AAV6-CAG-Cre

The midbrain dopamine system regulates a variety of behaviors via the dorsal and ventral striatum. To analyze the role of dopaminergic projections to the dorsal striatum (nigrostriatal projections) and ventral striatum (mesolimbic projections) in sleep-wake behaviors, the researchers selectively stimulated the nigrostriatal or mesolimbic projections chemogenetically and examined the effects on sleep in rats. Stimulation of the nigrostriatal pathway increased sleep and EEG delta power, whereas stimulation of the mesolimbic pathway decreased sleep and reduced cortical EEG power. These results suggest that midbrain dopamine signaling in the dorsal striatum or ventral striatum promotes sleep or wake, respectively.

To determine if selective stimulation of the mesolimbic pathway promotes wakefulness, researchers injected AAV6-CAG-Cre (AAV6-Cre) into the NAc and cre-dependent AAV-hM3Dq into the VTA (Figure 1A). This approach selectively inserted hM3Dq into the VTA dopamine neurons projecting to the NAc (Figure 1B–F). Five animals were excluded from the group analysis, as the expressions of hM3Dq-mCherry were also found in the medial part of the SNc. Anti-cre immunostaining was adopted to verify the AAV6-cre injections in the NAc and the retrograde AAV6-cre in the VTA (Figure 1D, E). Activation of VTA dopamine neurons by CNO (0.2 mg/kg) was verified by intense nuclear c-Fos immunofluorescence labeling (green fluorescence) within mCherry+VTA dopamine neurons (red fluorescence) (Figure 1F).

Figure 1. Chemogenetic stimulation of mesolimbic dopamine neurons. (Qiu M H, et al., 2019)