Noradrenergic axon terminals in the substantia gelatinosa of the rat spinal cord

Abstract

The noradrenergic terminals in the substantia gelatinosa of the dorsal horn of the cervical spinal cord of the rat were investigated by means of the histofluorescence technique and electron-microscopic cytochemistry using the glyoxylic acid-KMnO4 fixation technique. In accordance with the topographical distribution of fluorescent catecholaminergic fibers, noradrenergic terminals containing small granular vesicles were frequently observed electron microscopically in the outer layer of the substantial gelatinosa. These terminals were most frequently found to appose (without showing typical synaptic features, small-caliber dendrites, spine apparatus, and rarely, large caliber dendrites. Only in a few cases, the noradrenergic terminals exhibited typical synaptic contacts with dendritic elements of small size. In addition, noradrenergic terminals apposed non-noradrenergic terminals containing small agranular vesicles. In rats bearing surgical lesions of the dorsal roots, no noradrenergic terminal were found in contact with the degenerated axon terminals in the substantia gelatinosa. These findings suggest that the noradrenergic afferents to the substantia gelatinosa may exert their influence on sensory transmission via dorsal horn cells.

The actions of noradrenaline on neurones of the rat substantia gelatinosa in vitro.

“…Numerous noradrenaline containing fibres terminate in the dorsal horn ofthe spinal cord, particularly in the region of the substantia gelatinosa (s.g.) (lamina II of Rexed, 1952) (Dahlstrom & Fuxe, 1965; Satoh, Kashiba, Kimura & Maeda, 1982).…”

Inhibition by 5‐hydroxytryptamine and noradrenaline in substantia gelatinosa of guinea‐pig spinal trigeminal nucleus.

“…Consistent with roles for 5-HT and NA in antinociception, intrathecal administration of 5-HT or NA causes antinociception (Yaksh & Wilson, 1979;Reddy, Maderdrut & Yaksh, 1980) and 5-HT and NA antagonists reduce antinociception produced by supraspinal stimulation (Barbaro, Hammond & Fields, 1985;Jones & Gebhart, 1986a). One of the major sites of termination of the serotonergic and noradrenergic pathways in the dorsal horn are the cell bodies and dendrites of the substantia gelatinosa (SG), or lamina II of both the spinal trigeminal nucleus pars caudalis and the grey matter of the dorsal horn of the spinal cord (Satoh, Kashiba, Kimura & Maeda, 1982;Miletic, Hoffert, Ruda, Dubner, Shigenaga, 1984). The SG is also the primary site of termination of primary afferents which respond to noxious stimuli (Light & Perl, 1979;Sugiura, Lee & Perl, 1986).…”

Synaptic Arrangements Formed by Serotonin‐immunoreactive Axons in the Substantia Gelatinosa of the Rat Spinal Cord

“…5) and therefore it is possible that we overlooked a number of these junctions. However, in a study employing potassium permanganate fixation, Satoh, Kashiba, Kimura & Maeda (1982) have also described non-junctional varicosities in the substantia gelatinosa of the rat which probably contained monoamines (Hokfelt & Jonsson, 1968;Hokfelt & Ljungdahl, 1972). Light et al (1983) suggested that in the cat there were two types of varicosity, and one of these classes 'rarely exhibited synaptic contacts'.…”