Scanning Electron Microscope of Supraependymal Neuronal Circuits in the Third Ventricle of Rhesus Monkey Brain

The supraependymal neurons have been generally demonstrated lying over the nonciliated areas, specially CVOs, on the walls of the third cerebral ventricle of a variety of mammals. However, such neurons have till date been reported on the ciliated ependyma only inguinea pigs (Mitchell and Card, 1978). In the present study, third ventricles of nine adult monkeys of both the sexes were studied by routine scanning electron microscopy after perfusion fixation in 10 per cent neutral buffered formalin, dehydration with graded series of ethanol and amylacetate, critical-point-drying with liquid carbondioxide and sputter-coating with gold. Systematic scanning of the lateral wall of the third ventricle revealed that the ependymal surface could be divided into oligo-, and profusely ciliated zones. Pleomorphic supraependymal cells were noticed over the ciliated regions of the ventricularwall particularly between the thalamus and the mammillary region dorsal and caudal to the infundibular recess (Fig. 1). These neuron-like cells typically consisted of cell somas of variable configurations together with extensive networks of interconnected neuritic processes. At higher magnifications, the neuronal bodies depicted diverse structural modifications(Fig.2). Processes of variable diameters coursed over the ciliary carpet of the lateral wall of the third ventricle(Fig.3). At times, the processes exhibiting varicosities over the supramammillaryzone(Fig.4)coursed for variabledistances over the ependymal lining. The majority of such neuritic processes appeared to penetrate the underlying ventricular wall.