Distribution of Spinal Cord Nerve Endings Containing Various Neurotransmitters on a Continuous Density Gradient

Abstract

Homogenates of rat dorsal or ventral spinal cord were subjected to centrifugation on a continuous density gradient. The gradient was generated according to a new method with the aid of a microprocessor-controlled HPLC pump. The distribution of substance P-like immunoreactivity (SPI) and somatostatin-like immunoreactivity (SRIFI) across the gradient showed two peaks. The SPI peak seen at lower density was found only in dorsal spinal cord tissue. No peak of SPI was seen at this position in homogenates prepared from the spinal cords of capsaicin-pretreated rats. The second peak of SPI, found at a higher density, was accompanied by peaks in the levels of endogenous 5-hydroxytryptamine (5-HT), [14C]glycine, and [3H]norepinephrine uptake. This peak was seen at the same density in the dorsal and the ventral spinal cord. Tissue derived from capsaicin-pretreated rats exhibited one peak of SPI, accompanied by a maximum of [14C]glycine uptake. The uptake of [3H]gamma-aminobutyric acid ( [3H]GABA) was found to have a maximum at a somewhat lower density than that of [14C]glycine. It is concluded that the peak of SPI found at lower density in the dorsal spinal cord is associated with nerve endings belonging to capsaicin-sensitive primary afferents, while other endings, including those also containing 5-HT, are probably associated with the peak of SPI found at higher density.

Characterization of substance P release from the intermediate area of rat thoracic spinal cord

“…The existence of separate vesicle populations and vesicles containing multiple putative neurotransmitters implies that coexisting neurosubstances can be selectively released and regulated at different conditions. Studies of the storage sites for SP and 5-HT in the ventral spinal cord by immunoelectron microscopy (Pelletier et al, 1981) and by subcellular fractionation (Bucsics et al, 1984;Fried et al, 1989) indicate that SP is stored in large, dense-cored vesicles and 5-HT is stored mainly in small vesicles but also sometimes in large, SP-containing vesicles. The respective roles of small and large dense-cored vesicles are still poorly understood.…”

Differential Release of Endogenous 5‐Hydroxytryptamine, Substance P., and Neurokinin A from Rat Ventral Spinal Cord in Response to Electrical Stimulation

“…Studies of the storage sites for 5-HT and SP by immunoelectron microscopy (Pelletier et al,198 1) and by subcellular fractionation (Bucsics et al, 1984;Fried et al, 1988Fried et al, , 1989 indicate that SP and 5-HT are stored in different subcellular compartments in the ventral spinal cord, SP being stored in large, densecored vesicles and 5-HT mainly in small vesicles. This would provide a morphological basis for differential release of these compounds from nerve endings where they coexist.…”