Usefulness of TAO model to predict and manage the transformation in soil of carbon and nitrogen forms from West-Africa urban solid wastes.

The TAO model of Transformation of Added Organic materials (AOM) calibrated on AOMs and substrates of temperate areas was used to assess the transformations in soil of carbon and nitrogen forms of AOMs: raw materials, selected mixtures and composts from Ouagadougou urban wastes. AOMs were studied in terms of chemical and biochemical contents and for their C and N mineralization during incubations in a typical Ferric Lixisol of the sub-urban agriculture of Ouagadougou. The TAO model was used to predict the transformations of C (very labile, resistant and stable organic C) and N (very labile, resistant and stable organic N, produced and immobilized inorganic N) forms driven by AOM biochemical data. Without any change in calibration formulae, TAO predicted accurately the C transformations and inorganic N production of most of the tested AOMs, with a tendency to slightly overestimate C mineralization of previously well-composted materials and re-mineralization of immobilized N. Complementary adjustments using more complete data from laboratory experiments are suggested, but the model agrees with other data collected in the field and appears as a promising tool to optimise the management of urban wastes in the tropical area as well as for agro industrial organic fertilizers of the temperate zone. This application suggests ways to improve the management of urban wastes aiming to optimize agricultural yields, system sustainability and C sequestration in soil.

Patterns of dentate granule cell responses to perforant path stimulation in epileptic mice with granule cell dispersion.

In adult mice, intrahippocampal administration of kainic acid induces a structural modification of the granule cell layer reminiscent of granule cell dispersion (GCD) seen in humans with temporal lobe epilepsy. We tested that GCD might be involved in the patterns of granule cell responses to perforant path stimulation by recording field potentials in vivo after kainic acid-induced status epilepticus until the phase of chronic seizure activity in presence of GCD or after its alteration by K252a co-treatment, an inhibitor of tyrosine kinase activities. Stimulation triggered bursts of multiple population spikes, the number of which progressively increased with time whereas their amplitude decreased in parallel with the progressive decrease in granule cell density. The population spike threshold was reached for a lower excitatory synaptic drive than in controls, as assessed by the initial slope of the field excitatory post-synaptic potential. This indicates that, for identical synaptic responses, granule cells were closer to the firing threshold. Fast inhibition, assessed by paired pulse stimulation, was compromised immediately after the initial status epilepticus, consistent with the rapid loss of most hilar cells. Neither the epileptic course nor the epileptiform responses of the granule cells were modified and manipulation by alteration following GCD manipulation while granule cell neuropeptide-Y immunostaining was substantially decreased. In this mouse model of TLE, granule cells display a progressive increase in epileptiform responses to afferent input until the occurrence of spontaneous seizures. The population spike amplitude decreases in parallel with GCD while the granule cell excitability is enhanced. Consequently, data from field potentials in epilepsy experiments should be interpreted with care, taking into account the possible variations in the neuronal density in the recorded area.