Cortical Transplants Research Articles

Striatal, ventral mesencephalic and cortical transplants into the intact rat striatum: A neuroanatomical study

Intrastriatal transplantation of fetal striatal (STR), cortical (CTX), or ventral mesencephalic (VM) tissue into the normal striatum has been shown to produce behavioral deficits (38). Here, we have examined the cellular elements of the transplants and their connectivity with the host using histochemistry for cytochrome oxidase (CO) and acetylcholinesterase (AChE), immunocytochemistry for glial fibrillary acidic protein (GFAP), OX42, tyrosine hydroxylase (TH), dopamine β-hydroxylase (DBH), serotonin (5-HT), and cholecystokinin (CCK). Autoradiography for dopamine D 1 and D 2, muscarinic cholinergic, and serotonin 5-HT 1 and 5-HT 2 receptors at 5–15 months after transplantation was also investigated. CO staining showed that all transplants were metabolically active. The STR and VM transplants contained AChE-positive neurons and fibers. The CTX transplants exhibited AChE terminals with an appearance similar to that of the host cortex. AChE staining within the STR transplants was patchy. 5-HT-, TH-, and DBH-immunoreactive (IR) fibers were found in the STR and CTX transplants. In two of six CTX transplants, many TH-IR neurons were present. The VM transplants contained many TH-IR, 5-HT-IR, and DBH-IR cell bodies and fibers. CCK-IR stain was found in the VM transplant and was coextensive with regions containing TH-IR cell bodies. Fibers stained by all markers crossed the transplant and host border. Receptor autoradiography revealed that muscarinic cholinergic and 5-HT 2 receptors were present in the STR, CTX, and VM transplants. In addition, dopamine D 1 and D 2 receptors were present in the STR transplants. Intermittent heavy staining for GFAP and OX42 were observed along the border of most transplants and the hosts. It was noted that high densities and hypertrophy of GFAP- or OX42-stained astrocytes or microglia, respectively, were present in the transplants and adjacent host. OX42-stained macrophages were found in many transplants. The present results indicate that intra-striatal transplants into the intact normal brain express numerous histochemical, immunocytochemical, and receptor features characteristic of the appropriate adult tissues. The afferents from the host extend into the STR and CTX transplants, and neural fibers from the VM transplants grew into surrounding host tissue, suggesting possible anatomical connection. Ultrastructural evidence is needed to determine if these fibers form synaptic connections. The results from GFAP and OX42 immunocytochemical staining support the possibility suggested by behavioral studies that damage to the host brain is induced by neural transplantation.

Vibrissa-related behavior in mice: transient effect of ablation of the barrel cortex

Knowing that the mystacial vibrissae are an important part of the tactile sensory apparatus of rodents, we investigated the role of the barrel cortex - the endstation of the pathway between whiskerpad and cerebral cortex - in mouse behavior. We tested 15 female adult mice 2 and 10 weeks after both unilateral ablation of the barrel cortex and removal of the vibrissae on the same side in order to assess acute as well as transient effects of the cortical lesion. Two kinds of behavioral tests were performed on animals permanently provided with opaque lenses: one involved a passive stimulation of the vibrissae; the other was the 'gap-crossing' test which required the animal's active use of the vibrissae. Lesioned subjects did not show a deficit during passive stimulation of the vibrissae. On the contrary, there was a deficit during the gap-crossing test 2 weeks after the ablation of the barrel cortex. The deficit partly disappeared when the subjects were tested 10 weeks later. The results show that in mice, the barrel cortex is involved in the performance of complex behavioral tasks. The recovery of function could be due to changes in strategies to solve the gap-crossing test and/or to physical changes in neuronal circuitry. In either case, the results are relevant for the interpretation of cortical transplantation models using the whisker-to-barrel pathway.

A method using diI to study the connectivity of cortical transplants

Carbocyanine DiI is described as a suitable fluorescent tracer to investigate the connectivity of cortical transplants. DiI was applied in 2 ways: in tissue previously fixed with aldehydes, and in vivo for labelling the donor tissue prior to transplantation. When applied in fixed tissue DiI travelled anterogradely, allowing the study of efferent connections from the transplant to the host. When DiI was applied in vivo, it travelled retrogradely showing the afferents to the transplant from the host.

