The onset of diffuse noxious inhibitory controls in postnatal rat pups: a C-Fos study

The development of diffuse noxious inhibitory controls (DNIC) was studied i n postnatal rats aged 12, 21 and 42-days-old, using immunoreactive localiza tion of the c-fos protein products induced in the dorsal horn by noxious st imulation. The presence of DNIC was revealed by the reduction in the levels of Fos-like immunoreactivity that are normally induced by a standardized p rimary pinch stimulus when this stimulus was accompanied by a concurrent no xious stimulus (formalin) to a heterotopic body part. Significant reduction s were seen at postnatal day 42 (P42; 15% reduction) and P21 (17% reduction ), but concurrent stimulation had no significant effect at P12. These resul ts suggest that the system subserving DNIC is functionally mature by P21, b ut not effective at P12. This delayed maturation of an inhibitory system ma y underlie the extreme sensitivity to somatosensory stimulation seen in neo natal pups and premature infants. (C) 1998 Elsevier Science Ireland Ltd. Al l rights reserved.