Processing Of Itch In Cerebral Cortex

Itch is an unpleasant sensation that causes the desire to scratch. The majority of skin and systemic diseases are often accompanied by severe itch. Unfortunately, there is a lack of effective treatment for various kinds of itch. The main reason for such a situation is a lack of understanding of the neural mechanisms of itch. The current researches focus on exploring its peripheral and spinal mechanisms, few studies touch upon the neural mechanism of itch above spinal level. There have been some researches using brain imaging techniques to explore brain mechanisms of histamine-induced itch, results of which indicate that there are several brain regions are activated by histamine, including cingulate cortex, cerebellum, thalamus, the insula and supplementary motor cortex. On the other hand, only one report so far touches upon the brain mechanism of histamine-independent itch. Understanding of brain mechanisms for histamine-independent itch is of great interest for both basic science and clinic. In our study, we explored how our brain processes the itch information induced by cowhage, a non-histaminergic itch-inducing agent, using the functional magnetic resonance imaging technique. Furthermore, we compared the cowhage-induced brain activity with histamine-induced activity to find out similarities and differences between them.21subjects participated in our experiments. Histamine or cowhage as itch-inducing agents was applied in the skin of forearms. Inactive cowhage was used as control agent. Histamine was delivered to skin through histamine-containing inactive cowhage hairs which had been soaked in histamine solution. The subjects’ brains were scanned twice with a7day interval in the condition of either histamine or cowhage administration, respectively, in a random order. The scans started once itch stimuli were given, and lasted for10minutes. Our results showed that cowhage and histamine co-activated some brain areas, while also revealed notable differences. The brain areas activated by both stimuli were found in the thalamus and cerebellum. Cowhage induced a notably distinct and more extensive involvement of bilateral cerebellum, contralateral supplementary motor area, contralateral insula, contralateral pre-central gyrus, contralateral superior temporal cortex, contralateral thalamus, contralateral posterior cingulate cortex. Our preliminary finding suggests that histamine-dependent itch and histamine-independent itch have different neuronal mechanisms, including their different pathways at both peripheral and central nervous system. We use electrophysiological methods to further explore the neural mechanism of itch based upon the results from fMRI research. Electrophysiological recording technique is an important research tool in the field of neuroscience research, with rather high temporal and spatial resolution. Electrophysiological recordings can be made from either anesthetized or awake animals. Although it is more convenient to record in anesthetized animals, their brains could function quite differently from those of conscious animals. Effort has been made to successfully establish a platform for recording brain signals from conscious animals for the study of neuronal mechanism of itch signal processing. The platform includes S I head fixture device。...