Are CNS neurons polyploid? A critical analysis based upon cytophotometric study of the DNA content of cerebellar and olfactory bulbar neurons of the bat.

A cytophotometric study of the nuclear DNA content of bat cerebellar and olfactory bulbar neurons was performed with particular attention to corrections for distributional error and non-specific light loss and to selection of appropriate control nuclei for the establishment of reliable haploid and diploid DNA values. Feulgen stained sections were measured with an integrating, scanning microdensitometer for correction of distributional error. The values thus obtained were further corrected in 3 different ways to subtract the contribution of background absorbance at 546 nm. Bat haploid (1c) DNA values were derived from spermatozoa, and diploid (2c) values from pancreatic acinar cells, hepatocytes and non-hepatocyte liver cells. Microglia of olfactory bulb also had 2c values. After correction, all neurons measured, except Purkinje cells, had DNA values more closely approximating the tetraploid (4c) than the diploid (2c) level. Purkinje neurons had mean DNA values closer to 2c than to 4c, but inherent technical difficulties in measuring these very large, light staining nuclei has created less confidence in the values obtained than for those of the other neurons. This uncertainty, plus the apparent existence of two populations of Purkinje neurons, one 2c and the other hyperdiploid, suggested by the DNA distribution curves, make it difficult to eliminate the possibility of polyploidization of Purkinje neurons. A critical analysis of various cytophotometric, radioautographic and biochemical approaches to the problem of CNS neuron polyploidization has revealed potentially serious flaws in many of them, rendering virtually impossible interpretation of the numerous contradictory results in the literature. Standardization of the cytophotometric technique and improvement of the radioautographic approach seem to be prerequisite to the resolution of the existing dilemma.