1,348 research outputs found
Functional Convergence of Thalamic and Intrinsic Projections to Cortical Layers 4 and 6
Ascending sensory information is conveyed from the thalamus to layers 4 and 6 of the
sensory cortical areas. Interestingly, receptive field properties of cortical layer-6 neurons
differ from those in layer 4. Do such differences reflect distinct inheritance patterns from
the thalamus, or are they derived instead from local cortical circuits? To distinguish between
these possibilities, we utilized in vitro slice preparations containing the thalamo-cortical
pathways of the auditory and somatosensory systems. Responses from neurons in layers 4
and 6 that resided in the same column were recorded using whole-cell patch clamp. Laserscanning photostimulation via uncaging of glutamate in the thalamus and cortex was used to
map the functional topography of thalamo-cortical and intracortical inputs to each layer. In
addition, we assessed the functional divergence of thalamo-cortical inputs by optical imaging
of flavoprotein autofluorescence. We found that the thalamo-cortical inputs to layers 4 and
6 originated from the same thalamic domain, but the intracortical projections to the same
neurons differed dramatically. Our results suggest that the intracortical projections, rather
than the thalamic inputs, to each layer contribute more to the differences in their receptive
field propertiesВисхідний потік сенсорної інформації передається з таламуса до шарів 4 та 6 сенсорних кортикальних зон. Цікавим є
те, що властивості рецептивних полів у нейронів кортикального шару 6 є відмінними від таких у шарі 4. Чи відображають дані відмінності специфічні природжені патерни таламічних зв’язків або вони зумовлені специфікою локальних
кортикальних нейронних мереж? Щоб зробити вибір між такими можливостями, ми використали слайсові препарати in vitro, котрі вміщували таламо-кортикальні шляхи слухової
та соматосенсорної систем. Застосовуючи методику петчклемп у конфігурації «ціла клітина», ми відводили відповіді нейронів шарів 4 та 6, розташованих в одній і тій самій
кортикальній колонці. Для отримання карт функціональної
топографії таламо-кортикальних та інтракортикальних входів, до кожного із шарів ми використовували методику лазерної скануючої стимуляції, що забезпечувала вивільнення глутамату в таламусі та корі. Окрім того, ми оцінювали
функціональну дивергенцію таламо-кортикальних входів за
допомогою візуалізації аутофлуоресценції флавопротеїнів.
Було виявлено, що таламо-кортикальні входи до шарів 4 та
6 походили від ідентичних таламічних регіонів, тоді як інтракортикальні проекції до одних і тих самих нейронів значно відрізнялися. Наші результати примушують думати, що
саме інтракортикальні проекції того або іншого шару, а не
таламічні входи в більшій мірі визначають відмінності відповідних рецептивних полів у згаданих шарах
Forest harvesting impacts on microclimate conditions and sediment transport activities in a humid periglacial environment
Sediment transport activities in periglacial environments
are controlled by microclimate conditions (i.e., air and ground temperatures,
throughfall), which are highly affected by vegetation cover. Thus, there is
the possibility that forest harvesting, the most dramatic change to
vegetation cover in mountain areas, may severely impact sediment transport
activities in periglacial areas (i.e., soil creep, dry ravel). In this study,
we investigated changes in sediment transport activities following forest
harvesting in steep artificial forests located in a humid periglacial area of
the southern Japanese Alps. In the southern Japanese Alps, rainfall is
abundant in summer and autumn, and winter air temperatures frequently rise
above and fall below 0∘. Our monitoring by time lapse cameras
revealed that gravitational transport processes (e.g., frost creep and dry
ravel) dominate during the freeze–thaw season, while rainfall-induced
processes (surface erosion and soil creep) occur during heavy rainfall
seasons. Canopy removal by forest harvesting increased the winter diurnal
ground surface temperature range from 2.7 to 15.9 ∘C. Forest
harvesting also increased the diurnal range of net radiation and ground
temperature, and decreased the duration of snow cover. Such changes in the
microclimate conditions altered the type of winter soil creep from frost
creep to diurnal needle-ice creep. Winter creep velocity of ground surface
sediment in the harvested site (> 2 mm day−1 on the days
with frost heave) was significantly higher than that in the non-harvested
site (generally < 1 mm day−1). Meanwhile, sediment flux on
the hillslopes, as observed by sediment traps, decreased in the harvested
site. Branches of harvested trees left on the hillslopes captured sediment
moving downslope. In addition, the growth of understories after harvesting
possibly reduced surface erosion. Consequently, removal of the forest canopy
