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Optogenetic dissection of basolateral amygdala contributions to intertemporal choice in young and aged rats

Research Article
Cite this article as: eLife 2019;8:e46174 doi: 10.7554/eLife.46174
8 figures, 2 tables and 1 additional file

Figures

Schematics of intertemporal choice task and timing of light delivery.

(A) Schematic of the intertemporal choice task illustrating the choices and trial blocks across which the duration of the delay to the large reward increased. On each trial, rats were presented with two response levers that differed with respect to the magnitude and timing of associated reward delivery. Presses on one lever delivered a small (one food pellet), immediate reward, whereas presses on the other lever delivered a large (three food pellets), delayed reward. Trials were presented in a blocked design, such that the delay to the large reward increased across successive blocks of trials in a session. (B) Schematic of a single trial in the intertemporal choice task showing the task epochs during which light was delivered (represented by the green line). Using a within-subjects design, light was delivered during deliberation (from when levers are presented until a choice is made); small reward delivery; delay; large reward delivery; delay +large reward delivery; and intertrial interval (ITI).

https://doi.org/10.7554/eLife.46174.003
Functional inhibition of BLA pyramidal neurons via activation of halorhodposin.

(A) A two-photon reconstruction of a biocytin-filled eNpHR3.0-expressing BLA neuron demonstrates multiple primary dendritic branches and spiny dendritic arborizations typical of BLA pyramidal neurons. Scale bar represents 20 μm. (B) Light-induced activation of eNpHR3.0 (1 s), indicated by the green line, produced a robust outward current in virally-transfected neurons in young rats when voltage clamped at −70 mV. Illustrated current is the average response observed in 26 BLA neurons from three young rats. (C) Representative trace shows that 1 s activation of eNpHR3.0 was reliably able to silence young neurons when firing under moderate load. The square pulse below the voltage trace for this cell indicates the time of current injection through the patch pipette that was sufficient to induce firing. The green line above the voltage trace indicates time of 1 s activation of eNpHR3.0. D: Light-induced activation of eNpHR3.0 (4 s) also produced a robust outward current in young BLA neurons, with no evidence of rebound excitation after termination of the light pulse. Illustrated current is the average response observed in 16 cells from two young rats. (E-H) Illustrate results of experiments identical to those presented in panels A-D, except in aged virally-transfected BLA neurons. Specifically, panel E shows a representative two-photon reconstruction of a virally-transducedaged BLA neuron (scale bar, 20 μm). Panel F illustrates average response to 1 s activation of eNpHR3.0 observed in 28 BLA neurons from three aged rats. Panel G illustrates a representative response to 1 s eNpHR3.0 activation during a suprathreshold current injection in a virally-transduced aged BLA neuron. Panel H illustrates the average response to 4 s activation of eNpHR3.0 observed in 16 BLA neurons from two aged rats. Overall, aging had no significant effect on intrinsic properties of BLA neurons, or on the effects of eNpHR3.0 activation in virally-transduced neurons. Raw data for electrophysiological analyses are provided in Figure 2—source data 1.

https://doi.org/10.7554/eLife.46174.004
Verification of viral expression and fiber optic placements.

The extent of viral-transduction in young (left) and aged (right) rats is depicted in green. Darker green indicates areas of greater expression of AAV5-CamKIIα-eNpHR3.0-mCherry or AA5-CamKIIα-mCherry(centered on the BLA), whereas lighter green indicates less expression (margins of the BLA). Filled black circles represent optic fiber placements in the experimental (eNpHR3.0) groups, and open circles represent optic fiber placements in the control groups. Viral expression and fiber placements are mapped to standardized coronal sections corresponding to −2.12 mm through −3.30 mm from bregma according to the atlas of Paxinos and Watson (2005).

https://doi.org/10.7554/eLife.46174.006
Effect of age on actual delays and indifference point.

(A) Mean percent choice of the large reward in young and aged rats prior to initiation of BLA inactivation experiments. Note that delays to large reward delivery were adjusted individually for young (n = 8, open circles) and aged (n = 7, closed circles) rats in order to place all rats in the same parametric space. (B) Mean actual delays required to achieve the comparable young and aged rat choice performance shown in panel A. Aged rats required longer delays in Blocks 2 and 3 to achieve choice performance comparable to young rats. (C) The mean indifference point (the delay at which rats showed equivalent preference for the small and large rewards) was significantly greater in aged rats compared to young. In all panels, error bars represent the standard error of the mean (SEM). *p<0.05, main effect of age; ××p < 0.01, age × delay block interaction. Raw data for these graphs are provided in Figure 4—source data 1.

https://doi.org/10.7554/eLife.46174.007
Effect of BLA inactivation during the deliberation and small reward epochs.

