Targeting PPARα in the rat valproic acid model of autism: focus on social motivational impairment and sex-related differences

BACKGROUND

The social motivational theory of autism spectrum disorder (ASD) focuses on social anhedonia as key causal feature of the impaired peer relationships that characterize ASD patients. ASD prevalence is higher in boys, but increasing evidence suggests underdiagnosis and undertreatment in girls. We showed that stress-induced motivational anhedonia is relieved by repeated treatment with fenofibrate (FBR), a peroxisome proliferator-activated receptor α (PPARα) agonist. Here, we used the valproic acid (VPA) model of ASD in rats to examine male and female phenotypes and assess whether FBR administration from weaning to young adulthood relieved social impairments.

METHODS

Male and female rats exposed to saline or VPA at gestational day 12.5 received standard or FBR-enriched diet from postnatal day 21 to 48-53, when behavioral tests and ex vivo neurochemical analyses were performed. Phosphorylation levels of DARPP-32 in response to social and nonsocial cues, as index of dopamine D1 receptor activation, levels of expression of PPARα, vesicular glutamatergic and GABAergic transporters, and postsynaptic density protein PSD-95 were analyzed by immunoblotting in selected brain regions.

RESULTS

FBR administration relieved social impairment and perseverative behavior in VPA-exposed male and female rats, but it was only effective on female stereotypies. Dopamine D1 receptor signaling triggered by social interaction in the nucleus accumbens shell was blunted in VPA-exposed rats, and it was rescued by FBR treatment only in males. VPA-exposed rats of both sexes exhibited an increased ratio of striatal excitatory over inhibitory synaptic markers that was normalized by FBR treatment.

LIMITATIONS

This study did not directly address the extent of motivational deficit in VPA-exposed rats and whether FBR administration restored the likely decreased motivation to operate for social reward. Future studies using operant behavior protocols will address this relevant issue.

CONCLUSIONS

The results support the involvement of impaired motivational mechanisms in ASD-like social deficits and suggest the rationale for a possible pharmacological treatment. Moreover, the study highlights sex-related differences in the expression of ASD-like symptoms and their differential responses to FBR treatment.

DARPP-32 in the orchestration of responses to positive natural stimuli

Dopamine- and cAMP-regulated phosphoprotein (M_r 32 kDa, DARPP-32) is an integrator of multiple neuronal signals and plays a crucial role particularly in mediating the dopaminergic component of the systems involved in the evaluation of stimuli and the ensuing elaboration of complex behavioral responses (e.g., responses to reinforcers and stressors). Dopamine neurons can fire tonically or phasically in distinct timescales and in specific brain regions to code different behaviorally relevant information. Dopamine signaling is mediated mainly through the regulation of adenylyl cyclase activity, stimulated by D1-like or inhibited by D2-like receptors, respectively, that modulates cAMP-dependent protein kinase (PKA) function. The activity of DARPP-32 is finely regulated by its phosphorylation at multiple sites. Phosphorylation at the threonine (Thr) 34 residue by PKA converts DARPP-32 into an inhibitor of protein phosphatase 1, while the phosphorylation at the Thr75 residue turns it into an inhibitor of PKA. Thus, DARPP-32 is critically implicated in regulating striatal output in response to the convergent pathways that influence signaling of the cAMP/PKA pathway. This review summarizes some of the landmark and recent studies of DARPP-32-mediated signaling in the attempt to clarify the role played by DARPP-32 in the response to rewarding natural stimuli. Particularly, the review deals with data derived from rodents studies and discusses the involvement of the cAMP/PKA/DARPP-32 pathway in: 1) appetitive food-sustained motivated behaviors, 2) motivated behaviors sustained by social reward, 3) sexual behavior, and 4) responses to environmental enrichment.

