Quantitative stereology: the use of camera lucida for counting neurons by physical dissector method in chick brainstem auditory nuclei.

Subtle changes in neuron numbers during growth and ageing as well as consequent to manipulation, nutritional and environmental influences and following drug or toxin intake are best assessed quantitatively. The disector introduced in 1984 by Sterio is an unbiased, systematically randomised method for neuronal counting applied as an optical or physical method. The optical disector requires a confocal microscope or a conventional light microscope with high precision control and calibration of movement in depth through the ‘z’ axis. The physical disector requires overlapping of adjacent sections to eliminate overestimation in counting the neurons as may occur with the use of single sections. Various improvisations, such as projection systems and photomicrographs, used for this are expensive and cumbersome methods involving problems in correct matching of overlap between the adjacent sections. These methods are not feasible when many samples from several experimental conditions are to be evaluated for neuron counting. We report in this paper, our experience of using the camera lucida over the last ten years in counting the neurons in chick brainstem auditory nuclei.