Organizational and morphological features of cat sacrocaudal motoneurons

Abstract

We have investigated the organizational and morphological features of motoneurons from cat sacrocaudal spinal cord, the portion of the neuraxis that innervates the tail. This information is pertinent for development of a new model of spinal cord injury. An understanding of sacrocaudal circuitry is essential for physiological and behavioral assessment of the effects of sacrocaudal lesions. Observations from Nissl-stained sections corroborated Rexed's cytoarchitectural scheme. Putative motoneurons were located within two regions of the ventral horn: the ventromedial nucleus (lamina IX) and the nucleus commissuralis. To map motoneuron pools, cholera toxin-horseradish peroxidase conjugate was injected into each dorsal tail muscle. The dorsomedial muscle was innervated by ipsilateral nucleus commissuralis motoneurons. The dorsolateral and intertransversarius muscles were innervated by ipsilateral lamina IX and nucleus commissuralis motoneurons. Cell bodies of retrogradely labeled sacrocaudal motoneurons ranged from 22 to 82 microns in diameter; the unimodal distributions peaked between 45 and 50 microns. Dendritic trees of motoneurons, revealed by retrograde labeling or by intracellular injection with horseradish peroxidase, were extensive. Five to eight primary dendrites originated from the cell body. Dendritic branches extended throughout the ipsilateral ventral gray matter, with processes spreading into the surrounding white matter and the base of the dorsal horn. Dendrites from motoneurons with their soma in the lateral portion of lamina IX formed a longitudinal plexus at the gray/white border. Medial dendrites from motoneurons in the nucleus commissuralis formed bundles in the ventral gray commissure and spread throughout the contralateral ventral horn. It is speculated that contralateral dendrites subserve synchronized co-contraction of medial muscles from both sides of the tail.

N‐methyl‐D‐aspartate receptor blockade inhibits estrogenic support of dendritic growth in a sexually dimorphic rat spinal nucleus

“…Various aspects of dendritic and somal morphology in motoneurons have been studied in this regard (see, e.g., Ulfhake and Kellerth, 1981;Schoenen, 1982;Cameron et al, 1985; Cullheim et al, 1987a,b;Furicchia and Goshgarian, 1987;Ritz et al, 1992). To date, a variety of factors that influence the development of neuronal morphology have been identified, including location (Sprague and Ha, 1964;Sterling and Kuypers, 1967;Rose, 1981;Schoenen, 1982;Keirstead and Rose, 1983;Kurz et al, 1990; Sengelaub, 1993), targets (Sumner andWatson, 1971), glial interactions (Tropea et al, 1988;Johnson et al, 1989;Crandall et al, 1990), trophic substances (Snider, 1988), and afferents (Sprague and Ha, 1964;Sterling and Kuypers, 1968;Szekely, 1976;Bregman and Cruce, 1980;Egger et al, 1980;Kalb, 1994).…”

Caudal medullary pathways to lumbosacral motoneuronal cell groups in the cat: Evidence for direct projections possibly representing the final common pathway for lordosis

“…Motoneurons of this part of the muscle are located in the ventromedial nucleus at the level of S1. At the level of S2, the ventromedial nucleus contains motoneurons innervating intrinsic muscles of the proximal tail (Ritz et al, 1992). NRA projections have been observed to the ventromedial nucleus at levels L5-L6 and Sl-S2.…”

Persistent Sodium and Calcium Currents Cause Plateau Potentials in Motoneurons of Chronic Spinal Rats

“…Thus the main objective of the voltage-clamp experiments was to block the spikes and the associated AHPs, without blocking the TTX-sensitive persistent sodium current, so that this persistent sodium current could be measured before TTX application. A good voltage-clamp of the soma was sufficient for this purpose and a clamp of the dendrites was neither necessary nor possible because of the large dendritic trees of motoneurons (Ritz et al 1992). In fact, it is probable that unclamped channels on the dendrites produced most of the hysteresis of the PIC in voltage-clamp recording (Bennett et al 1998a;Hounsgaard and Kiehn 1993;Lee and Heckman 1996).…”