Neuroendocrine secretory protein 55 (NESP55) in the spinal cord of rat: an immunocytochemical study

The immunohistochemical expression of a novel chromogranin-like protein, neuroendocrine secretory protein 55 (NESP55), in the rat spinal cord was investigated. NESP55-immunoreactive cells were detected in the ventral horn, intermediate laminae, and deep dorsal horn, comprising motoneurons, autonomic neurons, and interneurons throughout all spinal segments. Within laminae I-II of the dorsal horn, one or two NESP55-positive cells were often seen. Nerve fibers also contained NESP55 immunoreactivity (IR) and were particularly prominent in the ventral horn. No nerve terminals/varicosities appeared to contain NESP55 in any spinal lamina. Double-staining experiments revealed that a high proportion of the NESP55-positive neurons were cholinergic. Moreover, NESP55-IR in the motoneurons was evenly distributed in the whole cytoplasm with a finely granular appearance. In contrast, the fluorescent material in the preganglionic neurons was concentrated in the perinuclear region and largely overlapped with the trans-Golgi network marker TGN38. Our data provide detailed morphological information on the distribution of NESP55-IR in the rat spinal cord. Also, the differential intracellular expression of NESP55-IR in the spinal motoneurons and autonomic neurons suggests that NESP55 may be processed into different secretory granules and may be involved in both constitutive and regulated pathways in these neurons.