Stress-Induced Sensitization of Dopamine and Norepinephrine Efflux in Medial Prefrontal Cortex of the Rat

Abstract: We examined whether prior exposure to chronic cold (17–28 days, 5°C) alters basal or stress-evoked (30-min tail shock) catecholamine release in medial prefrontal cortex, nucleus accumbens, and striatum, using in vivo microdialysis. Basal norepinephrine (NE) concentrations in medial prefrontal cortex did not differ between chronically cold-exposed rats and naive control rats (2.7 ± 0.3 vs. 2.5 ± 0.2 pg/20 µl, respectively). Basal dopamine (DA) efflux in any of the brain regions was not significantly different between chronically cold-exposed rats and naive rats. However, a trend for lower basal DA efflux in the cold-exposed relative to naive rats was observed in medial prefrontal cortex (1.5 ± 0.2 vs. 2.2 ± 0.3 pg/20 µl, respectively), nucleus accumbens (3.7 ± 0.8 vs. 5.4 ± 0.9 pg/20 µl, respectively), and striatum (4.4 ± 0.5 vs. 7.2 ± 1.5 pg/20 µl, respectively). In medial prefrontal cortex of rats previously exposed to cold, tail shock elicited a greater increase from baseline in both DA and NE efflux relative to that measured in naive rats (DA, 2.3 ± 0.3 vs. 1.2 ± 0.1 pg, respectively; NE, 3.8 ± 0.4 vs. 1.4 ± 0.2 pg, respectively). However, in nucleus accumbens or striatum of rats previously exposed to cold, the stress-induced increase in DA efflux was not significantly different from that of naive rats (nucleus accumbens, 1.8 ± 0.7 vs. 1.5 ± 0.3 pg, respectively; striatum, 1.9 ± 0.4 vs. 2.6 ± 0.7 pg, respectively). Thus, both cortical NE projections and cortically projecting DA neurons sensitize after chronic exposure to cold. In contrast, subcortical DA projections do not sensitize under these conditions.     

Phosphorylation of DARPP-32 Is Regulated by GABA in Rat Striatum and Substantia Nigra

Abstract: In the medium-sized spiny neurons of the striatonigral pathway, a cascade of events involving the activation of dopamine D₁ receptors, an increase in cyclic AMP, and activation of cyclic AMP-dependent protein kinase causes the phosphorylation of DARPP-32 on Thr³⁴, converting DARPP-32 into a powerful inhibitor of protein phosphatase-1. In the present study, the incubation of striatal or substantia nigra slices with GABA also increased the phosphorylation of DARPP-32 on Thr³⁴. GABA did not significantly increase cyclic AMP levels in slices. The phosphorylation of DARPP-32 by GABA was blocked in both brain regions by pretreatment of slices with the GABA_A receptor antagonist, bicuculline, but not with the GABA_B receptor antagonist, phaclofen. Moreover, the threonine phosphorylation of DARPP-32 produced by maximally effective doses of either forskolin (in striatum) or l -3,4-dihydroxyphenylalanine (in substantia nigra) was increased further by GABA. The data are consistent with a model in which GABA increases the phosphorylation state of DARPP-32 by inhibiting dephosphorylation of the protein by the calcium/calmodulin-dependent protein phosphatase, calcineurin.     

Chronic Administration of Lithium or Other Antidepressants Increases Levels of DARPP-32 in Rat Frontal Cortex

Abstract: We studied the chronic actions of lithium on rat brain by investigating its effects on cyclic AMP-dependent protein phos-phorylation by use of a back-phosphorylation procedure. We identified one heavily regulated phosphoprotein in frontal cortex as the 32-kDa dopamine- and cyclic AMP-regulated phosphoprotein (DARPP-32). Immunoblot experiments demonstrated that chronic lithium regulation of DARPP-32 back-phosphorylation is associated with equivalent increases in levels of DARPP-32 immunoreactivity. Lithium regulation of DARPP-32 immunoreactivity required chronic drug administration and was not observed in several other brain regions examined. Moreover, chronic administration of the antidepressant imipramine or tranylcypromine produced a similar increase in levels of DARPP-32 in frontal cortex, whereas other types of psychotropic drugs, including haloperidol. morphine, and cocaine, did not influence DARPP-32 levels. Increased levels of DARPP-32 could reflect a common functional effect on frontal cortex of long-term exposure to lithium and some other antidepressant medications, an effect possibly related to the clinical actions of these drugs.     

