Introduction

Parkinson’s disease (PD) patients exhibit non-motor alterations several years before the onset of classical motor symptoms (i.e., rigidity, resting tremor, and bradykinesia) [1]. Mood disorders such as anhedonia and depression are insidious non-motor symptoms of PD and very detrimental to the quality of life of PD patients [2]. These pre-motor symptoms may fluctuate in intensity and also may be dissociated from each other over time during the progression of PD [3].

Depression has a heterogeneous symptomatology and responsiveness to treatment. Anhedonia, a decreased ability to experience pleasure, is a core symptom of this mental illness [4], and its occurrence seems to be variable in intensity and duration depending on the subtype of depression affecting the patients [5]. Social isolation is present in PD patients [6] and is also a symptom found in some cases of depression [4]. Importantly, non-motor symptoms of PD are underdiagnosed and consequently undertreated [3], and it is critical to improve the knowledge about the neurobiology of these symptoms in PD patients to offer adequate therapeutic strategies. For instance, many PD patients experience apathy independently of depression [7], warring for a better comprehension of the relative modifications of different brain structures involved in the modulation of emotional responses to clarify this duality between depression and anhedonia in PD.

Dopaminergic degeneration of dorsolateral striatum (DLS) is a cardinal feature of PD, but it also affects other brain structures such as the pre-frontal (PFC) [8]. Functional connectivity between cortical and striatal neuronal systems plays a pivotal role in sensory, emotion, and motor functions [9–11]. However, the neurobiology of anhedonia and depression in PD is still poorly understood, and the possible different participation of the DLS and PFC to process different non-motor symptoms of PD remains unknown.

In this study, through the use of behavioral, neurochemical, and electrophysiological approaches, we investigated the temporal and the structural dissociation between the role of DLS and PFC in the appearance of anhedonia and defense behaviors relevant to depression in rats submitted to bilateral 6-hydroxydopamine (6-OHDA) lesions in the DLS. Our findings provide the first evidence of a dissociative involvement of the DLS and PFC, respectively, in anhedonic and defense behaviors relevant to depression in 6-OHDA-lesioned rats. These behavioral modifications were accompanied by temporal fluctuations in the dopaminergic receptor density, leading to altered pre-synaptic control and dopaminergic sensitivity in the DLS and in the PFC.

Methods and Materials

Animals

Male Wistar rats weighing 300–350 g, aged 12–16 weeks at the time of testing, were used. All procedures were approved by the Institutional Ethical Committee for the care and use of laboratory animals of the Federal University of Santa Catarina (CEUA PP00830/2013) and the Ethical Committee of the Center for Neuroscience of Coimbra.

Drugs and Stereotaxic Surgery

The dose of 6-OHDA (Sigma-Aldrich, USA) was selected (Supplementary data Fig. S1 and Fig. S2) at a dose of 10 μg/hemisphere and was bilaterally injected into the DLS (AP, + 0.2 mm; ML, ± 3.5 mm; DV, −4.8 mm from bregma and dura). All animals were administered intra-peritoneally (i.p.) with desipramine (20 mg/kg) (Sigma-Aldrich, USA) 30 min before surgery, in order to protect noradrenergic terminals from 6-OHDA toxicity. The stereotaxic surgery was performed under ketamine (75 mg/kg)/xylazine (8 mg/kg) i.p. anesthesia. Sham-operated rats followed the same protocol except for the fact that vehicle was injected instead of 6-OHDA. Fluoxetine (Sigma-Aldrich, USA) and bupropion (Sigma-Aldrich, USA) were dissolved in saline solution, and the dose of these drugs was selected based on previous studies [12, 13]. The behavioral experiments were carried out 7 or 21 days after the surgery and either transcardially perfused or killed by decapitation after halothane anesthesia following behavioral tests.

Behavioral Tests

Assessment of Motor Function

Spontaneous locomotor activity was assessed in the open field test and allowed to freely explore it during 15 min to measure, using the ANY-maze software (Stoelting, USA), the total distance travelled and the average speed as indicators of spontaneous locomotor activity, as described previously [14]. The balance and motor coordination of rats were tested in the accelerated rotarod (Insight, Ribeirão Preto, Brazil) with automatic increase speed of the cylinder rotation (phase 1–2, 16 rpm; phase 3–4, 20 rpm; phase 5–6, 25 rpm; phase 7–8, 28 rpm; phase 9–10, 37 rpm) to measure the latency to fall, as previously described [14]. The measurement of grip force was made using a computerized grip force meter (Grip Strength Meters, Columbus Instruments, Columbus, OH, USA), simultaneously evaluating the right and left limbs and expressing grip force as the difference in grams, as previously described [14].

