Figure 6

Nissl-stained histologies (A and C) and adjacent autoradiograms (ARG's; B and D) showing the third ventricle (A and B, respectively; bregma -3.3 mm) and aqueduct of Sylvius (C and D, respectively; bregma -7.6 mm) 2 min after infusion of ¹²⁵I-IGF-1 into one lateral ventricle (LV). 6A. This histological section cuts through the parietal cortex, hippocampus, and thalamus (the large, light gray mass below the hippocampus) as well as the third ventricle (3 V), which is torn at its ventral border. The latter is formed by the very thin median eminence, which is one of the circumventricular organs and often tears during sectioning. 6B. The ARG indicates considerable delivery of radioactivity to the dorsal (very dark and very full) and ventral parts of the 3 V within two min of ending the infusion. The lateral streak of black to the left of the dorsal 3 V is actually part of the latter that extends over the stria medullaris thalami, the white matter that forms the dorso-medial border of the thalamus. Some spreading of ¹²⁵I-activity into the tissue adjacent to the ventral part of the 3 V is evident on the ARG at this time. The most ventral portion of this part of the 3 V flairs over the median eminence; the CSF in these little pockets explains, in part, the dark streaks radiating from the bottom of the ventral part of the 3 V and over the median eminence. The streak on the left seems, however, strangely long and has seldom been seen by us before. It may be real; it may be an artifact. 6C. This histological section passes through the pineal gland, the superior colliculus (midbrain) and subiculum (cortical end of the hippocampus). The tiny dots surrounding the midbrain are clusters of small arteries and veins in the subarachnoid space and cisterns; at this level, the latter are the quadrigeminal (dorsal) and ambient (lateral) cisterns. 6D. This ARG shows a very high level of radioactivity in the CSF within the aqueduct after only 2 min of circulation and indicates the speed at which CSF flows from the lateral ventricle through the 3 V system, which includes many recesses, and into the aqueduct. Scale bar = 1.5 mm.