Neocortical Grafts Placed in the Infarcted Brain of Adult Rats: Few or No Efferent Fibers Grow from Transplant to Host

The present stud y examines the capacity of fetal neocortical grafts placed in a brain infarct to exchange axonal projections with the host brain. Five to 7 days after a middle cerebral artery occlusion in adult spontaneously hypertensive rats, dissociated neocortical primordium from fetuses of gestational age 15-16 days was implanted into the infarcted area. Four to 11 months later, the neural tracers Phaseolus vulgaris-leucoagglutinin and Fluoro-Gold were injected in the grafts and host neocortex. An extensive axonal network was present in the transplants but only one of eight rats with appropriate placed injections displayed efferent connections from transplant to host. The sparse axonal outgrowth indicates major limitations for fetal rat cortical grafts to form connections with host neural circuitries after an ischemic insult.     

Expression of zinc-positive cells and terminals in fetal neocortical homografts to adult rat depends on lesion type and rearing conditions

Zinc-positive neurons and terminals, known to be associated with the glutamatergic projections in the brain, can be demonstrated by the histochemical Timm method and later modifications thereof. The adult rat neocortex contain a uniform lamination of zinc-positive cells with specific projections to, e.g., the striatum. We have previously reported that fetal neocortical grafts implanted in the adult rat neocortex combined with rearing in an enriched environment can improve behavioral functions and reduce the secondary atrophy of thalamus after cortex infarction in adult rats. In order to examine whether the expression of zinc positivity is ontogenetically inherent to neocortical neurons we grafted fetal neocortical tissue to aspiration or ischemic lesions of the frontoparietal neocortex of adult rats, followed by histochemical visualization of the vesicular zinc pool by selenite or sulfide. One further aim of the study was to elucidate to what extent the distribution of zinc-containing neurons and terminals in the grafts depended on rearing under different environmental conditions. The foremost finding of the present study was that the overall density of zinc-containing terminals in fetal cortical transplants placed in brain infarcts of adult spontaneously hypertensive rats is higher when the rats are reared in an enriched environment. Moreover, the presence and expression of zinc-positive neurons and terminals do not seem to be ontogenetically inherent to the cortical neurons as the fetal neocortical grafts placed in aspiration lesions contained no zinc-selenide-positive neurons and few or no zinc-selenide-positive terminals. The presence or expression of zinc-positive cells may thus be induced by ingrowth of fibers and terminals from the host brain as transplants placed in the ischemic lesions expressed both zinc-positive neurons and terminals.     

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.     

Cholinergic Innervation of Fetal Neocortical Transplants Is Increased after Neutralization of Myelin-Associated Neurite Growth Inhibitors

Fetal neocortical transplants placed into adult neocortical sensorimotor aspiration lesions are known to receive afferent input from the adult host rat brain. As this input is less dense than normal, the present study was designed to investigate whether neutralization of myelin-associated neurite growth inhibitors NI-35/250 might promote host derived cholinergic innervation of fetal neocortical transplants. Adult rats received unilateral sensorimotor cortical aspiration lesions, and block grafts from embryonic day 14–15 neocortical tissue were placed immediately into the lesion cavities. Mouse hybridoma cells secreting either the monoclonal antibody IN-1, which blocks neurite growth inhibitors NI-35/250, or a control antibody or medium without cells were applied in millipore filter capsules directly over the fetal graft tissue. The brains were processed 12 weeks later for the visualization of acetylcholinesterase-positive, presumptive cholinergic fibers. We found an enhancement in the cholinergic innervation of fetal grafts in the recipients treated with the antibody IN-1 both in terms of fibers growing into the graft and of density within the center of the grafts. These results indicate that myelin-associated neurite growth inhibitors are involved in the development of host–transplant connectivity in the adult brain.     

Heterotopic neocortical transplants. An anatomical and electrophysiological analysis of host projections to occipital cortical grafts placed into sensorimotor cortical lesions made in newborn rats.

