Comparative neurochemical study of the thoracic and sacral intermediolateral nuclei in the rat.

BACKGROUND AND PURPOSE: In view of the known functional differences, the neurochemical character of the thoracic and sacral intermediolateral nuclei were compared.

METHODS: Neurons and the afferent fiber components were labeled using antibodies raised against neurofilament, neural nuclear protein, cholinacetyltransferase, nitric oxide synthase, neurokinin receptor-1, substance P, calcitonin gene-related peptide, micro-opiate receptor-1 and vesicular glutamate transporter type 1 in rats. Biontinylated isolectin IB4 was used to label unmyelinated primary afferent fibers. Specimens were analyzed with confocal laser microscope.

RESULTS AND CONCLUSIONS: The thoracic and sacral intermediolateral nuclei are similar in the chemical character of the neurons. In the thoracic segments the dendrites of the labeled neurons followed a transverse path towards the neurons located at both sides of the midline above the central canal. The transverse orientation of the dendrites in the sacral segment was less evident. Calcitonin gene-related peptide, isolectin IB4 and micro-opiate receptor-1 immunopositive afferent fibers arborize only in the sacral intermediolateral nucleus. We conclude that fine caliber primary afferent fibers, departing from the adjacent superficial dorsal horn, terminate in the sacral intermediolateral nucleus. It is probable that the preganglionic parasympathetic neurons in the nucleus receive synapses from the primary afferent fibers.