Abstract
Brain natriuretic peptide (BNP) exerts its functions through NP receptors. Recently, BNP has been shown to be involved in a wide range of functions. Previous studies reported BNP expression in the sensory afferent fibers in the dorsal horn (DH) of the spinal cord. However, BNP expression and function in the neurons of the central nervous system are still controversial. Therefore, in this study, we investigated BNP expression in the rat spinal cord in detail using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. RT-PCR analysis showed that BNP mRNA was present in the spinal cord and dorsal root ganglion (DRG). BNP immunoreactivity was observed in different structures of the spinal cord, including the neuronal cell bodies and neuronal processes. BNP immunoreactivity was observed in the DH of the spinal cord and in the neurons of the intermediate column (IC) and ventral horn (VH). Double-immunolabeling showed a high level of BNP expression in the afferent fibers (laminae I–II) labeled with calcitonin gene-related peptide (CGRP), suggesting BNP involvement in sensory function. In addition, BNP was co-localized with CGRP and choline acetyltransferase (ChAT) in the motor neurons of the VH. Together, these results indicate that BNP is expressed in sensory and motor systems of the spinal cord, suggesting its involvement in several biological actions on sensory and motor neurons via its binding to NP receptor-A (NPR-A) and/or NP receptor-B (NPR-B) at the spinal cord level.
Highlights
The natriuretic peptide (NP) family consists of atrial NP (ANP), brain NP (BNP) and C-type NP (CNP; Potter et al, 2009)
We confirmed the specificity of this antibody using Western blotting, where it recognized a single band for Brain natriuretic peptide (BNP) in rodent cells (Abdelalim and Tooyama, 2009)
It is known that Western blotting is effective for validating antibody specificity (Burry, 2000) and the antibody used in this study can be considered to recognize rat BNP protein
Summary
The natriuretic peptide (NP) family consists of atrial NP (ANP), brain NP (BNP) and C-type NP (CNP; Potter et al, 2009). BNP was originally discovered in the porcine brain, it is predominately produced from by the heart ventricles (Minamino et al, 1988; Abdelalim et al, 2006a,b). The physiological functions of BNP are induced by its binding to NP receptor-A (NPR-A; Misono et al, 2011). Some studies suggested that BNP could perform certain functions though it’s binding to NP receptor type B (NPR-B; Suga et al, 1992; Abdelalim and Tooyama, 2009). In response to BNP binding, both guanylyl cyclase receptors produce intracellular cyclic guanosine monophosphate (cGMP; Garbers, 1992). Several studies showed that BNP plays an essential role in cardiovascular homeostasis (Woodard and Rosado, 2007; Potter et al, 2009). Other reports demonstrated that BNP and its receptors are expressed in several cell types that are not related to cardiovascular control, indicating BNP involvement in several functions
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