Assessment of Emotional Parameters

The sucrose consumption test, frequently used to measure anhedonia [15], compared the consumption of water and of a 0.8 % sucrose solution during 48 h, as described previously [16]. Additionally, the splash test, which evaluates a form of motivational behavior considered to parallel some symptoms of anhedonia such as apathetic behavior [17], was carried out to measure the time spent grooming which was recorded for a period of 15 min after squirting a 10 % sucrose solution on the dorsal coat of the animals, as previously described [18]. Defense behaviors relevant to depression were evaluated in a forced swimming test, scoring the total duration of immobility and swimming during a 5-min test session in glass cylinders containing water, as previously described [14]. Social interaction was evaluated as previously described [19, 20] by measuring the amount of time spent by each rat in a pair sniffing, grooming, following, kicking, mounting, jumping on, wrestling/boxing, and crawling under/over the partner during a 10-min period of interaction. Anxiety-like behavior was evaluated using an elevated plus-maze by measuring during 5 min the percent open arm entries (% open arm entries: open entries / total entries × 100) and percent time on open arms (% open time), as previously described [14].

Immunohistochemistry

The density of tyrosine hydroxylase (TH) was evaluated in free-floating sections containing the DLS and substantia nigra (25 μm thick) stained with a rabbit anti-TH polyclonal antibody (1:1500, ab-112 Abcam, UK) followed by a goat anti-rabbit secondary antibody (1:2000; ab60317, ChromeoTM 546 Abcam, UK), and the fluorescent signals were detected using a fluorescent microscope (BioZero8000, Keyence Corp., Japan), as previously described [21].

Western Blotting

Striatum or PFC homogenates were separated by SDS-PAGE and, after electrotransfer, protein and molecular weight markers (BioRad, Mississauga, Canada) were revealed by Ponceau Red staining Then, membranes were incubated overnight at 4 °C with antibodies anti-D1R (sc-14001; Santa Cruz Biotechnology, USA), anti-D2R (sc-5303; Santa Cruz Biotechnology, USA), or anti-DAT (MAB369; Millipore, Germany) and, after washing, with horseradish peroxidase-conjugated anti-rabbit, anti-mouse, and anti-rat antibodies for 2 h. Blots were visualized using the PerkinElmer ECL system, as previously described [22].

Extracellular Electrophysiological Recordings

Electrophysiological recordings were carried out as previously described [23] by extracellularly recording population spikes (PSs) either in layer V of the medial prelimbic PFC upon stimulation of layers II/III in coronal slices (250–300 μm thick) containing the PFC or in the DLS upon stimulation of white matter above the DLS in slices (400 μm thick) containing the DLS. The intensity of stimulation was selected to yield 40–50 % of the maximum response, which was quantified by its population spike amplitude. Paired-pulse stimulation consisted of two stimuli delivered with an inter-stimuli interval of 50 or 250 ms for PFC slices or 20 or 160 ms for DLS slices. The paired-pulse ratio was calculated as the ratio of the second response to the first response. Dopamine (25, 50, 100 μM) was cumulatively added through the superfusion solution, and its effect estimated by changes of PS amplitude.

Experimental Protocol

Rats were first stereotaxically injected with 6-OHDA (or vehicle for controls) in the DLS (Supplementary data Fig. S3), and independent groups of animals were tested only once in the behavioral tasks after either 7 or 21 days: Motor function was first characterized using the rotarod, the open field, and the grip force tests; then, the rats were tested in the non-motor behavioral tasks such as sucrose preference and splash tests (anhedonia), forced swimming and social interaction (defense behaviors relevant to depression), and elevated plus-maze (anxiety-like behaviors). Some rats were then transcardially perfused, and their brains were processed for immunohistochemical quantification of tyrosine hydroxylase (TH) in the DLS and substantia nigra (SN). Other rats were killed and their brains were dissected for Western blotting quantification of D1R, D2R, and dopamine transporter in the striatum and PFC. A last set of rats were killed to carry out extracellular electrophysiological recordings in DLS and PFC slices. Finally, independent experiments were carried out following the same protocol, to test the impact of the antidepressant drugs fluoxetine or bupropion on the anhedonic-like and defense behaviors relevant to depression 7 and 21 days after 6-OHDA lesion.

