Zona Incerta GABAergic Output Controls a Signaled Locomotor Action in the Midbrain Tegmentum

Abstract

The zona incerta is a subthalamic nucleus proposed to link sensory stimuli with motor responses to guide behavior, but its functional role is not well established. Using mice of either sex, we studied the effect of manipulating zona incerta GABAergic cells on the expression of a signaled locomotor action, known as signaled active avoidance. We found that modulation of GABAergic zona incerta cells, but not of cells in the adjacent thalamic reticular nucleus (NRT), fully controls the expression of signaled active avoidance responses. Inhibition of zona incerta GABAergic cells drives active avoidance responses, while excitation of these cells blocks signaled active avoidance mainly by inhibiting cells in the midbrain pedunculopontine tegmental nucleus (PPT). The zona incerta regulates signaled locomotion in the midbrain.

Figure 1.

Active avoidance procedure and location of AAV injections and optical fibers. A, Schematic of the active avoidance procedure showing different trial types. B, Example of a parasagittal section showing a cannula tract (arrow) coursing to zona incerta. C, D, Example AAV injections in the zona incerta. The images blend a light image of the section with the green channel of the eYFP fluorescent image. The inset photomicrographs show the eYFP fluorescence alone. E, Example AAV injections in NRT. The images blend a light image of the section with the green channel of the eYFP fluorescent image. The inset photomicrograph shows the eYFP fluorescence alone. F, Reconstruction of optical fiber track endings in the zona incerta, PO thalamus, superior colliculus, and PPT for brains cut in the sagittal plane (1–2 mm lateral from the midline).

Figure 2.

Effect of inhibiting zona incerta GABAergic cells on active avoidance responses. A, Effect of green light applied in the zona incerta on ACS+LCS trials (blue) and on LCS alone trials (red) for mice that express eArch3.0 in GABAergic zona incerta cells (Vgat-ZI-Arch). ACS+LCS trials measure the effect of optogenetic stimulation on avoidance responses driven by the ACS. LCS alone trials measure the ability of the optogenetic stimulation to drive avoidance responses in the absence of the ACS. Plots in all figures display mean ± SEM, and asterisks denote Tukey’s tests. The plots also show data for the no opsin group of animals (open triangles), which compares the effect of all the light patterns used (combined together and delivered in various brain regions) versus ACS. The right panels show trial speed, trial velocity, and intertrial speed for the data in the left panels. The x-axis denotes green light power in mW. B, Effect of green light applied specifically in the zona incerta at different light powers on ACS+LCS trials (blue) and on LCS alone trials (red) for no opsin mice. The green light applied in zona incerta without opsin activation does not affect avoidance responses driven by the ACS and is not able to effectively drive avoidance responses in the absence of the ACS. The x-axis denotes green light power in mW.

Figure 3.

Effect of inhibiting zona incerta GABAergic cells in naive animals. Effect of green light applied in the zona incerta on LCS alone trials (without US) and ACS trials (without US) for mice that express eArch3.0 in GABAergic zona incerta cells (filled blue circles; Vgat-ZI-Arch-NoUs). The left panel displays trial and intertrial crossings (trial crossings are shuttling responses during the LCS or ACS, akin to avoids). The right panels display trial and intertrial speed for the data in the left panels. LCS alone trials without US measure the innate response of the optogenetic stimulation on shuttling and motor activity. For comparison, the left panels also overlay (open gray squares) data of LCS alone trials (with US) and ACS trials (with US) taken from Figure 2A. The x-axis denotes green light power in mW.

Figure 4.

Effect exciting zona incerta GABAergic cells or NRT GABAergic cells on active avoidance responses. A, Effect of low-power and medium-power blue light applied in the zona incerta on ACS+LCS trials for animals that express ChR2 in zona incerta GABAergic cells (Vgat-ZI-ChR2). The right panels show trial speed, trial velocity, and intertrial speed for the data in the left panels. The x-axis denotes blue light frequency trains of 1-ms pulses (Hz) or continuous pulses (Cont). B, Effect of medium-power and high-power blue light applied in the NRT on ACS+LCS trials for animals that express ChR2 in NRT GABAergic cells (Vgat-NR-ChR2). The right panels show trial speed, trial velocity, and intertrial speed for the data in the left panels. The x-axis denotes blue light frequency trains of 1-ms pulses (Hz) or continuous pulses (Cont).

Figure 5.

Effect of activating zona incerta GABAergic output fibers in PO thalamus on active avoidance responses. Effect of medium-power and high-power blue light applied in the PO thalamus on ACS+LCS trials for animals that express ChR2 in GABAergic fibers originating in the zona incerta (Vgat-ZI-ChR2→PO). The right panels show trial speed, trial velocity, and intertrial speed for the data in the left panels. The x-axis denotes blue light frequency trains of 1-ms pulses (Hz) or continuous pulses (Cont).

Figure 6.

Effect of inhibiting PO thalamus cells on active avoidance responses. Effect of green light applied in PO thalamus on ACS+LCS trials (blue) for mice that express eArchT3.0 in glutamatergic PO thalamus cells (CaMKII-PO-Arch). The plots also show data for the no opsin group of animals (open triangles), which compares the effect of all the light patterns used (combined together and delivered in various brain regions) versus ACS. The right panels show trial speed, trial velocity, and intertrial speed for the data in the left panels. The x-axis denotes green light power in mW.

Figure 7.

Effect of activating zona incerta GABAergic output fibers in superior colliculus on active avoidance responses. Effect of medium-power and high-power blue light applied in the superior colliculus on ACS+LCS trials for animals that express ChR2 in GABAergic fibers originating in the zona incerta (Vgat-ZI-ChR2→SC). The right panels show trial speed, trial velocity, and intertrial speed for the data in the left panels. The x-axis denotes blue light frequency trains of 1-ms pulses (Hz) or continuous pulses (Cont).

Figure 8.

Effect of activating zona incerta GABAergic output fibers in PPT on active avoidance responses. A, Effect of low-power and medium-power blue light applied in the PPT on ACS+LCS trials for animals that express ChR2 in GABAergic fibers originating in the zona incerta (Vgat-ZI-ChR2→PPT). The right panels show trial speed, trial velocity, and intertrial speed for the data in the left panels. The x-axis denotes blue light frequency trains of 1-ms pulses (Hz) or continuous pulses (Cont). B, Effect of medium-power and high-power blue light applied in the PPT on ACS+LCS trials for animals that express ChR2 in CaMKII-expressing cells originating in the zona incerta (CaMKII-ZI-ChR2→PPT). The right panels show trial speed, trial velocity, and intertrial speed for the data in the left panels. The x-axis denotes blue light frequency trains of 1-ms pulses (Hz) or continuous pulses (Cont).