Light-Induced CREB Phosphorylation and Gene Expression in Rat Retinal Cells

Abstract: The signal pathway for light-induced expression of c- fos and the neuropeptide somatostatin (SS) in rat retinal cells was investigated. Flashing light induced c- fos and SS mRNA in the inner nuclear layer and the ganglion cell layer. As both c- fos and SS genes have a cyclic AMP response element (CRE) in their promoters, CRE-binding protein (CREB) phosphorylation in retinal cells was examined with a phospho-CREB-specific antibody. Both flashing light and administration of the L-type Ca²⁺ channel activator Bay K 8644 induced phosphorylation of CREB in the nuclei of the amacrine cells and the ganglion cells where c- fos /SS mRNAs were expressed. These cells could be double-stained with anti-calmodulin kinase II (anti-CaM kinase II) monoclonal antibody and phospho-CREB-specific polyclonal antiserum after Bay K 8644 administration, indicating the colocalization of phosphorylated CREB at Ser¹³³ and CaM kinase II in the neural retina.     

"青春期"大鼠前额皮质内BDNF与trkB的表达

目的:探讨"青春期"大鼠前额皮质内BDNF与trkB的表达。方法:出生后35天大鼠作为"青春期"大鼠,出生后15天、75天大鼠分别作为幼年期与成年期对照,每组大鼠各6只,用ABC免疫组织化学方法与图像分析相结合技术检测前额皮质内BDNF与trkB免疫反应的强度和免疫阳性产物平均光密度值的变化。结果:各时间点大鼠前额皮质内均可见BDNF与trkB免疫阳性产物。35天组BDNF与trkB免疫反应最强,阳性产物平均光密度值最高,与其它两组相比差异有显著性(p<0.05)。结论:"青春期"大鼠前额皮质内BDNF与trkB高表达,提示在此时期内前额皮质对BDNF的需求最多。     

DARPP-32 Expression in Rat Brain After an Inhibitory Avoidance Task

Step-down inhibitory avoidance (IA) is usually acquired in one single trial, which makes it ideal for studying processes initiated by training, uncontaminated by prior or further trials, rehearsals, or retrievals. Biochemical events in the hippocampus related to long-term memory (LTM) formation have been extensively studied in rats using a one trial step-down IA task. DARPP-32 (dopamine and cAMP regulated phosphoprotein of Mr 32 kDa) is a cytosolic protein that is selectively enriched in medium spiny neurons in the neostriatum. It has been shown that activation of DARPP-32 and the resultant inhibition of PP-1 activity is critical for the expression of two opposing forms of brain synaptic plasticity, striatal LTD and LTP. Both forms of plasticity are also critically linked to the activation of DA receptors. It has been shown with studies in DARPP-32 KO mice an important role of this protein in mediating the effects of DA on long term changes in neuronal excitability and to our knowledge, no studies have examined the effect of IA task on DARPP-32 expression. In order to demonstrate changes in the protein expression profile we analyzed DARPP-32 levels in the striatum, prefrontal cortex (PFC), hippocampus and entorhinal cortex of Wistar rats after step-down IA learning. Our results showed that IA induced changes on DARPP-32 expression in striatum and hippocampus. DARPP-32 expression changes corroborate with changes in expression and phosphorylation of CREB, NMDA, AMPA after IA that has been reported. These changes suggest that DARPP-32 might play a central role in the IA, as previously described as an integrator of the dopaminergic signal.     

Stress Impacts the Regulation Neuropeptides in the Rat Hippocampus and Prefrontal Cortex

Adverse life experiences increase the lifetime risk to several stress‐related psychopathologies, such as anxiety or depressive‐like symptoms following stress in adulthood. However, the neurochemical modulations triggered by stress have not been fully characterized. Neuropeptides play an important role as signaling molecules that contribute to physiological regulation and have been linked to neurological and psychiatric diseases. However, little is known about the influence of stress on neuropeptide regulation in the brain. Here, we have performed an exploratory study of how neuropeptide expression at adulthood is modulated by experiencing a period of multiple stressful experiences. We have targeted hippocampus and prefrontal cortex (PFC) brain areas, which have previously been shown to be modulated by stressors, employing a targeted liquid chromatography‐mass spectrometry (LC‐MS) based approach that permits broad peptide coverage with high sensitivity. We found that in the hippocampus, Met‐enkephalin, Met‐enkephalin‐Arg‐Phe, and Met‐enkephalin‐Arg‐Gly‐Leu were upregulated, while Leu‐enkephalin and Little SAAS were downregulated after stress. In the PFC area, Met‐enkephalin‐Arg‐Phe, Met‐enkephalin‐Arg‐Gly‐Leu, peptide PHI‐27, somatostatin‐28 (AA1‐12), and Little SAAS were all downregulated. This systematic evaluation of neuropeptide alterations in the hippocampus and PFC suggests that stressors impact neuropeptides and that neuropeptide regulation is brain‐area specific. These findings suggest several potential peptide candidates, which warrant further investigations in terms of correlation with depression‐associated behaviors.     

