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, 9 (1), 20385

Optogenetic Stimulation of the VTA Modulates a Frequency-Specific Gain of Thalamocortical Inputs in Infragranular Layers of the Auditory Cortex

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Optogenetic Stimulation of the VTA Modulates a Frequency-Specific Gain of Thalamocortical Inputs in Infragranular Layers of the Auditory Cortex

Michael G K Brunk et al. Sci Rep.

Abstract

Reward associations during auditory learning induce cortical plasticity in the primary auditory cortex. A prominent source of such influence is the ventral tegmental area (VTA), which conveys a dopaminergic teaching signal to the primary auditory cortex. Yet, it is unknown, how the VTA influences cortical frequency processing and spectral integration. Therefore, we investigated the temporal effects of direct optogenetic stimulation of the VTA onto spectral integration in the auditory cortex on a synaptic circuit level by current-source-density analysis in anesthetized Mongolian gerbils. While auditory lemniscal input predominantly terminates in the granular input layers III/IV, we found that VTA-mediated modulation of spectral processing is relayed by a different circuit, namely enhanced thalamic inputs to the infragranular layers Vb/VIa. Activation of this circuit yields a frequency-specific gain amplification of local sensory input and enhances corticocortical information transfer, especially in supragranular layers I/II. This effects persisted over more than 30 minutes after VTA stimulation. Altogether, we demonstrate that the VTA exhibits a long-lasting influence on sensory cortical processing via infragranular layers transcending the signaling of a mere reward-prediction error. We thereby demonstrate a cellular and circuit substrate for the influence of reinforcement-evaluating brain systems on sensory processing in the auditory cortex.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Anatomical validation of fiber position relative to target side and optogenetic intracranial self-stimulation (A) Schematic overview of fiber implant position for optogenetic stimulation of the VTA, and the ipsilateral AI recording side. Dashed boxes indicate representative regions of interest shown in B) identified by yellow and red asterisks. (B) Top, YFP expression in the temporal cortex covering the region of AI after virus transduction of the VTA indicates fiber terminals from the VTA targeting mainly upper layers and collaterals in deeper layers (white arrows). YFP expression was detectable in multiple regions of the neocortex (not shown). Bottom, co-fluorescence of YFP (AAV-CamKIIα-C1V1 (E162T)-p2A-eYFP) and TH-immunostaining (Alexa Fluor 546). Area of co-fluorescence is indicative of overlapping neuronal populations expressing the virus and TH mainly found in the VTA, and not the substantia nigra. Scale bars indicate 250 and 200 µm, respectively. (C) Schematic representation of optogenetic intracranial self-stimulation: While nose-poking the lever, animals induce a light flash towards the VTA resulting in extensive self-stimulating behavior. (D) Gerbil skull with prominent landmarks (bregma, lambda and occipital crest) for anatomical reference modified from Radtke-Schuller et al. 2016. For experiments, bregma has been used for reference of medio-lateral (ML) and anterior-posterior (AP) position of the VTA. (E) Estimated actual AP/ML coordinates with mean coordinates (AP:−3.57 mm; ML: 584.14 µm) relative to bregma of the C1V1group (n = 7) as estimated with the gerbil brain atlas. (F) Fiber distance (mean ± SEM) towards area of co-fluorescence (146.8 ± 38.9 µm; n = 7). Compare with bottom picture of B). (G) Averaged lever pressing rates (lever presses/min) of the C1V1 (n = 12) and YFP (n = 8) groups over 10 days. A representative video of a C1V1 animal is accessible as Movie (See Video S1).
Figure 2
Figure 2
Electrophysiological measurements and effects of VTA stimulation on tone-evoked CSD profiles in AI (A) Schematic representation of the timeline of measurements. Pre baseline measurements (Tone stimulation: 0.125–32 kHz, tone duration: 200 ms, ISI: 0.6–0.8, 50 pseudorandomized repetitions, 65 dB SPL, 7.5 min) were performed until CSD patterns had stabilized (45–75 min). A single measurement of combined tone and laser stimulation (25 Hz, 473 nm, 10 mW) was carried out and followed by a series of post-measurements (up to 60 min). (B) Representative example of a CSD profile after BF- (top) and near-BF (bottom) stimulation before, during and 30 minutes after the combined tone/VTA-laser measurement from an animal of the C1V1 group. Before VTA stimulation, BF-evoked CSD profiles revealed a canonical feedforward pattern of stimulus-evoked current flow starting with initial sink components in cortical layers III/IV and Vb/VIa. Subsequent sink activity was found in layers Va, I/II and VIb. Activity after near-BF stimulation showed a less pronounced columnar activation in the pre-condition. During paired tone and VTA stimulation, both stimulation frequencies evoked stronger and prolonged translaminar current flow, which was still enhanced 30 minutes later. Cortical layers are indicated. Dashed vertical lines indicate tone onset and offset.
