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.

The beneficial effects of meditation: contribution of the anterior cingulate and locus coeruleus

“…Activation of the LC can produce profound antinociception (Tsuruoka et al, 2011, 2012; Hayashi et al, 2012) and can inhibit the nociceptive activity of spinal dorsal horn neurons and trigeminal subnucleus caudalis neurons (Hayashi et al, 2012). Nocioceptive signals from visceral organs and cutaneous receptive fields converge on single dorsal horn neurons.…”

“…Nocioceptive signals from visceral organs and cutaneous receptive fields converge on single dorsal horn neurons. Electrical stimulation of the LC inhibited both the visceral (colorectal distention) and the cutaneous pinch responses, with a reduction in the intensity-response magnitude curve without a change in the response threshold (Hayashi et al, 2012). …”

“…The reduced lower level processing in the primary somatosensory area, decreased thalamic activity and the intensity reductions associated with the higher dorsal AC and insula activity could be the result of the LC’s profound antinociceptive action on the ascending STT, reducing the response intensity magnitude curve without a change in response threshold (Hayashi et al, 2012). By this route, the AC activation of the LC may contribute to meditation-induced reduction of pain.…”