Antidepressant and pro-motivational effects of repeated lamotrigine treatment in a rat model of depressive symptoms

Background

Methods

Results

Limitations

Conclusions

5alpha-reductase inhibitors dampen L-DOPA-induced dyskinesia via normalization of dopamine D1-receptor signaling pathway and D1-D3 receptor interaction

Although 1-3,4-dihydroxyphenylalanine (L-DOPA) is the mainstay therapy for treating Parkinson's disease (PD), its long-term administration is accompanied by the development of motor complications, particularly L-DOPA induced dyskinesia (LID), that dramatically affects patients' quality of life. LID has consistently been related to an excessive dopamine receptor transmission, particularly at the down-stream signaling of the striatal D₁ receptors (D₁R), resulting in an exaggerated stimulation of cAMP-dependent protein kinase and extracellular signal-regulated kinase (ERK) pathway. We previously reported that pharmacological blockade of 5alpha-reductase (5AR), the rate-limiting enzyme in neurosteroids synthesis, attenuates the severity of a broad set of behavioral alterations induced by D₁R and D₃R activation, without inducing extrapyramidal symptoms. In line with this evidence, in a recent study, we found that inhibition of 5AR by finasteride (FIN) produced a significant reduction of dyskinesia induced by L-DOPA and direct dopaminergic agonists in 6-OHDA-lesioned rats. In the attempt to further investigate the effect of 5AR inhibitors on dyskinesia and shed light on the mechanism of action, in the present study we compared the effect of FIN and dutasteride (DUTA), a potent dual 5AR inhibitor, on the development of LID, on the therapeutic efficacy of L-DOPA, on the molecular alterations downstream to the D₁R, as well as on D₁R-D₃R interaction. The results indicated that both FIN and DUTA administration significantly reduced development and expression of LID; however, DUTA appeared more effective than FIN at a lower dose and produced its antidyskinetic effect without impacting the ability of L-DOPA to increase motor activation, or ameliorate forelimb use in parkinsonian rats. Moreover, this study demonstrates for the first time that 5AR inhibitors are able to prevent key events in the appearance of dyskinesia, such as L-DOPA-induced upregulation of striatal D₁R-related cAMP/PKA/ERK signaling pathways and D₁R-D₃R coimmunoprecipitation, an index of heteromer formation. These findings are relevant as they confirm the 5AR enzyme as a potential therapeutic target for treatment of dyskinesia in PD, suggesting the first ever evidence that neurosteroidogenesis may affect functional interaction between dopamine D₁R and D₃R.

Making Sense of Rodent Models of Anhedonia

A markedly reduced interest or pleasure in activities previously considered pleasurable is a main symptom in mood disorder and psychosis and is often present in other psychiatric disorders and neurodegenerative diseases. This condition can be labeled as "anhedonia," although in its most rigorous connotation the term refers to the lost capacity to feel pleasure that is one aspect of the complex phenomenon of processing and responding to reward. The responses to rewarding stimuli are relatively easy to study in rodents, and the experimental conditions that consistently and persistently impair these responses are used to model anhedonia. To this end, long-term exposure to environmental aversive conditions is primarily used, and the resulting deficits in reward responses are often accompanied by other deficits that are mainly reminiscent of clinical depressive symptoms. The different components of impaired reward responses induced by environmental aversive events can be assessed by different tests or protocols that require different degrees of time allocation, technical resources, and equipment. Rodent models of anhedonia are valuable tools in the study of the neurobiological mechanisms underpinning impaired behavioral responses and in the screening and characterization of drugs that may reverse these behavioral deficits. In particular, the antianhedonic or promotivational effects are relevant features in the spectrum of activities of drugs used in mood disorders or psychosis. Thus, more than the model, it is the choice of tests that is crucial since it influences which facets of anhedonia will be detected and should be tuned to the purpose of the study.

NMDA Receptors Play an Anti-aggregating Role in Human Platelets

Receptors for different monoamines, peptides and other neurohormones are present in the plasma membrane of platelets, and the sophisticated process of haemostasis is regulated by the interplay of their physiologic agonists (1). The recent report of a platelet binding* site for phencyclidine (2) suggested a possible role of N-methyl-D-aspartate (NMDA) receptors in platelet function. Isotherms of [3H]-glutamate (GLU), [3H]-CGP-39653, [3H]-glycine (GLY) and [3H]-MK-801 carried out in platelet membranes yielded Bmax and Kd values for these ligands similar to those present in neurons, and NMDA only partially displaced [3H]-GLU. In neurons [3H]-MK-801 binding is potentiated by GLU and/or GLY and, being specific for the open NMDA receptor channel species, it has a functional meaning. In platelet membranes neither GLU and/or GLY increased [3H]-MK-801 binding; thus suggesting that NMDA receptors in platelets are different from those present in neurons. GLU or NMDA alone did not induce platelet aggregation. However, both amino acids were antagonistic on the aggregating activity of arachidonic acid (AA), NMDA being 3 orders of magnitude more active than GLU, and NMDA also antagonized adenosine diphosphate (ADP) and platelet aggregating factor (PAF) induced platelet aggregation. Finally, NMDA increased cAMP levels in intact platelets, and such an effect did not occur in a Ca2+-free medium; yet, cAMP increase was not antagonized by the calmodulin inhibitor trifluoperazine (TFP). It was concluded that platelet membranes carry an NMDA receptor, functionally distinct from the neuronal one, which seems to play an anti-aggregating role.

