Characterization of trkB immunoreactive cells in the intermediolateral cell column of the rat spinal cord

Abstract

The objective of the present study was to characterize the trkB receptor immunoreactive (-ir) cells in the intermediolateral cell column (IML) of the upper thoracic spinal cord. Small trkB-ir cells (area =56.1 +/− 4.4 µm 2 ) observed in the IML showed characteristics of oligodendrocytes and were frequently observed in close apposition to choline acetyltransferase (ChAT)-ir cell bodies. Large trkB-ir cells (area =209.3 +/− 25.2 µm 2 ) showed immunoreactivity for the neuronal marker NeuN, indicating their neuronal phenotype, as well as for ChAT, a marker for preganglionic neurons. TrkB and ChAT were co-localized in IML neurons primarily in cases that had received in vivo administration of nerve growth factor (NGF). These findings reveal two different cell types, oligodendrocytes and neurons, in the IML of the spinal cord that show trkB immunoreactivity, suggesting their regulation by BDNF and/or NT-4. In addition, there is evidence that NGF may play a role in the regulation of trkB-ir preganglionic neurons in the IML. Keywords preganglionic neurons; BDNF; NT-4; oligodendrocytes; sympatheticThe regulation of neurons and glial cells in the spinal cord is poorly characterized. TrkB expressing cells have been reported in the spinal cord, suggesting that they are regulated by either brain derived neurotrophic factor (BDNF) and/or neurotrophin -4 (NT-4). For example, in the lower intermediolateral cell column (IML; T7-T10), pre-ganglionic neurons have been shown to express trkB mRNA, are trkB immunoreactive (-ir) [17], and appear to be dependent on neurotrophin-4 (NT-4) derived from adrenal medullary chromaffin cells for survival [16]. However, retrograde transport of NT-4 from the target could not be demonstrated in these preganglionic neurons, and thus the exact mechanisms involved in the NT-4-mediated survival of the lower intermediolateral cell column are not known. Preganglionic neurons located in the IML of the upper thoracic cord may be regulated by brain-derived neurotrophic factor (BDNF) , though these phenomena have not been well documented.In addition to preganglionic neurons, trkB-ir glial cells have been reported in the motor areas of the lumbar spinal cord [19] and were shown to be altered by exercise [13]. The extent to which the trkB-ir glial cells were present in the upper thoracic cord has not been described.*Corresponding author, Lori G. Isaacson, Center for Neuroscience and Behavior, Department of Zoology, Miami University, 280 Pearson Hall, Oxford, OH 45056, Fax: 513-529-6900, isaacslg@muohio.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. The go...

Distribution and phenotype of TrkB oligodendrocyte lineage cells in the adult rat spinal cord

“…As described in previous studies (Skup et al, 2002; Macias et al, 2007; McCartney et al, 2008; Coulibaly and Isaacson, 2012), TrkB cells frequently were observed in close proximity to neuronal cell bodies in the IML and the ventral horn and thus were categorized as perineuronal. In order to determine the overlap of these cells with OL lineage cells markers, the expression of NG2, CC1 and/or TrkB by perineuronal cells and their association with ChAT immunoreactive (-ir) ventral horn neurons were analyzed.…”

“…Subsequent studies from our laboratory confirmed that the TrkB cells were nonneuronal (McCartney et al, 2008), that many of the cells expressed CC1 (Coulibaly and Isaacson, 2012), and that they did not express markers for astrocytes or microglia (Skup et al 2002; Coulibaly, unpublished). Others have reported little colocalization of full length TrkB and GFAP in uninjured tissues, though reactive astrocytes can express full length TrkB following CNS injury (McKeon et al, 1997) and in models of multiple sclerosis (Colombo et al, 2012).…”

“…The minor proportion of small neurons in Lamina II of the dorsal horn that express TrkB (Salio et al, 2005) were not included in our analysis as the measuring box for the dorsal horn encompassed only the lowermost portion of Lamina II and included primarily Laminae III, IV,V. In addition to their larger size, the identity of TrkB neurons was verified by labeling with the NeuN marker (McCartney et al, 2008) a marker that shows specificity for neurons (Mullen et al, 1992). It should also be noted that the DAPI labeled nuclei exhibited by neurons typically were larger and paler when compared to dense, bright blue nuclei of the glial cells (See Figs.…”

“…Oligodendrocytes that express TrkB, the cognate receptor for brain derived neurotrophic factor (BDNF), have been reported in the adult spinal cord (Macias et al, 2007; McCartney et al, 2008; Coulibaly and Isaacson, 2012; Skup et al, 2002), suggesting that a least some cells in the OL lineage are responsive and/or regulated by BDNF. Indeed, numerous reports have indicated that BDNF can affect the cells in the OL lineage (Van’t Veer et al, 2009; VonDran et al, 2010).…”

Increased Cx32 expression in spinal cord TrkB oligodendrocytes following peripheral axon injury

“…In an effort to determine which cell type in the OL lineage was responsible for the increased number of plaques per cell, double labeling of Cx32 with the OL markers TrkB [17,18], CC1 [19], or NG2 [20] was carried out. In a recent study from our lab, the majority of TrkB cells (>80%) were shown to colocalize CC1, indicating their mature phenotype [18], yet a proportion of TrkB cells may represent a separate pool of OL linage cells [18] and thus TrkB cells were considered separately.…”