Projections from the nucleus reticularis magnocellularis to the rat cervical cord using electrical stimulation and iontophoretic injection methods

Abstract

The aim of this study is to clarify the fiber distribution of the nucleus reticularis magnocellularis (NRMC) and adjacent areas in the rat spinal cord. Biotinylated dextran amine was injected iontophoretically through a glass capillary into the areas, in which a single cell responded to noxious electrical stimulation of the sciatic nerve and to a pinch of the thigh skin with multiple spikes. Labeled fibers descended bilaterally through the ventral funiculi of the medulla oblongata and then through the ventral and lateral funiculi of the cervical cord with an ipsilateral predominance, and terminated in the spinal gray (laminae I-X). A single fiber sometimes ran through several laminae while bifurcating many short branches with axon varicosities and terminal buttons in one transverse section, that is, through laminae V, VII and X, through laminae V, IIl-IV and I-II, and through laminae VII to I-II. The present study showed that the wide distribution of a single fiber and a mass of fibers descending from the NRMC and adjacent areas might modulate not only somatic sensory and motor functions but also autonomic functions in the spinal cord.

Bulbospinal neurons of the rat rostromedial medulla are highly collateralized

“…Similar results were obtained in other retrograde tracer studies (Newman,1985; Kwiat and Basbaum,1992), although for the thoracic spinal cord a very strong ipsilateral predominance has been reported (Kausz,1991; Zhang et al,2000). In contrast to the general picture of bilateral symmetry obtained from retrograde tracing, results of anterograde tracing from the Gi and GiA indicate a marked ipsilateral predominance of axons and axon terminals in both white and gray matter, particularly for the GiA (Basbaum et al,1978; Zemlan et al,1984; Jones and Yang,1985; Watanabe et al,2003). As noted above with respect to projections to the cervical vs. lumbosacral spinal cord, a likely explanation of the apparent discrepancy in the degree of ipsilateral predominance in the anterograde vs. retrograde studies is that bulbospinal neurons may form a richer preterminal arbor ipsilaterally.…”

“…However, there is some uncertainty about the relative density of projections to cervical vs. lumbosacral levels. Several authors have reported a rostrocaudal gradient, based on anterograde tracing and antidromic microstimulation, with heavier terminations in rostral than caudal segments (Peterson et al,1975; Basbaum et al,1976; Jones and Yang,1985; Watanabe et al,2003). However, injecting a retrograde tracer into spinal gray matter at rostral and more caudal levels, Skagerberg and Bjorklund (1985) found a roughly uniform density of bulbospinal projections throughout the length of the spinal cord.…”

“…Experiments using methods capable of distinguishing neurons and nuclei with topographic vs. collateralized projections suggest a considerable degree of collateralization at both levels of analysis. One such method is the tracing of trajectories of individual axonal arbors (Peterson et al,1975; Jones and Light,1990; Watanabe et al,2003). Likewise, experiments using two distinguishable tracers injected at divergent spinal levels have revealed broad collateralization, with 40% of bulbospinal neurons of the NRM labeling with both tracers, for example, and nearly 70% of cells of the nucleus raphe pallidus (Rpa; Huisman et al,1981,1984; Martin et al,1981; Cavada et al,1984; Kausz,1991).…”

Alzheimer disease neuropathology:understanding autonomic dysfunction

“…The preganglionic neurons of the brainstem and spinal cord innervate the parasympathetic and sympathetic autonomic ganglia and the enteric nervous system which are directly related to cephalic, thoracic, abdominal and pelvic autonomic effectors. 24 , 43 - 46 These regions participate in the constitution of complex neural networks linking high-level cognitive and affective sites with lower integrating structures to influence autonomic, emotional and behavioral responses. 15 …”

Cannabinoid receptor 1 signaling in cardiovascular regulating nuclei in the brainstem: A review

“…It is heterogeneous in composition and contains multiple cell groups that are different in their neurochemical phenotype (e.g. rostroventrolateralis, gigantocellular nucleus, and paragigantocellularis lateralis [68–71] . Within the RVLM, the adrenergic group C1 neurons, alternatively known as adrenergic neurons, are defined based on their expression of phenylethanolamine-n-methyltransferase (PNMT) [72,73] .…”