Plates of presumptive occipital neocortex obtained from fetal rats at 14-16 days gestation were grafted into the cerebral hemisphere of newborn rats. The transplants were placed heterotopically into sensorimotor cortical lesion cavities made immediately prior to grafting. At maturity, some of the transplants were injected with the retrograde fluorescent tracers Fast Blue and Diamidino yellow. In other animals, single-unit activity in the transplants or in normal cortex was recorded using standard electrophysiological techniques. Histologically, host projections to the transplants were demonstrated by the presence of retrogradely labeled neurons in the host primary and secondary somatosensory cortices as well as several thalamic areas including the anteroventral, anteromedial, ventrobasal, mediodorsal and central medial nuclei. Additional labeling was found in the claustrum, lateral hypothalamus, zona incerta and basal forebrain. Electrophysiologically, transplant single-unit activity was evoked in 43/69 (62%) neurons by thalamic stimulation, but only 1/69 transplant neurons responded to electrical stimulation of the contralateral forepaw. In further work, volumetric measurements showed that the transplants did not ameliorate the thalamic atrophy found after neocortical lesions. These results are compared to previous studies involving the homotopic placement of sensorimotor cortical grafts.     

Efferent Projections to the Host Brain from Intrastriatal Striatal Mouse-to-rat Grafts: Time Course and Tissue-type Specificity as Revealed by a Mouse Specific Neuronal Marker

The developmental time-course and growth characteristics of efferent graft-to-host projections were studied from mouse fetal striatal grafts (E13 - 14) implanted as a cell suspension into the ibotenate-lesioned striatum of immunosuppressed adult rats. A cell surface monoclonal antibody specific for mouse neurons (M6) was used to identify the donor cells and their projections into the host brain. At 3 - 5 days after implantation, sparse fascicles of M6-positive graft-derived fibres extended for approximately 0.3 - 0.4 mm across the graft - host border into the surrounding host striatum. From the beginning they were selectively orientated in one direction, i.e. caudally along the myelinated fibre bundles of the internal capsule. At 8 days, the graft-derived fibres were more numerous and more densely labelled. They ran in dense fascicles inside the myelinated bundles of the host internal capsule and reached the rostral host globus pallidus, a distance of approximately 1.2 mm from the caudal tip of the graft. Two weeks after grafting, the M6-positive fibre fascicles were clearly seen to branch within the globus pallidus to form terminal-like networks. From this time onwards, the immunoreactivity of the outgrowing fibre fascicles gradually diminished, although small but dense terminal-like networks could be found in the host globus pallidus in most, but not all, of the rats at longer survival times (3 - 15 weeks). This is consistent with previous work showing that outgrowing axons lose their M6 immunoreactivity as they mature and become myelinated. Control grafts of fetal neocortical and fetal cerebellar tissue were used to assess the tissue-type specificity of the efferent fibre growth. The neocortical implants projected densely up to about 3 mm into the host brain, along the internal capsule and the corpus callosum and into the overlying cortex. By contrast, although the cerebellar grafts survived well, they showed very little efferent fibre growth. Double immunostaining for DARPP-32 and M6 revealed that all M6-positive fibre fascicles extending from the striatal (but not neocortical) grafts also showed DARPP-32 positivity, and thus that it was the DARPP-32-positive regions of the striatal grafts that projected to the host brain. It is concluded that graft-to-host projections, running along and inside host myelinated bundles, are formed from intrastriatal striatal grafts within 1 - 2 weeks of implantation. Grafts of neocortical tissue grew well along the same trajectory, whereas neurons of a type not normally projecting along the internal capsule, i.e. cerebellum, failed to extend axons over any significant distance along this trajectory.     

Changes in efferent and afferent connectivity in rats with induced cerebrocortical microgyria

Freezing injury to the cortical plate at postnatal day (P) 1 initiates a cascade of events that ultimately result in a focal neocortical malformation resembling human 4-layered microgyria. This malformation has been associated with widespread changes in neocortical and thalamic architecture and physiology. It was hypothesized that at least some of these alterations could result from connectional reorganization following early injury. The current experiment was designed to delineate the efferent and afferent connections between the cerebral hemispheres and between the cortex and thalamus of rats with induced cerebrocortical microgyria. Microgyria were induced in the parietal cortex of rats by freezing injury on postnatal day 1. In adulthood, injections of biotinylated dextran amine were made either in the microgyric cortex, in homologous regions of the opposite hemisphere, or in ipsilateral ventrobasal complex of the thalamus. Appropriately directed connections to homotopic areas were seen in some but not all microgyric rats. In addition, heterotopic projections to frontal and secondary sensorimotor cortices were noted. Projections from homotopic regions in the hemisphere opposite to the malformation terminated most often in the medial portions of the microgyrus or avoided it entirely. There were almost no thalamocortical or corticothalamic projections between the ventrobasal complex and the microgyrus itself, although a dense plexus of thalamocortical fibers was often noted at the border between the malformed and normal cortex. These connectional changes may help explain disturbances in architecture, physiology, and behavior associated with these focal malformations.     

