Immunohistochemical visualization of the nervous system in the porcine small intestine using antisera raised against the cytoskeletal proteins MAP1 and MAP2, in combination with neuropeptide immunocytochemistry.

This investigation was performed to determine whether antisera raised against microtubule-associated proteins, i.e. MAP1 and MAP2, may constitute an alternative to the silver-impregnation studies for the identification of the distinct morphological enteric neuronal cell types in the porcine small intestine. MAP1-immunostaining seems less suited since it preferentially stains the neuronal somata and axons and hardly permits to observe the dendritic processes. MAP2-immunostaining chiefly visualizes the perikaryal-dendritic domain and the proximal part of the axonal processes in the enteric neurons of the porcine gut. Hence, MAP2-immunostaining enables for the first time the unambiguous immunocytochemical identification of enteric multi(short)dendritic uniaxonal type I neurons. Double labelling techniques using antisera against MAP2 and substance P indicate that part of the type I neurons in the myenteric plexus of the porcine small intestine, which are taking part in an ascending pathway, are substance P-immunoreactive, whereas the substance P/neuromedin U-minineurons in the Meissner's plexus do not stain for MAP2. We may conclude that, although MAP2-immunostaining falls short of the quality achieved with silver-impregnation, the possibility to combine MAP2-immunostaining with neuropeptide immunocytochemistry to study the intestinal neurons has the advantage that part of the enteric neuron types stained with a distinct neurotransmitter or neuromodulator can be classified morphologically.