Promoting functional plasticity in the damaged nervous system

The Effectiveness of Paired Associative Stimulation on Motor Recovery after Stroke: A Scoping Review

Paired associative stimulation (PAS) is a non-invasive brain stimulation technique combining transcranial magnetic stimulation and peripheral nerve stimulation. PAS allows connections between cortical areas and peripheral nerves (C/P PAS) or between cortical regions (C/C PAS) to be strengthened or weakened by spike-timing-dependent neural plasticity mechanisms. Since PAS modulates both neurophysiological features and motor performance, there is growing interest in its application in neurorehabilitation. We aimed to synthesize evidence on the motor rehabilitation role of PAS in stroke patients. We performed a literature search following the PRISMA Extension for Scoping Reviews Framework. Eight studies were included: one investigated C/C PAS between the cerebellum and the affected primary motor area (M1), seven applied C/P PAS over the lesional, contralesional, or both M1. Seven studies evaluated the outcome on upper limb and one on lower limb motor recovery. Although several studies omit crucial methodological details, PAS highlighted effects mainly on corticospinal excitability, and, more rarely, an improvement in motor performance. However, most studies failed to prove a correlation between neurophysiological changes and motor improvement. Although current studies seem to suggest a role of PAS in post-stroke rehabilitation, their heterogeneity and limited number do not yet allow definitive conclusions to be drawn.

Schwann Cell-Derived Exosomes and Methylprednisolone Composite Patch for Spinal Cord Injury Repair

Spinal cord injury (SCI) can cause permanent loss of sensory and motor function, and there is no effective clinical treatment, to date. Due to the complex pathological process involved after injury, synergistic treatments are very urgently needed in clinical practice. We designed a nanofiber scaffold hyaluronic acid hydrogel patch to release both exosomes and methylprednisolone to the injured spinal cord in a non-invasive manner. This composite patch showed good biocompatibility in the stabilization of exosome morphology and toxicity to nerve cells. Meanwhile, the composite patch increased the proportion of M2-type macrophages and reduced neuronal apoptosis in an in vitro study. In vivo, the functional and electrophysiological performance of rats with SCI was significantly improved when the composite patch covered the surface of the hematoma. The composite patch inhibited the inflammatory response through macrophage polarization from M1 type to M2 type and increased the survival of neurons by inhibition neuronal of apoptosis after SCI. The therapeutic effects of this composite patch can be attributed to TLR4/NF-κB, MAPK, and Akt/mTOR pathways. Thus, the composite patch provides a medicine-exosomes dual-release system and may provide a non-invasive method for clinical treatment for individuals with SCI.

A Novel Neurorehabilitation Approach for Neural Plasticity Overstimulation and Reorganization in Patients with Neurological Disorders

Neurological disorders are those that are associated with impairments in the nervous system. These impairments affect the patient’s activities of daily living. Recently, many advanced modalities have been used in the rehabilitation field to treat various neurological impairments. However, many of these modalities are available only in clinics, and some are expensive. Most patients with neurological disorders have difficulty reaching clinics. This review was designed to establish a new neurorehabilitation approach based on the scientific way to improve patients’ functional recovery following neurological disorders in clinics or at home. The human brain is a network, an intricate, integrated system that coordinates operations among billions of units. In fact, grey matter contains most of the neuronal cell bodies. It includes the brain and the spinal cord areas involved in muscle control, sensory perception, memory, emotions, decision-making, and self-control. Consequently, patients’ functional ability results from complex interactions among various brain and spinal cord areas and neuromuscular systems. While white matter fibers connect numerous brain areas, stimulating or improving non-motor symptoms, such as motivation, cognitive, and sensory symptoms besides motor symptoms may enhance functional recovery in patients with neurological disorders. The basic principles of the current treatment approach are established based on brain connectivity. Using motor, sensory, motivation, and cognitive (MSMC) interventions during rehabilitation may promote neural plasticity and maximize functional recovery in patients with neurological disorders. Experimental studies are strongly needed to verify our theories and hypothesis.

