Age pigments in different populations of peripheral neurons in vivo and in vitro

The distribution and ultrastructure of lipopigments in the rat sympathetic, vagus and spinal ganglion neurons were studied in vivo and in vitro using fluorescence and electron microscopy. Newborn, 3-6 mo and 24-30 mo-old male Wistar rats were used. In vivo, the age pigments in the sympathetic neurons showed a tendency to form unipolar or bipolar caps, whereas in the vagus and spinal ganglion neurons pigment granules were packed in the peripheral area of the perikarya during aging. Ultrastructurally, lipid-like vacuoles and a rather homogeneous matrix were the components shared by pigment bodies of all types of peripheral neurons. However, pigment granules in sympathetic neurons frequently had a third, osmiophilic component, which likely represents neuromelanin. In vitro, the cytoplasmic area occupied by autofluorescent pigments was increased in most of the neurons. Some neurons, however, showed the same amount of lipopigments as in vivo. In electron microscopy, age pigment granules typical of each type of neuron were found, and their number and intracellular distribution seemed to be comparable with those in vivo. In most of the neurons cultured from all ages and of all types of ganglion, there appeared to be accumulations of another, very homogeneous and large type of pigment body. In some cases, they were structurally connected with classical pigment bodies or they had a finger print-like substructure. Large homogeneous pigment bodies were also seen in surrounding satellite cells. All these changes were most frequently seen in cultures of spinal ganglia from old animals. It is concluded that although classical age pigments maintain their characteristics in cultured peripheral neurons, there is, in addition, a rapid accumulation of ceroid-like pigments, which may be caused by the inability of the cultured neurons to cope with increased peroxidative damage.