ERK Is Involved in the Reorganization of Somatosensory Cortical Maps in Adult Rats Submitted to Hindlimb Unloading

Sensorimotor restriction by a 14-day period of hindlimb unloading (HU) in the adult rat induces a reorganization of topographic maps and receptive fields. However, the underlying mechanisms are still unclear. Interest was turned towards a possible implication of intracellular MAPK signaling pathway since Extracellular-signal-Regulated Kinase 1/2 (ERK1/2) is known to play a significant role in the control of synaptic plasticity. In order to better understand the mechanisms underlying cortical plasticity in adult rats submitted to a sensorimotor restriction, we analyzed the time-course of ERK1/2 activation by immunoblot and of cortical reorganization by electrophysiological recordings, on rats submitted to hindlimb unloading over four weeks. Immunohistochemistry analysis provided evidence that ERK1/2 phosphorylation was increased in layer III neurons of the somatosensory cortex. This increase was transient, and parallel to the changes in hindpaw cortical map area (layer IV). By contrast, receptive fields were progressively enlarged from 7 to 28 days of hindlimb unloading. To determine whether ERK1/2 was involved in cortical remapping, we administered a specific ERK1/2 inhibitor (PD-98059) through osmotic mini-pump in rats hindlimb unloaded for 14 days. Results demonstrate that focal inhibition of ERK1/2 pathway prevents cortical reorganization, but had no effect on receptive fields. These results suggest that ERK1/2 plays a role in the induction of cortical plasticity during hindlimb unloading

Flow Configuration Influence on Darcian and Forchheimer Permeabilities Determination

International audienceWithin the framework of fuel cells, porous materials are used for thefiltration purpose. Determining physical properties like porosity and permeabilityare of utmost importance to predict and manage filtration efficiency of thesematerials. Permeability of material is often determined experimentally in laboratorywith disc samples (the fluid is flowing through the porous material) that are notexactly similar to the tubes of realistic operating conditions (fluid is mainly flowing tangentially to the surface and only a small part is flowing through the material). Thus, the effect of a secondary outlet on the Darcian’s permeability characterization should be studied. In the current paper, we present a new test bench to determine experimentally the Darcy’s and Forchheimer’s permeabilities for a porous media by taking into account two outlets. The pressure, mass flow rate, and temperature are registered for three different setups: with secondary outlet (S.O) (a) 0 %, (b) 50 %, and (c) 100 % open. Then Darcy’s and Forchheimer’s permeabilities for these three cases are calculated and discussed in detail. It has been found that the S.O opening does not affect the Darcian’s permeability, but have substantial influence on the Forchheimer’s one

Contractile properties and myosin expression in rats born and reared in hypergravity.

The effects of hypergravity (HG) on soleus and plantaris muscles were studied in Long Evans rats aged 100 days, born and reared in 2- g conditions (HG group). The morphological and contractile properties and the myosin heavy chain (MHC) content were examined in whole muscles and compared with terrestrial control (Cont) age-paired rats. The growth of HG rats was slowed compared with Cont rats. A decrease in absolute muscle weight was observed. An increase in fiber cross-sectional area/muscle wet weight was demonstrated, associated with an increase in relative maximal tension. The soleus muscle changed into a slower type both in contractile parameters and in MHC content, since HG soleus contained only the MHC I isoform. The HG plantaris muscle presented a faster contractile behavior. Moreover, the diversity of hybrid fiber types expressing multiple MHC isoforms (including MHC IIB and MHC IIX isoforms) was increased in plantaris muscle after HG. Thus the HG environment appears as an important inductor of muscular plasticity both in slow and fast muscle types. </jats:p