Chronic co-implantation of ultraflexible neural electrodes and a cranial window

Significance: Electrophysiological recording and optical imaging are two prevalent neurotechnologies with complementary strengths, the combined application of which can significantly improve our capacity in deciphering neural circuits. Flexible electrode arrays can support longitudinal optical imaging in the same brain region, but their mechanical flexibility makes surgical preparation challenging. Here, we provide a step-by-step protocol by which an ultraflexible nanoelectronic thread is co-implanted with a cranial window in a single surgery to enable chronic, dual-modal measurements. Aim: The method uses 1 - μ m -thick polymer neural electrodes which conform to the site of implantation. The mechanical flexibility of the probe allows bending without breaking and enables long-lasting electrophysiological recordings of single-unit activities and concurrent, high-resolution optical imaging through the cranial window. Approach: The protocol describes methods and procedures to co-implant an ultraflexible electrode array and a glass cranial window in the mouse neocortex. The implantation strategy includes temporary attachment of flexible electrodes to a retractable tungsten-microwire insertion shuttle, craniotomy, stereotaxic insertion of the electrode array, skull fixation of the cranial window and electrode, and installation of a head plate. Results: The resultant implant allows simultaneous interrogation of brain activity both electrophysiologically and optically for several months. Importantly, a variety of optical imaging modalities, including wide-field fluorescent imaging, two-photon microscopy, and functional optical imaging, can be readily applied to the specific brain region where ultraflexible electrodes record from. Conclusions: The protocol describes a method for co-implantation of ultraflexible neural electrodes and a cranial window for chronic, multimodal measurements of brain activity in mice. Device preparation and surgical implantation are described in detail to guide the adaptation of these methods for other flexible neural implants and cranial windows.

Salamanders: The molecular basis of tissue regeneration and its relevance to human disease

Salamanders are recognized for their ability to regenerate a broad range of tissues. They have also have been used for hundreds of years for classical developmental biology studies because of their large accessible embryos. The range of tissues these animals can regenerate is fascinating, from full limbs to parts of the brain or heart, a potential that is missing in humans. Many promising research efforts are working to decipher the molecular blueprints shared across the organisms that naturally have the capacity to regenerate different tissues and organs. Salamanders are an excellent example of a vertebrate that can functionally regenerate a wide range of tissue types. In this review, we outline some of the significant insights that have been made that are aiding in understanding the cellular and molecular mechanisms of tissue regeneration in salamanders and discuss why salamanders are a worthy model in which to study regenerative biology and how this may benefit research fields like regenerative medicine to develop therapies for humans in the future.

Closing the Gap Between Mammalian and Invertebrate Peripheral Nerve Injury: Protocol for a Novel Nerve Repair

BACKGROUND

Outcomes after peripheral nerve injuries are poor despite current nerve repair techniques. Currently, there is no conclusive evidence that mammalian axons are capable of spontaneous fusion after transection. Notably, certain invertebrate species are able to auto-fuse after transection. Although mammalian axonal auto-fusion has not been observed experimentally, no mammalian study to date has demonstrated regenerating axolemmal membranes contacting intact distal segment axolemmal membranes to determine whether mammalian peripheral nerve axons have the intrinsic mechanisms necessary to auto-fuse after transection.

OBJECTIVE

This study aims to assess fusion competence between regenerating axons and intact distal segment axons by enhancing axon regeneration, delaying Wallerian degeneration, limiting the immune response, and preventing myelin obstruction.

METHODS

This study will use a rat sciatic nerve model to evaluate the effects of a novel peripheral nerve repair protocol on behavioral, electrophysiologic, and morphologic parameters. This protocol consists of a variety of preoperative, intraoperative, and postoperative interventions. Fusion will be assessed with electrophysiological conduction of action potentials across the repaired transection site. Axon-axon contact will be assessed with transmission electron microscopy. Behavioral recovery will be analyzed with the sciatic functional index. A total of 36 rats will be used for this study. The experimental group will use 24 rats and the negative control group will use 12 rats. For both the experimental and negative control groups, there will be both a behavior group and another group that will undergo electrophysiological and morphological analysis. The primary end point will be the presence or absence of action potentials across the lesion site. Secondary end points will include behavioral recovery with the sciatic functional index and morphological analysis of axon-axon contact between regenerating axons and intact distal segment axons.

RESULTS

The author is in the process of grant funding and institutional review board approval as of March 2020. The final follow-up will be completed by December 2021.

CONCLUSIONS

In this study, the efficacy of the proposed novel peripheral nerve repair protocol will be evaluated using behavioral and electrophysiologic parameters. The author believes this study will provide information regarding whether spontaneous axon fusion is possible in mammals under the proper conditions. This information could potentially be translated to clinical trials if successful to improve outcomes after peripheral nerve injury.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/18706.

Astrogliosis has Different Dynamics after Cell Transplantation and Mechanical Impact in the Rodent Model of Parkinson's Disease

Background:

Transplantation of fetal mesencephalic tissue is a well-established concept for functional reinnervation of the dopamine-depleted rat striatum. However, there is no extensive description of the glial response of the host brain following this procedure.

