Effects of adolescent exposure to cocaine on locomotor activity and extracellular dopamine and glutamate levels in nucleus accumbens of DBA/2J mice

Adolescents differ from adults in their acute sensitivity to several drugs of abuse, but little is known about the long-term neurobehavioral effects of adolescent drug exposure. To explore this further, we evaluated the locomotor responses to repeated cocaine administration in adolescent and adult male DBA/2J mice and alterations in extracellular levels of dopamine (DA) and glutamate (GLU) in the nucleus accumbens (NAc) in response to a subsequent cocaine challenge. Adolescent and adult mice were treated daily with saline or cocaine (10 mg/kg, i.p) for 9 consecutive days. Ten days following the last injection, animals were implanted with microdialysis probes and 24 h later microdialysis samples were collected before and after an acute cocaine challenge. Adolescents but not adults demonstrated development of behavioral sensitization to cocaine. Microdialysis procedures revealed that cocaine-treated mice displayed greater peak increases in extracellular DA in response to a subsequent cocaine challenge as compared to saline-treated mice, in contrast with lower peak increases in extracellular GLU. While adults exhibited greater peaks in extracellular DA in response to cocaine than adolescents did, adolescent mice presented a more rapid onset of peak extracellular DA levels than adults. Our results indicate differences in the behavioral and neurochemical responses to cocaine in adolescent versus adult mice, which may be relevant to the increased risk of developing addiction in humans who are exposed to drugs of abuse during adolescence. (C) 2007 Elsevier B.V. All rights reserved.

Population genetic analysis of large sequence polymorphisms in Plasmodium falciparum blood-stage antigens

Plasmodium falciparum, the causative agent of human malaria, invades host erythrocytes using several proteins on the surface of the invasive merozoite, which have been proposed as potential vaccine candidates. Members of the multi-gene PfRh family are surface antigens that have been shown to play a central role in directing merozoites to alternative erythrocyte receptors for invasion. Recently, we identified a large structural polymorphism, a 0.58 Kb deletion, in the C-terminal region of the PfRh2b gene, present at a high frequency in parasite populations from Senegal. We hypothesize that this region is a target of humoral immunity. Here, by analyzing 371 P. falciparum isolates we show that this major allele is present at varying frequencies in different populations within Senegal, Africa, and throughout the world. For allelic dimorphisms in the asexual stage antigens, Msp-2 and EBA-175, we find minimal geographic differentiation among parasite populations from Senegal and other African localities, suggesting extensive gene flow among these populations and/or immune-mediated frequency-dependent balancing selection. In contrast, we observe a higher level of inter-population divergence (as measured by F(st)) for the PfRh2b deletion, similar to that observed for SNPs from the sexual stage Pfs45/48 loci, which is postulated to be under directional selection. We confirm that the region containing the PfRh2b polymorphism is a target of humoral immune responses by demonstrating antibody reactivity of endemic sera. Our analysis of inter-population divergence suggests that in contrast to the large allelic dimorphisms in EBA-175 and Msp-2, the presence or absence of the large PfRh2b deletion may not elicit frequency-dependent immune selection, but may be under positive immune selection, having important implications for the development of these proteins as vaccine candidates. (C) 2009 Elsevier B.V. All rights reserved.

Comparative genomics of the neglected human malaria parasite Plasmodium vivax

The human malaria parasite Plasmodium vivax is responsible for 25 - 40% of the similar to 515 million annual cases of malaria worldwide. Although seldom fatal, the parasite elicits severe and incapacitating clinical symptoms and often causes relapses months after a primary infection has cleared. Despite its importance as a major human pathogen, P. vivax is little studied because it cannot be propagated continuously in the laboratory except in non- human primates. We sequenced the genome of P. vivax to shed light on its distinctive biological features, and as a means to drive development of new drugs and vaccines. Here we describe the synteny and isochore structure of P. vivax chromosomes, and show that the parasite resembles other malaria parasites in gene content and metabolic potential, but possesses novel gene families and potential alternative invasion pathways not recognized previously. Completion of the P. vivax genome provides the scientific community with a valuable resource that can be used to advance investigation into this neglected species.