Glutamatergic Control of Dopamine Release During Stress in the Rat Prefrontal Cortex

Abstract: In vivo microdialysis was used to assess the hypothesis that the stress-induced increase in dopamine release in the prefrontal cortex is mediated by stress-activated glutamate neurotransmission in this region. Local perfusion of an α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, blocked the stress-induced increase in dopamine levels, whereas an NMDA receptor antagonist, 2-amino-5-phosphonopentanoic acid, at the dose tested, was not able to alter this response significantly. These data indicate that the effect of stress on dopamine release in the prefrontal cortex is mediated locally by activation of AMPA/kainate receptors, which modulate the release of dopamine in this region.     

Effects of Antidepressant Drug Imipramine on Gene Expression in Rat Prefrontal Cortex

We have investigated gene expression changes produced by acute and chronic daily treatment with a prototypical antidepressant, imipramine, using DNA microarrays. The analysis of similarities in gene expression patterns among functionally related genes revealed four expression profile cluster areas that showed a highly significant overrepresentation of several functional classes. Genes encoding for proteins involved in cAMP metabolism, postsynaptic membrane proteins, and proto-oncogenes were overrepresented in different cluster areas. Furthermore, we found that serine proteases as a group were similarly regulated by chronic antidepressant treatment. Our data suggest that cAMP metabolism, synaptic function, and protein processing by serine proteases may be important targets of antidepressant treatment and potential objects for antidepressant drug development.     

记忆增强肽促进大鼠海马内CREB磷酸化

五肽ＺＮＣ（ＣＰＲ（ｐＢＧｌｕ－Ａｓｎ－Ｃｙｔ－Ｐｒｏ－Ａｒｇ－ＯＨ）是精氨酸加压素（ＡＶＰ）在脑内的天然酶解产物,具有促进学习记忆的中枢效应。为了进一步阐明其作用的分子机制,以整体大鼠海马及离体大鼠海马切片为对象,研究了ＺＮＣ（Ｃ）ＰＲ对ｃＡＭＰ反应元件结合蛋白（ＣＲＥＢ）磷酸化的作用。发现ＺＮＣ（Ｃ）ＰＲ及其类似物ＮＬＰＲ能诱导大鼠海马内ＣＲＥＢ磷酸２化,该作用能被其拮抗剂ＺＤＣ（Ｃ）ＰＲ、Ｇ     

Effects of Quinolinate-Induced Lesion of the Medial Prefrontal Cortex on Prefrontal and Striatal Concentrations of d-Serine in the Rat

Neurochemical Research - d-Serine has been shown to play an important role in the expression and control of a variety of brain functions by acting as the endogenous coagonist for the...     

Phosphorylation of DARPP-32, a dopamine- and cAMP-regulated phosphoprotein, by casein kinase II

