Locomotor-activated neurons of the cat. II. Noradrenergic innervation and colocalization with NEα_1a or NEα_2b receptors in the thoraco-lumbar spinal cord

Abstract

Norepinephrine (NE) is a strong modulator and/or activator of spinal locomotor networks. Thus noradrenergic fibers likely contact neurons involved in generating locomotion. The aim of the present study was to investigate the noradrenergic innervation of functionally related, locomotor-activated neurons within the thoraco-lumbar spinal cord. This was accomplished by immunohistochemical colocalization of noradrenergic fibers using dopamine-β-hydroxylase or NEα(1A) and NEα(2B) receptors with cells expressing the c-fos gene activity-dependent marker Fos. Experiments were performed on paralyzed, precollicular-postmamillary decerebrate cats, in which locomotion was induced by electrical stimulation of the mesencephalic locomotor region. The majority of Fos labeled neurons, especially abundant in laminae VII and VIII throughout the thoraco-lumbar (T13-L7) region of locomotor animals, showed close contacts with multiple noradrenergic boutons. A small percentage (10-40%) of Fos neurons in the T7-L7 segments showed colocalization with NEα(1A) receptors. In contrast, NEα(2B) receptor immunoreactivity was observed in 70-90% of Fos cells, with no obvious rostrocaudal gradient. In comparison with results obtained from our previous study on the same animals, a significantly smaller proportion of Fos labeled neurons were innervated by noradrenergic than serotonergic fibers, with significant differences observed for laminae VII and VIII in some segments. In lamina VII of the lumbar segments, the degree of monoaminergic receptor subtype/Fos colocalization examined statistically generally fell into the following order: NEα(2B) = 5-HT(2A) ≥ 5-HT(7) = 5-HT(1A) > NEα(1A). These results suggest that noradrenergic modulation of locomotion involves NEα(1A)/NEα(2B) receptors on noradrenergic-innervated locomotor-activated neurons within laminae VII and VIII of thoraco-lumbar segments. Further study of the functional role of these receptors in locomotion is warranted.

Differential modulation of crossed and uncrossed reflex pathways by clonidine in adult cats following complete spinal cord injury

“…It is probable that noradrenergic inputs are important regulators of interlimb coordination in the intact state. Furthermore, commissural interneurons interposed in crossed reflex pathways are located in laminae VI–VIII in the cat (Edgley et al 2003; Hammar et al 2004, 2007; Jankowska et al 2009), regions that are densely packed with locomotor‐related α 2 ‐noradrenergic receptors (Noga et al 2011).…”

Alterations of cAMP-dependent signaling in dystrophic skeletal muscle

“…This showed immunohistochemical signals of β 2 -AR in at least four different locations: (1) larger blood vessels (not depicted), (2) motoneurons (Figures 5A,B), (3) muscle fibers (Figure 5E, left panel), and (4) ill-defined anastomotic fibers (Figure 5E, on left panel see central part of the picture). Since the presence of β 2 -AR had been found by staining and anticipated to be present due to functional roles in blood vessels (Daly and McGrath, 2011), motoneurons (Melamed et al, 1976; Wohlberg et al, 1986; Bondok et al, 1988; Adachi et al, 1992; Parkis et al, 1995; Zeman et al, 2004; Tartas et al, 2010; Noga et al, 2011; Baker and Baker, 2012) and muscle fibers (Gross et al, 1976; Cairns and Dulhunty, 1993a,b; Cairns et al, 1993; Kokate et al, 1993; Navegantes et al, 1999, 2000, 2001, 2002, 2003, 2004; Prakash et al, 1999; Decostre et al, 2000; Gonçalves et al, 2012), our findings in wildtype muscles were corroborating previous reports. However, the difference between wildtype and dystrophic mdx muscles was striking, both with respect to neuronal as well as muscle staining: First, while the typical pretzel-shaped postsynaptic AChR signals in wildtype muscle were perfectly mirrored by presynaptic β 2 -AR staining (Figures 5A,B) in almost fibers, this was much rarer the case in mdx synapses (Figures 5C,D), which were also highly fragmented as reported previously (Torres and Duchen, 1987; Lyons and Slater, 1991; Grady et al, 2000).…”

Interação funcional entre o sistema colinérgico e adrenérgico na manutenção da massa muscular e da placa motora

“…This showed immunohistochemical signals of β 2 -AR in at least four different locations: (1) larger blood vessels (not depicted), (2) motoneurons (Figures 5A,B), (3) muscle fibers ( Figure 5E, left panel), and (4) ill-defined anastomotic fibers ( Figure 5E, on left panel see central part of the picture). Since the presence of β 2 -AR had been found by staining and anticipated to be present due to functional roles in blood vessels (Daly and McGrath, 2011), motoneurons (Melamed et al, 1976;Wohlberg et al, 1986;Bondok et al, 1988;Adachi et al, 1992;Parkis et al, 1995;Zeman et al, 2004;Tartas et al, 2010;Noga et al, 2011;Baker and Baker, 2012) and muscle fibers (Gross et al, 1976;Cairns and Dulhunty, 1993a,b;Cairns et al, 1993;Kokate et al, 1993;Navegantes et al, 1999Navegantes et al, , 2000Navegantes et al, , 2001Navegantes et al, , 2002Navegantes et al, , 2003Navegantes et al, , 2004Prakash et al, 1999;Decostre et al, 2000;Gonçalves et al, 2012), our findings in wildtype muscles were corroborating previous reports. However, the difference between wildtype and dystrophic mdx muscles was striking, both with respect to neuronal as well as muscle staining: First, while the typical pretzel-shaped postsynaptic AChR signals in wildtype muscle were perfectly mirrored by presynaptic β 2 -AR staining ( Figures 5A,B) in almost fibers, this was much rarer the case in mdx synapses (Figures 5C,D), which were also highly fragmented as reported previously (Torres and Duchen, 1987;Lyons and Slater, 1991;Grady et al, 2000).…”