Bulbar catecholaminergic neurons projecting to the thoracic spinal cord of the chicken. Evans Blue labeling study in combination with catecholamine histofluorescence.

This study was undertaken to map the location of cell groups in the chicken brain stem that project to the thoracic spinal cord by retrogradely transported Evans Blue (EB). The majority of EB-labeled neurons are located in an area between the nucleus vagus motorius (NVMD) and hypoglossus ventralis dorsomedialis, the nucleus raphis, the nucleus vestibularis ventrolateralis, the nucleus tegmentalis dorsalis (NTD) and the reticular formation. However, this procedure demonstrates that no cell bodies within the nucleus tractus solitarii project to the spinal cord, unlike those of mammals. It is possible that this difference may be involved in the existence of the diaphragma. Additionally, catecholamine (CA)-containing cells in the brain stem projecting to the thoracic spinal cord were investigated with the aid of a technique demonstrating both CA and EB fluorescence in the same neuron. The doubly labeled cells are constantly found to be located within such areas as the lateral reticular formation at the level of the NVMD, the ventrolateral reticular formation at the level of the nucleus abducens major, the NTD and the ventrolateral reticular formation at the level of the NTD. The doubly labeled neurons are most numerous in the medial part of the NTD in transverse section, reflecting a similar tendency in the mammalian locus coeruleus.