sincalide and true-blue

In the present study, we examined the peptidergic content of lumbar spinoreticular tract neurons in the colchicine-treated rat. This was accomplished by combining the retrograde transport of the fluorescent dye True Blue with the immunocytochemical labeling of neurons containing cholecystokinin-8, dynorphin A1-8, somatostatin, substance P or vasoactive intestinal polypeptide. After True Blue injections into the caudal bulbar reticular formation, separate populations of retrogradely labeled cells were identified as containing cholecystokinin-like, dynorphin-like, substance P-like or vasoactive intestinal polypeptide-like immunoreactivity. Retrogradely labeled somatostatin-like neurons were not identified in any of the animals examined. Each population of double-labeled cells showed a different distribution in the lumbar spinal cord. The highest yield of double-labeling occurred for cholecystokinin, with 16% of all intrinsic cholecystokinin-like neurons containing True Blue. These double labeled neurons were found predominantly at the border between lamina VII and the central canal region. About 11% of intrinsic vasoactive intestinal polypeptide-like neurons in the lumbar spinal cord were retrogradely labeled from the bulbar reticular formation. These neurons were found mostly in the lateral spinal nucleus, with only a few double-labeled cells located deep in the gray matter. Dynorphin-like double-labeled neurons were localized predominantly near the central canal; a smaller population was also seen in the lateral spinal nucleus. It was found that double-labeled dynorphin-like neurons made up 8% of all intrinsic dynorphin-like neurons. Retrogradely-labeled substance P-like neurons were rare; the few double-labeled neurons were found in the lateral spinal nucleus and lateral lamina V. These findings suggest a significant role for spinal cord peptides in long ascending systems beyond their involvement in local circuit physiology.

Topics: Afferent Pathways; Animals; Benzofurans; Dynorphins; Fluorescent Dyes; Immunohistochemistry; Male; Neuropeptides; Peptide Fragments; Rats; Rats, Inbred Strains; Reticular Formation; Sincalide; Somatostatin; Spinal Cord; Substance P