Relationship between lipofuscin granules and polyunsaturated fatty acids in the housefly, Musca domestica.

The fractional volume occupied by lipofuscin granules in epithelial cells of the midgut or oenocytes of abdominal fat body of 3-day-old and 13-day-old male houseflies was determined in two groups of flies by electron microscopic morphometry. One group had developed from larvae reared on diets containing no added polyunsaturated fatty acids and the second from larvae reared on diets containing added linoleic acid. No polyunsaturated fatty acids could be detected in the lipids of the first group of flies using a method which would have detected their presence in amounts greater than 0.1% of the total esterified fatty acids. The second group contained at least two hundred times more than this minimal level. The volume of lipofuscin granules increased significantly (p less than 0.01) (about threefold for the fat body and twofold in midgut cells) between 3 days and 13 days of age but no statistically significant difference was seen between the two groups of flies at the same age. The results show that if lipofuscin formation depends on the oxidation of polyunsaturated fatty acids in the housefly, then extremely small amounts of the acids are involved which lie below the detection limit of the methods employed. The age-associated small increase of extractable fluorescence seen previously in the linoleic acid group of flies is not associated with an increase in the lipofuscin granules.

The concentration of choline into specific regions of the thoracic ganglion in B-methylcholine fed houseflies.

When larvae of the housefly, Musca domestica, are reared on a diet in which most of the choline has been replaced by a choline analogue, B-methylcholine, the small amount of choline available to the insect is largely taken up into the nervous system where it is incorporated into phosphatidylcholine and acetylcholine. Using autoradiographic techniques it is shown that, in the thoracic ganglion, the phosphatidylcholine component of this preferentially accumulated choline is not evenly distributed throughout the tissue but that a well-defined pattern of patches of silver grains is found over certain areas of the neuropile. Underlying this pattern are axons and glial processes structurally indistinguishable from the axons and glia of adjacent areas which show a much lighter autoradiographic reaction. It is concluded that the axons which produce this high density of silver graining are cholinergic and have a high affinity for choline.

Associated changes in the size and number of mitochondria present in the midgut of the larvae of the housefly, Musca domestica and phospholipid composition of the larvae.

A possible relationship between the phospholipid base composition of larvae of the housefly and the size, number and total volume of midgut mitochondria was examined. The phospholipid composition of the larvae was altered by restricting the amount of choline, substituting choline by N-dimethylethyl-(2-hydroxyethyl)-ammonium salt or 2-N-dimethylaminoethanol and by the addition of 2-aminobutan-1-ol to the larval diet. Mitochondrial measurements were made on electron micrographs of the epithelial cells in the midgut of third instar larvae. Reduction in the normal proportion of phosphatidylcholine in the phospholipids of the larvae was associated with an increase in the average size of the mitochondria and a decrease in their number, probably due to enhanced mitochondrial fusion. The opposite effect was noted when phosphatidyl-2-aminobutan-1-ol was present as a part replacement of the phosphatidyl-ethanolamine normally present in the larvae. Larvae which contained both phosphatidyl-2-aminobutan-1-ol as well as reduced amounts of phosphatidylcholine, contained mitochondria which were intermediate in both size and number. The effects associated with the changes in phosphatidylcholine and phosphatidyl-2-aminobutan-1-ol were independent of each other. The presence of the analogue of phosphatidylcholine and phosphatidyldimethylaminoethanol had no significant effect on the mitochondrial distribution. Total mitochondrial volume remained unaffected by alterations in the phospholipid composition of the larvae.