Nucleus locus coeruleus: a morphometric Golgi study in rats of three age groups.

Using Rapid Golgi and Nissl techniques, 3 major cell types: fusiform, multipolar and ovoid shaped cells were identified in the nucleus locus coeruleus of male rats. Each cell type was described and quantitated as to age-related changes between 30 and 90 and between 90 and 220 days of age. The orientation and dendritic architecture of each type of cell in the locus coeruleus and relationship of these cells to blood vessels in the locus coeruleus and to surrounding structures is also described. One hundred neurons per age group were measured as to their maximal linear extent and the number of spines on the somal surfaces were counted. Dendritic number, linear extent, diameter and number of spines along a 50 microns segment near the mid-point of dendritic extensions in an equal number of primary and secondary dendrites were quantified for each age group and comparisons of these parameters between each cell group were made. Axons of each cell type were defined as to their origin and general orientation and trajectory. Axon collaterals of multipolar cells were shown to be recurrent in type projecting back onto the dendrites and soma of multipolar cells. One of the most striking findings was that between 30 and 90 days there were significant decreases in spine density on both primary and secondary dendrites in all three cell types in the locus coeruleus. This was followed by significant increases in spine density on both primary and secondary dendrites between 90 and 220 days in each of the 3 cell types. It is of interest that these age-related cell changes in spine density in the nucleus locus coeruleus are exactly out-of-phase with those of the nucleus raphe dorsalis.