(A) Inactivation of the BLA during the deliberation epoch (prior to a choice) resulted in a significant increase in preference for the large, delayed reward in both young (n = 8) and aged (n = 7) rats. (B) Effects of BLA inactivation during the deliberation epoch on trial-by-trial choice strategies. This analysis revealed that the increased choice of the large, delayed reward caused by BLA inactivation during deliberation (panel A) was due to an increase in the percentage of trials on which rats shifted to the large, delayed reward following a choice of the small, immediate reward. (C) Inactivation of the BLA during the small reward epoch resulted in a significant decrease in preference for the large, delayed reward in young (n = 6), but not aged (n = 6), rats. (D) Effects of BLA inactivation during the small reward epoch on trial-by-trial choice strategies. This analysis revealed that the decreased choice of the large, delayed reward in young rats caused by BLA inactivation during the small, reward epoch (panel C) was due to an increase in the percentage of trials on which rats ‘stayed’ on the small, immediate reward following a choice of this reward on the previous trial. In contrast, BLA inactivation during the same epoch in aged rats had no effect on trial-by-trial choice strategies. In all panels, error bars represent standard error of the mean (SEM). *p<0.05, **p<0.01, ***p<0.001, main effect of inactivation; ×××p < 0.001, inactivation × delay block interaction. Raw data for these graphs are provided in Figure 5—source data 1.

https://doi.org/10.7554/eLife.46174.009
Effect of BLA inactivation during outcomes associated with choice of the large reward.

(A) Inactivation of the BLA during the delay epoch resulted in no change in choice performance in either young (n = 6) or aged (n = 6) rats. (B) Inactivation of the BLA during the large reward epoch resulted in no change in choice performance in either young (n = 6) or aged (n = 6) rats. (C) Inactivation of the BLA during both the delay and large reward epochs resulted in no change in choice performance in either young (n = 3) or aged (n = 3) rats. Error bars represent standard error of the mean (SEM). Raw data for these graphs are provided in Figure 6—source data 1.

https://doi.org/10.7554/eLife.46174.015
Figure 6—source data 1

Hernandez et al. Figure 6 - source data 1

https://doi.org/10.7554/eLife.46174.016
Effect of BLA inactivation during the intertrial interval.

Inactivation of the BLA during the intertrial interval resulted in no change in choice performance in either young (n = 6) or aged (n = 6) rats. Error bars represent standard error of the mean (SEM). Raw data for these graphs are provided in Figure 7—source data 1.

https://doi.org/10.7554/eLife.46174.017
Effect of light delivery into BLA during the deliberation and small reward epochs in rats virally transduced with a control vector.

(A) Light delivery into the BLA during the deliberation epoch resulted in no change in choice performance in either young (n = 4) or aged (n = 4) control vector rats. (B) Light delivery into the BLA during the small reward epoch resulted in no change in choice performance in young (n = 4) control vector rats. Error bars represent standard error of the mean (SEM). Raw data for these graphs are provided in Figure 8—source data 1.

https://doi.org/10.7554/eLife.46174.019

Tables

Table 1
Effects of BLA inactivation on number of trials completed per session.
https://doi.org/10.7554/eLife.46174.011
EpochAgeLaser conditionMeanSEMStatistical comparisons
DeliberationYoungOff (Baseline)52.6880.81Laser condition: F(1,13)=0.180, p=0.678
Age: F(1,13)=0.162, p=0.694
Laser condition × Age: F(1,13)=3.264, p=0.094
On (Inactivation)51.6250.94
AgedOff (Baseline)51.7140.87
On (Inactivation)53.4291.003
Outcome
(small reward)
YoungOff (Baseline)52.6670.394Laser condition: F(1,10)=3.431, p=0.094
Age: F(1,10)=0.180, p=0.681
Laser condition × Age: F(1,10)=0.328, p=0.580
On (Inactivation)53.6670.635
AgedOff (Baseline)52.6390.394
On (Inactivation)53.1670.635
  1. Raw data for this table are provided in Table 1—source data 1.

Table 2
Effects of BLA inactivation on lever response latencies.
https://doi.org/10.7554/eLife.46174.013
EpochAgeLeverLaser conditionMean (sec)Std. errorStatistical analysis
DeliberationYoungLargeOff (Baseline)1.3850.174Laser condition:
Large: F(1, 13)=2.898, p=0.112
Small: F(1, 8)=2.050, p=0.190
Age:
Large:: F(1, 13)=1.988, p=0.182
Small: F(1, 8)=0.505, p=0.497
Laser condition × Age:
Large: F(1, 13)=0.588, p=0.457
Small: F(1, 8)=1.039, p=0.338
On (Inactivation)1.4420.204
SmallOff (Baseline)1.0830.187
On (Inactivation)1.5430.326
AgedLargeOff (Baseline)0.9560.186
On (Inactivation)1.1080.218
SmallOff (Baseline)1.0430.187
On (Inactivation)1.1200.326
Outcome
(small reward)
YoungLargeOff (Baseline)1.3220.136Laser condition:
Large: F(1, 10)=1.429, p=0.260
Small: F(1, 10)=3.225, p=0.103
Age:
Large: F(1, 10)=4.149, p=0.069
Small: F(1, 10)=1.157, p=0.307
Laser condition × Age:
Large: F(1, 10)=0.257, p=0.623
Small: F(1, 10)=0.004, p=0.954
On (Inactivation)1.2170.141
SmallOff (Baseline)1.1070.149
On (Inactivation)0.9380.054
AgedLargeOff (Baseline)0.9120.136
On (Inactivation)0.8700.141
SmallOff (Baseline)0.9620.149
On (Inactivation)0.8040.054
  1. Raw data for this table are provided in Table 2—source data 1.

Data availability

All data generated or analyzed during this study are included in the manuscript and supporting files.

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