A quantitative light and electron microscopic analysis of taurine‐like immunoreactivity in the dorsal horn of the rat spinal cord

Abstract

Taurine has been proposed as an inhibitory neurotransmitter or neuromodulator in the vertebrate central nervous system. Within the spinal cord, taurine has been shown to have a direct inhibitory effect on spinal neurons and to have a selective antinociceptive effect on chemically induced nociception. Although sufficient data exists to suggest that taurine plays a neurotransmitter or neuromodulatory role in the spinal cord, it is not known whether this amino acid is present in axon terminals nor if this amino acid has a unique pattern of distribution within spinal tissue. To address these questions a monoclonal antibody against taurine was employed to localize taurine-like immunoreactivity in the dorsal horn of the rat spinal cord by using both light and electron microscopic techniques. Taurine-like immunoreactivity was most dense and most prominent in laminae I and II of the dorsal horn. A moderate amount of immunoreactivity was also present in laminae VIII and IX and X while the remaining laminae were only lightly stained. In laminae I and II taurine-like immunostaining was evident within neuronal cell bodies, dendrites, myelinated and unmyelinated axons, axon terminals, and astrocytes and their processes. Cell counts of these two laminae indicated that approximately 30% of neuronal perikarya at the C2 level, 52% of neuronal perikarya at the T6 level, and 18% of neuronal perikarya at the L2 level of the cord exhibited taurine-like immunoreactivity. With preembedding diaminobenzidine staining, approximately 20% of the axons examined in laminae I and II were found to be immunoreactive for taurine. Using postembedding immunogold staining in combination with quantitative procedures, the highest densities of gold particles were found in axon terminals containing pleomorphic vesicles and forming symmetrical synapses (36.8 particles/micron2), in a subpopulation of myelinated axons (34.2 particles/micron2), in a subpopulation of neuronal dendrites (32.6 particles/micron2), and in capillary endothelial cells (39.8 particles/micron2). Moderate labeling occurred in astrocytes (20.9 particles/micron2) and neuronal perikarya (18.7 particles/micron2). The localization of taurine to presumptive inhibitory axon terminals provides anatomical support for the hypothesis that taurine may serve an inhibitory neurotransmitter role in the superficial dorsal horn of the spinal cord. On the other hand, its localization to astrocytes and endothelial cells within both the dorsal ventral horns implies that it serves other nonneuronal functions as well.

Immunohistochemical Localization of Taurine in the Male Reproductive Organs of the Rat

“…In neurons of the rat spinal cord, variable taurine immunostaining in their nuclei has been reported, being weak in some cells and as strong or stronger than in the cytoplasm in other cells (Lee et al 1992). A similar labeling pattern is documented here in Leydig cells and in other cell types.…”

Levels of Amino Acid Neurotransmitters during Neurogenesis and in Histotypic Cultures of Mouse Spinal Cord

“…An inhibitory neurotransmitter or neuromodulatory role for taurine has been shown in the spinal cord [22,62] and in other CNS regions [63][64][65][66]. The high levels of taurine detected from the embryonic period until the early postnatal development imply that it serves other functions aside from simple neurotransmission, which is consistent with its well-established function in the brain as a trophic factor, an osmoregulator and a membrane stabilizer [20,21,67].…”

“…Several lines of evidence suggest that taurine acts as an inhibitory neurotransmitter or neuromodulator in the spinal cord [18,19] and has been considered to be a stabilizer of excitable membranes, to function as an osmoregulator, and to play an important role during brain development [20,21]. The localization of taurine in presumptive inhibitory axon terminals provides anatomical support for the hypothesis that taurine may play an inhibitory role in the superficial dorsal horn of the spinal cord and may have a selective antinociceptive effect on chemically induced nociception [22]. On the other hand, its localization in astrocytes and endothelial cells within both the dorsal and ventral horns of the spinal cord relates to its involvement in osmoregulation [23].…”

Bicuculline-Sensitive Primary Afferent Depolarization Remains after Greatly Restricting Synaptic Transmission in the Mammalian Spinal Cord

“…Microdialysis experiments demonstrate taurine and ␤-alanine release following activation of primary afferents by as much as glutamate (Paleckova et al, 1992). There is also evidence of taurine-immunoreactive primary afferents (Lee et al, 1992).…”