methods for stereology

    This paper by Cannon and Greenemyre is important in that it shows that an immunochemical marker often cited as specific for all neurons may not be useful in examining neuron number in the SN.    

As noted by the authors, the ability to accurately count SN neurons is of critical importance since many preclinical models and methods for acheiving neuroprotection are based on this finding.  It is clear that many models used to induce parkinsonism (such as MPTP) can interfere with the ability to synthesize dopamine, and thus using tyrosine hydroxylase (TH ) alone as a marker can lead one to over estimate lesion size.  We have been quite successful using a Nissl counterstain along with TH staining to determine cell number.  The dopaminergic neurons in the SN have a fairly characteristic shape and can be distinguished form other neurons and glia by nucleus:cytoplasmic ratios.

    We have published a stereological analysis of dopaminergic neurons in mice that details these qualities.  While in normal mice, we have found that less than 3 percent of neurons do not stain with TH; this number is signficantly increased following MPTP.  The use of a phenotypic marker alone may account for the wide variability in neuron loss described with this toxin ranging from 40% (our studies)  to 75% (many others).