THE COLOCALIZATION OF PARVALBUMIN AND CALBINDIN-D28K WITH GABA IN THESUBNUCLEUS CAUDALIS OF THE RAT SPINAL TRIGEMINAL NUCLEUS

The colocalization of two calcium-binding proteins, parvalbumin (PV) a nd calbindin-D28k (CaB), which have been reported to be markers of spe cific subpopulations of neurons in the central nervous system, with th e inhibitory amino acid neurotransmitter gamma-amino-butyric acid (GAB A) was investigated in neurons of laminae I-IV of the subnucleus cauda lis of the rat spinal trigeminal nucleus by using post-embedding immun ocytochemical methods. Cells immunoreactive for PV, CaB, and GABA were found in all four laminae of the subnucleus caudalis. A substantial p roportion of PV-immunoreactive perikarya were also stained for GABA in laminae II and III (44.8% and 39.8%, respectively). However, the majo rity of PV-containing neurons in laminae I and IV (100% and 86%, respe ctively), as well as CaB-immunoreactive cells in all four laminae (98. 4%), were GABA-negative. These results show that, in contrast to highe r brain centers, PV-, CaB-, and GABA-immunoreactive perikarya represen t significantly different populations of neurons in the subnucleus cau dalis of the rat. In the light of the present findings, the difference s in the neurochemical properties of the subnucleus caudalis of the sp inal trigeminal nucleus and the spinal dorsal horn are also discussed.