Locus K: cuneate subnuclear regions in human dorsal column nuclei with neurochemical, cyto- and myeloarchitectural features of protopathic sensory nuclei

Abstract

This study is aimed to further characterize on a neurochemical, histological and morphometric ground the human Locus K, a newly identified region in the human nucleus cuneatus that shares neurochemical features with protopathic second order sensory nuclei (Del Fiacco et al., 2013; Serra et al., 2013). Human brainstem sections were observed by means of ABC immunohistochemistry for calcitonin gene-related peptide (CGRP), substance P (SP) and transient receptor potential vanilloid type-1 receptor (TRPV1), Kluver-Barrera, Black Gold kit II and Nissl staining followed by computerized analysis of cell size and density. As for CGRP and SP, at both pre- and postnatal age, immunoreactivity to TRPV1 occurs in Locus K with a distribution alike that present in the spinal trigeminal nucleus, caudal part. Morphometric analysis shows that, in adult tissue, the mean diameter and density of Nissl stained neurons in the Locus K are consistent with those of the caudal spinal trigeminal and solitary nuclei, and different from those in the gracile, cuneate and external cuneate nuclei. Kluver-Barrera and Black Gold kit II staining shows that myelinated fibres, abundant in the main cuneate, gracile and trigeminal magnocellular nuclei, are scarce in both the Locus K and trigeminal substantia gelatinosa. Immunohistochemical and cyto- and myeloarchitectural analysis uphold the parallel neurochemical and structural arrangement for Locus K and protopathic nuclei in the human medulla oblongata, and support the concept that Locus K represents a special component of the human dorsal column nuclei. Work funded by Fondazione Banco di Sardegna.