The morphology of single lateral vestibulospinal tract axons in the lower cervical spinal cord of the cat

Abstract

The intraspinal morphology of single lateral vestibulospinal tract (LVST) axons was investigated with the method of intra-axonal staining with horseradish peroxidase (HRP) and three-dimensional reconstruction of the axonal trajectory. Axons penetrated in the ventral funiculus at C5-C8 were identified as LVST axons by their monosynaptic responses to stimulation of the ipsilateral vestibular nerve and by their direct responses to stimulation of the ipsilateral Deiters' nucleus and LVST. Reconstructions were made from 34 well-stained LVST axons. Of these, 23 terminated in the brachial segments (C5-Th1) and the other 11 projected below Th2. These axons were traced over distances of 2.9-16.3 mm rostrocaudally. Within these lengths, one to seven axon collaterals (mean +/- S.D., 3.2 +/- 2.0, N = 19) were given off at right angles from the stem axons of LVST axons terminating in the brachial segments. The mean diameters of stem axons and primary collaterals were 4.5 microns and 1.6 micron, respectively. In the gray matter, collaterals ramified successively, pursued a delta-like path, and terminated mainly in laminae VII and VIII or lamina IX. The rostrocaudal extension of a single collateral was very restricted (mean +/- S.D., 760 +/- 220 microns, N = 16), in contrast to the extensive dorsoventral and mediolateral extent of the terminal arborization. There were usually gaps between adjacent collateral arborizations from the same stem axons, since the intercollateral distances ranged from 400 to 4,300 microns (mean = 1,490 microns). LVST axons terminating in brachial segments were divided into two groups--a medial group and a lateral group--on the basis of their projection sites in the transverse plane of the gray matter. The axons of the medial type had their main projection to laminae VII and VIII of Rexed, while those of the lateral type terminated in lamina IX. The terminal arborizations of the medial type LVST axons were mainly distributed over lamina VIII, where synaptic boutons appeared to make contact with proximal dendrites or somata of medium-sized and large neurons in the ventromedial nucleus and also in the medial portion of lamina VII adjacent to the central canal and dorsal to lamina VIII. Five out of 15 medial type axons had a bilateral projection. One or two collaterals of each of these axons crossed the midline through the anterior commissure and terminated in lamina VII or VIII. It was concluded that the contralateral projection was sparse.(ABSTRACT TRUNCATED AT 400 WORDS)

Projection patterns of single mossy fibers originating from the lateral reticular nucleus in the rat cerebellar cortex and nuclei

“…Trajectories of single-labeled axons were reconstructed on serial sections by connecting cut ends of an axon on one section to the corresponding cut ends of the same axon on the successive sections as was done with the intra-axonal injection of HRP (Futami et al, 1979;Shinoda et al, 1981Shinoda et al, , 1986Shinoda et al, , 1992. Reconstructions in the coronal plane were sometimes converted to those in the parasagittal plane, by measuring depths and replotted.…”

Monosynaptic EPSPs in cat lumbosacral motoneurones from group Ia afferents and fibres descending in the spinal cord.

“…The resulting composite EPSP would therefore have had a slower time course than the single-(or few-) fibre EPSPs recorded in the present experiments. The available histological evidence sheds little light on this discrepancy: vestibulospinal axons appear to make axodendritic as well as axosomatic synapses on motoneurones of the lower cervical spinal cord (Shinoda, Ohgaki & Futami, 1986), in much the same way as Ia afferents do on lumbosacral motoneurones (Brown & Fyffe, 1981 (Grillner et al 1970(Grillner et al , 1971Peterson, Pitts & Fukushima, 1979). The degree of divergence of single vestibulocollic neurones has also been reported to be low (Rapoport, Susswein, Uchino & Wilson, 1977 (Mendell & Henneman, 1971) and the terminals on the motoneurones are generally limited to a restricted postsynaptic site (Brown & Fyffe, 1981; but see Burke, Walmsley & Hodgson, 1979).…”

Organization of inputs to motoneurone pools in man.

“…It is known that some lateral vestibulospinal tract neurones branch and innervate the ventral spinal grey matter bilaterally (Shinoda, Ohgaki & Futami, 1986). Therefore, these vestibulospinal neurones could presynaptically synchronize the inputs to motoneurones bilaterally.…”