Tyrosine hydroxylase-immunoreactive projections from the caudal ventrolateral medulla to the subfornical organ in the rat.
The subfornical organ (SFO) is known to be innervated by noradrenergic fibers. One possible origin of these fibers, which carry peripheral baroreceptor information to enhance the activity of SFO neurons, is the nucleus tractus solitarius (NTS). To investigate possible sites of origin of the catecholaminergic projections to the SFO, a retrograde tracing method was combined with immunohistochemistry in the rat. Stereotaxical injection of a retrograde tracer, wheat germ agglutinin-conjugated horseradish peroxidase--colloidal gold complex, into the SFO from the dorsal aspect revealed retrogradely labeled neurons in several catecholaminergic cell groups. A substantial number of retrogradely labeled neurons showing tyrosine hydroxylase (TH) immunoreactivity were found in the NTS and ventrolateral medulla (VLM) at levels caudal to the obex and in the locus coeruleus, while retrogradely labeled neurons without TH immunoreactivity were found in the VLM at levels rostral to the obex and in the nucleus prepositus hypoglossi. When the tracer was injected into the structures dorsal to the SFO, including the triangular septal nucleus, the frequency of retrogradely labeled neurons in the NTS and VLM at the caudal level was very low. These findings indicate the existence of catecholaminergic projections from the VLM (probably A1) to the SFO, in addition to the noradrenergic projections from the NTS previously reported.
Kawano
H
H
Department of Anatomy, Saga Medical School, Nabeshima 5-1-1, Saga 849-8501, Japan. kawanoh@post.saga-med.ac.jp
Masuko
S
S
D000818:Animals; D000906:Antibodies; D002395:Catecholamines / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology* / Q000201:enzymology; D008854:Microscopy, Electron; D009434:Neural Pathways; D009474:Neurons / Q000201:enzymology / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D013356:Subfornical Organ / Q000166:cytology* / Q000201:enzymology; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis* / Q000276:immunology; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate
D000906:Antibodies; D002395:Catecholamines; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D014446:Tyrosine 3-Monooxygenase