Figure 3
Figure 3
Binned time courses of single-trial sink peak amplitude data of layer-specific CSD-traces Temporal development of single-trial sink peak amplitudes for early sink activity (sink onset <50 ms) in layers III/IV, Va and Vb/VIa and late sinks (sink onset >50 ms) in layers I/II and VIb for BF, near- and non-BFs. Layer I/II peak amplitudes showed a significant increase for the C1V1 group during laser and in post-measurements, surpassing the +10% criterion within the BF and near-BF bins. Significant differences from the control group are again revealed by LME models and indicated by asterisks. Layer I/II peak amplitudes in the YFP and control group did not show corresponding increases over the recording time but showed a decrease and recovery for the YFP group. Layer III/IV activity did not reveal differences over time for BF-evoked responses in all groups. With spectral distance from the BF the C1V1 group showed a moderate increase yielding significance at the >30 min time bin compared to control animals. Within the non-BF bin, peak amplitudes showed a significant decrease in the YFP group during and after laser stimulation. Layer Va peak amplitudes were most stable across time and groups only displaying a significant decrease for the YFP group in the non-BF bin a <30 min. Layer Vb/VIa peak amplitudes in the C1V1 group were significantly increased in all post-measurements after BF-stimulation. For stimulation with near-BF a similar trend was found. Significant changes between the YFP and control group were again due to decreased peak amplitudes in the YFP group. Layer VIb displayed a highly significant increase in the C1V1 group during laser stimulation, most prominent in the non-BF bin, and less prominent in near-BF and BF bins. Laser-induced increase only persisted for the next time bin, but then recovered to pre-condition. While the control group showed stable peak amplitudes over the time course, YFP animals again showed a moderate decrease most prominent in off-BF bins.
Figure 4
Figure 4
Layer-specific early and late changes of tuning sharpness of the C1V1 group For data from the C1V1 group, peak amplitudes within each layer were normalized to BF-responses before laser stimulation. We fitted a linear fit (dashed lines) across evoked responses across the BF-, near-BF- and non-BF-bins and calculated the slope as indicator for spectral tuning sharpness (for pre, laser, >30 min). Sharpest tuning properties of peak amplitudes were found in layers III/IV (slope of 0.28). Tuning in layers III/IV was not affected by VTA stimulation. Layers I/II showed less prominent tuning revealed by a shallower slope in the pre-condition. While VTA stimulation did not yield an immediate significant difference, slopes indicated a significantly sharper tuning >30 min after VTA stimulation (p < 0.01). This was due to mainly an increase in BF-evoked peak amplitudes in accordance with Fig. 5. Peak amplitudes in infragranular layers Vb/VIa showed a similar effect as layers I/II with a trend of sharper tuning during VTA stimulation that yielded significance >30 min later. In contrast, only in late infragranular layer VIb, peak amplitudes revealed a significantly shallower slope indicative of a broader frequency tuning during laser stimulation (Pre: laser; p < 0.01), which recovered after >30 min (Pre: <30 min; p = 0.1). This can be seen by the flat slope between non- and BF bins. Layer Va only showed a minor decrease of the slope during VTA stimulation that recovered partially >30 min later. Significances indicated are based on slope comparisons performed using the Ismeans package in R (version 2.27–62). For statistical explanation, see text.
Figure 5
Figure 5
