European Journal of Anatomy

Official Journal of The Spanish Society of Anatomy
Cover Volume 10 - Number 2
Eur J Anat, 10 (2): 61-74 (2006)

The ultrastructure of the lateral spinal nucleus

Rethelyi M.

Department of Anatomy, Histology and Embryology, Semmelweis University, Budapest, Hungary

ABSTRACT The lateral spinal nucleus (LSN) is located in the dorsal region of the lateral funiculus in the rodent spinal cord. Four to six medium-sized neurons were found in the cross section of the LSN. The neurons were surrounded by the fibers of the lateral funiculus. Small-diameter myelinated fibers and numerous unmyelinated fibers were seen. The unmyelinated fibers were 0.15 to 0.20 ?m in diameter; their diameters did not change, and they did not have synapsing en passant widening. Axon terminals in the dorsolateral funiculus (DLF) with various types of synaptic vesicles gathered around the neuronal perikarya as well as followed the straight dendrites and established axosomatic and axodendritic synapses. The most common type of axonal varicosities was the small-sized boutons -1.0 to 2.0 ?m in diameter - loosely filled with round, regular synaptic vesicles (Type I boutons). Dense core vesicles were regularly present in the varicosities. Type I boutons were found alone, but more often in groups. A characteristic synaptic arrangement was seen, in which Type I varicosities completely surrounded a thinner dendrite (rosette-shaped synaptic complexes). Type I boutons made both symmetrical and asymmetrical synaptic contacts. In the rosette-shaped synaptic complexes, the synapses were invariably of the asymmetrical type. Axon varicosities densely filled with ovoid synaptic vesicles (Type II boutons) were rarely seen. Axon varicosities of different diameters containing neurosecretory vesicles 130-140 nm in diameter were also found (Type III boutons). No synaptic specializations were found in connections with Type III varicosities. Substance-P labeled axon terminals outlined the dendrites in longitudinally cut sections. At ultrastructural level the SP positive boutons could be classified as Type I varicosities. The dendrites of the LSN neurons frequently coursed towards the pial surface of the spinal cord. Dendrites were found directly below the basal lamina or within the range of the most superficial 1 ?m-thick layer of the DLF. Superficially located dendrites often received synapsing axon terminals. Numerous LSN neurons could be labeled with antiserum detecting Type Ia metabotrop glutamate receptors. The labeled dendrites followed a straight course, approached the pial surface, and received numerous synapsing axon terminals. Some of the neurons could be labeled with NK-1 receptor antiserum.

Keywords: animal experiment, article, chemical labeling, controlled study, dendrite, dendritic cell, electron microscopy, female, lateral spinal nucleus, male, nerve ending, nonhuman, rat, spinal cord, spinal cord dorsal horn, synapse vesicle

European Journal of anatomy
ISSN 2340-311X (Online)