New strategies for embedding, orientation and sectioning of small brain specimens enable direct correlation to MR-images, brain atlases, or use of unbiased stereology

We present a newly developed brain slicing machine and technique for tissue embedding, which enable orientation of fresh or fixed brain tissue from sm all laboratory animals, in any given position, and subsequent tissue sectio ning into slabs with an optional thickness between 0.5 and 20 mm. The orien ted tissue slabs may be analysed directly, or processed further on a cryost at or vibratome, into thin stainable histological sections, and aligned to MR-images or brain atlases, depending on the reference used for the initial orientation. Additionally, we describe a new embedding medium (HistOmer) w hich is an alginate cold polymer ready for instant use after mixing with wa ter. HistOmer allows accurate positioning of the tissue during embedding, a nd at the same time supports and protects the embedded tissue during sectio ning. HistOmer is, therefore, described comprehensively and compared with o ther commonly used embedding media. This novel slicing technique may also, as illustrated, be used to perform isotropic random orientation of the embe dded tissue, before sectioning into tissue slabs of the same thickness. The technique thereby fulfills the requirements for optimal tissue sampling an d preparation needed for an unbiased stereologic analysis. (C) 2001 Elsevie r Science B.V. All rights reserved.