ΔFosB in the nucleus accumbens is critical for reinforcing effects of sexual reward

Sexual behavior in male rats is rewarding and reinforcing. However, little is known about the specific cellular and molecular mechanisms mediating sexual reward or the reinforcing effects of reward on subsequent expression of sexual behavior. This study tests the hypothesis that ΔFosB, the stably expressed truncated form of FosB, plays a critical role in the reinforcement of sexual behavior and experience‐induced facilitation of sexual motivation and performance. Sexual experience was shown to cause ΔFosB accumulation in several limbic brain regions including the nucleus accumbens (NAc), medial prefrontal cortex, ventral tegmental area and caudate putamen but not the medial preoptic nucleus. Next, the induction of c‐Fos, a downstream (repressed) target of ΔFosB, was measured in sexually experienced and naïve animals. The number of mating‐induced c‐Fos‐immunoreactive cells was significantly decreased in sexually experienced animals compared with sexually naïve controls. Finally, ΔFosB levels and its activity in the NAc were manipulated using viral‐mediated gene transfer to study its potential role in mediating sexual experience and experience‐induced facilitation of sexual performance. Animals with ΔFosB overexpression displayed enhanced facilitation of sexual performance with sexual experience relative to controls. In contrast, the expression of ΔJunD, a dominant negative binding partner of ΔFosB, attenuated sexual experience‐induced facilitation of sexual performance and stunted long‐term maintenance of facilitation compared to green fluorescence protein and ΔFosB overexpressing groups. Together, these findings support a critical role for ΔFosB expression in the NAc for the reinforcing effects of sexual behavior and sexual experience‐induced facilitation of sexual performance.     

Quantitative mapping of cocaine-induced ΔFosB expression in the striatum of male and female rats

ΔFosB plays a critical role in drug-induced long-term changes in the brain. In the current study, we evaluated locomotor activity in male and female rats treated with saline or cocaine for 2 weeks and quantitatively mapped ΔFosB expression in the dorsal striatum and nucleus accumbens of each animal by using an anti-FosB antibody that recognizes ΔFosB isoforms preferentially. Behavioral analysis showed that while there was little difference between males and females that sensitized to cocaine, nonsensitizing rats showed a large sex difference. Nonsensitizing males showed low behavioral activation in response to cocaine on the first day of treatment, and their activity remained low. In contrast, nonsensitizing females showed high activation on the first day of treatment and their activity remained high. Western blot and immunohistochemical analyses indicated that basal levels of ΔFosB were higher in the nucleus accumbens than the dorsal striatum, but that the effect of cocaine on ΔFosB was greater in the dorsal striatum. Immunostaining showed that the effect of cocaine in both the dorsal striatum and nucleus accumbens was primarily to increase the intensity of ΔFosB immunoreactivity in individual neurons, rather than to increase the number of cells that express ΔFosB. Detailed mapping of ΔFosB-labeled nuclei showed that basal ΔFosB levels were highest in the medial portion of the dorsal striatum and dorsomedial accumbens, particularly adjacent to the lateral ventricle, whereas the cocaine-induced increase in ΔFosB was most pronounced in the lateral dorsal striatum, where basal ΔFosB expression was lowest. Sex differences in ΔFosB expression were small and independent of cocaine treatment. We discuss implications of the sex difference in locomotor activation and regionally-specific ΔFosB induction by cocaine.     

ΔFosB in the supraoptic nucleus contributes to hyponatremia in rats with cirrhosis

Bile duct ligation (BDL), a model of hepatic cirrhosis, is associated with dilutional hyponatremia and inappropriate vasopressin release. ΔFosB staining was significantly increased in vasopressin and oxytocin magnocellular neurosecretory cells in the supraoptic nucleus (SON) of BDL rats. We tested the role of SON ΔFosB in fluid retention following BDL by injecting the SON (n = 10) with 400 nl of an adeno-associated virus (AAV) vector expressing ΔJunD (a dominant negative construct for ΔFosB) plus green fluorescent protein (GFP) (AAV-GFP-ΔJunD). Controls were either noninjected or injected with an AAV vector expressing only GFP. Three weeks after BDL or sham ligation surgery, rats were individually housed in metabolism cages for 1 wk. Average daily water intake was significantly elevated in all BDL rats compared with sham ligated controls. Average daily urine output was significantly greater in AAV-GFP-ΔJunD-treated BDL rats compared with all other groups. Daily average urine sodium concentration was significantly lower in AAV-GFP-ΔJunD-treated BDL rats than the other groups, although average daily sodium excretion was not different among the groups. SON expression of ΔJunD produced a diuresis in BDL rats that may be related to decreased circulating levels of vasopressin or oxytocin. These findings support the view that ΔFosB expression in SON magnocellular secretory cells contribute to dilutional hyponatremia in BDL rats.     