Functional integration of fetal cortical grafts into the afferent pathway of the rat somatosensory cortex (SmI)

The somatosensory area of fetal (E15-16) Sprague-Dawley rat neocortex was implanted into the barrel receptor area of adult first somatosensory cortex (SmI) to determine if it could be integrated into the host vibrissa-cortical pathway. Functional integration was tested 3-6 months later using the 2-deoxyglucose [44,45] (2-dg) method for estimation of glucose utilization. A variety of control grafts (cerebellum in SmI cortex, neocortex outside the host SmI cortex and appropriately placed neocortex in non-stimulated hosts) all had uniform 2-dg uptake (70 +/- 10 mumol/100 g/min) throughout each graft which averaged 42% less than non-stimulated host SmI cortex (121 +/- 6 mumol/100 g/min; p less than 0.001) but was 3-fold greater than white matter (24.8 +/- 3.1 mumol/100 g/min; p less than 0.001). In appropriately placed neocortical grafts, vibrissal stimulation produced 125% greater average 2-dg uptake (157 +/- 19 mumol/100 g/min) than control grafts (p less than 0.01). Such appropriately placed and stimulated neocortical grafts also contained focal areas of increased 2-dg uptake which were 43% greater than average graft uptake. These data suggest that fetal neocortical grafts were functionally integrated into the physiologically relevant afferent pathways of adult host brains.     

Nerve growth factor increases the size of intracortical cholinergic transplants

The effects of continuous intracortical mouse Nerve Growth Factor on fetal rat basal forebrain transplants in denervated adult rat neocortex were investigated. Enzyme-linked immunoassay (ELISA) was used to measure the time course of endogenous NGF protein production in neocortex, hippocampus, and basal forebrain in a cohort of animals receiving unilateral ibotenic acid (IBO) lesions of the nucleus basalis magnocellularis (nBM). A second cohort of IBO-nBM lesioned animals received transplants of fetal basal forebrain followed by two to four weeks of continuous NGF or cytochrome-C infusion into the ipsilateral frontoparietal neocortex. To study the effects of abnormally high NGF doses on transplanted and host tissue, the cumulative dose of intracortical NGF was on the order of micrograms, compared with maximum picogram levels of neocortical NGF produced following IBO-nBM lesions. A four-fold increase in transplant size, and greater cell and fiber densities were observed in NGF-treated compared with NGF-untreated transplants. No adverse histological effects of long-term, high-dose NGF treatment were observed on transplanted basal forebrain or host neocortical tissue. These data indicate that cholinergic-rich mammalian brain tissue and intrinsic host tissue can be stimulated by high doses exogenous NGF without obvious deleterious effects.     

Fetal neocortical grafts implanted in adult hypertensive rats with cortical infarcts following a middle cerebral artery occlusion: ingrowth of afferent fibers from the host brain.

This study is focused on the survival of fetal neocortical grafts placed in the infarcted adult host cortex of the spontaneously hypertensive rat and describes the ability of host axonal regeneration into the graft after a focal ischaemic lesion. Five to seven days following ligation of the right middle cerebral artery, dissociated neocortical primordium from fetuses of gestational age 12-18 days was implanted into the infarcted cortical area. Surviving transplants were seen in all rats, although grafts derived from gestational age 12-14 days displayed an irregular morphology rich in sinusoid-like cavities and containing fewer cells of apparently mature neuronal morphology. Grafts from older donors contained perikarya of neuronal appearance; however, they lacked normal cortical lamination. Ten days postgrafting, fibers stained by acetylcholinesterase histochemistry, dopamine-beta-hydroxylase, and 5-hydroxytryptamine immunohistochemistry were found in the grafts, and by 10-23 weeks after transplantation the fiber density had increased substantially. When the retrograde tracer Fluoro-Gold was injected into the grafted tissue, labeled cells were found in several subcortical nuclei of the host, including the nucleus basalis of Meynert, ventral pallidum, thalamus, dorsal raphe, locus coeruleus, as well as the ipsilateral and contralateral neocortex. This study shows that grafts of dissociated neocortical tissue exhibit good survival and growth potential when implanted into infarcted neocortex and that several nerve fiber systems of the adult host have a regenerative capacity sufficient to innervate the grafted tissue.     

