Functional differences between dorsal and ventral hippocampus revealed with AgNOR staining

by Scoville and Milner (1957), the important role of the hippocampus in the formation of memory has been extensively documented. Until now, a vast majority of actual experimental work with animals and humans has been done considering the hippocampus as a homogeneous structure with a unified functional role (Eichenbaum et al., 1999; O’Keefe et al., 1998). However, numerous studies report the morphological, neurochemical and functional differences between dorsal and ventral zones from hippocampus (Moser et al., 1993; Jung et al., 1994; Bannerman et al., 1999). According to these findings, the experimental research made on the hippocampus, mainly by lesion techniques, shows that the effect of such disruption is different depending on the affected site (Moser et al., 1993; Lorenzini et al., 1997; Levin et al., 1999). Additionally, the behavioral effects are supported by other neurochemical and physiological heterogeneity (Bruinink and Bischoff, 1993; Jung et al., 1994). Although a number of techniques offer a good approach to the functional study of central nervous system structures, silver staining of nucleolar organizer regions (AgNORs) is considered a rapid and easy way to obtain an estimation of protein synthesis rate (Crocker, 1996). This technique makes it possible to label the fibrillar centers, a nucleolar component involved in the synthesis of ribosomal RNA. The fibrillar centers are related morphologically with the NORs, sites composed of RNA and proteins, many of them argyrophilic. By using this technique these NOR-associated proteins are selectively stained; the result of this reaction is known as AgNOR dots, and the number and area of AgNORs are an accurate index of activity and cell proliferation in terms of protein synthesis (Derenzini et al., 1992; Ploton et al., 1992). The AgNOR technique alone or combinations with other histological stains have been used in various studies of the CNS with promising results in animals and humans (Fushiki et al., 1995; González-González et al., 1996; García-Moreno et al., 1997). By taking into consideration these studies, the present work aimed to evaluate the biosynthetic activity in CA1 and CA3 hippocampal areas from both the dorsal and ventral zones. The abovementioned AgNOR parameters were selected as adequate indexes of neural transcriptional activity.