Scott Newton, Brigham Young University
The ventral tegmental area (VTA) is known to controls the processing of rewarding and addictive behaviors. The VTA contains dopamine (DA) cells, which release DA to downstream targets in response to rewarding stimuli, and GABA cells, which modulate DA cell activity. Therefore, both cell types are involved in associative reward learning. Synaptic plasticity plays an important role in adaptive reward signaling within the VTA. Endocannabinoids mediate or modulate synaptic plasticity at synapses within the reward circuit. However, the source of endocannabinoids within the VTA is not well understood. Therefore, our goal was to describe the distribution of endocannabinoid biosynthetic enzyme mRNA within VTA neurons. We extracted single VTA neurons via whole cell patch clamp and used single-cell real-time quantitative PCR to identify DA and GABA neurons based on mRNA expression of cell-type specific targets. Additionally, electrophysiological properties such as action potential frequency and sag potential amplitude were examined between the two cell types. Concurrent with established observations, slower firing frequencies were observed in DAergic neurons, however overlap was identified between these two cell types. VTA neurons were then probed for endocannabinoid/ biosynthetic enzyme mRNA, such as N-acyl-phosphatidylethanolamine-specific phospholipase D (NAPE- PLD), diacylglycerol lipase α (DAGLα), and 12-lipoxygenase. We also probed for type I metabotropic glutamate receptor (mGluR) mRNA, as endocannabinoid synthesis requires mGluR activation. Our data demonstrate that endocannabinoid biosynthetic enzyme mRNA is expressed in both DAergic and GABAergic cells with concurrent expression of type I mGluRs. Next, to ensure mRNA expression was representative of protein content, slices were stained using immunohistochemistry for GAD67, DAGLα, NAPE-PLD and type I mGluRs. Positive labeling for these targets was observed in VTA neurons, supporting our RT-PCR results. Collectively, these data suggest DAergic and GABAergic cells of the VTA have the capability to produce endocannabinoids and potentially alter synaptic plasticity involved in reward and addiction.