Data Analysis and Statistics

Statistical analysis was performed by two-way analysis of variance (ANOVA) factorial followed by Newman-Keuls post hoc test, except the analysis of electrophysiological data that was carried out using Student’s t tests. The values are expressed as mean ± standard error of mean (s.e.m), and the significance level was P < 0.05.

Results

Intra-DLS 6-OHDA Injection Induces Partial Loss of Dopaminergic Neurons in the Nigrostriatal Pathway with No Motor Impairments

The intra-striatal administration of 6-OHDA caused a retrograde lesion of the nigrostriatal dopaminergic pathway (Fig. 1). In fact, both at 7 and at 21 days after 6-OHDA injection, the number of TH-positive cells was reduced by 6-OHDA compared to control in both the DLS (7 days, 63.0 ± 2.5 %, F (2, 21) = 423.0, P < 0.05; 21 days, 65.6 ± 1.8 %, F (2, 21) = 399.5, P < 0.05) (Fig. 1a, b) and SN (7 days, 50.0 ± 4.5 %, F (2, 21) = 20.26, P < 0.05; 21 days, 68.0 ± 4.4 %, F (2, 21) = 20.26, P < 0.05) (Fig. 1c, d); thus, there was a progression over time of the lesion only in the SN (Fig. 1c), and the same extent of degeneration was observed in both hemispheres (left and right) in the DLS and SN at both time points after 6-OHDA administration (Fig. 1).

Fig. 1
figure 1

6-Hydroxydopamine (6-OHDA) decreased the optical density of tyrosine hydroxylase (TH) in the dorsolateral striatum (DLS) and the number of TH-positive cells in the substantia nigra (SN) to a similar extent in both hemispheres left (L) and right (R) with no motor impairments. a Immunohistochemical quantification of TH staining in the DLS. b Representative coronal sections of the DLS. c Immunohistochemical quantification of TH-positive cells in the SN. d Representative coronal sections of the SN. e Total distance travelled during 15 min in the open field apparatus. f Average speed in the open field. g Latency to fall in the accelerated rotarod test. h Grip force test to evaluate the strength of the forelimbs. (*P < 0.05 vs. control group; # P < 0.05 vs. 6-OHDA group 7 days after injection, two-way ANOVA followed by the Newman-Keuls post hoc tests; N = 5–10 rats/group)

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However, the extent of 6-OHDA-induced dopaminergic injury was not sufficient to impair motor function, as assessed in different behavioral tests, namely, in the open field (Fig. 1e, f), rotarod (Fig. 1g), and grip force tests (Fig. 1h).

Decoupling Anhedonia and Defense Behaviors Relevant to Depression in 6-OHDA-Lesioned Rats

When compared to the control group, rats lesioned with 6-OHDA displayed a decreased sucrose consumption (F (1, 33) = 7.35, P < 0.05) (Fig. 2a) and a decreased time of grooming (F (1, 33) = 8.57, P < 0.05) (Fig. 2c) only 7 days after 6-OHDA injection (but not after 21 days), which is indicative of an anhedonic-like behavior. Conversely, in the forced swimming test, 6-OHDA-lesioned rats displayed an increased immobility time (F (1, 33) = 12.93, P < 0.05) (Fig. 2d) and a decreased swimming time (F (1, 33) = 13.22, P < 0.05) only at 21 days (but not after 7 days) after 6-OHDA injection (Fig. 2e). At this later time point after 6-OHDA injection (21 days), the lesioned rats also exhibited a significant reduction of social interaction behaviors (sniffing, grooming, following, kicking, mounting, jumping on, wrestling/boxing, and crawling under/over the partner) (Fig. 2f), which was not observed 7 days after 6-OHDA injection. On the other hand, 6-OHDA-lesioned rats did not exhibit a modified anxiety-like behavior in the elevated plus-maze at neither 7 nor 21 days after 6-OHDA injection (Supplementary data Fig. S4).

