NEUROANATOMY OF CARDIAC ACTIVITY-REGULATING CIRCUITRY - A TRANSNEURONAL RETROGRADE VIRAL LABELING STUDY IN THE RAT

The anatomy of cardiac activity-regulating circuitry was studied with retrograde transneuronal viral labelling after pseudorabies virus inje ctions into different parts of the rat heart. Transection of the spina l cord at Th1 was used to reveal selectively the parasympathetic neuro nal networks. Virus-labelled sympathetic preganglionic cells were foun d in the Th1-Th7 thoracic intermediolateral cell groups, with some add itional infections at Th8-Th11 after inoculations of the ventricular m yocardium. After ventricular injections the thoracic spinal labelling pattern was bilateral and after right atrial infection it was contrala teral. Approximately 20% of the parasympathetic preganglionic cells we re located in the dorsal motor vagus nucleus; the rest occupied positi ons in the peri-ambiguus area ventrolateral to the nucleus ambiguus. H ere and in the ventrolateral reticular formation myocardiotopy was fou nd. Supraspinal transneuronal infections were bilateral, showed no app arent side dominance and were found in the nucleus of the solitary tra ct, the area postrema, the raphe nuclei, the A5 group, the parabrachia l region, the periaqueductal grey, the hypothalamus, the amygdala and the cortex, in particular the anterior cingulate, the frontal, prelimb ic, infralimbic and insular cortices. Spinal transections at Th1 reduc ed the number of labelled cells, gave a right side labelling dominance and affected the infection patterns in the ventrolateral reticular ar ea, the raphe nuclei, the periaqueductal grey matter, the perifornical and retrochiasmatic area and the rostral parts of the insular cortex. The latter structures are linked selectively to the sympathetic inner vation of the heart. The anatomical and functional aspects of these fi ndings are discussed in relation to the autonomic control of heart act ivity.