Acute and conditioned hyperalgesic responses to illness.

It has been argued that pain functions to facilitate recovery from injury and/or illness by stimulating recuperative behaviors. If this is the case, then hyperalgesia might be expected to be part of the constellation of adaptations that occur during sickness. The present series of studies tested two agents that induce illness (lithium chloride and bacterial cell-wall endotoxin (lipopolysaccharide)) to determine their acute effects on pain responsivity in rats.