Expression and distribution of all dopamine receptor subtypes (D1–D5) in the mouse lumbar spinal cord: A real-time polymerase chain reaction and non-autoradiographic in situ hybridization study

Abstract

Dopamine is a catecholaminergic neuromodulatory transmitter that acts through five molecularlydistinct G protein-coupled receptor subtypes (D 1 -D 5 ). In the mammalian spinal cord, dopaminergic axon collaterals arise predominantly from the A11 region of the dorsoposterior hypothalamus and project diffusely throughout the spinal neuraxis. Dopaminergic modulatory actions are implicated in sensory, motor and autonomic functions in the spinal cord but the expression properties of the different dopamine receptors in the spinal cord remain incomplete. Here we determined the presence and the regional distribution of all dopamine receptor subtypes in mouse spinal cord cells by means of quantitative real time PCR and digoxigenin-label in situ hybridization. Real-time PCR demonstrated that all dopamine receptors are expressed in the spinal cord with strongly dominant D 2 receptor expression, including in motoneurons and in the sensory encoding superficial dorsal horn (SDH). Laser Capture Microdissection (LCM) corroborated the predominance of D 2 receptor expression in SDH and motoneurons. In situ hybridization of lumbar cord revealed that expression for all dopamine receptors was largely in the gray matter, including motoneurons, and distributed diffusely in labeled cell subpopulations in most or all laminae. The highest incidence of cellular labeling was observed for D 2 and D 5 receptors, while the incidence of D 1 and D 3 receptor expression was least. We conclude that the expression and extensive postsynaptic distribution of all known dopamine receptors in spinal cord corresponds well with the broad descending dopaminergic projection territory supporting an widespread dopaminergic control over spinal neuronal systems. The dominant expression of D 2 receptors suggests a leading role for these receptors in dopaminergic actions on postsynaptic spinal neurons. 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. (Joyce, 1983, Jackson and Westlind-Danielsson, 1994, Jaber et al., 1996, Missale et al., 1998. NIH Public AccessThe distribution of individual dopamine receptor subtypes has been analyzed in much detail, using immunohistochemistry, receptor ligand binding, or in situ hybridization (ISH) techniques. Most of this research has focused on the brain (Meador-Woodruff and Mansour, 1991, Weiner et al., 1991, Bergson et al., 1995, Yung et al., 1995, Gurevich and Joyce, 1999, Hurd et al., 2001, Kumar and Patel, 2007.There are extensive dopaminergic projections in the spinal cord (Skagerberg et al., 1982, Skagerberg and Bjorklund, 1985, Skagerberg et al., 1988, and a number of au...

Dopaminergic modulation of locomotor network activity in the neonatal mouse spinal cord

“…We provide evidence that activation of the D 2 receptors plays a role in dopamine's ability to reduce the frequency of the rhythm. Our experiments with D 3 KO mice suggest that the D 3 receptors may be constitutively involved in the regulation of rhythm frequency in the absence of dopamine; however, our data do not exclude a role for D 4 receptors that are also highly expressed within the ventral horn of the spinal cord (Zhu et al 2007). Collectively, these data provide a receptor-based understanding of dopamine's modulation of spinal cord CPGs.…”

“…Given that dopamine was capable of reducing rhythm frequency in the D 3 KO spinal cords and the more selective D 2 antagonist (L-741,626) of increasing rhythm fre- quency in the absence of D 1 receptor activity in WT cords, it is likely that D 2 receptors mediate this effect. These findings point to the fact that if we wish to fully understand the role that dopamine plays in the modulation of spinal motor circuits, we must not consider just the receptor families (i.e., D 1 -like and D 2 -like) but also the individual receptor types (i.e., D 1 -D 5 ), which are all expressed nonuniformly across the lumbar spinal cord, with all five receptor subtypes expressed in motor neurons (Zhu et al 2007). It should be noted that this receptor characterization was conducted in P14-age mice, and therefore consideration must be given to the potential developmental receptor expression profile in the first 5 postnatal days.…”

“…What we do know is that dopamine is released within the spinal cord during stepping activity (Gerin and Privat 1998;Jordan and Schmidt 2002) to alter motor output (Barbeau and Rossignol 1991;Clemens et al 2012;Han et al 2007;Han and Whelan 2009;Lapointe et al 2009;Madriaga et al 2004;McCrea et al 1997) and modulate sensory transmission in a variety of species. Dopaminergic fibers project from the diencephalon (A11 area), and all five dopamine receptors are present in the ventral horn of the adult mouse spinal cord (Holstege et al 1996;Qu et al 2006;Ridet et al 1992;Weil-Fugazza and Godefroy 1993;Yoshida and Tanaka 1988;Zhu et al 2007), where motor circuits are located. The five dopamine receptor types are divided into two dopamine receptor families that have been distinguished on the basis biochemical studies.…”

Dopamine triggers skeletal muscle tone by activating D1-like receptors on somatic motoneurons

“…Dopamine may also influence spinal motoneuron function directly. For example, dopamine cells in both the A10 and A11 groups directly project to spinal motoneurons (Qu et al 2006;Ridet et al 1992), which themselves express both D 1 -and D 2 -like dopamine receptors (Dubois et al 1986;Zhu et al 2007). Importantly, in vitro experiments show that dopamine directly modulates spinal motoneuron excitability (Han et al 2007).…”

“…Dopamine neurons in A10 and A11 cell groups synapse onto neurons in the spinal ventral horn (Bjorklund and Skagerberg 1979;Qu et al 2006;Ridet et al 1992;Skagerberg et al 1982), and dopamine nerve terminals are located in cranial motor pools (Mascaro et al 2005;Mong et al 1988;Travers and Norgren 1983). Presumptive motoneurons in both cranial and spinal motor pools express D 1 -and D 2 -like dopamine receptors (Dubois et al 1986;Lazarov et al 1998;Missale et al 1998;Zhu et al 2007). Dopamine release profiles in the vicinity of spinal motoneurons are correlated with changes in global motor activity (Gerin and Privat 1998).…”