The role of dopamine in sleep regulation and in mediating the effects of wake-promoting therapeutics is controversial. In this study, polygraphic recordings and caudate microdialysate dopamine measurements in narcoleptic dogs revealed that the wake-promoting antinarcoleptic compounds modafinil and amphetamine increase extracellular dopamine in a hypocretin receptor 2-independent manner. In mice, deletion of the dopamine transporter (DAT) gene reduced non-rapid eye movement sleep time and increased wakefulness consolidation independently from locomotor effects. DAT knock-out mice were also unresponsive to the normally robust wake-promoting action of modafinil, methamphetamine, and the selective DAT blocker GBR12909 but were hypersensitive to the wake-promoting effects of caffeine. Thus, dopamine transporters play an important role in sleep regulation and are necessary for the specific wake-promoting action of amphetamines and modafinil.

Cocaine and methylphenidate block uptake by neuronal plasma membrane transporters for dopamine, serotonin, and norepinephrine. Cocaine also blocks voltagegated sodium channels, a property not shared by methylphenidate. Several lines of evidence have suggested that cocaine blockade of the dopamine transporter (DAT), perhaps with additional contributions from serotonin transporter (5-HTT) recognition, was key to its rewarding actions. We now report that knockout mice without DAT and mice without 5-HTT establish cocaine-conditioned place preferences. Each strain displays cocaine-conditioned place preference in this major mouse model for assessing drug reward, while methylphenidate-conditioned place preference is also maintained in DAT knockout mice. These results have substantial implications for understanding cocaine actions and for strategies to produce anticocaine medications.Cocaine use is a principal drug abuse problem in the United States and other countries, contributing to substantial morbidity and mortality among the millions of individuals who use it each year (1). No current medication provides effective treatment for cocaine dependence (2). These facts give particular importance to defining the sites for cocaine reward in the brain so that they can be more accurately targeted by potential therapeutic agents.Several lines of evidence have provided support for a role of the dopamine transporter (DAT) as a primary site for cocaine reward. Structure-activity studies document good correlations between psychostimulant properties in tests of reward and their abilities to block DAT; poorer correlations are noted with their potencies in blocking other transporters (3, 4). Dopaminergic lesions blunt cocaine influences in model systems that test reward (5-7). Psychostimulants enhance dopamine release from dopaminergic circuits (8). Transgenic mice that overexpress DAT display enhanced cocaine-conditioned place preference (G.R.U., et al., unpublished observations). Finally, ''indifference'' to cocaine has been inferred from the reduced cocaine-stimulated locomotion recently described in mice that lack DAT (9, 10).There are also limitations to postulated direct relationships between DAT blockade and psychostimulant-induced reward. Among these are the failure of several compounds that potently inhibit dopamine uptake, including mazindol, to display substantial abuse liability in humans or animal model studies (11-13). Because mazindol potently inhibits dopamine and norepinephrine transport, but only weakly inhibits serotonin transport, this difference from cocaine could conceivably contribute to a distinct profile on tests of reward (14-16). These and other more indirect lines of evidence support the idea that cocaine's inhibition of serotonin uptake could also provide an alternative and plausible molecular site for contributions to cocaine reward (17)(18)(19).To test the dopamine-or serotonin-transporter dependence of cocaine reward, we have constructed DAT knockout mice and assessed cocaine-conditioned plac...

Morphine produces analgesia at opiate receptors expressed in nociceptive circuits. , ␦, and opiate receptor subtypes are expressed in circuits that can modulate nociception and receive inputs from endogenous opioid neuropeptide ligands. The roles played by each receptor subtype in nociceptive processing in drug-free and morphine-treated states have not been clear, however. We produced homologous, recombinant , opiate receptor, heterozygous and homozygous knockout animals that displayed Ϸ54% and 0% of wild-type levels of receptor expression, respectively. These mice expressed receptors and ␦ receptors at near wild-type levels. Untreated knockout mice displayed shorter latencies on tail f lick and hot plate tests for spinal and supraspinal nociceptive responses than wild-type mice. These findings support a significant role for endogenous opioid-peptide interactions with opiate receptors in normal nociceptive processing. Morphine failed to significantly reduce nociceptive responses in hot plate or tail f lick tests of homozygous receptor knockout mice, and heterozygote mice displayed right and downward shifts in morphine analgesia dose-effect relationships. These results implicate endogenous opioidpeptide actions at opiate receptors in several tests of nociceptive responsiveness and support receptor mediation of morphine-induced analgesia in tests of spinal and supraspinal analgesia.Morphine acts at seven transmembrane domain, G proteinlinked receptor products of genes encoding , , and ␦ opiate receptor subtypes (1-9). Each of these genes is expressed in neurons in several neuronal circuits implicated in nociception (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20).receptor mediation of much morphine-induced analgesia has been postulated (21, 22). However, studies using compounds with relative preferences for ␦ and receptors have suggested that these other two opiate receptor subtypes also might play significant roles in the analgesic responses induced by morphine-like drugs (22-26). The extent to which each of the three opiate receptor subtype gene products might participate in different features of opiate-or morphineinduced analgesia thus has remained unclear. Elucidation of the selective analgesic contributions of each opiate receptor subtype is of substantial potential importance for developing improved analgesic medications with minimal undesirable effects.Expression of endogenous opioid-peptide agonists, especially those derived from the preproenkephalin and preprodynorphin genes, in circuits associated with pain perception suggests that opioid-peptide interactions with opiate receptors could be well positioned to modulate nociceptive responses in the absence of exogenously administered opiate drugs (10,12,14,(27)(28)(29)(30)(31)(32). Studies of pain responses in animals and humans treated with opiate antagonists, however, have documented modifications in nociception in some but not all studies (33,34). These results also have left uncertainty about the power of endogenous opioid-peptide interactions with ...

