Emerging evidence has uncovered a vital role of nucleus accumbens (NAc) neurons that express the dopamine D1 receptor (D1R) and its upstream neural circuit in general anesthesia (GA) regulation. However, the underlying downstream neural basis of the modulation of GA emergence by NAcD1R neurons remains unknown. In the present study, we explored the downstream neural mechanism of NAcD1R neurons in the modulation of emergence from sevoflurane GA.
We traced the axonal projections of NAcD1R neurons using a cell type-specific anterograde tracing method and immunohistochemical techniques in D1R-Cre mice. Optogenetic stimulations combined with electroencephalogram/electromyogram recordings and behavioral tests were used to determine the effects of optogenetic activation of the axonal terminals of NAcD1R neurons on sevoflurane emergence during sevoflurane-induced continuous, steady-state general anesthesia (CSSGA) or burst-suppression oscillations.
Labeled efferent fibers of NAcD1R neurons were highly distributed in the ventral pallidum (VP), lateral hypothalamus (LH), and substantia nigra pars compacta. Optogenetic activation of the NAcD1R–VP circuit during CSSGA with sevoflurane induced cortical activation (mean ± standard deviation [SD]; delta power: prestimulation versus during stimulation, 48.7% ± 5.7% vs 35.1% ± 3.3%, P < .0001; beta power: 7.1% ± 2.7% vs 14.2% ± 3.3%, P = .0264) and behavioral emergence, and restored the righting reflex in 66.7% of ChR2 mice. Optogenetic stimulation of the NAcD1R–LH circuit also produced cortical activation (delta power: prestimulation versus during stimulation, 45.0% ± 6.5% vs 36.1% ± 4.6%, P = .0016) and behavioral emergence, and restored the righting reflex in 100% of the ChR2 mice during CSSGA with sevoflurane. Under a sevoflurane-induced burst-suppression state, NAcD1R–VP/LH circuit activation produced evidence of cortical activation (burst-suppression ratio [BSR]: NAcD1R–VP circuit, prestimulation versus during stimulation, 42.4% ± 4.0% vs 26.3% ± 6.0%, P = .0120; prestimulation versus poststimulation, 42.4% ± 4.0% vs 5.9% ± 5.6%, P = .0002; BSR: NAcD1R–LH circuit, prestimulation versus during stimulation, 33.3% ± 13.4% vs 5.1% ± 4.9%, P = .0177; prestimulation vs poststimulation, 33.3% ± 13.4% vs 3.2% ± 4.0%, P = .0105) and behavioral emergence.
Both NAcD1R–VP and NAcD1R–LH circuits are sufficient to promote reanimation from sevoflurane GA by simultaneously inducing cortical and behavioral emergence.