Hippocampus and Dentate Area of the European Hedgehog

Abstract

The hippocampal formation in the European hedgehog was examined with acetylcholinesterase (AChE) histochemistry and catecholamine histofluorescence in order to define the normal distribution of septohippocampal fibers and noradrenergic fibers, respectively, as well as to compare these inputs with the hippocampal cytoarchitecture as revealed with Nissl stain. In addition, alterations in the histochemical appearance following septohippocampal denervation were examined. Although the overall pattern of AChE-positive and noradrenergic fibers is similar to that observed in other mammals, some striking variations were observed, particularly within the dentate area. Thus, except for a heavily stained supragranular band, the AChE activity of the molecular layer is uniformly low without any obvious lamination, contrasting with the situation in most other mammalian species. The noradrenergic innervation of the dentate area showed the same density of fibers in the molecular layer and hilus, a pattern differing strikingly from the predominance of noradrenergic fibers in the hilus of other mammalian species. Such variations may reflect greater phylogenetic diversity in diffuse modulatory connections as compared with more precise topographical pathways.

Insectivora

“…West et al (1984) studied the staining characteristics of hippocampal components with Timm's heavy metal sulphide technique and argued that the hedgehog hippocampus may be used as a basal reference in comparative studies. Crutcher et al (1988) found some striking differences in AChE histochemistry and catecholamine histofluorescence from that observed in other mammals, particularly in the dentate area. They found for example uniformly low AChE activity of the molecular layer, and the same density of noradrenergic fibers in the molecular layer as in the hilus.…”

The importance of comparative studies and ecological validity for understanding hippocampal structure and cognitive function

“…The anatomical organization of the H F is quite different in mammals, birds, and reptiles, the most notable difference being the absence of a distinct dentate gyrus and Ammon's horn in birds and reptiles (Bingman et al, 1989). Somewhat smaller differences in anatomical organization or size can be found within mammals (Crutcher et al, 1988), within birds (Krebs et al, 1989;, between strains of laboratory rats (Lipp et al, 1987), and between sexes of field mice (Jacobs et al, 1990). The I-IF also differs with respect to the brain environment in which it functions.…”