Area dentata

Fig. I. Asp-like and Glu-like immunoreactivities in CAl and area dentata of hippocampus from slices of the hippocampal formation. The slices were fixed by immersion after incubation at physiological K" " concentration (5 mM). The photomicrograps show that Asp and Glu are localized with a zonal pattern, corresponding to the distribution of excitatory afferents. Symbols R, M, layers of hippocampus (radiatum and lacunosum moleculare). Mi, G, layers of area dentata (inner moleculare and granulare). Asterisks mark the obliterated fissura hippocampi. Scale bar = 100 pm.

Fig. 1. Left, the rat hippocampal region as seen in a horizontal section stained for AChE (c/. Fig. 2). The rectangle circumscribes a segment in the anterior part of regio superior. This rectangle is shown diagramatically in the 3 drawings on the right to illustrate A, the distribution of cell bodies B, AChE, and C, the types of neurones and synapses. An analogous situation exists for the area dentata. FH, fissura hippocampi B, basket cell P, pyramidal cell Com, commissural fibres Sch, Schaffer collaterals PP, perforant path. Excitatory synapses (o), inhibitory synapses ( ).

The hippocampal region comprises area dentata, hippocampus, subiculum, presubiculum, area retrosplenialis, parasubiculum and area entorhinalis. In this paper only the two former parts are dealt with. For nomenclature see Blackstad (1956). 

The areas dissected and the nomenclature are shown in Fig. 2. The results are mean values of 4-12 measurements from 1 to 7 different animals. ChAc values are expressed as //moles ACh synthesized/ h/g dry wt. and are taken from Fonnum (1970). AChE values are from Storm-Mathisen (1970) and are expressed as //moles acetylthiocholine hydrolysed/h/g dry wt. (hippocampus regio superior) or as //moles ACh hydrolysed/h/g dry wt. (area dentata). 

Combining experimental neuroanatomical techniques with quantitative histochemistry we made the following study (Storm-Mathisen, 1972). The afferents from the area entorhinalis (perforant path), the fimbria (from septum, columna fornicis and contralateral hippocampus) and the intrinsic fibres from area dentata to... 

Fig. 5. AChE-stained horizontal section of a rat brain 7 days after transection of fimbria (coarse arrow). Note massive reduction of staining intensity and loss of laminar staining pattern on operated side. Capillaries stain equally well on both sides (non-specific cholinesterase was not inhibited in this section). Small arrows point to limit between normally staining (intact) stria terminalis and pale fimbria on the operated side. S, septum F, fimbria AD, area dentata HI, hippocampus regio inferior HS, hippocampus regio superior SU, subiculum PS, presubiculum PA, parasubiculum ...

GAD AND ChAc IN HIPPOCAMPUS AND AREA DENTATA FOLLOWING TRANSECTION OF FIMBRIA... 

Fig. 6. Distribution of GAD in different zones of hippocampus regio superior and area dentata. Presentation as in Fig. 3, dissection described in Fig. 2. The mean activity of samples cut through all layers of hippocampus regio superior (activity unit) was in the series from hippocampus 44.5 4.7 tmoles/h/g dry wt. (S.D., 18 samples) and in that from area dentata 44.0 4.0 jttmoles/h/g dry wt. (S.D.. 8 samples). The data were from two animals and the numbers of samples for the different zones were A 10, Oi 7, Oe 7, P 7, Ri 6, Rm 10, Re 4, L 7, M 11, M 8, G 9 and H 8. (Reproduced from J. Neurochem. (1971), Storm-Mathisen and Fonnum, 18, 1105-1111.)...

The data on other transmitter candidates in the hippocampus are less complete. All parts of the hippocampal region contain noradrenaline (NA) terminals which are, however, diffusely distributed relative to ChAc and constitute but a small proportion of the afferents (Blackstad et al., 1967). The highest levels are found in hilus of area dentata and in stratum radiatum of regio inferior. The distribution of nerve terminals containing serotonin (5-HT) has not been described, apart from stating that it is different from that of NA terminals (Fuxe et al., 1970), probably because of the instability of the fluorescence obtained with this substance in the histochemical technique. However, there has been a report of 5-HT terminals on the pyramidal cell bodies in the cat (Eidelberg et al., 1967). 

Neuropathological studies in autistic brains have also demonstrated smaller neuronal size and increased cell packing density in the hippocampus, another limbic system structure. The morphology of hippocampal neurons in two cases of infantile autism was studied and investigators found smaller cells with reduced perikaryon area and dendritic branching in comparison with neurons of age-matched control children [63], This result is consonant with MRI results evidencing a smaller area dentata of the hippocampus in autistic children from 2 to 4 years [64]. However, the density and distribution of some 5-HT receptors in the hippocampus were not statistically different between autistic children and controls [65]. 

Fig. 1. Schematic drawing of hippocampus and slice preparation. (A) Dorsal view of the ventricular surface of the rat hippocampal formation, exposed by removing the neocortex. The hatched bar represents the approximate orientation for slicing. (B) Drawing of isolated hippocampal slice, cut in a near-saggital plane as shown in (A). SUB subiculum CAl, CAS region of small and large pyramids, respectively, from nomenclature of Lorente de No (1934) AD area dentata, containing the granule cell layer FISS hippocampal fissure, PP perforant path input to the granule cells, which send mossy-fiber axons (MF) that synapse on the apical dendrites of CAS pyramidal cells SR stratum radiatum, which includes the Schaffer collateral axons of the CAS pyramids SO stratum oriens, which also contains fibers afferent to pyramidal neurons. The alveus consists mainly of CAl pyramidal cell axons. (From Dingledine et al, 1980.)...

Hjorth-Simonsen, A. (1972) Projection of the lateral part of theentorhinal area to the hippocampus and fascia dentata. J. Comp. Neurol, 146, 219-232. 

Titulaer, M. N. G., Ghijsen, W. E. J. M., Kamphuis, W, De Rijk, T. C., and Lopes da Silva, F. H. (1995) Opposite changes in GABAa receptor function in the CA 3 area and fascia dentata of kindled rat hippocampus. J. Neurochem 64,2615—2621. Bradford, M M. (1976) A rapid and sensitive method for the quantification of microgram quantities of protein utilizing the principle of protein dye binding. Anal. Biochem 72,248—252... 

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