Fetal Cortical Transplants in Adult Rats Subjected toExperimental Brain Injury

Fetal cortical tissue was injected into injured adult rat brains following concussive fluid percussion (FP) brain injury. Rats subjected to moderate FP injury received E16 cortex transplant injections into lesioned motor cortex 2 days, 1 week, 2 weeks, and 4 weeks post injury. Histological assessment of transplant survival and integration was based upon Nissl staining, glial fibrillary acidic protein (GFAP) immunocytochemistry, and staining for acetylcholinesterase. In addition to histological analysis, the ability of the transplants to attenuate neurological motor deficits associated with concussive FP brain injury was also tested. Three subgroups of rats receiving transplant 1 week, 2 weeks, and 4 weeks post injury Were chosen for evaluation of neurological motor function. Fetal cortical tissue injected into the injury site 4 weeks post injury failed to incorporate with injured host brain, did not affect glial scar formation, and exhibited extensive GFAP immunoreactivity. No improvement in neurological motor function was observed in animals receiving transplants 4 weeks post injury. Conversely, transplants injected 2 days, 1 week, or 2 weeks post injury survived, incorporated with host brain, exhibited little GFAP immunoreactivity, and successfully attenuated glial scarring. However, no significant improvement in motor function was observed at the one week or two week time points. The inability of the transplants to attenuate motor function may indicate inappropriate host/transplant interaction. Our results demonstrate that there exists a temporal window in which fetal cortical transplants can attenuate glial scarring as well as be successfully incorporated into host brains following FP injury.

A preliminary study of homotopic fetal cortical and spinal cotransplants in adult rats

Neocortical and spinal tissue from a given E16–E17 rat fetus were homotopically transplanted into lesion sites of adult rats which had undergone combined cortical and complete lower thoracic spinal cord lesions. Spinal cord transplants were placed either directly into the gap in host spinal cord or embedded in a collagen matrix. Animals were killed from 4 days to 8 months and tissues were processed for light microscopy. All cortical transplants survived and integrated with host brain. Many axons appeared to grow between the cortical transplant and subjacent host parenchyma. Only collagen-embedded spinal transplants survived. At 8 months, two animals underwent spinal cord transection and HRP implantation two vertebral segments rostral to the spinal cord transplantation site. Both animals revealed HRP-labeled neurons in the cortical transplants. It was concluded that 1) homotopically transplanted fetal cortical tissue can survive and may be capable of extending axons to midthoracic levels, and 2) a collagen matrix may enhance the survival of fetal tissues transplanted into a complete gap in host spinal cord.

Fetal cortical transplants reduce motor deficits resulting from neonatal damage to the rat's frontal cortex

Motor deficits in the execution of grasping movements of the right forelimb were compared in normal female Wistar rats, in animals which sustained a neonatal lesion of the left frontal cortex and in animals which received immediately after the lesion a transplant obtained from the frontal cortex of E16 embryos. Behavioral testing was carried out from postnatal day 48 (D48) to D108. The animals were placed at the center of a circular wire grid which was turned upside down so that they hung by their 4 paws at a distance of 40 cm above the floor. The precision of grasping movements of the right limb and the number of falls were recorded during a 1 min session of active moving across the grid. The lesioned subjects were most impaired on both motor indices whereas the grafted animals although performing slightly poorer than the controls were, however, less impaired than the lesioned animals. Fetal cortical transplants, therefore, seem to promote functional recovery from neonatal cortical damage.

Selective elimination of axons extended by developing cortical neurons is dependent on regional locale: experiments utilizing fetal cortical transplants