Social and physical environments as a source of individual variation in the rewarding effects of testosterone in male California mice (Peromyscus californicus)

Despite extensive research revealing the occurrence of testosterone (T) pulses following social encounters, it is unclear how they lead to varied behavioral responses. We investigated the influence of residency (home versus unfamiliar environment) and social/sexual experience (pair-bonded, isolated or housed with siblings) on the plasticity of T's rewarding effects by measuring the development of conditioned place preferences (CPPs), a classical paradigm used to measure the rewarding properties of drugs. For pair-bonded males, T-induced CPPs were only produced in the environment wherein the social/sexual experience was accrued and residency status had been achieved. For isolated males, the T-induced CPPs only occurred when the environment was unfamiliar. For males housed with a male sibling, the T-induced CPPs were prevented in both the home and unfamiliar chambers. Our results reveal the plasticity of T's rewarding effects, and suggest that the behavioral functions of T-pulses can vary based on social/sexual experience and the environment in which residency was established. The formation of CPPs or reward-like properties of drugs and natural compounds can therefore exhibit malleability based on past experience and the current environment.     

Beneficial Effects of Highly Palatable Food on the Behavioral and Neural Adversities induced by Early Life Stress Experience in Female Rats

This study examined the effects of highly palatable food during adolescence on the psycho-emotional and neural disturbances caused by early life stress experience in female rats. Female Sprague-Dawley pups were separated from dam for 3 h daily during the first two weeks of birth (MS) or left undisturbed (NH). Half of MS females received free access to chocolate cookies in addition to ad libitum chow from postnatal day 28. Pups were subjected to the behavioral tests during young adulthood. The plasma corticosterone response to acute stress, ΔFosB and brain-derived neurotrophic factor (BDNF) levels in the brain regions were analyzed. Total caloric intake and body weight gain during the whole experimental period did not differ among the experimental groups. Cookie access during adolescence and youth improved anxiety-/depression-like behaviors by MS experience. ΔFosB expression was decreased, but BDNF was increased in the nucleus accumbens of MS females, and ΔFosB expression was normalized and BDNF was further increased following cookie access. Corticosterone response to acute stress was blunted by MS experience and cookie access did not improve it. Results suggest that cookie access during adolescence improves the psycho-emotional disturbances of MS females, and ΔFosB and/or BDNF expression in the nucleus accumbens may play a role in its underlying neural mechanisms.     

Geranylgeranylacetone protects mice against morphine-induced hyperlocomotion, rewarding effect, and withdrawal syndrome

There are few efficacious interventions to combat morphine dependence. Thioredoxin-1 (Trx-1) and heat shock protein 70 (Hsp70) are emerging as important modulators of neuronal function. They have been shown to be involved in cellular protective mechanisms against a variety of toxic stressors. This study was designed to investigate the effects of geranylgeranylacetone (GGA), a pharmacological inducer of Trx-1 and Hsp70, on morphine-induced hyperlocomotion, rewarding effect, and withdrawal syndrome. Trx-1 and Hsp70 expression was increased in the frontal cortex, hippocampus, ventral tegmental area, and nucleus accumbens of mice after GGA treatment. GGA administration reduced morphine-induced motor activity and inhibited conditioned place preference. GGA markedly attenuated the morphine-naloxone-induced withdrawal signs, including jumping, rearing, and forepaw tremor. Furthermore, the activation of cAMP-responsive element-binding protein and the expression of ΔFosB and cyclin-dependent kinase 5 were decreased in the nucleus accumbens by GGA treatment after morphine withdrawal. In the nucleus accumbens, GGA enhanced morphine-induced expression of Trx-1 and Hsp70 after morphine withdrawal. These results suggest that strengthening the expression of Trx-1 and Hsp70 in the brain by using noncytotoxic pharmacological inducers may provide a novel therapeutic strategy for morphine dependence. GGA could be a safe and novel therapeutic agent for morphine dependence.     

The role of tissue plasminogen activator in methamphetamine-related reward and sensitization

In the central nervous system, tissue plasminogen activator (tPA) plays a role in synaptic plasticity and remodeling. Our recent study has suggested that tPA participates in the rewarding effects of morphine by regulating dopamine release. In this study, we investigated the role of tPA in methamphetamine (METH)-related reward and sensitization. Repeated METH treatment dose-dependently induced tPA mRNA expression in the frontal cortex, nucleus accumbens, striatum and hippocampus, whereas single METH treatment did not affect tPA mRNA expression in these brain areas. The METH-induced increase in tPA mRNA expression in the nucleus accumbens was completely inhibited by pre-treatment with R(+)-SCH23390 and raclopride, dopamine D1 and D2 receptor antagonists, respectively. In addition, repeated METH treatment increased tPA activity in the nucleus accumbens. There was no difference in METH-induced hyperlocomotion between wild-type and tPA-deficient (tPA-/-) mice. On the other hand, METH-induced conditioned place preference and behavioral sensitization after repeated METH treatment were significantly reduced in tPA-/- mice compared with wild-type mice. The defect of behavioral sensitization in tPA-/- mice was reversed by microinjections of exogenous tPA into the nucleus accumbens. Our findings suggest that tPA is involved in the rewarding effects as well as the sensitization of the locomotor-stimulating effect of METH.     

