RESUMEN
Many neural interfacing strategies, such as the sieve electrode and the cultured probe, rely on neurite growth to establish neural contact. But this growth is subject to natural fasciculation, compromising the effectiveness of these interfacing strategies by reducing potential selectivity. This in vitro study shows that the fasciculation mechanism can be manipulated by providing an appropriate microchannel scaffold to guide and influence growth, thereby achieving a high degree of selectivity. The microchannels employed have a bifurcation from a primary channel into two secondary channels. This bifurcating microstructure was able to support and promote fasciculated growth over 70% of the time for microchannels widths of 2.5, 5, 10 and 20 microm. Fasciculation is shown to be a strong force during ingrowth, with the initiation of neurite separation related to random spatial exploration. Narrower microchannels initiate separated growth better. Once separated growth starts fasciculation results in an even distribution of neurite growth across the bifurcation. The reduction from 20 microm to 10 microm wide channels also resulted in a 3-fold decrease in ingrowing neurites performing 180 degrees turns to exit the microchannel via the entrance. No neurite turning was observed for both the 5 and 2.5 microm wide channels.
Asunto(s)
Regeneración Nerviosa/fisiología , Neuritas/fisiología , Neuronas/fisiología , Andamios del Tejido , Animales , Técnicas de Cultivo de Célula , Células Cultivadas , Diseño de Equipo , Ratas , Ratas Wistar , Grabación en VideoRESUMEN
The occurrence of fetal breathing movements was studied in relation to fetal behavioural states 1F and 2F, as recognized by the heart rate patterns A and B, respectively. Simultaneous recordings of fetal heart rate and body, eye and breathing movements were available for analysis (n = 88). These recordings, lasting > or = 2 h, had been made in healthy near-term fetuses during the afternoon or evening, starting about 1 h after the maternal meal. In the majority of recordings fetal breathing activity was lower during heart rate pattern A than during pattern B, but as the opposite occurred in 29/88 recordings (33%), the interstate difference was not significant (P = 0.052). Detailed analysis revealed that breathing movements were more numerous during pattern B than during pattern A if the incidence of breathing during a particular time period was low (30-40% of time). At a high overall breathing incidence (> 40%), however, breathing movements were more often present during pattern A than during pattern B. The latter occurred especially in the first hour of recording, i.e. less distant in time from maternal meals. We conclude that fetal breathing activity is generally higher during state 2F than during state 1F, but a clear-cut state-dependency is absent. Secondly, the relationship between the incidences of breathing during states 1F and 2F depends on the 'drive' or motivation (presumably the blood glucose content) to breathe.