In adult rats, cortical neurons that extend an exon through the pyramidal tract (a major subcortical efferent projection of the neocortex) are limited to layer V of about the rostral two-thirds of the neocortex. In neonates, however, pyramidal tract neurons are distributed throughout the neocortex, but all of those found in certain areas, such as the posterior occipital region (including primary visual cortex) selectively lose their pyramidal tract axon (Stanfield et al., 1982) yet maintain axon collaterals to other subcortical targets (O'Leary and Stanfield, 1985). To determine if the regional location of a developing pyramidal tract neuron critically influences the maintenance or elimination of the axon collaterals it initially extends, pieces of cortex from embryonic day 17 (E17) rat fetuses (exposed to 3H-thymidine on E15) were transplanted heterotopically into the cortex of newborn (PO) rats; rostral cortex was placed into the posterior occipital region (R----O), or posterior occipital cortex into a rostral cortical locale (O----R). The retrograde tracers Fast blue (FB) and Diamidino yellow (DY) were used to assay for the presence of specific populations of cortical projection neurons within the autoradiographically identified transplants. In terms of the extension and maintenance of pyramidal tract axons, the transplanted neurons behave like the host neurons of the recipient cortical region rather than like those of their site of origin. At P40, following FB injections into the pyramidal decussation on P34, pyramidal tract neurons are labeled within the O----R transplants, but none can be labeled within R----O transplants, although in the same R----O cases transplanted neurons are labeled by an injection of DY in the superior colliculus. However, at P13 pyramidal tract neurons can be identified within the R----O transplants, as well as in the host occipital cortex, following injections made on P9, a period when the distribution of pyramidal tract neurons in normal rats is widespread (Stanfield and O'Leary, 1985b). In a second series of host rats, on P34 FB was injected in the pyramidal decussation of the O----R cases, or in the superior colliculus of the R----O cases, and in both groups DY was injected into the region of contralateral cortex homotopic for the new location of the transplant. On P40, in both the O----R and R----O transplants, many neurons singly labeled with FB or DY are found, but no double dye-labeled cells are seen.(ABSTRACT TRUNCATED AT 400 WORDS)

Fetal cortical transplants into neonatal rats respond to thalamic and peripheral stimulation in the adult. An electrophysiological study of single-unit activity

Plates of presumptive sensorimotor neocortex obtained from fetal rats at 14—16 days gestation were grafted into the cerebral hemisphere of 0- to 1-day-old newborn rats. The transplants were placed into small lesion cavities in the sensorimotor cortical area made immediately prior to grafting. At 4–5 months of age, single-unit activity in the transplants (TP) or normal cortex (NCX) was recorded under ketamine HCI anesthesia using standard electrophysiological techniques. Over 90% of cells in both the transplants ( n = 63) and normal cortex ( n = 39) responded to ventral thalamic stimulation. Their average response latencies were similar (11.48 ±0.56 ms in TP, 12.77 ±1.20 ms in NCX, mean ±S.E.M., no significant difference), as were their average responses of slightly more than 1 spike per thalamic stimulus (1.24±0.08 in TP, 1.07±0.01 in NCX, no significant difference). In addition, 64% (30/47) of transplant cells and 44% (14/32) of normal cells also responded to electrical stimulation of the contralateral forepaw, and here also the latencies were similar (16.11±0.67 ms in TP, 14.30±0.78 ms in NCX). The spontaneous neuronal activity obsserved within the transplants was also comparable to that seen in normal cortex, as measured by comparison of spontaneous interspike interval (ISI) histograms (median ISI of 84.5 for TP and 80.5 for NCX) and comparison of the burst index (% of intervals 5 ms, 14.7% for TP and 10.5% for NCX). These results are compared to those found in several recent studies where fetal cortex is grafted into adult hosts.

Fetal cortical transplants reduce the thalamic atrophy induced by frontal cortical lesions in newborn rats.

Fetal neocortical tissue was grafted into frontal cortex lesion cavities made in newborn rats. After survival periods extending up to 14 months, volumetric measurements of the total thalamus and of the lateral, medial and anterior thalamic compartments showed an amelioration of the thalamic atrophy that normally is found after cortical lesions. These results correspond to previous findings demonstrating interconnections between fetal cortical transplants and the host thalamus.

Fetal neocortical transplants grafted into cortical lesion cavities made in newborn rats receive multiple host afferents. A retrograde fluorescent tracer analysis

Several reports have demonstrated efferent projections from fetal neocortical transplants placed in the cerebral cortex of newborn rats. Fewer studies have examined transplant afferents, and these have primarily used techniques based on the axonal transport of horseradish peroxidase. In the present study, we extend these initial findings on transplant afferent connections by using retrogradely transported fluorescent dyes to demonstrate a topographic and more extensive pattern of cortical transplant afferents than has been previously reported. Fetal neocortical tissue was grafted into frontal cortical lesion cavities made by aspiration in newborn rats. At 1.5-10 months later, the fluorescent dyes Fast blue and Diamidino yellow were injected into the transplants. Subsequent histological analysis demonstrated numerous retrogradely labeled fluorescent neurons within the host thalamus and cerebral cortex as well as several other areas of the host brain. The neurons were primarily single-labeled and generally found in areas that normally project to the ablated area of the cortex. The topographic distribution of retrograde labeling in several animals with non-overlapping dye injections confined to the transplants suggests that the host projections were distributed selectively within the grafts. These results support and extend previous studies suggesting the use of fetal neocortical tissue in repair of the neonatally damaged central nervous system.