CART peptides are modulators of mesolimbic dopamine and psychostimulants

CART peptide produces behavioral effects when injected into the VTA or nucleus accumbens. In the VTA, the peptide behaves like an endogenous psychostimulant and produces increased locomotor activity and conditioned place preference. Since this is blocked by dopamine receptor blockers, it presumably involves release of dopamine. But in the nucleus accumbens, CART peptide reduces the locomotor-increasing effects of cocaine. This suggests that the peptide is an interesting target for medications development.     

A decrease in the addition of new cells in the nucleus accumbens and prefrontal cortex between puberty and adulthood in male rats

Adolescence involves shifts in social behaviors, behavioral flexibility, and adaptive risk‐taking that coincide with structural remodeling of the brain. We previously showed that new cells are added to brain regions associated with sexual behaviors, suggesting that cytogenesis may be a mechanism for acquiring adult‐typical behaviors during adolescence. Whether pubertal cell addition occurs in brain regions associated with behavioral flexibility or motivation and whether these patterns differ between pubertal and adult animals had not been determined. Therefore, we assessed patterns of cell proliferation or survival in the prefrontal cortex and nucleus accumbens. Pubertal and adult male rats were given injections of bromo‐deoxyuridine (BrdU). To assess cell proliferation, half of the animals from each group were sacrificed 24 h following the last injection. The remaining animals were sacrificed at Day 30 following the last injection to evaluate cell survival. Adult animals had significantly lower densities of BrdU‐immunoreactive (ir) cells in the prefrontal cortex, irrespective of post‐BrdU survival time, whereas in the nucleus accumbens, adult animals had a lower density of BrdU‐ir cells at the short survival time; however, the density of BrdU‐ir cells was equivalent in pubertal and adult animals at the longer survival time. These data provide evidence that cell addition during puberty may contribute to the remodeling of brain regions associated with behavioral flexibility and motivation, and this cell addition continues into adulthood, albeit at lower levels. Higher levels of cell proliferation or survival in younger animals may reflect a higher level of plasticity, possibly contributing to the dynamic remodeling of the pubertal brain. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 633–642, 2014     

Nociceptin differentially affects morphine-induced dopamine release from the nucleus accumbens and nucleus caudate in rats

The effects induced by nociceptin on morphine-induced release of dopamine (DA), 3,4-dihydroxyphenilacetic acid (DOPAC) and homovanillic acid (HVA) in the nucleus accumbens and nucleus caudate were studied in rats by microdialysis with electrochemical detection. Nociceptin administered intracerebroventricularly (i.c.v.) at doses of 2, 5 and 10 nmol/rat changed neither DA nor metabolites release in the shell of the nucleus accumbens or in the nucleus caudate. Morphine administered intraperitoneally (i.p.) (2, 5, and 10 mg/kg) increased DA and metabolites release more in the shell of the nucleus accumbens than in the nucleus caudate. When nociceptin (5 or 10 nmol) was administered 15 min before morphine (5 or 10 mg/kg), it significantly reduced morphine-induced DA and metabolites release in the shell of the nucleus accumbens, whereas only a slight, nonsignificant reduction was observed in the nucleus caudate. Our data indicate that nociceptin may regulate the stimulating action associated with morphine-induced DA release more in the nucleus accumbens than in the nucleus caudate, and are consistent with recent observations that nociceptin reversed ethanol- and morphine-induced conditioned place preference. Therefore, the nociceptin-induced reduction of DA release stimulated by morphine in the nucleus accumbens, and the results obtained with nociceptin in the conditioned place preference procedure suggest a role for nociceptin in the modulation of the behavioral and neurochemical effects of abuse drugs.     

