Contribution of AMPA and NMDA receptors in the spontaneous firing patterns of single neurons in autaptic culture.

Single neurons in an autaptic culture exhibit various types of firing pattern with different firing durations and rhythms. However, a neuron with autapses has often been modeled as an oscillator providing a monotonic firing pattern with a constant periodicity because of the lack of a mathematical model. In the work described in this study, we use computational simulation and whole-cell patch-clamp recording to elucidate and model the mechanism by which such neurons generate various firing pattens. In the computational simulation, three types of spontaneous firing pattern, i.e., short, long-lasting, and periodic burst firing patterns are realized by changing the combination ratio of N-methyl-d-aspartate (NMDA) to α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) conductance. These three types of firing patterns are also observed in the experiments where neurons are cultured in isolation on micropatterned substrates. Using the AMPA and NMDA current models, we discuss that, in principle, autapses can regulate rhythmicity and information selection in neuronal networks.

Sex allocation of a cosexual wind-pollinated tree, Quercus dentata, in terms of four currencies.

Sex allocation of a cosexual wind-pollinated species, Quercus dentata (Fagaceae), was analyzed using biomass, carbon, nitrogen and phosphorus as currencies based on data accumulated for 61 individuals from 1997-2004. Strongly female-biased sex allocation was indicated when measured in terms of biomass and carbon, but no significant bias was detected when measured in terms of nitrogen or phosphorus. From an adaptive viewpoint, there is little support for strong female-biased sex allocation, suggesting that sex allocation in terms of nitrogen or phosphorus is closer to the real picture. The relative sex allocation considerably varied from year to year, but the relative femaleness of individuals in the population was rather constant across years. No significant correlation was observed between relative sex allocation and fecundity or tree height, but individuals that showed very low fecundity tended to produce only acorns.

Differentiation and hybridization between Quercus crispula and Q. dentata (Fagaceae): insights from morphological traits, amplified fragment length polymorphism markers, and leafminer composition.

Quercus crispula and Q. dentata (Fagaceae) are dominant members of cool-temperate forests of Japan and are assumed to hybridize in nature. To characterize and discriminate these two species and their hybrids, we carried out multivariate analysis using several morphological traits and principal coordinate analysis using molecular (amplified fragment length polymorphism [AFLP]) data. Further, we examined the composition of Phyllonorycter species (leafmining insects) on individuals from a mixed forest. Morphological traits and Phyllonorycter composition differ enough in these two oak species to be useful for identification of species and hybrids. AFLP data, however, are less informative because the degree of molecular differentiation between the two species is low. Nine out of 105 individuals from a mixed stand had intermediate morphologies according to the multivariate analysis, and eight out of the nine individuals had intermediate Phyllonorycter composition in either one or both of the two study years. These eight individuals were tentatively assigned as hybrids or backcross individuals, and the remaining individual with intermediate morphologies was assigned as Q. dentata according to its Phyllonorycter composition and the AFLP analysis.