also mentions how blocking this nervous system activation causes less lipolsis when fasting.