Gene-targeted mice lacking the AMPA receptor subunit glutamate receptor-A (GluR-A or GluR1) and mice with cytotoxic hippocampal lesions were compared with wild-type and sham-operated controls, respectively, on a conditional learning task using an elevated T-maze. Floor inserts (white perspex vs wire mesh) provided a conditional cue indicating in which goal arm a food reward was to be found. The relationship between the floor insert and the rewarded goal arm was constant throughout the experiment. Both lesioned and knock-out mice were able to acquire the task if the floor inserts extended throughout the entire maze, including the start arm and both goal arms. In contrast, both lesioned and knock-out mice were unable to acquire the task if the floor inserts were only present in the start arm of the maze. The absence of the conditional cue (the floor insert) at the time when the place-reward association was experienced thus critically determined whether or not the mice were impaired. We suggest that hippocampal GluR-A-dependent synaptic plasticity contributes to a memory system in rodents for encoding both the spatial and temporal contexts (the where and the when) associated with a particular event.
Nucleotide sequences from the ND3, ND4L, and ND4 genes of the mitochondrial DNA of deer mice (Peromyscus) from Triangle Island, British Columbia, were analyzed and compared with those from reference samples of the geographically proximal species Peromyscus maniculatus and Peromyscus keeni. Variation among the deer mice from Triangle Island comprised four sequences with a total sequence divergence of 0.093%. One of these sequences characterized 52% of the 27 individuals analyzed; each of the other sequence variants occurred in smaller, but similar, proportions of the population sample. Phylogenetic and distance-clustering analyses uniformly grouped the sequences from the Triangle Island population and placed them within a cluster otherwise comprised of the P. keeni reference samples. The reference samples of P. maniculatus clustered distinctly and significantly outside of the P. keeni/Triangle Island deer mouse assemblage. These data indicate that, in contradiction to their current formal recognition as P. maniculatus, the deer mice from Triangle Island are representative of, and should be taxonomically relegated to, P. keeni.
Nucleotide sequences from the ND3, ND4L, and ND4 genes of the mitochondrial DNA of deer mice (Peromyscus) from Triangle Island, British Columbia, were analyzed and compared with those from reference samples of the geographically proximal species Peromyscus maniculatus and Peromyscus keeni. Variation among the deer mice from Triangle Island comprised four sequences with a total sequence divergence of 0.093%. One of these sequences characterized 52% of the 27 individuals analyzed; each of the other sequence variants occurred in smaller, but similar, proportions of the population sample. Phylogenetic and distance-clustering analyses uniformly grouped the sequences from the Triangle Island population and placed them within a cluster otherwise comprised of the P. keeni reference samples. The reference samples of P. maniculatus clustered distinctly and significantly outside of the P. keeni/Triangle Island deer mouse assemblage. These data indicate that, in contradiction to their current formal recognition as P. maniculatus, the deer mice from Triangle Island are representative of, and should be taxonomically relegated to, P. keeni.Résumé : Les séquences de nucléotides des gènes ND3, ND4L et ND4 de l'ADN mitochondrial ont été analysées chez les Peromyscus de l'île Triangle en Colombie-Britannique et comparées à celles d'échantillons de référence de Peromyscus maniculatus et de Peromyscus keeni provenant la région géogaphique immédiate. La variation chez les souris sylvestres de l'île Triangle implique quatre séquences, pour une divergence totale de 0,093 %. L'une de ces séquences a été trouvée chez 52 % des 27 souris examinées, chacune des autres variantes était présente dans des proportions moins élevées, mais similaires de la population étudiée. Des analyses phylogénétiques et des analyses de groupements basées sur les distances ont réuni de manière uniforme toutes les séquences de la population de l'île Triangle dans un même groupement, qui englobe aussi les échantillons de référence de P. keeni . Les échantillons de référence de P. maniculatus forment un groupement distinct significativement éloigné de celui formé par P. keeni et le peuplement de souris sylvestres de l'île Triangle. En dépit de l'identification actuelle de ces souris sous le nom de P. maniculatus, nos données indiquent que les souris sylvestres de l'île Triangle correspondent à l'espèce P. keeni et qu'elles devraient être reconnues comme telles taxonomiquement.[Traduit par la Rédaction] 2260 Chirhart et al.
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