DARPP-32 (dopamine- and cAMP-regulated phosphorprotein, Mr = 32,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) is an inhibitor of protein phosphatase-1 and is enriched in dopaminoceptive neurons possessing the D1 dopamine receptor. Purified bovine DARPP-32 was phosphorylated in vitro by casein kinase II to a stoichiometry greater than 2 mol of phosphate/mol of protein whereas two structurally and functionally related proteins, protein phosphatase inhibitor-1 and G-substrate, were poor substrates for this enzyme. Sequencing of chymotryptic and thermolytic phosphopeptides from bovine DARPP-32 phosphorylated by casein kinase II suggested that the main phosphorylated residues were Ser45 and Ser102. In the case of rat DARPP-32, the identification of these phosphorylation sites was confirmed by manual Edman degradation. The phosphorylated residues are located NH2-terminal to acidic amino acid residues, a characteristic of casein kinase II phosphorylation sites. Casein kinase II phosphorylated DARPP-32 with an apparent Km value of 3.4 microM and a kcat value of 0.32 s-1. The kcat value for phosphorylation of Ser102 was 5-6 times greater than that for Ser45. Studies employing synthetic peptides encompassing each phosphorylation site confirmed this difference between the kcat values for phosphorylation of the two sites. In slices of rat caudate-putamen prelabeled with [32P]phosphate, DARPP-32 was phosphorylated on seryl residues under basal conditions. Comparison of thermolytic phosphopeptide maps and determination of the phosphorylated residue by manual Edman degradation identified the main phosphorylation site in intact cells as Ser102. In vitro, DARPP-32 phosphorylated by casein kinase II was dephosphorylated by protein phosphatases-1 and -2A. Phosphorylation by casein kinase II did not affect the potency of DARPP-32 as an inhibitor of protein phosphatase-1, which depended only on phosphorylation of Thr34 by cAMP-dependent protein kinase. However, phosphorylation of DARPP-32 by casein kinase II facilitated phosphorylation of Thr34 by cAMP-dependent protein kinase with a 2.2-fold increase in the Vmax and a 1.4-fold increase in the apparent Km. Phosphorylation of DARPP-32 by casein kinase II in intact cells may therefore modulate its phosphorylation in response to increased levels of cAMP.     

Local Influence of Endogenous Norepinephrine on Extracellular Dopamine in Rat Medial Prefrontal Cortex

Abstract: Noradrenergic and dopaminergic projections converge in the medial prefrontal cortex and there is evidence of an interaction between dopamine (DA) and norepinephrine (NE) terminals in this region. We have examined the influence of drugs known to alter extracellular NE on extracellular NE and DA in medial prefrontal cortex using in vivo microdialysis. Local application of the NE uptake inhibitor desipramine (1.0 µM) delivered through a microdialysis probe increased extracellular DA (+149%) as well as NE (+201%) in medial prefrontal cortex. Furthermore, desipramine potentiated the tail shock-induced increase in both extracellular DA (stress alone, +64%; stress + desipramine, +584%) and NE (stress alone, +55%; stress + desipramine, +443%). In contrast, local application of desipramine did not affect extracellular DA in striatum, indicating that this drug does not influence DA efflux directly. Local application of the α₂-adrenoceptor antagonist idazoxan (0.1 or 5.0 mM) increased extracellular NE and DA in medial prefrontal cortex. Conversely, the α₂-adrenoceptor agonist clonidine (0.2 mg/kg; i.p.) decreased extracellular NE and DA in medial prefrontal cortex. These results support the hypothesis that NE terminals in medial prefrontal cortex regulate extracellular DA in this region. This regulation may be achieved by mechanisms involving an action of NE on receptors that regulate DA release (heteroreceptor regulation) and/or transport of DA into noradrenergic terminals (heterotransporter regulation).     

Wnt-5a-induced Phosphorylation of DARPP-32 Inhibits Breast Cancer Cell Migration in a CREB-dependent Manner

