There have been studies on the relationship of THC and D1 receptors on D1 receptor's density. In a study conducted with African Green Monkeys, it was found that caudate putamen (CPu), which expresses D1 and D2 heteromer, exhibited a significant increase in the number of neurons compared to the control group. As for nucleus accumbens (NAc), it was also observed that the group using THC showed an increase in the density of D1-D2 heteromers. Specifically, they used a proximity ligation assay to determine D1-D2 heteromer levels, and found that, compared to the control group, the THC group showed a 3-fold increase in positive signal. The research also indicated that, following THC administration, neurons exhibited diversity, with most having approximately 4 fluorescent signals per neuron, while a few displayed as many as 17 signals, whereas others had 2-4 signals per nuclei. However, to know if D1-D2 heterodimerization increase by THC is connected to the D1 or D2 receptor ratio level, RT-PCR was carried out on extracts from caudate-putamen and NAc to determine the mRNA expression levels of D1 and D2. As for D2 or the dopamine transporter DAT, there was no significant effect on mRNA expression, but for the D1 receptor, persistent THC usage up-regulated mRNA expression .