ANATOMY OF MEDULLARY AND PERIPHERAL AUTONOMIC NEURONS INNERVATING THENEONATAL PORCINE HEART

Gross and microscopic anatomical investigations were carried out in 14 piglets aged from 4 to 66 days. True Blue (7-50 mu l) and Diamidino Y ellow (7-50 mu l) were injected individually into 2 different cardiac sites (the right atrial ganglionated plexus, the inferior vena cava, i nferior atrial ganglionated plexus, the right atrium or the right vent ricle). Gross anatomy: Globular superior cervical and nodose ganglia, elongated stellate ganglia, multiple small middle cervical ganglia and multiple small mediastinal ganglia along the course of cardiopulmonar y nerves were identified. Microscopic anatomy: Neurons innervating spe cific cardiac regions or intrinsic cardiac ganglionated plexuses were distributed relatively evenly among stellate (primarily in their crani al poles) and middle cervical ganglia bilaterally, fewer labeled neuro ns being located in the superior cervical and mediastinal ganglia bila terally. Parasympathetic efferent preganglionic neurons associated wit h either intrinsic cardiac ganglionated plexus studied were identified primarily throughout the ventrolateral region (the external formation ) of the nucleus ambiguus bilaterally. Labeled neurons were also ident ified throughout the right and left nodose ganglia. Individual neurons did not project axons to different cardiac regions, as no double-labe led neurons were identified. No correlation between age and the number s and locations of labeled neurons was apparent. Thus, porcine sympath etic efferent neurons which innervate individual cardiac regions, incl uding intrinsic cardiac ganglionated plexuses, lie scattered primarily throughout the right and left mediastinal and middle cervical ganglia as well as the cranial poles of stellate ganglia at birth, apparently changing little during the First 2 months of age. Porcine cardiac par asympathetic efferent preganglionic neurons are located primarily in t he external formation of the nucleus ambiguus bilaterally at birth. Th e numbers of afferent cardiac neurons distributed throughout the nodos e ganglia bilaterally also change little during that time. It is concl uded that most of the autonomic neurons which innervate the heart are in place at birth.