The Ventral Pallidum (VP) is an area of the brain that is part of the Basal Ganglia system. The VP is involved in regulating motivation and reward learning, connected with a variety of other brain regions, including another part of the Basal Ganglia called the Nucleus Accumbens (NAc). The NAc is also heavily implicated in motivation and reward learning, and a large part of the connections between these two brain regions are inhibitory. These inhibitory signals are known as GABAergic signals, because they occur via GABA, the primary inhibitory neurotransmitter in the brain. When these GABAergic projections from the NAc to the VP are activated, they send inhibitory signals to the neurons that they connect to in the VP. The same is true when GABAergic projections from the VP to the NAc are activated. These bidirectional inhibitory connections are involved in how we learn about rewards, such as food, and our motivation for these rewards. For instance, if you turn off the connections between these two brain regions so that they can no longer communicate, there is an increase in attentiveness to cues signaling food. So the next time you find yourself paying particular attention to a sign for your favorite restaurant, that’s your NAc – VP connections at work.
These images are of the VP from a transgenic rat, and we can see both a broad view of the area in the first image, and a second more zoomed in look at a few neurons in the next image. In both images, the blue comes from the fluorescent Nissl stain, which nonspecifically marks all of the neurons in this area. In yellow is a subpopulation of neurons that contain Gad1, a gene that helps make GABA. The yellow comes from a virus marked with yellow fluorescent protein (YFP) that was injected into the brain of this transgenic rat. This transgenic rat has a special genetic “tag” called cre that tags the Gad1 gene, and our virus can only enter cells that contain cre. As such, only the neurons that contain cre, in this case the Gad1 neurons, are yellow. This specific virus not only allows us to visualize these neurons, but it also allows us to manipulate these neurons using optogenetics. You can read more about optogenetics in in my previous post here. Together these images are showing a combination of tools used by researchers: transgenic rats, cre dependent viruses, and optogenetics. These behind the scenes tools allow researchers to investigate the role of the VP and its Gad1 subpopulation in reward learning, motivation, and so much more.
Contributed by Maddie Ray, a third year PhD graduate student at Boston College, and our Featured Artist for the fall of 2018. To meet Maddie and see more of her art, click here.