0124 BIDIRECTIONAL CHEMOGENETIC CONTROL OF GABA NEURONS IN THE VENTRAL TEGMENTAL AREA MODULATES AROUSAL IN MICE

Abstract

Many sedative and anesthetic drugs potentiate GABAA receptors in the brain, but their neuroanatomic sites of action are less clear. GABA neurons in the rostromedial tegmental nucleus (RMTg) of the ventral tegmental area (VTA) inhibit neighboring dopamine neurons that have been shown to promote wakefulness. Using bidirectional chemogenetics, we tested the hypothesis that GABA neurons in this region modulate arousal. Vesicular GABA Transporter (VGAT)-Cre mice (n=10) underwent bilateral RMTg injections of viral constructs that elicit Cre-dependent expression of Designer Receptors Exclusively Activated by Designer Drugs (DREADDs). A mixture of two constructs was used to induce co- expression of stimulatory (Gq-coupled) M3-DREADDs and inhibitory (Gi-coupled) kappa opioid receptor DREADDs (KORD) in GABA neurons. Control VGAT-Cre mice (n=9) were injected with a null viral construct that encodes neither receptor. Co-expression of M3 and KORD DREADDs in the same neurons allows for activation by clozapine-N-oxide (CNO) and inhibition by salvinorin B (SalB). The open field test and rotarod were used to assess motor activity and coordination. In the open field test, CNO decreased the total distance traveled in the M3/KORD group (3.7 ± 4.5cm) compared to the control group (11.0 ± 4.5cm, p<0.01), and SalB had the opposite effect (M3/KORD group=19.7 ± 4.4cm; control group=14.6 ± 3.4cm, p=0.01). On the rotarod, the total run time decreased after CNO in the M3/KORD group (baseline=162 ± 53sec, CNO=71 ± 56sec, p<0.01) but SalB had no statistically significant effect. In control mice, neither CNO nor SalB produced statistically significant changes on the rotarod. Activation of RMTg GABA neurons decreases behavioral signs of motor activity and coordination suggesting that the VTA may be an important neuroanatomic site where sedatives and anesthetics act to decrease arousal. It is likely that the behavioral effects of GABAergic activation are primarily due to inhibition of neighboring VTA dopamine neurons that promote wakefulness. However, inhibition of GABA neurons only produced a modest increase in arousal during the awake state, suggesting that these neurons are already quiescent during wakefulness. Supported by NIH grant R01-GM104948.