Processing of c-tactile information in the spinal cord

Abstract

Functional brain imaging places C-tactile (CT) fibres within an interoceptive network that is important for the sensation of pleasurable touch and emotional well-being, but the circuits that relay this information from periphery to forebrain are not well understood. In vivo single unit recordings from projection neurons in lamina I of the rat spinal cord showed that the activity of CT fibres is integrated with that of nociceptors before being relayed to the brainstem parabrachial nucleus. There is at least one interneuron in the pathway that relays CT activity from mechanoreceptor to lamina I output neuron, with preliminary data suggesting that such interneurons express the γ isoform of protein kinase C and receive inputs from vesicular glutamate transporter three-labelled primary afferents. A role for CT fibres in mechanical allodynia is also suggested, as pilot data shows that these fibres can provide low-threshold inputs to sensitized nociceptive-specific lamina I projection neurons. Thus, the homeostatic signal provided via CT fibres can be directly modulated by pain, placing the CT system firmly within an interoceptive network that regulates the body’s internal environment.