Normal and abnormal development of the intrapericardial arterial trunks in humans and mice.

AIMS: The definitive cardiac outflow channels have three components: the intrapericardial arterial trunks; the arterial roots with valves; and the ventricular outflow tracts (OFTs). We studied the normal and abnormal development of the most distal of these, the arterial trunks, comparing findings in mice and humans. METHODS AND RESULTS: Using lineage tracing and three-dimensional visualization by episcopic reconstruction and scanning electron microscopy, we studied embryonic day 9.5-12.5 mouse hearts, clarifying the development of the OFTs distal to the primordia of the arterial valves. We characterize a transient aortopulmonary (AP) foramen, located between the leading edge of a protrusion from the dorsal wall of the aortic sac and the distal margins of the two outflow cushions. The foramen is closed by fusion of the protrusion, with its cap of neural crest cells (NCCs), with the NCC-filled cushions; the resulting structure then functioning transiently as an AP septum. Only subsequent to this closure is it possible to recognize, more proximally, the previously described AP septal complex. The adjacent walls of the intrapericardial trunks are derived from the protrusion and distal parts of the outflow cushions, whereas the lateral walls are formed from intrapericardial extensions of the pharyngeal mesenchyme derived from the second heart field. CONCLUSIONS: We provide, for the first time, objective evidence of the mechanisms of closure of an AP foramen that exists distally between the lumens of the developing intrapericardial arterial trunks. Our findings provide insights into the formation of AP windows and the variants of common arterial trunk.

A simple method for characterizing passive and active neuronal properties: application to striatal neurons.

The study of active and passive neuronal dynamics usually relies on a sophisticated array of electrophysiological, staining and pharmacological techniques. We describe here a simple complementary method that recovers many findings of these more complex methods but relies only on a basic patch-clamp recording approach. Somatic short and long current pulses were applied in vitro to striatal medium spiny (MS) and fast spiking (FS) neurons from juvenile rats. The passive dynamics were quantified by fitting two-compartment models to the short current pulse data. Lumped conductances for the active dynamics were then found by compensating this fitted passive dynamics within the current-voltage relationship from the long current pulse data. These estimated passive and active properties were consistent with previous more complex estimations of the neuron properties, supporting the approach. Relationships within the MS and FS neuron types were also evident, including a graduation of MS neuron properties consistent with recent findings about D1 and D2 dopamine receptor expression. Application of the method to simulated neuron data supported the hypothesis that it gives reasonable estimates of membrane properties and gross morphology. Therefore detailed information about the biophysics can be gained from this simple approach, which is useful for both classification of neuron type and biophysical modelling. Furthermore, because these methods rely upon no manipulations to the cell other than patch clamping, they are ideally suited to in vivo electrophysiology.