Fasting biases μ-opioid receptors toward β-arrestin2-dependent signaling in the accumbens shell

The μ-opioid receptor (MOR) and dopamine D₁ receptor are co-expressed in the medium spiny neurons of striatal areas and the signaling pathways activated by these two receptors are in functional competition. However, in certain conditions an integrated response mediated by the dopamine D₁ receptor transduction system is observed. In mice, morphine administration induces hypermotility and this response has been described in terms of a β-arrestin2-dependent mechanism that favors prevalent dopamine D₁ receptor activation. In rats, acute morphine administration induces hypermotility only when the animals are food-deprived (FD). We aimed to further investigate the functional interaction between the MOR and dopamine D₁ receptors in striatal areas and we studied the effects of acute pharmacological MOR stimulation on motility and nucleus accumbens shell (NAcS) dopamine D₁ receptor signaling in control rats and rats with reduced β-arrestin2 expression in the NAcS, either non food-deprived (NFD) or FD. Motility and dopamine D₁ receptor signaling increased only in FD rats in a β-arrestin2-dependent way. Moreover, FD rats showed a β-arrestin2-dependent increase in the levels of MOR-dopamine D₁ receptor heteromeric complexes in the NAcS. Sucrose consumption is accompanied by release of endogenous opioids and dopamine in the NAcS. We then examined MOR-dopamine D₁ receptor interactions after sucrose consumption. Sucrose increased NAcS dopamine D₁ receptor signaling in NFD and FD rats, and a reduction in β-arrestin2 expression prevented this effect selectively in FD rats. These results show the β-arrestin2-dependent prevalence of dopamine D₁ receptor signaling in response to acute morphine or sucrose consumption elicited by food deprivation in rats.

PPARα modulation of mesolimbic dopamine transmission rescues depression-related behaviors

Depressive disorders cause a substantial burden for the individual and the society. Key depressive symptoms can be modeled in animals and enable the development of novel therapeutic interventions. Chronic unavoidable stress disrupts rats' competence to escape noxious stimuli and self-administer sucrose, configuring a depression model characterized by escape deficit and motivational anhedonia associated to impaired dopaminergic responses to sucrose in the nucleus accumbens shell (NAcS). Repeated treatments that restore these responses also relieve behavioral symptoms. Ventral tegmental area (VTA) dopamine neurons encode reward and motivation and are implicated in the neuropathology of depressive-like behaviors. Peroxisome proliferator-activated receptors type-α (PPARα) acutely regulate VTA dopamine neuron firing via β2 subunit-containing nicotinic acetylcholine receptors (β2*nAChRs) through phosphorylation and this effect is predictive of antidepressant-like effects. Here, by combining behavioral, electrophysiological and biochemical techniques, we studied the effects of repeated PPARα stimulation by fenofibrate on mesolimbic dopamine system. We found decreased β2*nAChRs phosphorylation levels and a switch from tonic to phasic activity of dopamine cells in the VTA, and increased phosphorylation of dopamine and cAMP-regulated phosphoprotein Mr 32,000 (DARPP-32) in the NAcS. We then investigated whether long-term fenofibrate administration to stressed rats reinstated the decreased DARPP-32 response to sucrose and whether this effect translated into antidepressant-like properties. Fenofibrate restored dopaminergic responses to appetitive stimuli, reactivity to aversive stimuli and motivation to self-administer sucrose. Overall, this study suggests PPARα as new targets for antidepressant therapies endowed with motivational anti-anhedonic properties, further supporting the role of an unbalanced mesolimbic dopamine system in pathophysiology of depressive disorders.