Fetal frontal cortex transplant (14C) 2-deoxyglucose uptake and histology: survival in cavities of host rat brain motor cortex

Fetal frontal neocortex from 18-day-old rat embryonic brain was transplanted into cavities in 30-day-old host motor cortex. Sixty days after transplantation, 5 of 15 transplanted rats had surviving fetal transplants. The fetal cortex transplants were physically attached to the host brain, completely filled the original cavity, and had numerous surviving cells including pyramidal neurons. Cell lamination within the fetal transplant was abnormal. The (14C) 2-deoxyglucose uptake of all five of the fetal neocortex transplants was less than adjacent cortex and contralateral host motor-sensory cortex, but more than adjacent corpus callosum white matter. The results indicate that fetal frontal neocortex can be transplanted into damaged rat motor cortex. The metabolic rate of the transplants suggests they could be partially functional.     

Integration of neocortical embryonal grafts with the neocortex of host rats examined by Leao's spreading cortical depression

Cortical spreading depression (SD) was used to assess the density and organization of neural elements in neocortical transplants and their connectivity with the host brain. Embryonal neocortex (E14) was transplanted into cavities in the frontoparietal cortex of 3-month-old rats. SD elicited in the cortex of anesthetized host rats (n = 12) 3 to 8 months after transplantation did not penetrate into the grafts. SD could be elicited in large transplants but did not propagate to the surrounding host neocortex. Spontaneous unit activity in the transplants was affected by SD elicited in the neocortex of the host rats anesthetized with urethane. Most units (n = 49) displayed excitatory-inhibitory (52%) or inhibitory (29%) reactions, whereas purely excitatory reactions were less frequent (8%). The results suggest that the packing density of neurons in the transplant can support SD but that the conditions at the graft-host boundary (glial scar, scarcity of neurons) stop SD propagation. High reactivity of the graft neurons to SD in the host neocortex indicates that afferentation from the host brain represents an important, predominantly excitatory contribution to the spontaneous activity of the transplant.     

Topographic distribution of efferent fibers originating from homotopic or heterotopic transplants: heterotopically transplanted neurons retain some of the developmental characteristics corresponding to their site of origin

The present study was undertaken to determine whether the topographical distribution of cortical efferents is exclusively dependent on environmental cues or is also controlled by intrinsic factors. For that purpose, we used a sensitive tract tracing method (Phaseolus vulgaris leucoagglutinin) to compare the pattern of efferent fibers of homotopic and heterotopic transplants of embryonic (E16) neocortex. Our findings indicate that transplants of embryonic sensorimotor cortex placed homotopically in the sensorimotor cortex of newborn rats distribute a set of efferent projections not fundamentally different from that of normal sensorimotor cortex. The pattern of efferents arising from transplants of embryonic occipital cortex heterotopically placed in the sensorimotor cortex of newborns is strikingly different. Heterotopically transplanted neurons: (i) only rarely contact normal targets of the motor cortex; (ii) systematically project towards normal targets of the visual cortex (primary and secondary visual cortical areas, dorsal and ventral lateral geniculate nuclei, lateral dorsal and lateral posterior thalamic nuclei, anterior pretectal nucleus and superficial and intermediate layers of the superior colliculus); (iii) distribute fibers to structures normally receiving fibers from both motor and visual cortices (caudate-putamen, pontine nuclei), either exclusively into the visual cortico-recipient zone of the structure or into both visual and motor cortico-recipient zones. Taken together, these results seem to indicate that the heterotopically transplanted cells have retained certain anatomical characteristics of their locus of origin.     

