The sodium-dependent, high affinity serotonin [5-hydroxytryptamine (5-HT)] transporter (5-HTT) provides the primary mechanism for inactivation of 5-HT after its release into the synaptic cleft. To further evaluate the function of the 5-HTT, the murine gene was disrupted by homologous recombination. Despite evidence that excess extracellular 5-HT during embryonic development, including that produced by drugs that inhibit the 5-HTT, may lead to severe craniofacial and cardiac malformations, no obvious developmental phenotype was observed in the 5-HTT-/- mice. High affinity [3H]5-HT uptake was completely absent in 5-HTT-/- mice, confirming a physiologically effective knockout of the 5-HTT gene. 5-HTT binding sites labeled with [125I] 3 beta-(4'-iodophenyl)tropan-2 beta-carboxylic acid methyl ester were reduced in a gene dose-dependent manner, with no demonstrable binding in 5-HTT-/- mutants. In adult 5-HTT-/- mice, marked reductions (60-80%) in 5-HT concentrations were measured in several brain regions. While (+)-amphetamine-induced hyperactivity did not differ across genotypes, the locomotor enhancing effects of (+)-3, 4-methylenedioxymethamphetamine, a substituted amphetamine that releases 5-HT via a transporter-dependent mechanism, was completely absent in 5-HTT-/- mutants. Together, these data suggest that the presence of a functional 5-HTT is essential for brain 5-HT homeostasis and for 3,4-methylenedioxymethamphetamine-induced hyperactivity.

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...

A single 15-microg dose of 2009 H1N1 vaccine was immunogenic in adults, with mild-to-moderate vaccine-associated reactions. (ClinicalTrials.gov number, NCT00938639).

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.

The aim of the present study was to investigate the mechanisms underlying the desensitization of 5-HT 1A receptors in the dorsal raphe and hypothalamus of serotonin (5-HT) transporter knockout mice (5-HTT Ϫ/Ϫ). The density of 5-HT 1A receptors in the dorsal raphe was reduced in both male and female 5-HTT Ϫ/Ϫ mice. This reduction was more extensive in female than in male 5-HTT Ϫ/Ϫ mice. 8-OH-DPAT-induced hypothermia was absent in female 5-HTT Ϫ/Ϫ and markedly attenuated in 5-HTT ϩ/Ϫ mice. The density of 5-HT 1A receptors also was decreased significantly in several nuclei of the hypothalamus, amygdala, and septum of female 5-HTT Ϫ/Ϫ mice. 5-HT 1A receptor mRNA was reduced significantly in the dorsal raphe region, but not in the hypothalamus or hippocampus, of female 5-HTT ϩ/Ϫ and 5-HTT Ϫ/Ϫ mice. G-protein coupling to 5-HT 1A receptors and G-protein levels in most brain regions were not reduced significantly, except that G o and G i1 proteins were reduced modestly in the midbrain of 5-HTT Ϫ/Ϫ mice. These data suggest that the desensitization of 5-HT 1A receptors in 5-HTT Ϫ/Ϫ mice may be attributable to a reduction in the density of 5-HT 1A receptors. This reduction is brain region-specific and more extensive in the female mice. The reduction in the density of 5-HT 1A receptors may be mediated partly by reduction in the gene expression of 5-HT 1A receptors in the dorsal raphe, but also by other mechanisms in the hypothalamus of 5-HTT Ϫ/Ϫ female mice. Finally, alterations in G-protein coupling to 5-HT 1A receptors are unlikely to be involved in the desensitization of 5-HT 1A receptors in 5-HTT Ϫ/Ϫ mice. Key words: 5-HT 1A receptors; 5-HT 1A mRNA; 5-HT transporter knock-out mice; G-protein coupling; hypothermia; gender difference; autoradiography; competitive RT-PCR; in situ hybridizationIncreasing evidence suggests that the function of serotonin (5-HT) transporter is important in the regulation of emotional states. For example, polymorphisms in the 5Ј regulatory region and intron 2 of the 5-HT transporter (5-HTT) gene, which affects 5-HTT expression, may be related to neuroticism and some affective disorders (Lesch et al., 1996;Mazzanti et al., 1998;MacKenzie and Quinn, 1999;Greenberg et al., 2000;Stoltenberg and Burmeister, 2000). Also, the 5-HTT is the target of a widely used class of antidepressant drugs: the selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine (Prozac). The 5-HTT removes released 5-HT from serotonergic nerve terminals and along axons (Zhou et al., 1998). In doing so, the 5-HTT terminates the activation of postsynaptic 5-HT receptors by extracellular 5-HT. It is believed that the effects of 5-HTT on the regulation of emotion are mediated by adaptive changes in the serotonergic system induced by alterations in extracellular 5-HT concentration. Therefore, studying the mechanisms underlying the effects of 5-HTT on emotion will have a significant impact on our understanding of the etiology of psychiatric disorders and should help to develop better therapeutic approaches for psychiatric d...

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The aim of the present studies was to determine the effects of reduced or absent serotonin (5-HT) transporters (5-HTTs) on 5-HT 2A and 5-HT 2C receptors. The density of 5-HT 2C receptors was significantly increased in the amygdala and choroid plexus of 5-HTT knockout mice. On the other hand, the density of 5-HT 2A receptors was significantly increased in the hypothalamus and septum, but reduced in the striatum, of 5-HTT knockout mice. However, 5-HT 2A mRNA was not changed in any brain region measured. 5-HT 2C mRNA was significantly reduced in the choroid plexus and lateral habenula nucleus of these mice. The function of 5-HT 2A receptors was evaluated by hormonal responses to (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Oxytocin, but not adrenocorticotrophic hormone or corticosterone, responses to DOI were significantly greater in 5-HTT knockout mice. In addition, G q and G 11 proteins were not significantly changed in any brain region measured. The present results suggest that the constitutive alteration in the function of 5-HTTs changes the density of 5-HT 2A and 5-HT 2C receptors in a brain region-specific manner. These changes may not be mediated by alterations in their gene expression or in the level of G q/11 proteins. The alterations in these receptors may be related to the altered behaviors of 5-HTT knockout mice. Keywords: DOI binding, in situ hybridization, 5-HT 2A mRNA, 5-HT 2C mRNA, G q/11 proteins, hormones.