Aims:

The present study aimed to quantitatively and qualitatively analyse astrogliosis surrounding intrastriatal grafts and compare it to the reaction to mechanical injury with the transplantation instrument only.

Study Design:

Animal experimentation.

Methods:

The standard 6-hydroxydopamine-induced unilateral model of Parkinson’s disease was used. The experimental animals received transplantation of a single-cell suspension of E14 ventral mesencephalic tissue. Control animals (sham-transplanted) were subjected to injury by the transplantation cannula, without injection of a cell suspension. Histological analyses were carried out 7 and 28 days following the procedure by immunohistochemistry assays for tyrosine hydroxylase and glial fibrillary acidic protein. To evaluate astrogliosis, the cell density and immunopositive area were measured in distinct zones within and surrounding the grafts or the cannula tract.

Results:

Statistical analysis revealed that astrogliosis in the grafted striatum increased from day 7 to day 28, as shown by a significant change in both cell density and the immunopositive area. The cell density increased from 816.7±370.6 to 1403±272.1 cells/mm² (p<0.0001) аnd from 523±245.9 to 1164±304.8 cells/mm² (p<0.0001) in the two zones in the graft core, and from 1151±218.6 to 1485±210.6 cells/mm² (p<0.05) for the zone in the striatum immediately adjacent to the graft. The glial fibrillary acidic protein-expressing area increased from 0.3109±0.1843 to 0.7949±0.1910 (p<0.0001) and from 0.1449±0.1240 to 0.702±0.2558 (p<0.0001) for the same zones in the graft core, and from 0.5277±0.1502 to 0.6969±0.1223 (p<0.0001) for the same area adjacent to the graft zone. However, astrogliosis caused by mechanical impact only (control) did not display such dynamics. This finding suggests an influence of the grafted cells on the host’s glia, possibly through cross-talk between astrocytes and transplanted neurons.

Conclusion:

This bidirectional relationship is affected by multiple factors beyond the mechanical trauma. Elucidation of these factors might help achieve better functional outcomes after intracerebral transplantation.

Mechanisms and use of neural transplants for brain repair

Under appropriate conditions, neural tissues transplanted into the adult mammalian brain can survive, integrate, and function so as to influence the behavior of the host, opening the prospect of repairing neuronal damage, and alleviating symptoms associated with neuronal injury or neurodegenerative disease. Alternative mechanisms of action have been postulated: nonspecific effects of surgery; neurotrophic and neuroprotective influences on disease progression and host plasticity; diffuse or locally regulated pharmacological delivery of deficient neurochemicals, neurotransmitters, or neurohormones; restitution of the neuronal and glial environment necessary for proper host neuronal support and processing; promoting local and long-distance host and graft axon growth; formation of reciprocal connections and reconstruction of local circuits within the host brain; and up to full integration and reconstruction of fully functional host neuronal networks. Analysis of neural transplants in a broad range of anatomical systems and disease models, on simple and complex classes of behavioral function and information processing, have indicated that all of these alternative mechanisms are likely to contribute in different circumstances. Thus, there is not a single or typical mode of graft function; rather grafts can and do function in multiple ways, specific to each particular context. Consequently, to develop an effective cell-based therapy, multiple dimensions must be considered: the target disease pathogenesis; the neurodegenerative basis of each type of physiological dysfunction or behavioral symptom; the nature of the repair required to alleviate or remediate the functional impairments of particular clinical relevance; and identification of a suitable cell source or delivery system, along with the site and method of implantation, that can achieve the sought for repair and recovery.

In vivo stimulation of early peripheral axon regeneration by N-propionylmannosamine in the presence of polysialyltransferase ST8SIA2

The key enzyme of sialic acid (Sia) biosynthesis is the bifunctional UDP-N-acetylglucosamine 2-epimerase/ManNAc kinase (GNE/MNK). It metabolizes the physiological precursor ManNAc and N-acyl modified analogues such as N-propionylmannosamine (ManNProp) to the respective modified sialic acid. Polysialic acid (polySia) is a crucial compound for several functions in the nervous system and is synthesized by the polysialyltransferases ST8SIA2 and ST8SIA4. PolySia can be modified in vitro and in vivo by metabolic glycoengineering of the N-acyl side chain of Sia. In vitro studies show that the application of ManNProp increases neurite outgrowth and accelerates the re-establishment of functional synapses. In this study, we investigate in vivo how ManNProp application might benefit peripheral nerve regeneration. In mice expressing axonal fluorescent proteins (thy-1-YFP), we transected the sciatic nerve and then replaced part of it with a sciatic nerve graft from non-expressing mice (wild-type mice or St8sia2(-/-) mice). Analyses conducted 5 days after grafting showed that systemic application of ManNProp (200 mg/kg, twice a day, i.p.), but not of physiological ManNAc (1 g/kg, twice a day, i.p.), significantly increased the extent of axonal elongation, the number of arborizing axons and the number of branches per regenerating axon within the grafts from wild-type mice, but not in those from St8sia2(-/-) mice. The results demonstrate that the application of ManNProp has beneficial effects on early peripheral nerve regeneration and indicate that the stimulation of axon growth depends on ST8SIA2 activity in the nerve graft.

