Study Brain 244

The rat, 294g, arrived the day before. When perfused after 121 days it was 450 g and had a mastoid infection. Two ‘OT’ cuts were made, on 6/28/73, by orienting a 1.4mm loop with squared ends vertically, at an anterolateral angle of ~30 deg with the midline, with its anterior end 2mm lateral and 0.5mm caudal to bregma, and lowering it to the floor of the skull. This was first done of the left side; after withdrawing and re-locating the device a similar cut was made by lowering it on the right and implanting it. The pupils, 0.5mm diameter under bright lighting, enlarged briefly to 1.0mm after the first cut then constricted as before. Then another device, H-style and 1.5mm wide, was oriented ML in the ‘AC’ position, which was calculated to cutting the anterior forceps of the anterior commissure, with its medial wire 2mm anterior to bregma and 1.5 mm lateral. There are five slides of its series of horizontal sections, 10 um thick and mounted every tenth; the Permount has become frosted over some of the sections.

At the bottom of the image, the healed cut can be seen. Detour of caudate putamen bundle neuron populations medially and laterally.

(424) AC cut 1.3mm (26d) in caudate putamen with medial arm 1.2mm lateral to the midline (24d). The cut is knit together and vascular; there are massive detours around the ends and some crossing. (323) the detour of the MCP projection is especially massive. The caudal axon bundles are bent towards the ends; the rostral ones face the incision and have fewer axons. (322) the lateral population of CP axons is massively reoriented laterally.In (325) the AC cut is 1.4mm (28d) wide with its medial arm 1.5mm lateral to the midline (30d). It just behind the AP axon population traversing the nucleus accumbens and spans the diagonal band (?). The healing is orderly; both detour. The ‘scar’, loosely organized, is crossed in a medial and lateral location by a few fine axons.

The OT implant is 1mm (21d) and there is an orderly new reorganization of cerebral peduncle it intercepted which now no longer commingles with the posterior hypothalamic population of axons. The pattern of MFB and of CP axons is now parallel to the cut which has blood vessels parallel to it also.

Left: Intact caudate putamen Right: Healed caudate putamen

The unmarked OT cut, in ~ the mirror-image of the location of the implant, does not show that segregation. Its apparent change is 21d long but the rostral part of it is crossed by axons. The general orientation of these axons is not as regimentedly parallel as the ones next to the cut on the other side. Compare the axon populations anterior and posterior to those cuts. (323) The cut anterior forceps of the anterior commissure abuts the marked cut. The obvious dark background stain of the unmarked cut is now 650 um long. The MFB axons adjacent to it do not have the smooth, straight appearance of those by the implant on the other side. Neither scar seems highly vascularized.

(322) The unmarked scar-appearance is now 650 um long, in the peduncular part of the hypothalamus, bounded by a rather organized peduncular population of axons and a hypothalamic one. They interweave rostral to the obvious defect. Then, next to the peduncle, the peduncular axons are organized parallel to the defect. Then, more caudally, AP axons of the ventromedial nucleus which are now aggregated in a structure, are parallel the medial edge of this cut while axons of the zona incerta are organized perpendicular to it. The implant side has a black deposit medial to the cut that obscures its structure.

(314) shows a detour of both forceps of anterior commissure around the implant. The posterior forceps orients smoothly towards the midline. At the end the two populations mesh together. (313) shows a bundle of the anterior thalamic radiation abutting the cut near the end that has the AC detour and detouring. This continues through (311)

(235) shows the unmarked cut. It now has a caudal black deposit. Rostral, in the line of the cut, is a linear assortment of a greater cell density than in the surrounding structure. It is crossed by fine axons with no particular orientation. In (233&4) there is a medial bundle of thalamic radiation axons in the anterior that stains darker brown. The apparent cut cannot be defined because its caudal portion has an obscuring deposit and its rostral portion has ‘vacancies’ that may have been created postlesion in formerly intact tissue. (231&2 and 226) = frosted. (225) A has a typical detour of caudate putamen bundle populations medially and laterally. The intercepted tissue is well vascularized with blood vessels parallel to the line of incision, and the cut is crossed by fine axons with no particular orientation. The implant-cut has a typically oriented medial and lateral detour of the thalamic radiation bundles; the medial is especially dense. Very interestingly there are ‘vacancies rostral to the cut that are crossed by new populations of disorganized axons! These appearances are scattered throughout this side of the thalamus and suggest that hemorrhage in axon bundles may have become repaired in this way. The unmarked cut has no obvious scarring; its caudal portion is vascularized. (222-4) is similar. (221) is frosted.

(135) a ~line of ‘vacancies’ in the hippocampus suggests that the unmarked cut was there; this ois confirmed in (134) by the little rostal detour of te alveus and in (133) by the discontinuity of the bulky alveus, where only few fine axons remain. The cut pyramidal layer has re-cinected at another level. In (132) the mossy fiber layer may be the one crossing the defect. (131), mostly frosted, shows an anterior detour of the anterior forceps of the corpus callosum. (125) The implant has an enlarged lateral ventricle with, caudally, a detour of alveus. In (124) the detour is at the level pf corpus callosum and there is an axon-crossed ‘cavity”. The anterior cut, in cortex and heavily vascularized, has a medial and lateral detour of caudal axon populations that continue as rostral reoriented populations. The lateral arm in cortex, 2.5mm lateral, (50d), has a new set of neurons to compare the intact side.

The unmarked cut location in the hippocampus is not obvious (124-2) but leave a tract in (121) that will do as a reference. Interestingly, the lateral side parallel to the corpus callosum orientation, is traversed by a blood vessel that abuts the cut perpendicularly. The marked cut, in HC and CC becomes defined by a large cavity. (122) (115) the ML cut is crossed, scar vascular, detours persist.

All cortex cuts are crossed in Row 1. (113)