Repetitive acute pain in infancy increases anxiety but does not alter spatial learning ability in juvenile mice

We assessed the long-term behavioural effects of a single acute or repetitive inflammatory pain experienced during infancy. Groups of male and female CD1 mice were subjected to either an acute single pain, i.e. a tail clip or sham pain at P8, or acute repetitive pain in the form of needle pricks or sham pain from P8 to P14. All of the subjects were tested in the elevated plus maze at P30 and in the Morris Water Maze from P31 to P38. Mice in the acute single pain and sham groups did not differ on measures of anxiety in the plus maze. Mice in the repetitive pain group demonstrated significantly more anxious behaviours than controls in the elevated plus maze as they spent less time in the open arms, made fewer open arm entries, displayed fewer head dips and showed more stretch attend postures. There were no effects of single or repetitive pain treatments in the latency to find the hidden platform in the Morris Water Maze. Overall, these data suggest that acute repetitive pain experienced during infancy may increase anxiety later in life but it does not influence spatial learning as measured in the Morris Water Maze. The origin of the anxiogenic profile shown in the acute repetitive pain mice may be a result of changes in neural circuitry or context dependent learning and is currently under further investigation with this paradigm.