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Rationale: The Netrin-1/DCC guidance cue pathway is critically involved in the adolescent organization of the mesocorticolimbic dopamine circuitry. Adult mice heterozygous for Dcc show reduced dopamine release in the nucleus accumbens in response to amphetamine and, in turn, blunted sensitivity to the rewarding effects of this drug. Objective: Here, we tested whether the protective effects of Dcc haploinsufficiency are specific to stimulant drugs of abuse or instead extrapolate to opioids and ethanol. Methods: We used the place preference paradigm to measure the rewarding effects of cocaine (20 mg/kg), morphine (5 or 10 mg/Kg), or ethanol (20%) in adult (PND 75) male Dcc haploinsufficient mice or their wild-type litter mates. In a second experiment, we compared in these two genotypes, in vivo dopamine release in the nucleus accumbens after a single i.p. injection of morphine (10 mg/kg). Results: We found reduced morphine-induced dopamine release in the nucleus accumbens of Dcc haploinsufficient male mice, but, contrary to the effects of stimulant drugs, there is no effect of genotype on morphine-induced conditioned preference. Conclusion: These findings show that reduced drug-induced mesolimbic dopamine in Dcc haploinsufficient male mice protects specifically against the rewarding effects of stimulant drugs, but not against the rewarding properties of morphine and ethanol. These results suggest that these drugs exert their rewarding effect via different brain circuits. [ABSTRACT FROM AUTHOR]

Rationale: We previously reported that stressors increase medial prefrontal cortex (PFC) glutamate (GLU) levels as a result of activating callosal neurons located in the opposite hemisphere and that this PFC GLU stress response is regulated by GLU-, dopamine- (DA-), and GABA-sensitive mechanisms (Lupinsky et al. 2010). Objectives: Here, we examine the possibility that PFC DA regulates the stress responsivity of callosal neurons indirectly by acting at D and D receptors located on GABA interneurons. Methods: Microdialysis combined with drug perfusion (reverse dialysis) or microinjections was used in adult male Long-Evans rats to characterize D, D, and GABA receptor-mediated regulation of the PFC GABA response to tail-pinch (TP) stress. Results: We report that TP stress reliably elicited comparable increases in extracellular GABA in the left and right PFCs. SCH23390 (D antagonist; 100 μM perfusate concentration) perfused by reverse microdialysis attenuated the local GABA stress responses equally in the left and right PFCs. Intra-PFC raclopride perfusion (D antagonist; 100 μM) had the opposite effect, not only potentiating the local GABA stress response but also causing a transient elevation in basal (pre-stress) GABA. Moreover, unilateral PFC raclopride microinjection (6 nmol) attenuated the GLU response to TP stress in the contralateral PFC. Finally, intra-PFC baclofen perfusion (GABA agonist; 100 μM) inhibited the local GLU and GABA stress responses. Conclusions: Taken together, these findings implicate PFC GABA interneurons in processing stressful stimuli, showing that local D, D, and GABA receptor-mediated changes in PFC GABA transmission play a crucial role in the interhemispheric regulation of GLU stress responsivity. [ABSTRACT FROM AUTHOR]

Rationale: Signaling through the netrin-1 receptor, deleted in colorectal cancer (DCC), in dopamine neurons controls the extent of their innervation to the medial prefrontal cortex (mPFC) during adolescence. In mice, dcc haploinsufficiency results in increased mPFC dopamine innervation and concentrations in adulthood. In turn, dcc haploinsufficiency leads to resilience to the effects of stimulant drugs of abuse on dopamine release in the nucleus accumbens and behavior. Objectives: First, we set out to determine whether increased mPFC dopamine innervation causes blunted behavioral responses to amphetamine in adult dcc haploinsufficient mice. Second, we investigated whether unc5c, another netrin-1 receptor expressed by dopamine neurons, is involved in these effects. Third, we assessed whether haploinsufficiency of netrin- 1 itself leads to blunted behavioral responding to amphetamine, whether this phenotype emerges before or after adolescence and whether increased mPFC dopamine input is the underlying mechanism. Results: Adult, but not adolescent, dcc, unc5c and netrin-1 haploinsufficient mice exhibit blunted behavioral responses to amphetamine. Furthermore, adult dcc, unc5c, and netrin- 1 haploinsufficient mice have exaggerated mPFC dopamine concentrations in comparison to their wild-type littermates. Importantly, resilience to amphetamine-induced behavioral activation in all the three mouse models is abolished by selective dopamine depletion in the medial prefrontal cortex. Conclusions: dcc, unc5c, or netrin- 1 haploinsufficiency leads to increased dopamine content in the mPFC and to resilience against amphetamine-induced behavioral activation. Our findings raise the hypothesis that DCC, UNC5C, and netrin-1 act in concert to organize the adolescent development of mesocortical dopamine innervation and, in turn, determine behavioral responses to drugs of abuse. [ABSTRACT FROM AUTHOR]

