CALRETININ MESSENGER-RNA AND IMMUNOREACTIVITY IN THE MEDULLARY RETICULAR-FORMATION OF THE RAT - COLOCALIZATION WITH GLUTAMATE RECEPTORS

Calretinin-positive cells were identified in the medullary reticular f ormation of the rat by both immunohistochemistry and in situ hybridiza tion histochemistry. In addition, double immunocytochemical labeling w as used to examine the degree of colocalization of calretinin with Glu R(2)/R(3), GluR(4) and GluR(5-7) glutamate receptor subtypes. Results indicated regional variation in calretinin expression across reticular formation regions with the exception of the lamest cells which were m ostly calretinin-positive. Calretinin mRNA was particularly abundant i n the parvocellular reticular nucleus. Most calretinin-immunoreactive cells also expressed at least one of the glutamate receptor subtypes e xamined with the exception of the smallest calretinin-positive cells o f the parvocellular reticular formation which were generally not immun oreactive for any of the glutamate receptors examined. Calretinin immu noreactivity was colocalized with immunoreactivity for all three gluta mate receptor subtypes examined in most of the large cells of the reti cular formation. Immunoreactivity for the GluR, antibody was least abu ndant in the reticular formation and GluR, immunoreactive cells were l east likely to co-express calretinin. These results suggest that calre tinin and glutamate receptor antibodies may be used to identify specif ic subsets of reticular formation neurons.