Vasopressin innervation of monkey spinothalamic tract neurons

Chapter 13 Descending inhibitory systems

“…Descending axon terminals have direct contacts with presumed pain-relay neurons of the spinal dorsal horn (e.g. Westlund et al, 1990), electrical stimulation of the brainstem induced inhibitory postsynaptic potentials in nociceptive neurons of the spinal dorsal horn (Giesler et al, 1981;Light et al, 1986) and spinal application of noradrenaline, a transmitter released from descending axons, hyperpolarized a population of nociceptive spinal neurons (North and Yoshimura, 1984). These findings indicate that neurotransmitters released from descending axons may block the ascending pain signal by producing a hyperpolarization of spinal relay neurons (direct postsynaptic inhibition; Fig.…”

“…At the spinal cord level, several pain inhibitory mechanisms may be activated by noradrenaline released from descending pathways. First, direct catecholaminergic innervation of the cell bodies of spinothalamic tracts neurons provides a structural basis for postsynaptic noradenergic inhibition of spinal pain-relay neurons (Westlund et al, 1990). Second, in the superficial laminas of the spinal dorsal horn noradrenaline activates a population of small, lowthreshold units that are likely to be inhibitory interneurons (Millar and Williams, 1989).…”

Glutamatergic and GABAergic input to rat spinothalamic tract cells in the superficial dorsal horn

“…A variety of neurotransmitters and/or neuromodulators are contained within the terminals arising from these three sources. Thus far, terminals on STT cells in cat or monkey have been shown to contain enkephalin (ENK; Ruda, 1982;Ruda et al, 1984), substance P (SP; Csrlton et al, 19851, calcitonin gene-related peptide (CGRP;, serotonin (5-HT; Ruda and Coffield, 1983;Hylden et al, 1986;LaMotte et al, 19881, norepinephrine (Westlund et al, 1990a, vasopressin (Westlund et al, 1990b), glycine (GLY; Lekan et al, 19901, glutamate (GLU;Westlund et al, 19921, and y-aminobutyric acid (GABA, Carlton et al, 1992). To date, nothing is known about the synaptology of the STT system in rodents.…”