Topographical localization of lipofuscin pigment in the brain of the aged fat-tailed dwarf lemur (Cheirogaleus medius) and grey lesser mouse lemur (Microcebus murinus): comparison to iron localization.

The present study was undertaken to explore the distribution of lipofuscin in the brain of cheirogaleids by autofluorescence and compare it to other studies of iron distribution. Aged dwarf (Cheirogaleus medius) and mouse (Microcebus murinus) lemurs provide a reliable model for the study of normal and pathological cerebral aging. Accumulation of lipofuscin, an age pigment derived by lipid peroxidation, constitutes the most reliable cytological change correlated with neuronal aging. Brain sections of four aged (8-15 year old) and 3 young (2-3 year old) animals were examined. Lipofuscin accumulation was observed in the aged animals but not in the young ones. Affected regions include the hippocampus (granular and pyramidal cells), where no iron accumulation was observed, the olfactory nucleus and the olfactory bulb (mitral cells), the basal forebrain, the hypothalamus, the cerebellum (Purkinje cells), the neocortex (essentially in the pyramidal cells), and the brainstem. Even though iron is known to catalyse lipid oxidation, our data indicate that iron deposits and lipofuscin accumulation are not coincident. Different biochemical and morphological cellular compartments might be involved in iron and lipofuscin deposition. The nonuniform distribution of lipofuscin indicates that brain structures are not equally sensitive to the factors causing lipofuscin accumulation. The small size, the rapid maturity, and the relatively short life expectancy of the cheirogaleids make them a good model system in which to investigate the mechanisms of lipofuscinogenesis in primates.

Laminar organization of acetylcholinesterase and cytochrome oxidase in the lateral geniculate nucleus of prosimians.

Hess and Rockland [Hess and Rockland (1983) Brain Res. 289, 322-325] proposed that the distribution of acetylcholinesterase within the lateral geniculate nucleus might correlate with the daily activity patterns shown by primates. In diurnal primates, the magnocellular laminae show a greater acetylcholinesterase reaction product. In nocturnal primates, the parvocellular laminae are more heavily stained. We have examined the laminar distribution of acetylcholinesterase and cytochrome oxidase in the lateral geniculate nucleus of a series of rare prosimian primates. In all prosimians examined, the most dense acetylcholinesterase reaction product is seen in the parvocellular layers of the lateral geniculate nucleus. Heavy cytochrome oxidase activity is seen in both the magnocellular and parvocellular layers, but not the koniocellular layers of the prosimian lateral geniculate nucleus. We have also employed a polyclonal antibody to choline acetyltransferase to examine the laminar organization or cholinergic activity in the Galago (Bushbaby) lateral geniculate nucleus. We report that choline acetyltransferase immunoreactivity does not correlate with acetylcholinesterase activity in the prosimian lateral geniculate nucleus. Although the lateral geniculate nucleus is more immunoreactive than most other thalamic structures and although the intercalated koniocellular laminae demonstrate somewhat lighter choline acetyltransferase immunoreactivity, no great difference in staining intensity is seen between the parvocellular and magnocellular laminae. In addition, we examined the phenotype of known inputs to assess the laminar specificity of cholinergic projections to the bushbaby lateral geniculate nucleus. Layer VI of primary visual cortex, which is known to be a source of acetylcholinesterase in the parvocellular layers, does not contain cholinergic cells, nor does the pretectal nucleus, which projects mainly to the parvocellular layers. The parabigeminal nucleus is cholinergic; however, this nucleus is known to project to the koniocellular layers, along with the non-cholinergic superior colliculus. Finally, the pedunculopontine tegmental nucleus, which provides a strong input to many regions of the thalamus, including the lateral geniculate nucleus, is cholinergic. The laminar organization of its input to the lateral geniculate nucleus is not known. Increased acetylcholinesterase reaction product within the parvocellular layers of the lateral geniculate nucleus is common to all strepsirhine primates. The pattern is also seen in the only two nocturnal haplorhine primates, Tarsius and Aotus (owl monkey). The relation of this increased acetylcholinesterase activity to cholinergic function remains unclear.(ABSTRACT TRUNCATED AT 400 WORDS)