Basal Fos immunoreactivity in myenteric neurons of guinea pig

The enteric nervous system (ENS) is capable of mediating intestinal reflexes in the absence of connections to the CNS. Nuclear immunoreactivity for Fos, a protein encoded by the c-fos proto-oncogene, has previously been used to visualize activated cells. We have attempted to use a commercial antibody to Fos to investigate the proportion of activated neurons in the myenteric ganglia of guinea pigs. Neuronal nuclei which demonstrated Fos Immunoreactivity (F-IR) were counted in preparations fixed immediately after removal from the animals. Demonstration of all myenteric neurons in adjacent segments by staining with cuprolinic blue revealed that neurons with F-IR comprised a subset (65-75%) of all neurons. These results have led us to conclude that ENS has a basal activity for intestinal functions and this could be demonstrated easily by Fos immunoreactivity.