Expression of c-fos mRNA and c-fos Protein in Neocortical Transplants Placed into Excitotoxin-Induced Lesions in Adult Rats

Using anatomical and electrophysiological methods, previous studies from this laboratory demonstrated that fetal neocortical block transplants placed into the excitotoxically ablated cortex of adult rats can establish functional connections with the host central nervous system. In order to further examine functional integration at the level of genomic activation/molecular signaling systems, transplants were analyzed for the presence of c-fos mRNA and Fos protein-labeled cells following a 20-min exposure of the animal to a novel open-field environment. This behavioral testing paradigm, which previously was shown to induce expression of c-fos mRNA in several brain regions including the sensorimotor cortex, was administered at 3 months after grafting. The transplants were found to express c-fos mRNA as well as c-fos protein following novelty exposure. These labeled cells were distributed primarily along the peripheral margin of the grafts. This study therefore suggests that at least some neurons within transplants become integrated with the host pathways at the level of molecular signal transduction.     

Status marmoratus in fetal cortical transplants

Adult rats received unilateral transplants of either embryonic day-17 fetal neocortex or striatum. Sixty-two percent of the fetal neocortical transplants grafted into the striatum, and 25% of these neocortical transplants placed in host neocortex had regions of hypermyelination, whereas none of the striatal transplants showed such an effect. There are similarities between these neuropathologic findings and status marmoratus in humans and animals with perinatal hypoxic injuries.     

Development of fetal retina,tectum, and cortex transplanted to the superior colliculus of adult rats

Earlier studies showed that embryonic retina, cortex, or tectum transplanted adjacent to the superior colliculus of newborn host rats differentiated many of the histological features appropriate for the donor region and developed interconnections with the host nervous system. In the study presented here, the same regions were transplanted to the brain of adult host rats and the development of these transplants was compared to those into newborn hosts. Retina, rostral tectum, or occipital cortex was dissected from donor rat embryos on gestational day 14 or 15. A portion of cortex was aspirated in 2-;menth-old host rats to expose the right superior colliculus, and one of the donor tissues was placed adjacent to the colliculus in each host. Two to 4 months after transplantation, transplant histology and neuronal interconnections between the transplant and host nervous system were studied by using Nissl and neurofibrillar stains and ³H-proline and HRP tract tracing techniques. Four main points can be drawn from these results. First, 80% of the transplants survived in adult hosts –a percentage comparable to that found in newborn hosts. Second, each of the types of tissues transplanted differentiated histological characteristics appropriate for its site of origin, although the degree of differentiation was always much less than in transplants to newborns. Third, the transplants developed only relatively local projections into the host cortex and superior colliculus. This contrasts with the extensive projections found from the transplants into the brain of newborn hosts. Fourth, no definitive projections from the host retina or brain were identified to any of the transplants into adults, whereas both cortical and tectal transplants into newborns received projections from the host.     

Neocortical transplants in the micrencephalic rat brain: Morphology and behavior

Normal fetal (E18) neocortical tissue transplanted into the hypoplastic posterior neocortex of infant (10 +/- 2-day-old) rats with transplacentally induced micrencephaly developed into very large, healthy, and permanent transplants. Although the cellular organization within the transplants rarely resembled that of normal rat neocortex, the transplants formed a broad area of interface with the host brain and established fiber connections with it. When tested at 2 months and 1-year-of-age, the presence of the transplant had no significant effect on the typically abnormal performance of micrencephalic rats on two tests of unspecific function, open field activity and maze learning. However, a small group of micrencephalic rats in whom the transplant tissue had failed to fill in the small brain lesions inescapably inflicted during surgery, showed greater behavioral deficits than the micrencephalic controls, suggesting that the transplant had corrected the lesion effect.     

Development of spinal cord projections from neocortical transplants heterotopically placed in the neocortex of newborn hosts is highly dependent on the embryonic locus of origin of the graft

