Histological and histochemical studies on the subfornical organ of the squirrel monkey

Summary

Detailed studies have been made on the distribution of several enzymes in the subfornical organ (SFO) of the squirrel monkey. In this species, the nerve cells of the SFO show reactions of varying intensity for enzymes of the glycolytic and aerobic pathways. The nerve cells, glial cells and ependymal cells of the SFO and the choroid plexus are equipped with enzymes of the Embden-Meyerhof (EM) pathway, pentose cycle and tricarboxylic acid (TCA) cycle. Many nerve cells and oligodendroglia in the body of this organ are rich in enzymes of the TCA cycle and the pentose cycle and thus presumably have the capacity of producing adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH₂) [reduced triphosphopyridine nucleotide (TPNH)]. In the neurons, ATP is probably used as energy for synaptic transmission, active transport, secretion and various other metabolic processes, whereas NADPH₂ is used for synthetic processes such as the production of fatty acids and some amino acid conversion (e.g., conversion of phenylalanine into tyrosine). The SFO and its stalks contain both cholinergic and adrenergic neurons and fibers. The outermost layer of the perivascular sheath gives a positive reaction for enzymes of the gylcolytic pathways (EM pathway, pentose cycle and TCA cycle), whereas the inner layer of this sheath shows negligible activity for these enzymes. On the other hand, the whole sheath (inner and outer layers) exhibits strong staining for Mg⁺⁺-activated adenosine triphosphatase (ATPase), and moderate staining for Ca⁺⁺-activated ATPase. This sheath, rich in ATPase, may carry on active transport and such related functions. Since the outermost layer contains various enzymes of the glycolytic pathways, it is possible that the ATP required for these functions is produced in this layer.