Long-term potentiation in superficial spinal dorsal horn: A pain amplifier

Abstract

Long-term potentiation of synaptic strength (LTP) is one of the most intensively studied models of lasting signal amplification in the nervous systems. LTP has also been identified at synapses between small primary afferent Aδ- or C-fibres, many of which are nociceptive, and 2nd order neurons in superficial spinal dorsal horn. In the present chapter we review fundamental properties of spinal LTP and we describe different induction protocols including electrical nerve stimulation, acute nerve injury and noxious stimulation such as capsaicin or formalin intraplantar injections. The presently known signal transduction pathways leading to LTP in pain pathways include activation of NMDA receptor and NK1 receptors for substance P, opening of T-type voltage-gated calcium channel, release of Ca2+ from intracellular stores, as well as activation of PKC and CaMKII. These signalling pathways are similar to those leading to hyperalgesia. The converging and independent evidence summarized in this chapter suggests that LTP at the first synapse in pain pathways may underlie various forms of hyperalgesia following trauma, inflammation or nerve injury.