Previous experiments based on heterotopic transplantation paradigms have indicated that the distribution of efferents developed by layer V pyramidal cells seems to be related to where in the neocortex the cells develop and not to where they were generated. The present study was undertaken in an attempt to obtain a quantitative estimation of the weight of extrinsic factors in the development of neocortical efferents. Fragments of embryonic (E15–E19) frontal or occipital cortex were grafted homotopically or heterotopically into the frontal or occipital cortex of newborn rats. As adults, the hosts received an injection of a retrograde tracer into the pyramidal tract decussation, and the distribution of the subsequent cell labeling was examined in each category of transplant. The mean numbers of labeled cells were 725 in frontal-to-frontal transplants and 250 in frontal-to-occipital transplants. In occipital-to-frontal transplants, the numbers of labeled cells were extremely low, ranging from 0 to 14. Finally, as expected, practically no cell labeling was found in occipital-to-occipital transplants. Thus, transplants of presumptive frontal origin systematically develop and maintain in adulthood a spinal cord projection even though they are placed in the host occipital cortex. Conversely, transplants of presumptive occipital origin are practically incapable of maintaining a spinal cord projection in adulthood even though they are placed in the host frontal cortex. It seems, therefore, that the generation of regional differences in efferent connectivity found in the mature cortex depends on early regional specification within the neocortical neuroepithelium. © 1996 Wiley-Liss, Inc.     

Chronic nicotine treatment prevents neuronal loss in neocortex resulting from nucleus basalis lesions in young adult and aged rats

In both young adult and aged rats, we tested the ability of chronically administered nicotine to rescue neocortical neurons from transneuronal degeneration resulting 5 mo after ibotenic acid (IBO) lesioning of the nucleus basalis magnocellularis (NBM). Young adult (2–3 mo-old) and aged (20–22-mo-old) rats were given unilateral infusions of IBO (5 μg/1 μL) at two sites within the NBM. Following surgery, animals began receiving either daily ip injections of nicotine (0.2 mg/kg) or saline vehicle. Treatment continued for 5 mo, at which time all animals were sacrificed and their brains processed histologically. For each brain, computer-assisted image analysis was then used to analyze the unlesioned (left) and lesioned (right) side of five nonconsecutive brain sections from parietal cortex Layers II–IV and V. NBM lesioning in both young adult and aged vehicle-treated rats resulted in a significant 16–21% neuronal loss ipsilateral to NBM lesioning in neocortical Layers II–IV. Aged NBM-lesioned rats also exhibited a significant 12% neuronal loss in neocortical Layer V ipsilaterally. By contrast, those NBM-lesioned young adult and aged rats that received daily nicotine treatment postsurgery did not show any ipsilateral neuronal loss in the same parietal cortex areas, indicating that chronic nicotine treatment prevented the transneuronal degeneration of neocortical neurons resulting 5 mo afer NBM lesioning. Nicotine treatment alone did not have any effect on neuronal density, neuronal size, or glial cell numbers in the neocortex. The neuroprotective/neurotrophic action of nicotine in the neocortex following NBM lesions may involve activation of pre- and/or postsynaptic nicotinic receptors to maintain depolarizing influences or neurotrophin synthesis, or it may involve nicotine’s ability to increase glucose utilization and cerebral blood flow.     

Biochemical and anatomical analysis of cholinergic, noradrenergic and serotonergic innervation of fetal neocortical transplants placed in excitotoxin-induced neocortical lesions of adult rats

Fetal neocortical block transplants were implanted into the excitotoxically ablated sensorimotor cortex of adult rats in order to examine the density of innervation and distribution of presumptive host derived afferent fibers within these transplants. Cholinergic fiber innervation was examined at 3 months post grafting by measuring acetylcholinesterase (AChE) and choline acetyl-transferase (ChAT) enzyme activities within the grafts and within the corresponding host cortex by radiochemical enzyme assays as well as by AChE histochemistry for the visualization of AChE positive fibers. Noradrenergic and serotonergic inputs were examined by high performance liquid chromatography (HPLC) measurements of noradrenaline (NA) and serotonin (5-hydroxytryp-tamine, 5-HT) concentrations as well as by tyrosine hydroxylase (TH) and 5-HT immunocytochemistry for the visualization of monoaminergic fiber distribution. Our results demonstrated that the grafts contained significantly lower levels of neurotransmitter markers when compared to normal unablated cortex. The anatomical analysis showed an unequal fiber distribution within the transplants. Areas adjacent to the host tissue revealed a relatively dense fiber innervation when compared to the density observed within the more central parts of the transplants, and the anatomical data therefore supported the biochemical data in suggesting an overall lower cholinergic and monoaminergic innervation of fetal neocortical transplants placed into the lesioned adult cortex when compared to normal cortex.