Tumor cell migration plays a central role in the process of cancer metastasis. We recently identified dopamine and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) as an antimigratory phosphoprotein in breast cancer cells. Here we link this effect of DARPP-32 to Wnt-5a signaling by demonstrating that recombinant Wnt-5a triggers cAMP elevation at the plasma membrane and Thr34-DARPP-32 phosphorylation in MCF-7 cells. In agreement, both protein kinase A (PKA) inhibitors and siRNA-mediated knockdown of Frizzled-3 receptor or Gα_s expression abolished Wnt-5a-induced phosphorylation of DARPP-32. Furthermore, Wnt-5a induced DARPP-32-dependent inhibition of MCF-7 cell migration. Phospho-Thr-34-DARPP-32 interacted with protein phosphatase-1 (PP1) and potentiated the Wnt-5a-mediated phosphorylation of CREB, a well-known PP1 substrate, but had no effect on CREB phosphorylation by itself. Moreover, inhibition of the Wnt-5a/DARPP-32/CREB pathway, by expression of dominant negative CREB (DN-CREB), diminished the antimigratory effect of Wnt-5a-induced phospho-Thr-34-DARPP-32. Phalloidin-staining revealed that that the presence of phospho-Thr-34-DARPP-32 in MCF-7 cells results in reduced filopodia formation. In accordance, the activity of the Rho GTPase Cdc42, known to be crucial for filopodia formation, was reduced in MCF-7 cells expressing phospho-Thr-34-DARPP-32. The effects of DARPP-32 on cell migration and filopodia formation could be reversed in T47D breast cancer cells that were depleted of their endogenous DARPP-32 by siRNA targeting. Consequently, Wnt-5a activates a Frizzled-3/Gα_s/cAMP/PKA signaling pathway that triggers a DARPP-32- and CREB-dependent antimigratory response in breast cancer cells, representing a novel mechanism whereby Wnt-5a can inhibit breast cancer cell migration.Breast cancer is the most common form of cancer in women. Whereas the prognosis for breast cancer patients without local or distal dissemination is relatively favorable, the prognosis is considerably worse once distal metastasis has been established. It is therefore imperative to identify molecular targets and develop novel antimetastatic therapies that will stop, reduce, or delay the dissemination and growth of breast cancer metastasis.We recently isolated the dopamine and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32),² from a human breast expression library, as a DDR1-binding partner (1). Introduction of DARPP-32 in breast cancer cells lacking endogenous expression of this protein inhibited cell migration in a phospho-Thr-34-DARPP-32-dependent manner (1). DARPP-32 was originally identified 25 years ago as a dopamine and cAMP target enriched in dopaminoceptive neurones (2). Since then, a large body of work has shown that DARPP-32 is crucial for signal transmission by a wide array of neurotransmitters and drugs of abuse. DARPP-32 can act as either a phosphatase inhibitor or a kinase inhibitor depending on its phosphorylation state. Phosphorylation of Thr-34 by protein kinase A (PKA) converts DARPP-32 into a potent inhibitor of protein phosphatase-1 (PP1) (3), whereas phosphorylation at Thr-75 by Cdk5 turns DARPP-32 into an inhibitor of PKA (4). Downstream of DARPP-32 it has been shown that the activity of CREB and c-fos are strongly attenuated in DARPP-32 knockout mice (5). Despite the substantial amount of work done on DARPP-32 over the past 25 years, the role of this phosphoprotein outside the neuronal system has only recently started to be explored.Regarding the role of DARPP-32 in cancer, overexpression of DARPP-32 has been reported in gastric, colon, and prostate cancer (6, 7). In contrast, patients with esophageal squamous cell carcinoma that lacks DARPP-32 expression have reduced survival when compared with patients with DARPP-32-expressing esophageal squamous cell carcinomas (8, 9). Furthermore, DARPP-32 is needed to get a fully differentiated thyroid cell phenotype, and transformation of thyroid cells by constitutively activated Ras resulted in a loss of DARPP-32 expression (10). Thus, the role of DARPP-32 in cancer is somewhat uncertain, and little is known about the cell signaling mechanisms behind a possible suppressor or promotor role of DARPP-32 in cancer.Wnt-5a is a non-canonical member of the Wnt family of secreted glycoproteins that acts through the family of Frizzled G-protein-coupled receptor, Ror2, and co-receptors such as, LRP5/6, to mediate important events during development and cancer (11–15). In the breast, the non-transforming Wnt-5a has been shown to inhibit epithelial cell migration (16), and in breast cancer, expression of Wnt-5a has been shown to be a predictor of longer disease-free survival (17). Wnt-5a expression has been shown to increase activation of the receptor tyrosine kinase DDR1 in breast epithelial cells upon plating on collagen (18). As DDR1 is a collagen-binding adhesion receptor important for cell migration (19), and its binding partner DARPP-32 is a phospho-dependent antimigratory molecule (1), we wanted to test whether the functional overlaps between DARPP-32 and Wnt-5a, could be a result of Wnt-5a acting upstream in the signaling process leading to DARPP-32 phosphorylation.Here we demonstrate that Wnt-5a can trigger a Frizzled-3/Gαs/cAMP signal that results in PKA-dependent phosphorylation of DARPP-32. Furthermore, we show that phospho-DARPP-32 potentiates Wnt-5a-mediated CREB activity and suppresses filopodia formation.     

