The colocalization of parvalbumin and calbindin-D28k with GABA in the subnucleus caudalis of the rat spinal trigeminal nucleus.

The colocalization of two calcium-binding proteins, parvalbumin (PV) and calbindin-D28k (CaB), which have been reported to be markers of specific subpopulations of neurons in the central nervous system, with the inhibitory amino acid neurotransmitter gamma-amino-butyric acid (GABA) was investigated in neurons of laminae I-IV of the subnucleus caudalis of the rat spinal trigeminal nucleus by using post-embedding immunocytochemical methods. Cells immunoreactive for PV, CaB, and GABA were found in all four laminae of the subnucleus caudalis. A substantial proportion of PV-immunoreactive perikarya were also stained for GABA in laminae II and III (44.8% and 39.8%, respectively). However, the majority of PV-containing neurons in laminae I and IV (100% and 86%, respectively), as well as CaB-immunoreactive cells in all four laminae (98.4%), were GABA-negative. These results show that, in contrast to higher brain centers, PV-, CaB-, and GABA-immunoreactive perikarya represent significantly different populations of neurons in the subnucleus caudalis of the rat. In the light of the present findings, the differences in the neurochemical properties of the subnucleus caudalis of the spinal trigeminal nucleus and the spinal dorsal horn are also discussed.