PPAR-alpha agonists as novel antiepileptic drugs: preclinical findings

Nicotinic acetylcholine receptors (nAChRs) are involved in seizure mechanisms. Hence, nocturnal frontal lobe epilepsy was the first idiopathic epilepsy linked with specific mutations in α4 or β2 nAChR subunit genes. These mutations confer gain of function to nAChRs by increasing sensitivity toward acetylcholine. Consistently, nicotine elicits seizures through nAChRs and mimics the excessive nAChR activation observed in animal models of the disease. Treatments aimed at reducing nicotinic inputs are sought as therapies for epilepsies where these receptors contribute to neuronal excitation and synchronization. Previous studies demonstrated that peroxisome proliferator-activated receptors-α (PPARα), nuclear receptor transcription factors, suppress nicotine-induced behavioral and electrophysiological effects by modulating nAChRs containing β2 subunits. On these bases, we tested whether PPARα agonists were protective against nicotine-induced seizures. To this aim we utilized behavioral and electroencephalographic (EEG) experiments in C57BL/J6 mice and in vitro patch clamp recordings from mice and rats. Convulsive doses of nicotine evoked severe seizures and bursts of spike-waves discharges in ∼100% of mice. A single dose of the synthetic PPARα agonist WY14643 (WY, 80 mg/kg, i.p.) or chronic administration of fenofibrate, clinically available for lipid metabolism disorders, in the diet (0.2%) for 14 days significantly reduced or abolished behavioral and EEG expressions of nicotine-induced seizures. Acute WY effects were reverted by the PPARα antagonist MK886 (3 mg/kg, i.p.). Since neocortical networks are crucial in the generation of ictal activity and synchrony, we performed patch clamp recordings of spontaneous inhibitory postsynaptic currents (sIPSCs) from frontal cortex layer II/III pyramidal neurons. We found that both acute and chronic treatment with PPARα agonists abolished nicotine-induced sIPSC increases. PPARα within the CNS are key regulators of neuronal activity through modulation of nAChRs. These effects might be therapeutically exploited for idiopathic or genetically determined forms of epilepsy where nAChRs play a major role.

F2-isoprostane receptors on hepatic stellate cells

F2-isoprostanes are considered as the most reliable markers of oxidative stress and can be used to evaluate the oxidative status in a number of human pathologies. Besides being markers of oxidative stress, F2-isoprostanes proved to be mediators of important biological effects and would act through the activation of receptors analogous to those for thromboxane A2. In a previous work, we provided evidence that F(2)-isoprostanes, generated during carbon tetrachloride-induced hepatic fibrosis, mediate hepatic stellate cell (HSC) proliferation and collagen hyperproduction. To investigate whether TxA2 receptor (TxA2r or TPr) is involved in the effects of F2-isoprostanes on HSC, experiments on DNA synthesis were carried out in the presence of 8-epi-prostaglandin F(2alpha) (8-epi-PGF(2alpha)) or the TxA2r-specific agonist I-BOP ([1S-[1alpha,2alpha(Z),3beta(1E,3S*), 4alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid). Both agonists significantly stimulated DNA synthesis, which was almost completely inhibited by the TxA2r-specific antagonist SQ29548 ([1S-[1alpha,2alpha(Z),3alpha,4alpha]]-7-[3-[[2-[(phenylamino)carbonyl] hydrazino] methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptanoic acid), suggesting that much of the effect of 8-epi-PGF(2alpha) is mediated by the TxA2r. Further studies showed that increasing concentrations of SQ29548 progressively inhibit DNA synthesis, suggesting a possible competitive antagonism between the two molecules. In addition, we demonstrated that the stimulatory effect of 8-epi-PGF(2alpha) on collagen synthesis could be mediated by TxA2r. The occurrence of TxA2r on HSC was also investigated using western blotting analysis and immunocytochemistry, which reveals that TP is distributed both on plasma membranes and within the cells. Moreover, binding studies indicated the presence of a specific binding site for 3H-SQ29548 on HSC. Competition binding studies indicated that 8-epi-PGF(2alpha) and I-BOP were both able to displace 3H-SQ29548 binding with a very different affinity (K(i)=4.14+/-1.9 x 10(-6) M and K(i)=1.15+/-0.3 x 10(-9) M, respectively), suggesting the involvement of a modified form of isoprostane receptor, homologous to the classic thromboxane A2-binding site in F2-isoprostanes-evoked responses on HSC.