Temporal development of early and late AVREC and ResidualCSD activity (A) Grand average traces of the BF-evoked AVREC (top) and ResidualCSD (bottom) of the C1V1 group (n = 12) for binned pre, laser and post (<30, >30 & >45 min)-measurements. Right, insets illustrate that AVREC activity is mainly associated with local columnar activity, while the ResidualCSD quantifies contributions from lateral corticocortical input (cf Happel et al., ,). (B) Temporal time courses of Pre-normalized early/late AVREC and early/late ResidualCSD traces of C1V1 (red), control (blue) and YFP (green) groups (n = 12, n = 7, n = 7, respectively) shown for BF stimulation. Early AVREC signal displayed a significant increase in post-measurements for the C1V1 group whereas time courses of the control and YFP groups were stable. Late AVREC signal showed no significant differences between either group. RMS ResidualCSD values of early and late time windows displayed a similar temporal development as the early AVREC becoming significantly increased in the later post-measurements within the C1V1 group. Control and YFP groups showed no significant changes over time. Note the peaking in the early ResidualCSD RMS during laser stimulation, which is only present in the C1V1 group. Asterisks mark significant changes according to the applied mixed linear models of the normalized data towards the control group (see Materials and Methods). (C) Tuning curves of the RMS value normalized to BF-evoked responses in the pre-condition for early/late AVREC and early/late ResidualCSD for binned time points for C1V1 group. Note the general increase of the overall tuning curve relative to pre measurements.
Figure 6
Figure 6
Normalized single-trial early and late AVREC and ResidualCSD RMS values over time. (A) Temporal time course of averaged early single-trial RMS AVREC (top) and ResidualCSD (bottom) values normalized to pre-measurements. Data for BF, near-BF and non-BF stimulation is shown separately and was binned for pre-measurements, laser, and post-measurements (<30 min, >30, >45 min). Note the prominent increase of early RMS AVREC values for the C1V1 group whereas control and YFP group displayed a more stable or decreasing time course, respectively. Also, early RMS ResidualCSD values significantly increased during and after the Laser measurements for BF, near- and non-BF bins of the C1V1 group, whereas YFP and control display a more stable time course. (B) Temporal time course of late Pre-normalized RMS AVREC and ResidualCSD values of single-trial data for BF, near-BF and non-BF. Late RMS AVREC values for the C1V1showed a mild, yet not significant, increase that did not surpass the +10% criterion. The control group displayed a stable and slightly declining time course for the late RMS AVREC values, while the YFP group showed a moderate decrease that recovered over time. Late RMS ResidualCSD values increased during and after the Laser measurements for BF, near- and non-BF bins of the C1V1 group, whereas YFP and control groups both showed a more stable time course. Significances in (A,B) were calculated using mixed linear models on the normalized data. Asterisks indicate corresponding significances in comparison to the control group, in case values exceed the ±10% pre-criterion. Single-trial CSD data in following figure is presented equally.
Figure 7
Figure 7
Schematic illustration of convergent deep layer inputs from sensory thalamus and VTA. VTA projections mainly target upper and infragranular layers of the gerbil auditory cortex (see also Fig. 1B). Stimulating the VTA projections led to a frequency-specific gain amplification of early sensory-evoked responses in thalamocortical recipient layers Vb/VIa. This gain increase effectuated an enhanced spectral tuning representation in supragranular layers I/II. The supragranular gain modulation might hence be inherited via intratelencephalic neurons targeting upper layers and bypassing granular input circuits, may originate from a direct influence of dopamine released in upper layers or a combination of both. MGB, medial geniculate body.

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References

    1. Ohl FW. Role of cortical neurodynamics for understanding the neural basis of motivated behavior - lessons from auditory category learning. Curr. Opin. Neurobiol. 2014;31:88–94. doi: 10.1016/j.conb.2014.08.014. - DOI - PubMed
    1. Bromberg-Martin ES, Matsumoto M, Hikosaka O. Dopamine in motivational control: rewarding, aversive, and alerting. Neuron. 2010;68:815–34. doi: 10.1016/j.neuron.2010.11.022. - DOI - PMC - PubMed
    1. Schultz W. Neuronal Reward and Decision Signals: From Theories to Data. Physiol. Rev. 2015;95:853–951. doi: 10.1152/physrev.00023.2014. - DOI - PMC - PubMed
    1. Bao S, Chan VT, Merzenich MM. Cortical remodelling induced by activity of ventral tegmental dopamine neurons. Nature. 2001;412:79–83. doi: 10.1038/35083586. - DOI - PubMed
    1. Hui GK, et al. Conditioned tone control of brain reward behavior produces highly specific representational gain in the primary auditory cortex. Neurobiol. Learn. Mem. 2009;92:27–34. doi: 10.1016/j.nlm.2009.02.008. - DOI - PMC - PubMed
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