Inhibitory Amino Acid Transmitters Associated With Axons in Presynaptic Apposition to Cutaneous Primary Afferent Axons in the Cat Spinal Cord

The study aimed to characterize the transmitter content of structures in presynaptic apposition to the central terminals of cutaneous afferent fibers in the cat spinal cord. Researchers identified axons in the Aαβ conduction velocity range in adult cats and examined 99 labeled boutons through serial sections. They found that approximately 80% of boutons from rapidly adapting and hair-follicle afferents were postsynaptic to other axons, compared to 50% from slowly adapting axons. Immunogold reactions showed that 80% to 100% of boutons presynaptic to primary afferents were immunoreactive for γ-aminobutyric acid (GABA), with most also enriched with glycine. The study concluded that presynaptic inhibition of these cutaneous primary afferents was primarily mediated by GABAergic interneurons containing glycine.