Effects of Social Isolation and Housing Supplementation on Neuropathic Nociception in Rats

Abstract

Although only limited data have been published regarding the effects of environmental variables on pain, the available information suggests that the perception of pain in humans and nociception in rodents is affected by external surroundings. To better understand how the environment alters nociception, this study examined the effects of social isolation and cage complexity on the severity and duration of nerve injury-induced nociceptive behaviors. Male, Sprague-Dawley rats were used in this study, and researchers blinded to the housing treatment groups collected all data. Baseline behavioral measurements, including paw withdrawal latency to a heat stimulus and paw withdrawal threshold to a mechanical stimulus, were taken at the onset of the investigation. Rats were randomly assigned to the four housing treatment groups: (1) one rat per cage, standard cage conditions, (2) one rat per cage, supplemented cage conditions, (3) three rats per cage, standard cage conditions, and (4) three rats per cage, supplemented housing conditions. Both the standard and supplemented cage conditions provided food, water, and bedding; however, the supplemented cage condition also included objects that increased the cage complexity (polycarbonate shelters, rodent toys, things to gnaw and chew, etc.). Following a six-week period in their assigned housing condition, pre-nerve injury behavioral data were collected, and then each rat underwent the partial sciatic nerve ligation surgery. Post-surgical behavioral data were collected at 1, 7, 14, 21, 28, and 35 days. The data indicate that social interaction and supplementation decrease nociceptive behaviors.