1. Carrageenan has been shown to alter transduction capacities of high-threshold mechanoreceptors of the goat palatal mucosa. Assessments were made of the contributions of carrageenan-induced edema to the sensitization of mechanonociceptors (mechanically insensitive afferents) and intense pressure receptors of the palatal mucosa of the goat. The degree of edema was assessed by measurement of changes in tissue compliance produced by carrageenan. The impact of a simulated edema on both dynamic and static aspects of transduction were examined. The following observations were made. 2. Tissue compliance of the ventral zone of the incisal papilla (IP) was decreased after carrageenan treatment (0.042-0.014 mm/g). Tissue compliance changes were large for small displacements (< 1.4 mm), where displacement curves were substantially linear. For large displacements (> 1.4 mm), there was an exponential relationship between displacement and reactive force, and the compliance was unchanged. The exponential component may have represented the contribution of the maxillary bone compliance measures. 3. A simulated edema was created to assess the effects of edema on afferent reactivity. Saline was used to create the simulated edema by using changes in tissue compliance as a means of matching simulated to carrageenan-induced edema. An analysis of linear and exponential phases of saline or carrageenan-induced changes in tissue compliance indicated that saline injections produced a good approximation of the changes in linear properties, but diverged from a match of the exponential phase of carrageenan edema. 4. Assessments were made of modifications in nociceptor reactivity after simulated edema or retested controls (n = 47). There was little indication that edema influenced quantitative aspects of either static or dynamic force transduction. Mechanonociceptors, but not intense pressure receptors, sensitized after repeated intense stimulation (mean decline of dynamic activation threshold of 42 +/- 16 g/mm2, mean +/- SE). Artificial edema did not further contribute to this sensitization. 5. Qualitative features of stimulus transduction were modified by simulated edema. Eleven of 17 afferents without initial static or dynamic transduction capacity acquired the capacity after artificial edema. 6. Although most aspects of force transduction were unaffected by artificial edema, displacement transduction was considerably shifted. Artificial edema decreased the threshold and shifted the displacement range over which nociceptors transduced dynamic and static aspects of force (threshold decreased from 1,894 +/- 229 to 1,456 +/- 194 mum; range decreased 239 +/- 99 mum). 7. It was concluded the contribution of edema to allodynia and hyperalgesia is best understood in terms of its contribution to population-coding mechanisms that are brought about by changes in transmission properties. By increasing the security of hydrostatic coupling between stimuli and receptors, edema promotes both dynamic and static transduction by recruiting populations of nociceptors that lie on the fringe of a stimulus. The force transduction relationships of more proximal receptors, with secure stimulus-receptor coupling, are unaffected by edema but manifest large shifts in their relationship to tissue displacement.
