Stereological estimation of numerical densities of glutamatergic principal neurons in the mouse hippocampus.

Recent studies have emphasized functional dissociations between dorsal and ventral hippocampus in learning, emotion, and affect. A rigorous quantitative analysis concerning lamellar cytoarchitecture would be important for promoting further research on the regional differentiation of the hippocampus. Here, we stereologically estimated the numerical densities (NDs) of glutamatergic principal neurons in the mouse hippocampus and encountered the significant differences along the dorsoventral axis. In the CA1 region, the NDs of CA1 pyramidal neurons were almost three times higher at the dorsal level (447.5 x 10(3)/mm(3)) than at the ventral level (180.5 x 10(3)/mm(3)); meanwhile, along the transverse axis, the NDs were significantly higher in the proximal portion than in the distal portion both at the dorsal and ventral levels. An EF-hand calcium-binding protein, calbindin D28K, was expressed in approximately 45% of CA1 pyramidal neurons both at the dorsal and ventral level. In the CA3 region, there were no significant differences in the NDs along the dorsoventral and transverse axes (dorsal, 165.2 x 10(3)/mm(3); ventral, 172.4 x 10(3)/mm(3)). In the dentate gyrus (DG), the NDs of granule cells were significantly higher at the dorsal level (916.7 x 10(3)/mm(3)) than at the ventral level (788.9 x 10(3)/mm(3)). The significant differences were observed only in the suprapyramidal blade, but not in the infrapyramidal blade. Then, we calculated the total neuron numbers contained in a 300-microm-thick hypothetical transverse slice of the hippocampus and found that the ratios of GABAergic to glutamatergic neuron numbers were two to three times higher in the ventral slice than in the dorsal slice. The ratios of numbers of eight GABAergic neuron subtypes to principal cells indicate structural dissociations in the neural network between dorsal and ventral slices. These findings provide an essential quantitative basis for elucidating mechanisms of distinct neural circuits underlying various hippocampal functions.

Jinno S ，Kosaka T 《-》

Topographic differences in adult neurogenesis in the mouse hippocampus: a stereology-based study using endogenous markers.

The hippocampus plays a critical role in various cognitive and affective functions. Increasing evidence shows that these functions are topographically distributed along the dorsoventral (septotemporal) and transverse axes of the hippocampus. For instance, dorsal hippocampus is involved in spatial memory and learning whereas ventral hippocampus is related to emotion. Here, we examined the topographic differences (dorsal vs. ventral; suprapyramidal vs. infrapyramidal) in adult neurogenesis in the mouse hippocampus using endogenous markers. The optical disector was applied to estimate the numerical densities (NDs) of labeled cells in the granule cell layer. The NDs of radial glia-like progenitors labeled by brain lipid binding protein were significantly lower in the infrapyramidal blade of the ventral DG than in other subdivisions. The NDs of doublecortin-expressing cells presumed neural progenitors and immature granule cells were significantly higher in the suprapyramidal blade of the dorsal DG than in the other subdivisions. The NDs of calretinin-expressing cells presumed young granule cells at the postmitotic stage were significantly higher in the suprapyramidal blade than in the infrapyramidal blade in the dorsal DG. No significant regional differences were detected in the NDs of dividing cells identified by proliferating cell nuclear antigen. Taken together, these findings suggest that a larger pool of immature granule cells in dorsal hippocampus might be responsible for spatial learning and memory, whereas a smaller pool of radial glia-like progenitors in ventral hippocampus might be associated with the susceptibility to affective disorders. Cell number estimation using a 300-μm-thick hypothetical slice indicates that regional differences in immature cells might contribute to the formation of topographic gradients in mature granule cells in the adult hippocampus. Our data also emphasizes the importance of considering such differences when evaluating changes in adult neurogenesis in pathological conditions and following experimental procedures.

Jinno S 《-》

Patterns of expression of calcium binding proteins and neuronal nitric oxide synthase in different populations of hippocampal GABAergic neurons in mice.

