Interactive three-dimensional atlas of the rat parahippocampal-hippocampal region.

M.P. Witter^1,2, I.M.F. Hammer², K. Haugen², E.I. Moser², M.-B. Moser^2
1Dept Anat & Neurosci, VU Med. Ctr. (Amsterdam); ²Ctr Biol of Memory, NTNU (Trondheim, NO)

The parahippocampal cortices are receiving increased attention as potential storage sites for spatial memory and as mediators of hippocampal-neocortical interactions in memory formation more generally. Analyses of parahippocampal and hippocampal function rely critically on the use of in vivo electrophysiological, pharmacological or behavioural methods. The outcome of studies using these methods depends critically on the ability to precisely map the location of recording and/or lesion sites. Here we present a newly developed high-resolution three-dimensional cytoarchitectonic atlas of the rat hippocampal-parahippocampal region aiming to facilitate the precise mapping of brain manipulations. The atlas is based on sections taken in the three standard planes, coronal, horizontal, and sagittal, and all data are provided within the framework of a 3-D surface rendering of the rat brain. For the preparation we used 4 male Long-Evans rats. Following transcardial perfusion, the brains were sectioned in the three planes mentioned and 30 µm sections were collected into 6 equally spaced series for further processing. Sections were subsequently stained for Nissl substance, and for Neu-N, parvalbumin, and calbindin, using appropriate antibodies. Additional material, stained for myelinated fibers (Klüver-Barrera and Loyez stain), acetylcholinesterase and heavy metals (Timm stain), was available for further reference. Digital pictures acquired with a Zeiss Axio Imager.Z1 microscope were processed to enhance contrast and brightness, and borders between areas of interest were added. All sections and related information were entered into Neurolucida and three dimensional renderings were made using the solid modelling module. Occasional inconsistencies were corrected manually and the final dataset prepared. We have used this atlas now in a number of studies and it has proved to be a flexible and highly precise reference tool as well as educational aid.