Fig. 2
figure 2

Temporal dissociation between anhedonic-like and defense behaviors in 6-hydroxydopamine (6-OHDA)-lesioned rats. 6-OHDA decreased sucrose preference when compared to control group 7 days after 6-OHDA injection, (a) and this anhedonic-like behavior was not present 21 days after the 6-OHDA injection (b). The same pattern of response was observed in the splash test, confirming that anhedonic-like behavior was present only after 7 days (c). 6-OHDA increased the immobility time (d) and decreased the swimming time (e) in the forced swimming test only 21 days after 6-OHDA injection. In the social interaction test, 6-OHDA increased the social isolation when compared to control group only 21 days after 6-OHDA injection (f). (*P < 0.05 vs. control group, two-way ANOVA followed by the Newman-Keuls post hoc tests; N = 8–10 rats/group)

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The 6-OHDA-induced anhedonia observed only at 7 days was prevented by a treatment with bupropion (10 mg/kg, i.p., during 7 days) in both the sucrose preference task (F (1, 27) = 7.73, P < 0.05) (Fig. 3a) and in the splash test (F (1, 26) = 62.52, P < 0.05) (Fig. 3c). The treatment with fluoxetine (10 mg/kg, i.p., during 7 days) prevented the impairments induced by 6-OHDA only in splash test (F (1, 28) = 46.39, P < 0.05) (Fig. 3d) but not in sucrose preference task (F (1, 27) = 1.14, P > 0.05) (Fig. 3b). Regarding the 6-OHDA-induced defense behaviors relevant to depression observed only at 21 days, a chronic i.p. treatment during 21 days with both fluoxetine (10 mg/kg) or bupropion (10 mg/kg) prevented these alterations in immobility time (bupropion, F (1, 28) = 18.05, P < 0.05; fluoxetine, F (1, 27) = 19.85, P < 0.05) (Fig. 3e, f). Likewise, the 6-OHDA-induced decreased investigation time in the social interaction test observed only at 21 days was also prevented by a chronic i.p. treatment during 21 days with both fluoxetine (10 mg/kg; F (1, 26) = 33.21, P < 0.05) or bupropion (10 mg/kg; F (1, 28) = 8.4 1, P < 0.05) (Fig. 3g, h).

Fig. 3
figure 3

The effects of bupropion (10 mg/kg, i.p.) and fluoxetine (10 mg/kg, i.p.) on the anhedonic-like and defense behaviors of 6-hydroxydopamine (6-OHDA)-lesioned rats. Treatment with bupropion (a), but not with fluoxetine (b), during 7 days reversed the anhedonic-like behaviors induced by 6-OHDA lesion. Both bupropion (c) and fluoxetine (d) treatments during 7 days reversed the 6-OHDA-induced reduction of grooming time in splash test. Chronic treatments during 21 days with bupropion or fluoxetine reversed the helpless behavior in the forced swimming test (e, f) and social isolation (g, h) induced by 6-OHDA. (Sucrose preference test, *P < 0.05 vs. when compared sucrose consumption with water consumption in the test phase by each group; # P < 0.05 vs. sucrose consumption of control group, two-way ANOVA. Splash, forced swimming, and social interaction tests, *P < 0.05 vs. control group; # P < 0.05 vs. 6-OHDA group, two-way ANOVA followed by the Newman-Keuls post hoc tests; N = 8–10 rats/group)

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6-OHDA Induces Time-Dependent Changes of Dopamine Receptors (D1R and D2R) and Transporter (DAT) in the Striatum and PFC

The observed anhedonic and defense behaviors relevant to depression caused by 6-OHDA administration were accompanied by temporal fluctuations of the density of dopaminergic markers. Thus, 6-OHDA increased the density of D1R (F (1, 18) = 8.99, P < 0.05) (Fig. 4a) and D2R (F (1, 18) = 3.68, P < 0.05) (Fig. 4b) in the striatum after 7 days, which returned to control levels at 21 days after 6-OHDA administration (Fig. 4a, b). By contrast, 6-OHDA did not modify the density of either D1R or D2R in the PFC either after 7 days or after 21 days (Fig. 4d, e). Finally, we report that 6-OHDA decreased DAT density both in the striatum (F (1, 18) = 10.58, P < 0.05) (Fig. 4c) as well as in the PFC (F (1, 17) = 13.65, P < 0.05) (Fig. 4f) only at 21 days.