We examined the expression of calcium binding proteins parvalbumin (PV), calretinin (CR), and calbindin D28K (CB), and neuronal nitric oxide synthase (nNOS) in gamma-aminobutyric acid (GABA)ergic neurons of the mouse hippocampus, with particular reference to areal and dorsoventral differences. First, we estimated the colocalization of the calcium binding proteins and nNOS. GABAergic neurons containing both PV and nNOS, i.e., PV-immunoreactive (-IR)/nNOS-IR neurons, were rare in Ammon's horn but frequent in the dentate gyrus (DG). CR-IR/nNOS-IR neurons and CB-IR/nNOS-IR neurons were frequent in Ammon's horn but rare in the DG. In the entire hippocampus, the percentage of CR-IR neurons containing nNOS was significantly higher at the ventral level (44.3%) than at the dorsal level (17.0%). The percentage of CB-IR neurons containing nNOS was also significantly higher at the ventral level (42.3%) than at the dorsal level (29.3%). Next, we estimated the numerical densities (NDs) of calcium binding protein-containing GABAergic neurons. The ND of PV-IR neurons was comparable at the dorsal (1.16 x 10(3)/mm(3)) and ventral levels (1.23 x 10(3)/mm(3)), respectively. The ND of CR-IR neurons was less at the dorsal level (0.52 x 10(3)/mm(3)) than at the ventral level (0.64 x 10(3)/mm(3)). The ND of CB-IR neurons was also less at the dorsal level (0.91 x 10(3)/mm(3)) than at the ventral level (1.57 x 10(3)/mm(3)). Overall, approximately half of the GABAergic neurons contained one of the three calcium binding proteins (45% at the dorsal level and 47% at the ventral level). These data establish a baseline for examining potential roles of GABAergic neurons in hippocampal network activity in mice.

Jinno S ，Kosaka T 《JOURNAL OF COMPARATIVE NEUROLOGY》

Quantitative analysis of neuronal nitric oxide synthase-immunoreactive neurons in the mouse hippocampus with optical disector.

Jinno S ，Aika Y ，Fukuda T ，Kosaka T ... -  《JOURNAL OF COMPARATIVE NEUROLOGY》

Patterns of expression of neuropeptides in GABAergic nonprincipal neurons in the mouse hippocampus: Quantitative analysis with optical disector.

Neuropeptides are widely distributed in the central nervous system and are considered to play important roles in the regulation of neuronal activity. This study shows the patterns of expression of four neuropeptides [neuropeptide Y (NPY), somatostatin (SOM), cholecystokinin (CCK), and vasoactive intestinal polypeptide (VIP)] in gamma-aminobutyric acid (GABA)-ergic neurons of the mouse hippocampus, with particular reference to the areal and dorsoventral difference. First, we estimated the numerical densities (NDs) of GABAergic neurons containing these neuropeptides using the optical disector. The NDs of NPY- and SOM-positive GABAergic neurons were generally higher than those of CCK- and VIP-positive GABAergic neurons. In the whole area of the hippocampus, the ND of NPY-positive GABAergic neurons showed no significant dorsoventral difference (1.90 x 10(3)/mm(3) in the dorsal level, 2.09 x 10(3)/mm(3) in the ventral level), whereas the ND of SOM-positive GABAergic neurons was higher in the ventral level (1.44 x 10(3)/mm(3)) than in the dorsal level (0.80 x 10(3)/mm(3)). The ND of CCK-positive GABAergic neurons was also higher in the ventral level (0.57 x 10(3)/mm(3)) than in the dorsal level (0.33 x 10(3)/mm(3)). Similarly, the ND of VIP-positive GABAergic neurons was higher in the ventral level (0.61 x 10(3)/mm(3)) than in the dorsal level (0.43 x 10(3)/mm(3)). Next, we calculated the proportions of GABAergic neurons containing these neuropeptides among the total GABAergic neurons. In the whole area of the hippocampus, NPY-, SOM-, CCK-, and VIP-positive neurons accounted for about 31%, 17%, 7%, and 8% of GABAergic neurons, respectively. The present data establish a baseline for examining potential roles of GABAergic neurons in the hippocampal network activity in mice.

Jinno S ，Kosaka T 《JOURNAL OF COMPARATIVE NEUROLOGY》