Differential Expression of Apoptotic Proteins Following Hypoxia-induced CREB Phosphorylation in the Cerebral Cortex of Newborn Piglets

The present study investigates the correlation between the hypoxia-induced phosphorylation of cyclic AMP response element binding protein and the expression of apoptotic proteins (proapoptotic proteins Bax and Bad and antiapoptotic proteins Bcl-2 and Bcl-xl) during hypoxia in the cerebral cortex of newborn piglets. Piglets were divided into normoxic (Nx) and hypoxic (Hx, FiO₂ = 0.06 for 1 h) groups. Cerebral tissue hypoxia was documented by ATP and phosphocreatine (PCr) levels. Ser¹³³ phosphorylation of cyclic AMP response element binding (CREB) protein was determined by Western blot analysis using a specific anti-phosphorylated Ser¹³³-CREB protein antibody. The expression of apoptotic proteins was determined by using specific anti-Bax, anti-Bad, anti-Bcl-2 and anti-Bcl-xl antibodies. ATP and PCr values (μmoles/g brain) in Hx were significantly different from Nx (ATP: 4.40 ± 0.39 in Nx vs. 1.19 ± 0.44 in Hx, P < 0.05 vs. Nx; PCr: 3.60 ± 0.40 in Nx vs. 0.70 ± 0.31 in Hx, P < 0.05 vs. Nx). Ser¹³³ phosphorylated CREB protein (OD × mm²) was 74.55 ± 4.75 in Nx and 127.13 ± 19.36 in Hx (P < 0.05 vs. Nx). The expression of proapoptotic proteins Bax and Bad increased and strongly correlated with the increase in CREB protein phosphorylation (correlation coefficient r = 0.82 and r = 0.85, respectively). The expression of antiapoptotic proteins Bcl-2 and Bcl-xl did not show correlation with CREB protein phosphorylation. We conclude that cerebral hypoxia results in differential regulation of CREB protein-mediated expression of proapoptotic and antiapoptotic proteins in the cerebral cortex of newborn piglets. We propose that the increased expression of proapoptotic vs antiapoptotic genes will lead to an increased potential for apoptotic programmed cell death in the Hx newborn brain.     

Acute NMDA Receptor Antagonism Disrupts Synchronization of Action Potential Firing in Rat Prefrontal Cortex

Antagonists of N-methyl-D-aspartate receptors (NMDAR) have psychotomimetic effects in humans and are used to model schizophrenia in animals. We used high-density electrophysiological recordings to assess the effects of acute systemic injection of an NMDAR antagonist (MK-801) on ensemble neural processing in the medial prefrontal cortex of freely moving rats. Although MK-801 increased neuron firing rates and the amplitude of gamma-frequency oscillations in field potentials, the synchronization of action potential firing decreased and spike trains became more Poisson-like. This disorganization of action potential firing following MK-801 administration is consistent with changes in simulated cortical networks as the functional connections among pyramidal neurons become less clustered. Such loss of functional heterogeneity of the cortical microcircuit may disrupt information processing dependent on spike timing or the activation of discrete cortical neural ensembles, and thereby contribute to hallucinations and other features of psychosis induced by NMDAR antagonists.     

Virus-Mediated shRNA Knockdown of Prodynorphin in the Rat Nucleus Accumbens Attenuates Depression-Like Behavior and Cocaine Locomotor Sensitization

Dynorphins, endogenous opioid peptides that arise from the precursor protein prodynorphin (Pdyn), are hypothesized to be involved in the regulation of mood states and the neuroplasticity associated with addiction. The current study tested the hypothesis that dynorphin in the nucleus accumbens (NAcc) mediates such effects. More specifically, we examined whether knockdown of Pdyn within the NAcc in rats would alter the expression of depressive-like and anxiety-like behavior, as well as cocaine locomotor sensitization. Wistar rats were injected with adeno-associated viral (AAV) vectors encoding either a Pdyn-specific short hairpin RNA (AAV-shPdyn) or a scrambled shRNA (AAV-shScr) as control. Four weeks later, rats were tested for anxiety-like behavior in the elevated plus maze test and depressive-like behavior in the forced swim test (FST). Finally, rats received one daily injection of saline or cocaine (20 mg/kg, i.p.), followed by assessment of locomotion for 4 consecutive days. Following 3 days of abstinence, the rats completed 2 additional daily cocaine/saline locomotor trials. Pdyn knockdown in the NAcc led to a significant reduction in depressive-like behavior in the FST, but had no effect on anxiety-like behavior in the elevated plus maze. Pdyn knockdown did not alter baseline locomotor behavior, the locomotor response to acute cocaine, or the initial sensitization of the locomotor response to cocaine over the first 4 cocaine treatment days. However, following 3 days abstinence the locomotor response to the cocaine challenge returned to their original levels in the AAV-shPdyn rats while remaining heightened in the AAV-shScr rats. These results suggest that dynorphin in a very specific area of the nucleus accumbens contributes to depressive-like states and may be involved in neuroadaptations in the NAcc that contribute to the development of cocaine addiction as a persistent and lasting condition.