The Inhibitory Neuronal Circuit of Spinal Cord in Neuropathic Pain

Abstract

Aim of review:Inhibitory interneurons, including GABAergic neurons and glycine neurons, regulate nociceptive information and non-nociceptive information in spinal dorsal horn. Emerging evidence showed that disinhibition of inhibitory interneurons of neuronal circuit in spinal dorsal horn is a pivotal mechanism of neuropathic pain after nerve injury. Method: In this view, we summarized the recent researches of the structure of inhibitory neurons in spinal dorsal horn and disinhibition of inhibitory interneurons after nerve injury and discussed the primary mechanism. Recent findings: Much progress has been made with the construction of inhibitory neuronal network in spinal dorsal horn and the dysfunction of inhibitory interneurons in these networks since inhibitory interneurons in spinal dorsal horn firstly integrate nociceptive information and non-nociceptive information from primary afferent fiber and separate non-nociceptive stimuli from nociceptive information. Disinhibitory of inhibitory interneurons underlies hyperalgesia and allodynia after nerve injury. Summary: Loss of inhibitory function of neurons in inhibitory network in the dorsal horn contributes to hyperalgesia and allodynia. The findings of these inhibitory networks provide a new evidence for preventing and curing neuropathic pain.ABSTRACT N europathic pain is a challenge for clinicians because the treatment of neuropathic pain is still unsatisfactory. Therefore, increasing understanding of the mechanisms that underlie neuropathic pain will be beneficial for the discovery of new molecular therapy targets. The gate control theory of pain is one of important mechanisms of pain. The theory is the idea that physical pain is modulated by interaction between different neurons. According to the postulate of Melzack and Wall (1), the nerve fibers project to the substantia gelatinosa (SG) of the dorsal horn and the first central transmission cells of the spinal cord. Inhibitory interneurons in the SG act as the gate and determine which signals should reach the T cells and then go further through the spinothalamic tract to reach the brain. Thus, spinal inhibitory interneurons play an important role in maintaining normal pain. Spinal dorsal horn is the first site of integration of nociceptive and nonnociceptive information within the central nervous system (CNS). Under normal physiological conditions, spinal inhibitory interneurons, including gammaaminobutyric acid (GABA) neurons and glycine neurons, form axo-axonic contacts with the termination of primary afferent fiber (PAF), exerting presynaptic inhibition control over sensory transmission. Meanwhile, these inhibitory interneurons generate postsynaptic inhibi-