Recent studies have implicated alterations in the expression of polyamine-related genes in the brains of suicide completers including widespread downregulation of spermidine/spermine N1-acetyltransferase, the key enzyme in polyamine catabolism, suggesting compensatory mechanisms attempting to increase brain levels of polyamines. Given the complexity of the polyamine system, quantification of the levels of the polyamines is an essential step in understanding the downstream effects of dysregulated gene expression. We developed a method using high-resolution capillary gas chromatography (GC) in combination with mass spectrometry (MS) for quantitation of polyamines from post-mortem brain tissue, which allowed us to accurately measure spermidine and putrescine concentrations in post-mortem brain tissues. Using this method, we analyzed putrescine and spermidine levels in a total of 126 samples from Brodmann areas 4, 8/9, and 11, from 42 subjects, comprising 16 suicide completers with major depression, 13 non-depressed suicide completers, and 13 control subjects. Both putrescine and spermidine levels fell within the expected nanomolar ranges and were significantly elevated in the brain of suicide completers with a history of major depression as compared with controls. These results were not accounted by possible confounders. This is the first GC–MS study to analyze the expression of putrescine and spermidine from post-mortem brain tissue and confirms the hypothesis raised by previous studies indicating alterations in putrescine and spermidine levels in suicide/major depression. [ABSTRACT FROM AUTHOR]

Early environment can shape the development and function of the mesocorticolimbic dopamine (DA) system and represents a possible risk factor for adult pathologies. One critical variable in the early environment is nutrition, and exposure to high fat (HF) in adulthood is known to change this DA system. We tested whether perinatal HF intake in rats could have long-term effects on DA function and behavior in adult offspring. Rat dams were fed either a control (5% fat, CD) or high fat (30% fat, HF) diet during the last week of gestation and lactation, and adult offspring were tested (PND 56–90) after weaning on CD. Locomotor responses to acute and repeated doses of d-amphetamine (AMP, 0.75 mg/kg bw) were determined as were indices of DA function in the ventral tegmental area (VTA), nucleus accumbens (NAc), and the prefrontal cortex (PFC). Adult HF offspring displayed increased tyrosine hydroxylase expression in the VTA and NAc and significant increases in DA and DOPAC content in the NAc, suggesting an elevated DA tone in this target field. In the NAc, there were no significant changes in D1, D2 receptors, or DA transporter (DAT) levels between diet groups. Perinatal HF feeding reduced AMP-induced locomotion and behavioral sensitization to AMP, suggesting that early diet might have caused long-lasting desensitization of postsynaptic receptor mechanisms in the NAc. Our results demonstrate that both synthetic activity in VTA neurons and the responsiveness of accumbens DA neurons is altered by maternal nutrition. These effects subside long after termination of exposure to the HF diet. [ABSTRACT FROM AUTHOR]

The medial prefrontal cortex (PFC) receives stress-sensitive dopamine (DA) and noradrenergic (NE) projections from the ventral tegmental area and locus coeruleus, respectively, and evidence from various sources point to a complex functional interaction between these two systems. Stress will also stimulate DA transmission in the nucleus accumbens (NAcc), and our previous work has shown that this response is under the indirect inhibitory control of a DA-sensitive mechanism in PFC. We examined the possibility that the NAcc DA stress response is also modulated by prefrontal cortical NE. We used voltammetry to study in freely behaving rats the effects of local applications of alpha1 (benoxathian 0.1, 1, 10 nmol), alpha2 (SKF86466), and beta1/2 (alprenolol) receptor selective antagonists into the PFC on the NAcc DA response to tail-pinch stress. The NAcc DA stress response was dose-dependently inhibited by local PFC blockade of alpha1 receptors. Additional tests revealed, however, that the DA stress response in NAcc is unaffected after local alpha1 receptor activation with cirazoline. Furthermore, at equivalent doses, neither alpha2 nor beta1/2 receptor blockade significantly affected the NAcc DA stress response. These data indicate that stress-induced activation of subcortical DA transmission is modulated by the NE input to PFC acting at alpha1 receptors. They suggest that, under normal circumstances, this system exerts a facilitatory or enabling influence on the NAcc DA stress response. [ABSTRACT FROM AUTHOR]

Rationale: The dopamine (DA) projection to the basolateral amygdala (BLA) modulates nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) DA transmission. Given the involvement of the BLA, and of NAc and mPFC DA, in select forms of information processing, we sought to determine the role of BLA DA in modulating prepulse inhibition (PPI) and latent inhibition (LI). Objective: The effects of BLA D1 (SCH 23390) and D2/D3 (raclopride) receptor blockade on PPI and LI were examined. Methods: Separate groups of male Long-Evans rats received bilateral intra-BLA infusions of SCH 23390 (3.2 or 6.4 µg/0.5 µl per side), raclopride (2.5 or 5.0 µg/0.5 µl per side) or saline prior to testing. In two experiments, the effects of BLA DA receptor antagonism on PPI of the acoustic startle response (ASR) and LI of conditioned taste aversion were determined. A control group received bilateral intrastriatal infusions of SCH 23390 or raclopride prior to PPI testing. Results: Intra-BLA SCH 23390 or raclopride had no effect on the ASR. Intra-BLA SCH 23390 enhanced and raclopride disrupted PPI, both in a dose-related manner. Intra-striatal SCH 23390 or raclopride had no effect on PPI or ASR magnitude. Finally, BLA DA receptor blockade had no effect on LI. Conclusions: These results indicate that PPI is modulated by BLA DA and suggest that this modulation occurs independently of changes in NAc and/or mPFC DA transmission. They also suggest that BLA DA is not involved in modulating LI and add to evidence indicating that PPI and LI are mediated by different neural substrates. [ABSTRACT FROM AUTHOR]