The medial temporal lobe supports conceptual implicit memory

The medial temporal lobe (MTL) is generally thought to be critical for explicit, but not implicit, memory. Here, we demonstrate that the perirhinal cortex (PRc), within the MTL, plays a role in conceptually-driven implicit memory. Amnesic patients with MTL lesions that converged on the left PRc exhibited deficits on two conceptual implicit tasks (i.e., exemplar generation and semantic decision). A separate functional magnetic resonance imaging (fMRI) study in healthy subjects indicated that PRc activation during encoding of words was predictive of subsequent exemplar generation. Moreover, across subjects, the magnitude of the fMRI and behavioral conceptual priming effects were directly related. Additionally, the PRc region implicated in the fMRI study was the same region of maximal lesion overlap in the patients with impaired conceptual priming. These patient and imaging results converge to suggest that the PRc plays a critical role in conceptual implicit memory, and possibly conceptual processing in general.     

Single unit analysis of odour quality coding by the olfactory antennal receptor system of the Colorado beetle

Peripheral events underlying plant odour quality discrimination in the Colorado beetle were investigated. Responses to saturated and unsaturated C-6 alcohols and aldehydes (“green leaf” volatiles) and to other plant compounds were recorded extracellularly. The olfactory receptors could respond by inhibition and/or excitation; inhibition was especially observed at the higher stimulus intensities. Variations in the response patterns were analyzed for a number of receptors constituting a representative sample, as indicated by rank correlation between mean spike responses and electroantennogram amplitudes for each odour stimulus. Application of cluster analysis showed that the olfactory receptors may be divided into two main groups, one reacting differentially to the complex of “green leaf” volatiles and their isomers, and another group showing a selective sensitivity to the aromatic compound methylsalicylate. Evidence is provided suggesting that individual olfactory sensilla can be innervated by more than one functional type of receptor unit. Responses to natural plant odours support the conclusion that plant odour quality is encoded by response patterning across a limited number of olfactory receptor types. The findings are discussed in relation to concepts of chemosensory coding and to the behaviour of the Colorado beetle.

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Analyse Cellulaire du Codage de la Qualité des Odeurs par le Système de Récepteurs Antennaires Olfactifs Chez le Doryphore

Résumé On a étudié la capacité de distinguer la qualité des odeurs végétales chez le doryphore. On a enregistré extracellulairement les réactions de cellules de récepteur olfactif séparées à des C-6 alcools et des aldéhydes saturés et insaturés (substances volatiles de la “feuille verte”) et à d'autres composés végétaux. Les récepteurs olfactifs pouvaient réagir par inhibition et/ou par excitation; on a particulièrement observé l'inhibition aux intensités élevées de stimulus. Les variations des types de réactions ont été analysées pour un certain nombre de récepteurs, qui constituent un échantillon représentatif, sur la base de la corrélation de rang entre les réactions de pointe moyennes et les amplitudes de l'électroantennogramme pour chaque odeur-stimulus. L'application d'une analyse en grappe a montré que les récepteurs olfactifs peuvent être divisés en deux groupes principaux, un groupe qui réagit de fa?on différentielle au complexe des substances volatiles de la “feuille verte” et de leurs isomères et un autre groupe qui a une sensibilité sélective à l'égard du composé aromatique méthylsalicylate. Le premier groupe a été subdivisé en différents types de récepteurs avec des réactions qui se chevauchent. Il semble que les sensilles olfactives individuelles peuvent être innervées par plus d'un type fonctionnel de cellule réceptrice. Les réactions aux odeurs végétales naturelles enregistrées appuient la conclusion que la qualité d'une odeur végétale est codée par un modèle de réaction pour un nombre limité de types de récepteurs olfactifs. On discute les résultats par rapport aux concepts du codage chimiosensoriel et par rapport au comportement du doryphore.

     

Phosphorylation of centromeric histone H3 variant regulates chromosome segregation in Saccharomyces cerevisiae

The centromeric histone H3 variant (CenH3) is essential for chromosome segregation in eukaryotes. We identify posttranslational modifications of Saccharomyces cerevisiae CenH3, Cse4. Functional characterization of cse4 phosphorylation mutants shows growth and chromosome segregation defects when combined with kinetochore mutants okp1 and ame1. Using a phosphoserine-specific antibody, we show that the association of phosphorylated Cse4 with centromeres increases in response to defective microtubule attachment or reduced cohesion. We determine that evolutionarily conserved Ipl1/Aurora B contributes to phosphorylation of Cse4, as levels of phosphorylated Cse4 are reduced at centromeres in ipl1 strains in vivo, and in vitro assays show phosphorylation of Cse4 by Ipl1. Consistent with these results, we observe that a phosphomimetic cse4-4SD mutant suppresses the temperature-sensitive growth of ipl1-2 and Ipl1 substrate mutants dam1 spc34 and ndc80, which are defective for chromosome biorientation. Furthermore, cell biology approaches using a green fluorescent protein–labeled chromosome show that cse4-4SD suppresses chromosome segregation defects in dam1 spc34 strains. On the basis of these results, we propose that phosphorylation of Cse4 destabilizes defective kinetochores to promote biorientation and ensure faithful chromosome segregation. Taken together, our results provide a detailed analysis, in vivo and in vitro, of Cse4 phosphorylation and its role in promoting faithful chromosome segregation.