The brain vesicular monoamine transporter (VMAT2) pumps monoamine neurotransmitters and Parkinsonism-inducing dopamine neurotoxins such as 1-methyl-4-phenyl-phenypyridinium (MPP ؉ ) from neuronal cytoplasm into synaptic vesicles, from which amphetamines cause their release. Amphetamines and MPP ؉ each also act at nonvesicular sites, providing current uncertainties about the contributions of vesicular actions to their in vivo effects. To assess vesicular contributions to amphetamine-induced locomotion, amphetamine-induced reward, and sequestration and resistance to dopaminergic neurotoxins, we have constructed transgenic VMAT2 knockout mice. Heterozygous VMAT2 knockouts are viable into adult life and display VMAT2 levels one-half that of wild-type values, accompanied by smaller changes in monoaminergic markers, heart rate, and blood pressure. Weight gain, fertility, habituation, passive avoidance, and locomotor activities are similar to wild-type littermates. In these heterozygotes, amphetamine produces enhanced locomotion but diminished behavioral reward, as measured by conditioned place preference. Administration of the MPP ؉ precursor N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine to heterozygotes produces more than twice the dopamine cell losses found in wild-type mice. These mice provide novel information about the contributions of synaptic vesicular actions of monoaminergic drugs and neurotoxins and suggest that intact synaptic vesicle function may contribute more to amphetamine-conditioned reward than to amphetamine-induced locomotion.

Polygenic risk scores (PRS) have attenuated cross-population predictive performance. As existing genomewide association studies (GWAS) were predominantly conducted in individuals of European descent, the limited transferability of PRS reduces its clinical value in non-European populations and may exacerbate healthcare disparities. Recent efforts to level ancestry imbalance in genomic research have expanded the scale of non-European GWAS, although they remain under-powered. Here we present a novel PRS construction method, PRS-CSx, which improves cross-population polygenic prediction by integrating GWAS summary statistics from multiple populations. PRS-CSx couples genetic effects across populations via a shared continuous shrinkage prior, enabling more accurate effect size estimation by sharing information between summary statistics and leveraging linkage disequilibrium (LD) diversity across discovery samples, while inheriting computational efficiency and robustness from PRS-CS. We show that PRS-CSx outperforms alternative methods across traits with a wide range of genetic architectures and cross-population genetic correlations in simulations, and substantially improves the prediction of quantitative traits and schizophrenia risk in non-European populations.

Cocaine blocks uptake by neuronal plasma membrane transporters for dopamine (DAT), serotonin (SERT), and norepinephrine (NET). Cocaine reward͞reinforcement has been linked to actions at DAT or to blockade of SERT. However, knockouts of neither DAT, SERT, or NET reduce cocaine reward͞reinforcement, leaving substantial uncertainty about cocaine's molecular mechanisms for reward. Conceivably, the molecular bases of cocaine reward might display sufficient redundancy that either DAT or SERT might be able to mediate cocaine reward in the other's absence. To test this hypothesis, we examined double knockout mice with deletions of one or both copies of both the DAT and SERT genes. These mice display viability, weight gain, histologic features, neurochemical parameters, and baseline behavioral features that allow tests of cocaine influences. Mice with even a single wild-type DAT gene copy and no SERT copies retain cocaine reward͞reinforcement, as measured by conditioned place-preference testing. However, mice with no DAT and either no or one SERT gene copy display no preference for places where they have previously received cocaine. The serotonin dependence of cocaine reward in DAT knockout mice is thus confirmed by the elimination of cocaine place preference in DAT͞SERT double knockout mice. These results provide insights into the brain molecular targets necessary for cocaine reward in knockout mice that develop in their absence and suggest novel strategies for anticocaine medication development.

Cocaine conditioned place preference (CPP) is intact in dopamine transporter (DAT) knockout (KO) mice and enhanced in serotonin transporter (SERT) KO mice. However, cocaine CPP is eliminated in double-KO mice with no DAT and either no or one SERT gene copy. To help determine mechanisms underlying these effects, we now report examination of baselines and drug-induced changes of extracellular dopamine (DA ex ) and serotonin (5-HT ex ) levels in microdialysates from nucleus accumbens (NAc), caudate putamen (CPu), and prefrontal cortex (PFc) of wild-type, homozygous DAT-or SERT-KO and heterozygous or homozygous DAT/SERT double-KO mice, which are differentially rewarded by cocaine. Cocaine fails to increase DA ex in NAc of DAT-KO mice. By contrast, systemic cocaine enhances DA ex in both CPu and PFc of DAT-KO mice though local cocaine fails to affect DA ex in CPu. Adding SERT to DAT deletion attenuates the cocaine-induced DA ex increases found in CPu, but not those found in PFc. The selective SERT blocker fluoxetine increases DA ex in CPu of DAT-KO mice, while cocaine and the selective DAT blocker GBR12909 increase 5-HT ex in CPu of SERT-KO mice. These data provide evidence that (a) cocaine increases DA ex in PFc independently of DAT and that (b), in the absence of SERT, CPu levels of 5-HT ex can be increased by blocking DAT. Cocaine-induced alterations in CPu DA levels in DAT-, SERT-, and DAT/SERT double-KO mice appear to provide better correlations with cocaine CPP than cocaine-induced DA level alterations in NAc or PFc.

Our findings suggest that GLO1 deficits and carbonyl stress are linked to the development of a certain subtype of schizophrenia. Elevated plasma pentosidine and concomitant low vitamin B(6) levels could be the most cogent and easily measurable biomarkers in schizophrenia and should be helpful for classifying heterogeneous types of schizophrenia on the basis of their biological causes.