Behavioral expression of cocaine sensitization in rats is accompanied by a distinct pattern of modifications in the PKA/DARPP-32 signaling pathway

Repeated cocaine administration induces behavioral sensitization and modifications in the phosphorylation pattern of dopamine and cAMP-regulated phosphoprotein of Mr 32,000 (DARPP-32), characterized by a tonic increase in the Thr75 phosphorylated form, and a decrease in the Thr34 phosphorylated form. This study further investigated the correlations between cocaine sensitization and modifications in the DARPP-32 phosphorylation pattern, cAMP-dependent protein kinase (PKA) activity, and mGluR5 tone in the medial prefrontal cortex and nucleus accumbens. Behavioral sensitization and modifications in these neurochemical markers followed a similar temporal pattern. Moreover, in sensitized rats acute cocaine administration modified phosphorylation levels of Thr75- and Thr34-DARPP-32, GluR1, and NR1 subunits in the nucleus accumbens only at a dose double the efficacious dose in control rats. These results suggest that the high levels of phospho-Thr75 DARPP-32 maintain PKA in a prevalent inhibited state. Furthermore, in sensitized rats the acute administration of 6-methyl-2-(phenylethynyl)-pyridine, a mGluR5 antagonist, reinstated the phosphorylation levels of Thr75- and Thr34-DARPP-32, GluR1, and NR1 to control values, and a subsequent cocaine challenge did not elicit a sensitized response. These data suggest that a tonic increase in mGluR5 transmission in cocaine-sensitized rats sustains both the increase in phospho-Thr75 DARPP-32 levels and the expression of behavioral sensitization.

The mesolimbic dopaminergic response to novel palatable food consumption increases dopamine-D1 receptor-mediated signalling with complex modifications of the DARPP-32 phosphorylation pattern

Acute cocaine administration increases extraneuronal dopamine and Thr34 phosphorylation of dopamine- and cAMP-regulated phosphoprotein (M(r) 32 kDa; DARPP-32) in striatal and cortical areas. Novel palatable food consumption increases extraneuronal dopamine in the same areas. We examined the DARPP-32 phosphorylation pattern in food non-deprived rats at different times after vanilla sugar consumption. The phosphorylation state of DARPP-32 and two cAMP-dependent protein kinase (PKA) substrates, GluR1 and NR1, were detected by immunoblotting. Thirty to 45 min after vanilla sugar consumption, phospho-Thr34 DARPP-32, GluR1 and NR1 levels increased in the nucleus accumbens, and phospho-Thr75 DARPP-32 levels decreased. At 60 min, all parameters returned to baseline values. However, 2 and 3 h after vanilla sugar consumption, phospho-Thr34 DARPP-32 levels decreased, while phospho-Thr75 DARPP-32 levels increased. In contrast to the pattern observed in the NAcS, no delayed changes in DARPP-32 phosphorylation were observed in the mPFC. Both early and delayed DARPP-32, GluR1 and NR1 phosphorylation changes were prevented by a dopamine D1 receptor antagonist administration. The delayed modifications in nucleus accumbens DARPP-32 phosphorylation were prevented by an mGluR5 antagonist administration. The mesolimbic dopaminergic response to an unfamiliar taste is correlated to a gustatory memory trace development, and the observed changes in DARPP-32 phosphorylation may be part of this process.

Sardinian alcohol-preferring rats show low 5-HT extraneuronal levels in the mPFC and no habituation in monoaminergic response to repeated ethanol consumption in the NAcS

Sardinian ethanol-preferring (sP), non-preferring (sNP), and Wistar rats show similar dopaminergic response to vanilla sugar consumption in nucleus accumbens shell (NAcS) and medial prefrontal cortex (mPFC), and similarly learn a vanilla sugar-sustained appetitive behavior. In this study we investigated whether in satiated sP, sNP, and Wistar rats vanilla sugar would also elicit a serotonergic response in NAcS and mPFC, and whether in these areas voluntary ethanol consumption would elicit dopaminergic and/or serotoninergic responses. In the NAcS, all rats showed similar serotonin increases in response to the two meals and similar development of rapid habituation. In the mPFC, Wistar and sNP rats showed similar serotonin increases after two vanilla sugar meals, while sP rats, which had low serotonin basal levels, did not show a serotonergic response. When presented with a 10% ethanol solution, Wistar and sP rats rapidly consumed it, while sNP rats did not. In the NAcS, Wistar and sP rats presented dopamine and serotonin increases in response to ethanol. However, while Wistar rats showed habituation in their response, sP rats did not. In the mPFC, ethanol induced similar dopamine increases in Wistar and sP rats; serotonin increases were observed only in Wistar rats. In conclusion, all three lines showed increased serotonin release in response to palatable food, but they profoundly differed in their response to ethanol. In fact, only Wistar and sP rats drank ethanol, Wistar rats showed a monoaminergic response similar to that obtained after palatable food, while sP rats did not develop habituation, suggesting that they perceived ethanol as a more relevant stimulus.