Fig. 4
figure 4

6-Hydroxydopamine (6-OHDA) differently altered the density of dopamine receptors (D1R and D2R) and dopamine transporter (DAT) with time (7 and 21 days after 6-OHDA injection) in the striatum and pre-frontal cortex (PFC). Western blot quantification of D1R (a), D2R (b), and DAT (c) in striatum; D1R (d), D2R (e), and DAT (f) in PFC. (*P < 0.05 vs. control group, # P < 0.05 vs. 6-OHDA group 7 days after injection, two-way ANOVA followed by the Newman-Keuls post hoc tests; N = 5 rats/group)

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6-OHDA Induces Temporal Dissociation of Dopamine Sensitivity in the DLS and PFC

Electrophysiological recordings in the DLS or in PFC revealed that the 6-OHDA administration did not alter the stimulus-sensitivity curve at either 7 or 21 days after lesion (Supplementary data Fig. S5). Paired-pulse stimulation showed a significant decrease of paired-pulse facilitation in the DLS only at 7 (but not 21) days after 6-OHDA lesion (Fig. 5a), indicative of an early striatal pre-synaptic disruption, whereas paired-pulse stimulation was not modified in the PFC either 7 or 21 days after 6-OHDA administration (Fig. 5e).

Fig. 5
figure 5

6-Hydroxydopamine (6-OHDA) induces a temporal and structural dissociation of dopamine sensitivity in excitatory synapses of the dorsolateral striatum (DLS) and in the medial prefrontal cortex (PFC). In population spikes recorded in the DLS (a), the paired-pulse facilitation (ratio of the second vs. first pulse, P2/P1 ratio, with an inter-pulse interval of 20 ms) was decreased at 7 but not at 21 days after injection of 6-OHDA (b). Dopamine (25 and 50 μM) increased synaptic transmission in the DLS, when compared to control group at 7 days after the injection of 6-OHDA (c) but was devoid of effects at 21 days after 6-OHDA injection (d). In population spikes recorded in layer 5 of the PFC (e), the paired-pulse facilitation (ratio of the second vs. first pulse, P2/P1 ratio, with an inter-pulse interval of 50 ms) was not altered either at 7 but not at 21 days after 6-OHDA injection (f). Dopamine sensitivity was not affected 7 days after 6-OHDA injection (g), but there was a decreased sensitivity (25 and 50 μM) to inhibit synaptic transmission 7 days after the injection of 6-OHDA when compared to control group at (h). (*P < 0.05 vs. control group, Student’s t test; N = 4 rats/group)

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Since 6-OHDA induces different time-dependent changes of dopamine receptors (D1R and D2R) and DAT in the striatum and PFC, we next investigated possible 6-OHDA-induced changes of dopamine sensitivity on synaptic transmission in DLS and PFC slices. In contrast to slices from control rats, dopamine increased synaptic transmission in the DLS at concentrations of 25 μM (75 ± 31 % over baseline, n = 4, P < 0.05) and 50 μM (64 ± 35 % over baseline, n = 4, P < 0.05) at 7 days (Fig. 5b) but not at 21 days (Fig. 5c) after 6-OHDA lesion. By contrast, in the PFC, there was no alterations of dopamine sensitivity at 7 days (Fig. 5f), but we observed a decreased dopamine sensitivity selectively at 21 days after the 6-OHDA lesion (21 ± 6 % inhibition by 25 μM dopamine in 6-OHDA-lesioned vs. 62 ± 5 % inhibition in control, n = 4, P < 0.05; 35 ± 5 % inhibition by 50 μM dopamine in 6-OHDA-challenged vs. 67 ± 7 % inhibition in control, n = 4, P < 0.05 (Fig. 5g).

Discussion

The present study demonstrates that a mild bilateral dopaminergic lesion of the rat DLS, which was insufficient to trigger motor deficits, mimicked some core non-motor symptoms of PD such as anhedonia and defense behaviors relevant to depression, as occurs in the prodrome phase of PD. Most importantly, we observed a temporal dissociation between anhedonia and defense behaviors relevant to depression that was coupled with a parallel temporal dissociation of neurochemical and electrophysiological alterations in the dorsolateral striatum and in the pre-frontal cortex. This indicates a dissociated neurobiological basis for the depressive and anhedonic symptoms in early PD.

