Neurotransmitters and receptors in the dorsal horn of the spinal cord

Abstract

Modulation of the sensory input can occur within the dorsal horn of the spinal cord where the primary afferent fibers synapse with neurons that transmit to the higher centers. The transmission of the sensory information begins with activation of the peripheral receptors of primary afferent neurons whose cell bodies lie within the dorsal root ganglia and whose central terminals project to secondary neurons in the dorsal horn of the spinal cord. Several neurotransmitters and a large variety of receptors have been found in the superficial laminae of the dorsal horn. The present work reviews the major classes of transmitters and receptors that have been implicated in the transmission and modulation of spinal afferent and pain processing. The role of excitatory and inhibitory amino acids, tachykinin and opioid peptides, calcitonin gene-related peptide (CGRP), nociceptin and nocistatin, biogenic amines, acetylcholine, ATP, nitric oxide as well as capsaicin and vanilloid receptors will be discussed along with the most recent developments in the field. It seems probable that transmission of the somatosensory information from the primary afferent fibers to the secondary dorsal horn neurons depends on the balance between the excitatory effects of excitatory amino acids and the inhibitory actions of several other transmitter systems.