Quantitative analysis of GABAergic neurons in the mouse hippocampus, with optical disector using confocal laser scanning microscope

The numerical densities (NDs) of glutamic acid decarboxylase (GAD) 67 immun oreactive (IR) neurons in the mouse hippocampus were estimated according to the optical disector method using a confocal laser scanning microscope (CL SM), and the cell sizes of disector-counted neurons were measured. Particul arly, we focused on the dorsoventral differences of the NDs and cell sizes in individual subdivisions and layers. The NDs of GAD67-IR neurons were lar ger at the ventral level than at the dorsal level in most subdivisions and layers, except in the stratum pyramidale (SP) of the CA1 region and stratum radiatum (SR) of the CA3 region. In the whole hippocampus, the ND of GAD67 -IR neurons was 5.7 +/- 0.2 X 10(3)/mm(3) at the dorsal level, and 7.3 +/- 0.3 X 10(3)/mm(3) at the ventral level. The laminar differences showed that the NDs of GAD67-IR neurons in the principal cell layers were generally la rger than those in the dendritic layers in each subdivision. The ND of GAD6 7-IR neurons was largest in the SP of the CAI region at the dorsal level (1 3.5 +/- 0.9 X 10(3)/mm(3)), and smallest in the molecular layer (ML) of the dentate gyrus (DG) at the dorsal level (1.7 +/- 0.2 X 10(3)/mm(3)). The me an cell sizes of GAD67-IR neurons also showed prominent dorsoventral and la minar differences. In the CA3 region, the mean cell size of GAD67-IR neuron s was smaller at the dorsal level than at the ventral level, while in the D G, it was larger at the dorsal level than at the ventral level. On the othe r hand, the mean cell size of GAD67-1R neurons in the CAI region showed no significant dorsoventral difference. In the whole hippocampus, the mean cel l size of GAD67-IR neurons was slightly smaller at the dorsal level (somati c profile area 149.2 +/- 2.5 mu m(2)) than at the ventral level (154.2 +/- 2.9 mu m(2)). The laminar differences showed that the mean cell sizes of GA D67-IR neurons in the principal cell layers were generally larger than thos e in the dendritic layers in each subdivision. The mean cell size of GAD67- IR neurons was largest in the SP of the CA3 region at the ventral level (18 0.7 +/- 5.7 mu m(2)), and smallest in the stratum lacunosum-moleculare (SLM ) of the CA3 region at the dorsal level (115.9 +/- 7.9 mu m(2)). The cell s ize distributions in individual layers revealed that GAD67-IR neurons were roughly classified into two subgroups. The composition of these subgroups s uggested the heterogeneity of GAD67-IR neurons in the mouse hippocampus in view of cell size. (C) 1998 Elsevier Science B.V. All rights reserved.