Length measurement: new developments in neurostereology and 3D imagery

Quantification of linear biological structures has important applications i n neuroscience; for example, the length of neurotransmitter-specific axonal innervation or length of dendritic processes within particular brain struc tures. Until recently, however, there have been practical limitations in th e application of stereological tools for the unbiased estimation of object length on tissue sections. The recent development of efficient new approach es allows for the wider application of theoretically unbiased sampling and estimation techniques that are devoid of the assumptions and models of earl ier methods. In this review, we outline the historical background and recen t advances in the estimation of total length for biological objects on tiss ue sections, including a practical method to estimate the length of choline rgic fibers using newly developed methods. These newer methods also take ad vantage of three-dimensional image datasets and virtual probes, techniques that may have wider application in quantitative morphometry. (C) 2000 Elsev ier Science B.V. All rights reserved.