Article Figures & Data
Figures
- Figure 1.
Experimental timeline. Rats underwent a 6 d pavlovian conditioned approach (PavCA) procedure, where a neutral lever cue (CS) was paired with a banana-flavored pellet reward (US) following CS retraction. Each session included 25 CS–US pairings (ITI: 30–60 s). Following a resting period of 1–3 weeks, rats were anesthetized and ex vivo brain slices were prepared. See Extended Data Figure 1-1 for distribution of recovery times across phenotypes. Medium spiny neurons (MSNs) were visualized and whole-cell current-clamp recordings were performed in the nucleus accumbens core and shell. Created with BioRender.
- Figure 2.
Classification of pavlovian conditioned approach phenotypes. Rats were classified as sign-trackers (ST; n = 10), goal-trackers (GT; n = 7), or intermediate responders (IR; n = 14) based on their lever and magazine bias during PavCA. A, Each PavCA trial involved the extension of a lever cue (CS) followed by food pellet delivery (US) after 10 s (intertrial interval: 30–60 s). B, STs approach the lever during the CS, despite no need for interaction for reward. C, GTs approach the magazine, the site of food delivery, in response to the CS. D, Distribution of ST (score ≥ 0.5), GT (score ≤ −0.5), and IR (−0.5 < score < 0.5) phenotypes. E, PavCA index scores for ST, GT, and IR groups across six training sessions, illustrating the divergence of phenotypes over time. Data are presented as mean ± SEM. Diagrams created with BioRender.
- Figure 3.
Behavioral differences in lever pressing and magazine entries during PavCA. STs and GTs differed in the number, latency, and probability of lever presses and magazine entries across six PavCA sessions. A, Lever press number, B, latency, and C, probability over sessions for STs, GTs, and IRs. D, Magazine entry number, E, latency, and F, probability across sessions. STs primarily engaged in lever-oriented behaviors, whereas GTs displayed magazine-oriented behaviors. IRs showed intermediate responding between the two groups. Data are presented as mean ± SEM.
- Figure 4.
Passive membrane properties of NAc MSNs in ST, GT, and IR rats. A, Diagram showing the NAc core and shell subregions where whole-cell recordings were made. B, Resting potential and C, input resistance in the NAc core showed no significant differences between STs, GTs, and IRs. D, In the NAc shell, STs had a more hyperpolarized resting membrane potential compared with GTs. E, No differences in input resistance were observed across groups in the NAc shell. Significance for Tukey's post hoc test is shown as **p < 0.01. Data are presented as mean ± SEM. See Extended Data Figure 4-1 for per-animal mean electrophysiological properties of NAc MSNs and Extended Data Figure 4-2 for exploratory regressions between PavCA index and intrinsic properties.
- Figure 5.
Differential hyperpolarizing responses of NAc MSNs in STs, GTs, and IR. A, D, Representative voltage traces from current-clamp recordings of MSNs in the NAc core and shell from STs, GTs, and IRs. B, E, Voltage/current relationship: STs exhibited significantly lower hyperpolarization in response to negative current injections compared with GTs in the core and to both GTs and IRs the NAc shell. No differences were found between phenotypes in response to depolarizing current injections. C, F, Sag ratio: No significant differences were observed between phenotypes in the sag ratio in the NAc core or shell. Significance for mixed-effects model planned comparisons (phenotype × current interaction) is shown as *p < 0.05, **p < 0.01, #p = 0.05. Data are presented as mean ± SEM.
- Figure 6.
Distinct firing properties of NAc MSNs in STs, GTs, and IRs. A, D, Representative current-clamp traces from MSNs in the NAc core and shell following 350 pA (top) and 500 pA (bottom) current injections in STs, GTs, and IRs. B, C, In the NAc core, STs exhibited the lowest number of spikes and firing frequency, while GTs and IRs did not differ from one another. E, F, In the NAc shell, IRs had significantly higher spikes than STs and greater firing frequency compared with both STs and GTs, with no differences between STs and GTs. Significance for mixed-effects model planned comparisons (phenotype × current interaction) is shown as *p < 0.05, **p < 0.01, ****p < 0.0001. Data are presented as mean ± SE.M.
Tables
- Table 1.