Deficits in Beam‐Walking After Neonatal Motor Cortical Lesions are not Spared by Fetal Cortical Transplants in Rats

Adult rats that sustained unilateral motor cortical lesions at birth demonstrated deficits in traversing an elevated narrow beam. These deficits, manifested by hindlimb slips off the edge of the beam, were not spared in animals that received fetal cortical transplants into the lesion cavity immediately after lesion placement.

Transplantation of embryonic ventral forebrain grafts to the neocortex of rats with bilateral lesions of nucleus basalis magnocellularis ameliorates a lesion-induced deficit in spatial memory

Embryonic ventral forebrain grafts containing developing cholinergic cells were transplanted to the neocortex of rats with bilateral quisqualic acid lesions of the nucleus basalis magnocellularis. A lesion-induced deficit on performance of a spatial alternation test of memory was reduced by such transplants. When the same animals were treated with the acetylcholinesterase inhibitor physostigmine (0.05 mg/kg), however, performance on the behavioral task was not further promoted, and therefore, under these conditions, the cholinergic cortical transplants appear not to be subject to modulation by anticholinesterase drugs.

Electrophysiological research into afferent connections of embryonic neocortex allotransplants grafted into the association cortex of adult rats

Grafts of the rat fetal neocortex at the 17–18th day of gestation were placed in the cavity made by aspiration in the primary visual or somatosensory cortex of adult rats. Findings from electrophysiological research performed 3–3.5 months after this transplant showed that neurons of this transplant responded to sensory stimulation specific to the cortical regions replaced by the transplant in 50% of animals. This response was evoked by stimulating local receptive fields displaying a topical organization pattern in a proportion of the animals. Neuronal response in the transplant indicated that the usual field of vision previously existing on the replaced portions of visual cortex had been restored. Electrical stimulation applied locally to a number of brain structures showed that the transplants received afferent inputs from the thalamic nucleus normally projecting to the cortical region replaced by the graft, as well as from homotopic sites on the contralateral cortex. Latencies and time course of neuronal response to stimulating these regions of the host brain resemble those observed in the normal. Afferent inputs from the host brain to cortical transplants thus emulate normal cortical input. Possible mechanisms underlying reinnervation of the grafts are discussed.

Examination of autologous and embryonic cortical brain tissue transplantation to adult brain cortex in rats.

Autologous and embryonic cortical brain tissue was transplanted to adult rats in order to reconstruct experimentally degenerated cortical brain tissue. Rats were decapitated within 6 or 12 weeks. Viability of the graft tissues was studied by light and electron microscopy. Embryonic cortical brain tissue grafts became enlarged but adult cortical brain tissue grafts were found to be unaltered. Electron-microscopically observed mitochondria and other cell organellae and the newly vascularized areas clearly showed that the graft tissues were alive.

Chapter 48 Multiple trophic influences which act on developing retinal ganglion cells: studies of retinal transplants

This chapter discusses and identifies molecules present in the pathway of growing retinal axons in the developing brain, which might serve as an adhesive substrate. The chapter focuses on the multiple trophic influences, which act on developing retinal ganglion cells. Transplants of retina placed over the superior colliculus of newborn rats form extensive axonal connections with the primary visual nuclei of the host brain. Significantly, different results are obtained, when retina is transplanted to the visual cortex of newborn rats. Collectively, the results make two important points: first, ganglion cells degenerate if unable to form connections in their proper terminal nuclei, and second, retinal axons whether in cortex or colliculus appear to select a very specific path to grow, based on local environmental cues. Transplantation studies offer evidence that laminin is a substrate for retinal axon growth, and fetal retina transplanted adjacent to the colliculus of adult host rats exhibits very limited axon growth into the host brain. Axons from cortical transplants run rostrally and caudally in rather tight tracts deep in the brainstem; however, it remains for future work to distinguish the substrate molecules followed by each axon population.