Synthetic peptides in the form of dendrimers become resistant to protease activity

In previous papers, we observed that dendrimers of peptide mimotopes of the nicotinic receptor ligand site are strong antidotes against the lethality of the nicotinic receptor ligand alpha-bungarotoxin. Although their in vitro activity is identical to that of dendrimers, the corresponding monomeric peptide mimotopes are not effective in vivo. Because the higher in vivo efficiency of dendrimers could not in this case be related to polyvalent interaction, the stability to blood protease activity of monomeric versus tetrabranched dendrimeric mimotope peptides was compared here by incubating three different mimotopes with human plasma and serum. Unmodified peptides and cleaved sequences were followed by high pressure liquid chromatography and mass spectrometry. Tetrabranched peptides were shown to be much more stable in plasma and also in serum. To assess the notable stability of multimeric peptides, different bioactive neuropeptides, including enkephalins, neurotensin and nociceptin, were synthesized in monomeric and tetrabranched forms and incubated with human plasma and serum and with rat brain membrane extracts. All the tetrabranched neuropeptides fully retained biological activity and generally showed much greater stability to blood and brain protease activity. Some tetrabranched peptides were also resistant to trypsin and chymotrypsin. Our findings provide new insights into the possible therapeutic use of bioactive peptides.

Acquisition of an appetitive behavior prevents development of stress-induced neurochemical modifications in rat nucleus accumbens

In rats, exposure to chronic unavoidable stress produces a decrease in dopamine output in the nucleus accumbens shell that is accompanied by a decreased density of the dopamine transporter and an increased activity of the dopamine-D(1) receptor complex. These modifications have been hypothesized to be adaptive to decreased dopamine output in stressed rats. We investigated whether the learning of an appetitive behavior sustained by palatable food, which is associated with increased dopamine output in the nucleus accumbens shell as measured by microdialysis experiments, would affect the modifications induced by chronic stress exposure on dopamine transporter density and dopamine-D(1) receptor complex activity in the nucleus accumbens. Rats exposed to chronic unavoidable stress after acquisition of the appetitive behavior showed a higher dopamine extraneuronal release in the nucleus accumbens shell than that of stressed animals, and similar to that of control rats. Moreover, previous acquisition of the appetitive behavior prevented development of a stress-induced decrease in dopamine transporter density, measured by [(3)H]-WIN 35428 binding, a stress-induced increase in dopamine-D(1) receptor density, measured by binding of [(3)H]-SCH 23390, and SKF 38393-stimulated adenylyl cyclase activity in the nucleus accumbens. These results support the hypothesis that changes induced in pre- and postsynaptic dopaminergic transmission by chronic stress exposure are related to decreased dopamine output.

Selective modifications in the nucleus accumbens of dopamine synaptic transmission in rats exposed to chronic stress

Stressful events are accompanied by modifications in dopaminergic transmission in distinct brain regions. As the activity of the neuronal dopamine (DA) transporter (DAT) is considered to be a critical mechanism for determining the extent of DA receptor activation, we investigated whether a 3-week exposure to unavoidable stress, which produces a reduction in DA output in the nucleus accumbens shell (NAcS) and medial prefrontal cortex (mPFC), would affect DAT density and DA D1 receptor complex activity in the NAcS, mPFC and caudate-putamen (CPu). Rats exposed to unavoidable stress showed a decreased DA output in the NAcS accompanied by a decrease in the number of DAT binding sites, and an increase in the number of DA D1 binding sites and Vmax of SKF 38393-stimulated adenylyl cyclase. In the mPFC, stress exposure produced a decrease in DA output with no modification in DAT binding or in DA D1 receptor complex activity. Moreover, in the CPu stress exposure induced no changes in DA output or in the other neurochemical variables examined. This study shows that exposure to a chronic unavoidable stress that produces a decrease in DA output in frontomesolimbic areas induced several adaptive neurochemical modifications selectively in the nucleus accumbens.