by forest harvesting directly impacts the microclimate conditions (i.e.,
diurnal range of ground temperature and net radiation, duration of snow
cover) and increases frequency and velocity of periglacial soil creep, while
sediment flux on hillslopes is decreased by branches left on the hillslopes
and recovery of understories. The impact of forest harvesting on sediment
transport activity is seasonally variable in humid periglacial areas, because
microclimate conditions relevant to both freeze–thaw processes and
precipitation-induced processes control sediment transport.</p
Flowering Times of Wild Arabidopsis Accessions From Across Norway Correlate With Expression Levels of FT, CO, and FLC Genes
Temperate species often require or flower most rapidly in the long daylengths, or photoperiods, experienced in summer or after prolonged periods of cold temperatures, referred to as vernalization. Yet, even within species, plants vary in the degree of responsiveness to these cues. In Arabidopsis thaliana, CONSTANS (CO) and FLOWERING LOCUS C (FLC) genes are key to photoperiod and vernalization perception and antagonistically regulate FLOWERING LOCUS T (FT) to influence the flowering time of the plants. However, it is still an open question as to how these genes vary in their interactions among wild accessions with different flowering behaviors and adapted to different microclimates, yet this knowledge could improve our ability to predict plant responses in variable natural conditions. To assess the relationships among these genes and to flowering time, we exposed 10 winter-annual Arabidopsis accessions from throughout Norway, ranging from early to late flowering, along with two summer-annual accessions to 14 weeks of vernalization and either 8- or 19-h photoperiods to mimic Norwegian climate conditions, then assessed gene expression levels 3-, 5-, and 8-days post vernalization. CO and FLC explained both FT levels and flowering time (days) but not rosette leaf number at flowering. The correlation between FT and flowering time increased over time. Although vernalization suppresses FLC, FLC was high in the late-flowering accessions. Across accessions, FT was expressed only at low FLC levels and did not respond to CO in the late-flowering accessions. We proposed that FT may only be expressed below a threshold value of FLC and demonstrated that these three genes correlated to flowering times across genetically distinct accessions of Arabidopsis
MR Imaging-Based Correction for Partial Volume Effect Improves Detectability of Intractable Epileptogenic Foci on Iodine 123 Iomazenil Brain SPECT Images: An Extended Study with a Larger Sample Size
BACKGROUND AND PURPOSE: It has been suggested, on the basis of a previous pilot study conducted in a small number of patients, that MR imaging-based PVE correction in I-123 iomazenil brain SPECT improves the detectability of cortical epileptogenic foci. In the present study, we performed an investigation by using a larger sample size to establish the effectiveness of the PVE correction and to conduct a detailed evaluation based on the histologic classification of lesions
Activation of Ca 2ϩ -Dependent K ϩ Current by Nordihydroguaiaretic Acid in Porcine Coronary Arterial Smooth Muscle Cells 1
ABSTRACT The effects of nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor and an antioxidant, on membrane currents were examined in single smooth muscle cells isolated from porcine coronary artery. Spontaneous transient outward currents (STOCs) recorded at Ϫ30 mV were markedly enhanced by NDGA (Ն10 M). Pretreatment with caffeine and ryanodine abolished STOCs and reduced NDGA-induced increase in outward current at Ϫ30 mV by ϳ60%. NDGA showed dual action on an outward current elicited by step depolarization from Ϫ60 to 0 mV: inhibition and enhancement at concentrations of 3 and Ն10 M, respectively. In the presence of Cd 2ϩ , the inhibition of outward current by NDGA disappeared and the enhancement remained. NDGA inhibited both the voltage-dependent Ca 2ϩ channel current (IC 50 ϭ 2.5 M) and the delayed rectifier K ϩ current (IC 50 ϭ 9.8 M). The NDGA-induced enhancement of STOCs and outward currents on depolarization was abolished by 100 nM iberiotoxin but was not affected by glibenclamide or apamin. Under current clamp mode, 30 M NDGA significantly hyperpolarized myocytes. The application of lipoxygenase inhibitors (caffeic acid and esculetin), a cyclooxygenase inhibitor (indomethacin), antioxidants (ascorbic acid and erythorbic acid), and structural-related compounds of NDGA (catechol and dopamine) did not enhance K ϩ currents. These results indicate that the opening of the large conductance Ca 2ϩ -dependent K ϩ channel by NDGA, which is independent of its lipoxygenase inhibition or antioxidant effect, results in membrane hyperpolarization
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