The localization of primary efferent sympathetic neurons innervating the porcine thymus – a retrograde tracing study

Abstract

The autonomic nervous system is a sophisticated and independent structure composed of two antagonistic (opposing) divisions (sympathetic and parasympathetic) that control many vital functions including: homeostasis maintenance, heart rate, blood circulation, secretion, etc. Thymus is one of the most important primary lymphoid organs playing a role in the developing of a juvenile's immune system mainly by maturation, development, and migration of T-cells (T lymphocytes). In the last decades, several studies identifying sources of the thymic autonomic supply have been undertaken in humans and several laboratory rodents but not in higher mammals such as the pig. Therefore, in the present work, retrograde tracing technique of Fast Blue and DiI was used to investigate the sources of sympathetic efferent supply to the porcine thymus. After Fast Blue injection into the right lobe of the thymus, the presence of Fast Bluepositive neurons was found in the unilateral cranial cervical ganglion (82.8 ± 3.0% of total Fast Blue-positive neurons) as well as in the middle cervical ganglion (17.2 ± 3.0%). Injection of DiI resulted in the presence of retrograde tracer in neurons of the cranial cervical ganglion (80.4 ± 2.3% of total amount of DiI-labelled neurons), the middle cervical ganglion (18.4 ± 1.9%), and the cervicothoracic ganglion (1.2 ± 0.8%). The present report provides the first data describing in details the localization of primary efferent sympathetic neurons innervating the porcine thymus.