The present model of 6-OHDA administration together with desipramine triggered a stable decrease of TH immunoreactivity in the striatum but an evolving dopaminergic lesion in the substantia nigra (40 % at 7 days and 68 % at 21 days), as occurs in PD patients [1]. Importantly, this observed extent of dopaminergic degeneration was not sufficient to impair motor function, as gauged by the lack of modification of the performance in the open field (horizontal activity), rotarod (balance and coordination), and grip force (strength of the forelimbs) tests. However, this mild dopaminergic damage triggered mood-related behavioral alterations, such as anhedonia, defense behaviors, and impaired social interaction, as also observed in previous studies [24–26]; thus, this 6-OHDA-based model is an experimental model well-suited to evaluate behaviors related to symptoms occurring in the PD prodrome [3, 27, 28], without affecting motor functions that could confound the interpretation of emotional parameters associated to defense behaviors relevant to depression and anhedonia. Furthermore, we now confirmed that fluoxetine and the atypical antidepressant drug bupropion prevented the appearance of these behavioral alterations, further validating the pertinence of these alterations to the PD-related depressive status [29, 30]. This is particularly relevant since PD patients exhibit a wide range of non-motor symptoms such as anhedonia, depression, and anxiety that affect their quality of life and represent a major unmet therapeutic need [2, 3, 6].

A main finding of the present study was the temporal dissociation of the appearance of these different behavioral alterations: thus, anhedonic-like behaviors, evaluated in sucrose preference and in splash tests, were observed at early (7 days) but not at later (21 days) time points after 6-OHDA injection; by contrast, defense behaviors relevant to depression were present only at later periods (21 days) after 6-OHDA injection. Interestingly, parkinsonian patients also exhibit this dissociation of symptoms of anhedonia and depression [31, 32]. Since 6-OHDA triggers functional alterations in the striatum [33, 34] as well as in the PFC [35, 36] and these two interconnected brain regions [37, 38] are involved in the control of motivation, reward, and defense behaviors relevant to depression [reviewed in [39–42], we explored neurochemical and electrophysiological alterations in these two brain regions at 7 and at 21 days after 6-OHDA administration to gain a mechanistic insight on this temporal dissociation between anhedonia and defense behaviors relevant to depression. We observed that the appearance of anhedonia at 7 days was selectively associated with an increased density of both D1 and D2 receptors in the striatum, together with a decreased short-term plasticity and increased dopaminergic sensitivity in corticostriatal synapses. This is in notable agreement with the involvement in operant motivation of aberrant dopaminergic signaling in the striatum [43–46], suggesting that abnormal dopaminergic control of striatal function might be selectively associated with the hedonic alterations observed 7 days after 6-OHDA administration. This is re-enforced by the observation that there was a parallel disappearance of anhedonic behavior as well as striatal dopaminergic alterations at 21 days after 6-OHDA administration. By contrast, at 21 days after 6-OHDA administration, we observed the emergence of defense behaviors relevant to depression that paralleled the appearance of changes now in the PFC, typified by a reduction of the density of DAT and a decreased inhibition by dopamine of excitatory transmission in the PFC. This is in agreement with the involvement of the PFC in the control of emotional responses [reviewed in [39–42] and in the appearance of non-motor symptoms in PD [27, 28]. Also, PFC dysfunction underlies major depressive disorders [40, 47, 48] with preserved or disrupted hedonic function [49] and is also involved in the emergence of social phobia and their comorbidities [50]. This tentative association of PFC modifications with helpless and social impaired behaviors is re-enforced by the observation that there was a lack of neurochemical and electrophysiological modifications at 7 days after 6-OHDA administration, which paralleled the lack of modification of defense behaviors relevant to depression. These observations lead us to propose that the behavioral dissociation between anhedonia and defense behaviors relevant to depression could be related to time-dependent alternations in these two different brain regions, namely, the striatum and PFC, respectively. This is line with the complex impact [51, 52] of the dopaminergic system in the control of anhedonia and other defense behaviors relevant to depression [reviewed in [53, 54] and with the different levels of dopaminergic denervation causing different changes in dopaminergic signaling in different brain regions [55]. This is also in notable agreement with some clinical studies suggesting a different involvement of different brain areas in the relationship of anhedonia and depression in PD patients [32, 56].

Overall, these results provide pioneering evidence of a temporal and structural dissociation of the role of DLS and PFC related to different non-motor behavioral impairments in rats submitted to 6-OHDA. These behavioral modifications are accompanied by different temporal fluctuations in the striatum and PFC of the dopaminergic receptor density, leading to altered pre-synaptic control and dopaminergic system sensitivity. This sheds new light on the neurobiological basis underlying the dissociation of anhedonia and defense behaviors relevant to depression in early PD, although the exact pathophysiological mechanisms underlying these conditions still need to be clarified.