Electrophysiological passive and active properties of medium spiny neurons in the core and shell of nucleus accumbens of STs, GTs, and IRs rats
Core Shell Sign-trackers Goal-trackers Intermediates Sign-trackers Goal-trackers Intermediates Passive membrane properties Resting membrane potential, mV −81 ± 1 (23) −80 ± 1 (17) −81.5 ± 0.8 (31) −82.9 ± 0.7 (19) −79.4 ± 0.9 (23) −80.6 ± 0.8 (15) Cell capacitance, pF 150 ± 8 (23) 130 ± 7 (17) 122 ± 5 (31) 105 ± 6 (19) 88 ± 4 (23) 86 ± 6 (15) Input resistance, MΩ 69 ± 7 (23) 77 ± 7 (17) 71 ± 6 (31) 80 ± 8 (19) 99 ± 7 (23) 97 ± 7 (15) Active membrane properties V/I curve (−500 to 0 pA) −11.9 ± 0.2 (19) −13.6 ± 0.2 (18) −13.3 ± 0.2 (18) −14.3 ± 0.3 (15) −16.4 ± 0.2 (23) −16.9 ± 0.3 (11) V/I curve (0 to +100 pA) 5.3 ± 0.4 (19) 6.2 ± 0.4 (18) 5.6 ± 0.4 (18) 7.7 ± 0.6 (15) 8.4 ± 0.5 (23) 9.8 ± 0.6 (11) Sag ratio at −500 pA, mV 1.026 ± 0.003 (19) 1.031 ± 0.003 (18) 1.029 ± 0.003 (18) 1.045 ± 0.004 (15) 1.050 ± 0.002 (23) 1.053 ± 0.006 (11) Number of spikes, AP# 4.7 ± 0.2 (23) 6.4 ± 0.2 (17) 5.7 ± 0.2 (31) 6.5 ± 0.3 (19) 7.0 ± 0.2 (23) 8.3 ± 0.3 (15) Firing frequency, Hz 10.0 ± 0.4 (23) 13.7 ± 0.4 (17) 12.2 ± 0.3 (31) 14.0 ± 0.5 (19) 14.6 ± 0.5 (23) 17.7 ± 0.6 (15) Current to threshold, pA 981 ± 56 (20) 875 ± 60 (16) 879 ± 42 (27) 836 ± 63 (19) 711 ± 45 (23) 694 ± 40 (13) AP threshold, mV −45 ± 1 (20) −44 ± 1 (16) −45 ± 1 (27) −45 ± 2 (19)* −41 ± 1 (23) −39 ± 2 (13) Δ RMP/AP threshold, mV 36 ± 2 (20) 35 ± 1 (16) 37 ± 8 (27) 37 ± 2 (19) 38 ± 1 (23) 42 ± 2 (13) AP amplitude, mV 53.9 ± 0.9 (20) 53 ± 1 (16) 51 ± 1 (27) 53 ± 1 (19) 53 ± 2 (23) 49 ± 2 (13) Δ RMP/AP amplitude, mV 135 ± 1 (20) 132 ± 2 (16) 132 ± 1 (27) 135 ± 1 (19) 133 ± 2 (23) 130 ± 2 (13) Δ AP threshold/AP amplitude, mV 99 ± 2 (20) 97 ± 2 (16) 96 ± 2 (27) 97 ± 2 (19)* 94 ± 2 (23) 88 ± 3 (13) AP half-width, ms 0.72 ± 0.02 (20)* 0.68 ± 0.02 (16) 0.65 ± 0.01 (27) 0.70 ± 0.02 (19) 0.68 ± 0.02 (23) 0.69 ± 0.02 (13) Table lists mean ± SEM (sample size) for passive and active properties of core and shell MSNs for STs, GTs, and IRs. Significance for Tukey's post hoc test between STs and IRs is shown as *p < 0.05.
Figure 1-1
Distribution of recovery times across phenotypes. Days post-PavCA training to slice preparation are shown for each phenotype. The intended design was a 7-day recovery period; however, because behavioral cohorts were staggered so that each day a rat was ready for recordings, some animals (8 of 31) were recorded beyond 7 days due to equipment availability and scheduling constraints. All phenotypes were represented across the 1–3 week recovery period. Download Figure 1-1, DOCX file.
Figure 4-1
Per-animal mean electrophysiological properties of NAc MSNs. Passive and active membrane properties were averaged per animal (one point per rat) and plotted for the NAc core and shell. For passive properties, no overall phenotype effects were observed, but a planned comparison confirmed that STs exhibited significantly more hyperpolarized RMP in the shell compared to GTs. For active properties, mixed-effects analyses did not reveal overall differences across phenotypes, but a planned comparison showed a significant ST vs GT interaction in the core for action potential number across current steps, in line with the cell-level findings. Core vs shell comparisons further revealed significant excitability differences for STs and IRs but not GTs. Significance for mixed-effects model planned comparisons and planned unpaired t-test is shown as *p < 0.05, ****p < 0.0001. Data are presented as mean ± S.E.M. Download Figure 4-1, TIF file.
Figure 4-2
Exploratory regressions between PavCA index and intrinsic properties. (A–C) NAc core: PavCA index vs number of spikes at 500 pA (A), resting membrane potential (B), and input resistance (C). (D–F) NAc shell: PavCA index vs number of spikes at 500 pA (D), resting membrane potential (E), and input resistance (F). Each point represents one animal; solid lines show linear regression with 95% CI (dotted). Regression results (R², p) are shown on each panel. Download Figure 4-2, TIF file.
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