Comparison of unbiased stereological estimation of total number of cresyl violet stained neurons and parvalbumin positive neurons in the adult human spiral ganglion

Estimation of total number of neurons in the spiral ganglion (SG) at various ages and their functional status is important as these neurons are constantly exposed to noise and other environmental factors that may lead to neuronal loss with aging due to excitotoxic damage. Parvalbumin (PV) is a calcium-binding protein (CBP), found in highly metabolically active neurons. It helps in buffering cytosolic calcium, which is essential for neurotransmitter release. The neurons in the adult human SG express PV more strongly than other CBPs like calbindin and calretinin. These CBPs can be used as signatures to recognise neurons. In the present study, we quantified the number of neurons expressing PV by unbiased stereology and compared it to the number of neurons stained by cresyl violet (CV), which is a Nissl stain, in the adult human SG. Five adult human cadaveric temporal bones were obtained from the forensic science mortuary, after due clearance from the institute ethics committee. Independent CV stained and PV immunostained sections were used to estimate the total number of neurons (optical fractionator), with StereoInvestigator (SI) software. The estimated total number of SG neurons was 27,485 ± 3251 and 26,705 ± 1823 in the PV and CV stained sections, respectively. There was no significant difference between the estimates (p = 0.552). Therefore, CV staining is simpler and more cost effective when estimating neuronal number. Although PV stains spiral ganglion neurons (SGNs) with a greater intensity and provides a functional status, its tedious protocol limits its use for quantification.