During Human Melanoma Progression AP‐1 Binding Pairs are Altered with Loss of c‐Jun In Vitro

We demonstrated previously that c‐Jun, JunB and c‐Fos RNA were dysregulated in metastatic melanoma cells compared with normal human melanocytes. The purpose of this study was to evaluate the distribution in composition of AP‐1 dimers in human melanoma pathogenesis. We investigated AP‐1 dimer pairing in radial growth phase‐like (RGP) (w3211) and vertical growth phase‐like (VGP) (w1205) human melanoma cells and metastatic cell lines (cloned from patients, c83‐2c, c81‐46A, A375, respectively) compared with melanocytes using electrophoretic mobility shift assay (EMSA), Western blot and transfection analyses. There are progressive variations in AP‐1 composition in different melanoma cell lines compared with normal melanocytes, in which c‐Jun, JunD and FosB were involved in AP‐1 complexes. In w3211, c‐Jun, JunD and Fra‐1 were involved in AP‐1 binding, while in w1205, overall AP‐1 binding activity was decreased significantly and supershift binding was detected only with JunD antibodies. In metastatic c81‐46A and A375 cells, only JunD was involved in AP‐1 binding activity, but in a third (c83‐2c) c‐Jun, JunD and Fra‐1 were present. Western blot evaluation detected c‐Jun in melanocytes and w3211, but this component was decreased significantly or was not detectable in w1205, c81‐46A and A375 cells. In contrast, JunD protein was elevated in c81‐46A and c83‐2c cells compared with melanocytes and RGP and VGP cell lines. Normal melanocytes and c83‐2c cells (which have c‐Jun involved in AP‐1 binding), transfected with c‐Jun antisense and treated with cisplatin, showed higher viability compared with untransfected cells, while in c81‐46A cells (in which only JunD is detectable) no change in cell viability was observed following treatment with cisplatin and c‐jun antisense transfection. A dominant‐negative c‐Jun mutant (TAM67) significantly increased the soft agar colony formation of w3211 and c83‐2c cells. These results suggest that components of AP‐1, especially c‐Jun, may offer a new target for the prevention or treatment of human melanoma progression.     

Morphine Dependence is Attenuated by Treatment of 3,4,5-Trimethoxy Cinnamic Acid in Mice and Rats

The effect of 3, 4, 5-trimethoxy cinnamic acid (TMCA) against morphine-induced dependence in mice and rats was investigated. Mice were pretreated with TMCA and then morphine was injected intraperitoneally; whereas rats were treated with TMCA (i.p.) and infused with morphine into the lateral ventricle of brain. Naloxone-induced morphine withdrawal syndrome and conditioned place preference test were performed. Moreover, western blotting and immunohistochemistry were used to measure protein expressions. Number of naloxone-precipitated jumps and conditioned place preference score in mice were attenuated by TMCA. Likewise, TMCA attenuated morphine dependent behavioral patterns such as diarrhea, grooming, penis licking, rearing, teeth chattering, and vocalization in rats. Moreover, the expression levels of pNR1and pERK in the frontal cortex of mice and cultured cortical neurons were diminished by TMCA. In the striatum, pERK expression was attenuated despite unaltered expression of pNR1 and NR1. Interestingly, morphine-induced elevations of FosB/ΔFosB⁺ cells were suppressed by TMCA (50, 100 mg/kg) in the nucleus accumbens sub-shell region of mice. In conclusion, TMCA could be considered as potential therapeutic agent against morphine-induced dependence.

     

Signal transductions induced by bone morphogenetic protein-2 and transforming growth factor-beta in normal human osteoblastic cells

Transforming growth factor beta (TGF-beta) activates Ras/MAPK signaling in many cell types. Because TGF-beta and BMP-2 exert similar effects, we examined if this signaling is stimulated by both factors and analyzed the relationship between this signaling and the Smads in osteoblasts. BMP-2 and TGF-beta stimulated Ras, MAPK, and AP-1 activities. The DNA binding activities of c-Fos, FosB/Delta FosB, Fra-1, Fra-2, and JunB were up-regulated whereas JunD activity was decreased. c-Fos, FosB/Delta FosB, and JunB were associated with Smad4. The stimulation of AP-1 by BMP-2 and TGF-beta was dependent on Smad signaling, and anti-Smad4 antibody interfered with AP-1 activity. Thus, BMP-2 and TGF-beta activate both Ras/MAPK/AP-1 and Smad signaling in osteoblasts with Smads modulating AP-1 activity. To determine the roles of MAPK in BMP-2 and TGF-beta function, we analyzed the effect of ERK and p38 inhibitors on the regulation of bone matrix protein expression and JunB and JunD levels by these two factors. ERK and p38 mediated TGF-beta suppression of osteocalcin and JunD as well as stimulation of JunB. p38 was essential in BMP-2 up-regulation of type I collagen, fibronectin, osteopontin, osteocalcin, and alkaline phosphatase activity whereas ERK mediated BMP-2 stimulation of fibronectin and osteopontin. Thus, ERK and p38 differentially mediate TGF-beta and BMP-2 function in osteoblasts.