The combined use of immunohistochemistry and intracellular staining with horseradish peroxidase for light and electron microscopic studies of transmitter-identified inputs to functionally characterized neurons.

Physiologically identified triceps surae alpha motoneurons in the cat were stained intracellularly with horseradish peroxidase (HRP). After fixation with 2% glutaraldehyde and treatment with sodium borohydride, spinal cord sections were incubated with rabbit antiserum against thyrotropin-releasing hormone (TRH) and rabbit peroxidase-antiperoxidase complex. Light microscopically detected close contacts between immunoreactive nerve terminals and intracellularly HRP-stained profiles were studied under the electron microscope. In this way, synaptic contacts between TRH-immunoreactive boutons and functionally characterized alpha motoneurons could be demonstrated.