Fetal frontal cortex transplanted to injured motor/sensory cortex of adult rats: Reciprocal connections with host thalamus demonstrated with WGA-HRP

Fetal frontal cortex was transplanted into lesion cavities formed in host motor/sensory cortex of adult rats. Eight to twenty-eight weeks later wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) was injected into host thalamus and the brain was sectioned and reacted using a sensitive TMB procedure. A large amount of fine granular WGA-HRP was detected in most transplants. This could represent anterograde transport demonstrating that injured adult host thalamic neurons sprouted axons into fetal cortical transplants. Conversely, none or very few retrogradely labeled pyramidal neurons were present in the transplants. This indicates that pyramidal neurons in transplants either did not sprout into adult host brain or sprouted such short distances that they did not pick up the WGA-HRP. These results are compatible with the hypothesis that high trophic/growth factor levels in newborn or fetal brain and low levels in adults determine the more extensive connections seen in newborn hosts compared with those in adult transplanted hosts. The data are also consistent with the proposal that adult host brains impair axonal growth. Functionally, the data suggest that although corticofugal effects of fetal cortical transplants in adult host brains are likely to be limited, transplants could exert beneficial trophic effects on adult host thalamic neurons.

Fetal frontal cortex transplanted to injured motor/sensory cortex of adult rats. I. NADPH-diaphorase neurons

Fetal frontal cortex from 18-d-old embryonic rat brain was transplanted into cavities of juvenile host motor/sensory cortex. Two to seven months later, sections were reacted for NADPH-diaphorase (NADPH-d) enzyme histochemistry. NADPH-d-positive neurons survived in 11 of 13 grafts. All but one of the transplants had reduced numbers of these neurons, although in 3 transplants the reductions were moderate and not statistically significant. The distribution and morphology of NADPH-d neurons within most grafts was comparable to that of NADPH-d neurons in normal host cortex. At the margin of the 2 transplants with no NADPH-d neuronal perikarya, NADPH-d fibers crossed from host to transplant as far as a millimeter into the transplant, and on rare occasions, the host neurons that gave rise to these fibers were identified. This suggests that host-transplant interactions are possible. One transplant had an abnormally large number of NADPH-d-positive neurons and fibers, possibly due to selective survival of these neurons. The data reported here for NADPH-d in cortical transplants may also apply to neuropeptide Y (NPY), since nearly all neocortical NPY neurons also contain NADPH-d.

Role of the target in directing the outgrowth of retinal axons: transplants reveal surface-related and surface-independent cues.

In the present investigation we have examined whether retinal axons can be directed to the superior colliculus via an alternate route when they do not have access to their normal substrates along the optic tract. To address this issue we transplanted embryonic mouse retinae into the midbrain parenchyma and to various positions around the outer surface of the midbrain of newborn rats and then examined the development of projections from the transplanted tissue. The projections from cortical grafts placed in the midbrain were studied to determine whether axons from different classes of neurons respond to the same cues for outgrowth. When retinae were placed within the midbrain close to the cerebral aqueduct, axons projected dorsally to the superficial layers of the superior colliculus. Directed outgrowth was seen from the earliest time a projection could be detected and was independent of whether the superior colliculus still received host optic afferents. In contrast, the major projection from similarly placed cortical transplants was directed toward the ventral part of the midbrain. Deafferentation of midbrain corticorecipient areas did not affect the projection patterns from either type of graft. Projections from retinae placed more ventrally in the midbrain tegmentum could not be detected. However, retinae placed on the surface of the midbrain, even as far ventral as the cerebral peduncle at the level of the inferior colliculus, always had a projection to the superior colliculus that ran along the brainstem surface. These observations suggest that the superior colliculus exerts a positive influence on the growth of optic axons to the midbrain. However, while target cues appear to be able to support retinal axon growth through the midbrain parenchyma, their range appears to be limited, and at distances beyond the extent of their influence, optic fiber outgrowth occurs only over the surface of the brain. It is suggested, therefore, that there are both local surface-related and target-derived surface-independent cues that guide optic axons to the tectum in developing mammals.

Myelin Basic Protein Expression after Cortical Transplants into Shiverer Brain

Myelin Basic Protein Expression after Cortical Transplants into Shiverer Brain

Embryonic Cortical Transplants Survive in Middle Cerebral Artery Territory after Permanent Arterial Occlusion in Adult Rats

Embryonic Cortical Transplants Survive in Middle Cerebral Artery Territory after Permanent Arterial Occlusion in Adult Rats