RESUMEN
The purpose of these studies were threefold. Firstly, to further characterize the effect of perforant path transection on a test of short-term memory: delayed matching (or nonmatching)-to-position [D(N)MTP]. Secondly, to evaluate the effect of a transient cerebral ischaemia in the same task. Both surgical procedures were chosen as they produce a CNS lesion similar to that described in Alzheimer's Disease (AD). Thirdly, the effect of the acetylcholinesterase inhibitor, donepezil (Aricept(R), E2020), on the resulting cognitive impairment was studied. Perforant path transection produced a robust, delay-dependent impairment of choice accuracy in rats performing either a delayed matching- or nonmatching-to-position task. Sample latency was also reduced following lesion, yet the lesion-induced impairment was not affected by increasing the response requirement at the sample stage. An 11-min period of transient ischaemia (two-vessel occlusion model) resulted in almost complete loss of hippocampal CA1 pyramidal cells and a delay-dependent impairment in DMTP performance. However, unlike perforant path lesions, this deficit was unstable and declined in magnitude over the experimental period. Increasing the delay interval restored this deficit. Donepezil, at doses that robustly attenuated a scopolamine (0.06 mg/kg s.c.)-induced DMTP accuracy impairment in naïve, unoperated rats, had no effect against either lesion-induced impairment. The results are considered in terms of the effectiveness of acetylcholinesterase inhibitors in noncholinergic-based preclinical cognitive models.
Asunto(s)
Enfermedad de Alzheimer/tratamiento farmacológico , Isquemia Encefálica/complicaciones , Inhibidores de la Colinesterasa/farmacología , Hipocampo/efectos de los fármacos , Indanos/farmacología , Trastornos de la Memoria/tratamiento farmacológico , Antagonistas Muscarínicos/farmacología , Vía Perforante/fisiopatología , Piperidinas/farmacología , Escopolamina/farmacología , Enfermedad de Alzheimer/patología , Enfermedad de Alzheimer/fisiopatología , Animales , Infarto Encefálico/complicaciones , Infarto Encefálico/patología , Infarto Encefálico/fisiopatología , Isquemia Encefálica/patología , Isquemia Encefálica/fisiopatología , Muerte Celular/efectos de los fármacos , Muerte Celular/fisiología , Modelos Animales de Enfermedad , Donepezilo , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas/fisiología , Hipocampo/patología , Hipocampo/fisiopatología , Masculino , Trastornos de la Memoria/inducido químicamente , Trastornos de la Memoria/fisiopatología , Vía Perforante/lesiones , Vía Perforante/cirugía , Ratas , Ratas Wistar , Tiempo de Reacción/efectos de los fármacos , Tiempo de Reacción/fisiología , Daño por Reperfusión/complicaciones , Daño por Reperfusión/patología , Daño por Reperfusión/fisiopatologíaRESUMEN
Supplementation with phytase is an effective way to increase the availability of phosphorus in seed-based animal feed. The biochemical characteristics of an ideal phytase for this application are still largely unknown. To extend the biochemical characterization of wild-type phytases, the catalytic properties of a series of fungal phytases, as well as Escherichia coli phytase, were determined. The specific activities of the fungal phytases at 37 degreesC ranged from 23 to 196 U. (mg of protein)-1, and the pH optima ranged from 2.5 to 7.0. When excess phytase was used, all of the phytases were able to release five phosphate groups of phytic acid (myo-inositol hexakisphosphate), which left myo-inositol 2-monophosphate as the end product. A combination consisting of a phytase and Aspergillus niger pH 2.5 acid phosphatase was able to liberate all six phosphate groups. When substrate specificity was examined, the A. niger, Aspergillus terreus, and E. coli phytases were rather specific for phytic acid. On the other hand, the Aspergillus fumigatus, Emericella nidulans, and Myceliophthora thermophila phytases exhibited considerable activity with a broad range of phosphate compounds, including phenyl phosphate, p-nitrophenyl phosphate, sugar phosphates, alpha- and beta-glycerophosphates, phosphoenolpyruvate, 3-phosphoglycerate, ADP, and ATP. Both phosphate liberation kinetics and a time course experiment in which high-performance liquid chromatography separation of the degradation intermediates was used showed that all of the myo-inositol phosphates from the hexakisphosphate to the bisphosphate were efficiently cleaved by A. fumigatus phytase. In contrast, phosphate liberation by A. niger or A. terreus phytase decreased with incubation time, and the myo-inositol tris- and bisphosphates accumulated, suggesting that these compounds are worse substrates than phytic acid is. To test whether broad substrate specificity may be advantageous for feed application, phosphate liberation kinetics were studied in vitro by using feed suspensions supplemented with 250 or 500 U of either A. fumigatus phytase or A. niger phytase (Natuphos) per kg of feed. Initially, phosphate liberation was linear and identical for the two phytases, but considerably more phosphate was liberated by the A. fumigatus phytase than by the A. niger phytase at later stages of incubation.