title: A possible synaptic configuration underlying coeruleospinal inhibition of visceral nociceptive transmission in the rat.
abstract: A synaptic arrangement underlying descending inhibition from the locus coeruleus/subcoeruleus (LC/SC) on visceral nociceptive transmission in the spinal cord was investigated in the anesthetized rat. Extracellular recordings were made from the L(6)-S(2) segmental level using a carbon filament glass microelectrode (4-6 MΩ). Colorectal distention (CRD) was produced by inflating a balloon inside the descending colon and rectum. All neurons tested responded to both CRD and to cutaneous pinch (a force of 613 g/mm(2)), indicating that nociceptive signals from visceral organs and nociceptive signals from the cutaneous receptive field converge on a single neuron. These neurons were divided into two groups based on their response to CRD: short latency-abrupt and short latency-sustained neurons. Electrical stimulation of the LC/SC (30 or 50 μA, 100 Hz, 0.1 ms pulses) inhibited both CRD-evoked and cutaneous pinch-evoked responses in short latency-abrupt and short latency-sustained neurons. When graded CRD (20, 40, 60, and 80 mmHg) was delivered, LC/SC stimulation produced a reduction in slope of the linear CRD intensity-response magnitude curve without a change in the response threshold in both short latency-abrupt (n = 42) and short latency-sustained neurons (n = 11). This result suggests that coeruleospinal inhibition of visceral nociceptive transmission is due to a synaptic configuration in which inhibitory and excitatory terminals are in close spatial proximity, including presynaptic inhibition.
authors.affiliation: Department of Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Bunsho
authors.initials: B
authors.lastname: Hayashi
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Tsuruoka
authors.forename: Masako
authors.initials: M
authors.lastname: Maeda
authors.forename: Junichiro
authors.initials: J
authors.lastname: Tamaki
authors.forename: Tomio
authors.initials: T
authors.lastname: Inoue
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001703:Biophysics; D003106:Colon / Q000294:innervation; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000379:methods*; D007839:Functional Laterality; D008125:Locus Coeruleus / Q000502:physiology*; D008297:Male; D009433:Neural Inhibition / Q000502:physiology*; D010812:Physical Stimulation / Q000009:adverse effects; D011601:Psychophysics; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000502:physiology; D012867:Skin / Q000294:innervation; D013116:Spinal Cord / Q000502:physiology*; D059265:Visceral Pain / Q000628:therapy*