Optimization of dopaminergic neuron counting in substantia nigra of parkinsonian mice

Abstract

Parkinson’s disease (PD) results from the degeneration of dopaminergic (DA-ergic) neurons of substantia nigra pars compacta (SNc). The disease is modeled in mice by the administration of a neurotoxin precursor 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Neurotoxin efficiency is estimated by reduced number of DA-ergic neurons in SNc. Cell counting on serial sections is very laborious and expensive and, therefore, is not widely used in spite of its high precision. The well-known Konigsmark’s formula (KF) allows one to perform counting on sections chosen with a certain interval rather than to utilize serial sections. However, its precision decreases with increasing interval and other parameters. In this paper, we described the mathematical method of approximation (MA) by improving KF. MA maintains counting precision and allows one to reduce the time and expenses for material processing and analysis. Two groups of C56/BL mice were used in this study. The first group received 8 mg/kg MPTP twice with a 1-week interval and showed a 20% decrease in the DA-ergic neurons in SNc. The second group received 12 mg/kg MPTP four times with a 2-h interval and showed a 40% decrease in DA-ergic neurons in SNc. Degeneration was obvious mostly within the middle part of SNc in rostracaudal direction and was more apparent in animals exposed to the high neurotoxin dose. Dramatic differences were observed in the number of neurons between sections, which substantially decreased the precision of FK (6% error with counting in every 5th section), whereas the precision of MA was fairly good (4% error with counting in every 7th section). Thus, we developed anMA that allows one to decrease time and material expenses for estimating the DA-ergic number of cells in SNc of parkinsonian mice.