Chronotropic responses of chick atria to field stimulation after various neural crest ablations.

Three models of altered autonomic innervation of the chick heart have been developed in the last few years. These include sympathetically aneural heart, parasympathetically aneural heart, and heart with cholinergic innervation reconstituted from the nodose placodes. The neural status of these hearts has been assessed by a variety of morphological and biochemical methods, but the functional status of innervation is not known. In the present study, we have used electrocardiography and field stimulation to determine the functional neural status of the three different innervation models. The RR and QTc intervals were measured to assess the dominant autonomic tone and autonomic dysfunction in the heart. Even though the RR and QTc intervals were found to be identical in sham and experimental embryos, field stimulation of superfused atria showed that the sympathetically aneural heart has functional cholinergic innervation but lacks any sympathetic response. Hearts from embryos which were parasympathetically aneural lacked a cholinergic response to field stimulation and were judged to be functionally parasympathetically aneural. Hearts with cholinergic ganglia reconstituted from the nodose placodes have normal RR and QTc intervals as well as a normal cholinergic response to field stimulation. The results indicate that these neurons are functionally indistinguishable from neural crest-derived neurons.