Central circuits that subserve pain of different behavioural significance and their descending control
|Department of Physiology, University of Bristol , UK|
In 1942 Thomas Lewis predicted that nociceptive inputs arising from cutaneous versus visceral structures must activate distinct neuronal circuits in the CNS in order to co-ordinate organ specific changes in autonomic outflow. Technological advances have since confirmed Lewis’ prediction in certain key regions of the CNS and have incorporated it into the broader context that pains of different behavioural significance are represented in distinct CNS circuits. Evidence will be presented to support the view that the midbrain periaqueductal grey is a focus of delineated circuits, that mediate active versus passive coping strategies, which aid survival by co-ordinating changes in behaviour, autonomic outflow and sensory processing that are appropriate to meet the demands of different psychological and environmental stressors. It is suggested that these represent neural systems that have evolved to deal with real life problems.
The protective role of descending control of spinal nociception, as one component of these co-ordinated responses, will be discussed. Consideration will be given to how maladaptive alterations in descending controls can transform this protective function and may contribute to the shift from acute to chronic pain.