DEVELOPMENTAL DYNAMICS OF PURKINJE-CELLS AND DENDRITIC SPINES IN RAT CEREBELLAR CORTEX

Quantitative morphological changes of the developing Purkinje cells we re studied from 6 to 90 postnatal (PN) days in the IVth lobule of verm is in the cerebellum of rats. The soma size (mean diameter) of Purkinj e cells increased rapidly between 6 PN (on average 10 mu m) and 18 PN (about 17 mu m) days; it did not change between 18 and 25 PN days, but increased moderately again between 25 and 48 PN days (22-23 mu m) and stabilized on the same value. In contrast, the number of Purkinje cel ls/100 mu m (the ''linear density'') decreased rapidly from 6 to 18 PN days. The molecular layer area belonging to 1 Purkinje cell increased rapidly from 6 to 25 PN days (from about 370 to 6,200 mu m(2)) and le ss rapidly between PN days 30 to 48 (up to 9,300 mu m(2)), followed by a moderate decrease at PN day 90 (about 6,600 mu m(2)). The volume be longing to 1 Purkinje cell dendritic arbor was about 5,500 mu m(3) at PN day 6, 93,000 mu m(3) at PN day 25, and 100,000 mu m(3) at PN day 9 0. The numerical density of dendritic spines in the molecular layer sh owed a biphasic curve: a rapid increase from PN days 6 to 21 followed by a significant but short decrease at PN day 25, moderate rise from P N days 25 to 48, and a subsequent decline between PN days 48 and 90. T he number of spines belonging to 1 Purkinje cell showed two developmen tal ''peaks'': the first peak at 21 PN days was moderate (5.6 x 10(4) spines/Purkinje cell) while the second maximum at 48 PN days was more significant (1.2 x 10(5) spines/Purkinje cell), which then declined to 6.3 x 10(4) spines/Purkinje cell at PN day 90. It is suggested that t he temporary overproduction and the following decline in the number of Purkinje dendritic spines during the development of the cerebellar co rtex may be the morphological indicator of the dynamics of synaptogene tic and of synaptic stabilization processes. (C) 1994 Wiley-Liss, Inc.