Interaction between adrenergic fibers and intermediate cholinergic neurons in the rat spinal cord: a new double-immunostaining method for correlated light and electron microscopic observations.

Relationships between cholinergic neurons and adrenergic fibers in the intermediate region of the rat thoracic spinal cord were examined using a new immunohistochemical double-staining method for light and electron microscopic observations. Cholinergic neurons were labeled by a monoclonal antibody to choline acetyltransferase and stained bluish green by 5-bromo-4-chloro-3-indolyl-beta-D-galactoside reaction products using beta-galactosidase as a marker. On the same sections, adrenergic fibers were labeled by a polyclonal antiserum to phenyl-ethanolamine-N-methyltransferase and stained brown by diaminobenzidine reaction products using peroxidase as a marker. After embedding in Epon, the sections were examined in the light and electron microscopes. In the light microscope, choline acetyltransferase-like immunoreactive cells were seen in the four discrete areas of the intermediate region: the principal intermediolateral nucleus, the central autonomic nucleus, the intercalated nucleus and the funicular intermediolateral nucleus. These cell groups seemed to be connected to each other by their processes, and they showed a "ladder-like appearance" as a whole. Phenylethanolamine-N-methyltransferase-like immunoreactive fibers were present only along this "ladder-like structure" and were the most rich in the principal intermediolateral nucleus. In the electron microscope, some of the choline acetyltransferase-like immunoreactive neurons, which were identified by light micrographs, were found to receive synaptic inputs from phenylethanolamine-N-methyltransferase-like immunoreactive boutons in the principal intermediolateral nucleus. These findings suggest that the adrenergic axons in the principal intermediolateral nucleus directly affect the activity of the cholinergic preganglionic sympathetic neurons.