Differential Effects of Aging on Fore– and Hindpaw Maps of Rat Somatosensory Cortex

Getting older is associated with a decline of cognitive and sensorimotor abilities, but it remains elusive whether age-related changes are due to accumulating degenerational processes, rendering them largely irreversible, or whether they reflect plastic, adaptational and presumably compensatory changes. Using aged rats as a model we studied how aging affects neural processing in somatosensory cortex. By multi-unit recordings in the fore- and hindpaw cortical maps we compared the effects of aging on receptive field size and response latencies. While in aged animals response latencies of neurons of both cortical representations were lengthened by approximately the same amount, only RFs of hindpaw neurons showed severe expansion with only little changes of forepaw RFs. To obtain insight into parallel changes of walking behavior, we recorded footprints in young and old animals which revealed a general age-related impairment of walking. In addition we found evidence for a limb-specific deterioration of the hindlimbs that was not observed in the forelimbs. Our results show that age-related changes of somatosensory cortical neurons display a complex pattern of regional specificity and parameter-dependence indicating that aging acts rather selectively on cortical processing of sensory information. The fact that RFs of the fore- and hindpaws do not co-vary in aged animals argues against degenerational processes on a global scale. We therefore conclude that age-related alterations are composed of plastic-adaptive alterations in response to modified use and degenerational changes developing with age. As a consequence, age-related changes need not be irreversible but can be subject to amelioration through training and stimulation

A model of sand transport in Treporti channel: northern Venice lagoon

The origin of the sands in the Venice lagoon has been the subject of an extensive field survey in parallel with numerical modelling. Four transects along Treporti and Burano canals were conducted from which 33 bottom sediment samples were collected. These samples were analysed for grain size and sorting to examine any trends in the granulometry of these sediments that might shed light on transport paths. The modelling study consists of three parts: the sediment transport model sedtrans96 was used with a finite-element hydrodynamic model (Shyfem) and an empirical wave model (US Army Corps of Engineering) to simulate sand transport in the Treporti canal. A type of link box model was created where finite elements of the hydrodynamic model have been combined to macro-boxes on which the water and sediment flux over the sections, and a mass balance has been computed. Several grain size classes were simulated; the distributions before and after the simulation were examined. Idealised wind and tidal values were initially used to force 12 h simulations to test the sediment transport sensitivity. Finally, a full-year simulation (1987) has been carried out using measured tidal and wind data. Only a part of Venice lagoon was covered by the simulation: a major channel (Treporti) running from Lido inlet towards the northern lagoon. The total sand transport through all of the sections was computed for 1 year. Sediment mass balance was determined, and the resulting trends of erosion and deposition were computed. There were no trends in the median grain diameter and sorting of bottom samples from the Treporti canal; all sands were fine (120 ?m, one outlier of 300 ?m was removed). The absence of a trend in grain size suggests that there is no significant import of sand to the lagoon through the Lido inlet. The results from the simulations seem therefore to confirm the hypothesis of reworking of sand within the lagoon. The computed erosion is some centimeters per year diagnostic of channel scouring and enlargement with time. The Treporti canal is subject to strong current velocities of around 1 m/s, which hold fine sand in suspension and thus prevent sedimentation

Lateral Organ Boundaries Domain transcription factors direct callus formation in Arabidopsis regeneration

The remarkable regeneration capability of plant tissues or organs under culture conditions has underlain an extensive practice for decades. The initial step in plant in vitro regeneration often involves the induction of a pluripotent cell mass termed callus, which is driven by the phytohormone auxin and occurs via a root development pathway. However, the key molecules governing callus formation remain unknown. Here we demonstrate that Arabidopsis LATERAL ORGAN BOUNDARIES DOMAIN (LBD)/ASYMMETRIC LEAVES2-LIKE (ASL) transcription factors are involved in the control of callus formation program. The four LBD genes downstream of AUXIN RESPONSE FACTORs (ARFs), LBD16, LBD17, LBD18 and LBD29, are rapidly and dramatically induced by callus-inducing medium (CIM) in multiple organs. Ectopic expression of each of the four LBD genes in Arabidopsis is sufficient to trigger spontaneous callus formation without exogenous phytohormones, whereas suppression of LBD function inhibits the callus formation induced by CIM. Moreover, the callus triggered by LBD resembles that induced by CIM by characteristics of ectopically activated root meristem genes and efficient regeneration capacity. These findings define LBD transcription factors as key regulators in the callus induction process, thereby establishing a molecular link between auxin signaling and the plant regeneration program