Chapter 55: neural transplantation

The history of cell transplantation in the nervous system is reviewed in four main sections. The "early era" spans the period from 1890 to 1940, during which the first attempts at cell transplantation in the brain were undertaken. Many contemporary themes were first addressed such as surgical factors to achieve survival of grafted cells and how that should be assessed, immunological factors, use of tumors as a readily viable cell source; and use of the anterior eye chamber as a model transplantation site. However, such studies generally exhibited only low levels of viability or successful implantation. The "middle era" from 1940 to 1970 spans the period when the techniques for viable and reliable cell transplantation using embryonic donor tissues implanted into sites with effective vascularization were first established in brain and neuroendocrine systems in a limited number of specialist centers. However, although sometimes impressive, these results were at variance with the prevailing view that the adult mammalian brain is immutable and resistant to plasticity, growth or regeneration, and were largely ignored. The "modern era," since 1970, began with the pioneering studies that combined cell transplantation with the use of improved histochemical and ultrastructural anatomical techniques to demonstrate selectivity, specificity and regenerative capacity of implanted cells, and the slow acceptance that the adult brain does exhibit considerable potential for plasticity and repair. The last three decades have witnessed the identification of reliable and efficient transplantation technologies combined with progressively refined methods of molecular, cellular, biochemical, physiological and functional analysis. This now enables the ready use of cell transplantation as a powerful novel method within the neuroscience tool-kit, which is being used: to analyze normal organization and function of the nervous system; to reveal the biological mechanisms and principles of neuronal development, regeneration and plasticity; and to study the principles of surgically directed cell therapies for promoting plasticity, replacement and repair in response to injury and disease. The final section reviews recent progress in translating cell transplantation to the clinic for application in Parkinson's and other central nervous system diseases.

Neural Transplantation in Animal Models of Dementia

Neural transplantation provides a powerful novel technique for investigating the neurobiological basis and potential strategies for repair of a variety of neurodegenerative conditions. The present review considers applications of this technique to dementia. After a general introduction (section 1), attempts to replace damaged neural systems by transplantation are considered in the context of distinct animal models of dementia. These include grafting into aged animals (section 2), into animals with neurotransmitter-selective lesions of subcortical nuclei, in particular involving basal forebrain cholinergic systems (section 3), and into animals with non-specific lesions of neocortical and hippocampal systems (section 4). The next section considers the alternative use of grafts as a source of growth/trophic factors to inhibit degeneration and promote regeneration in the aged brain (section 5). Finally, a number of recent studies have employed transplanted tissues to model and study the neurodegenerative processes associated with ageing and Alzheimer's disease taking place within the transplant itself (section 6). It is concluded (section 7) that although neural transplantation does not offer any immediate prospect of therapeutic repair in clinical dementia, the technique does offer a powerful neurobiological tool for studying the neuropathological processes involved in both spontaneous degeneration and specific diseases of ageing. New understandings derived from neural transplantation may be expected to lead to rational development of novel strategies to inhibit the neurodegenerative process and to promote regeneration in the aged brain.

Temperature and time interval for culture of postmortem neurons from adult rat cortex

For a model of neurological disease and ischemia, we extended recent work to culture adult postmortem rat brain neurons. Frontal cortex sections were removed from adult rats immediately following sacrifice and at different postmortem intervals and with the brain at either 22 degrees C or 4 degrees C. Brain could be stored four times longer at 4 degrees C between sacrifice and neuronal disaggregation to achieve the same 20% recovery of live cells from those plated compared to 22 degrees C. Each milligram of rat frontal cortex was estimated by the optical disector method to contain 160,000 neurons. When cells were isolated as rapidly as possible, 9% of the neurons originally present in the brain were viable. Various postmortem intervals from 2 to 24 hr resulted in a reduction from 6% to 3% of the cells originally present. After 5 days in culture, viable neurons were 23-42% of those isolated. Neuron-like cells that survived represented 40-75% of the viable cells, or 0.5-2.75% of those originally estimated to be present in the brain. Electrophysiology experiments show that cells isolated 0 and 24 hr postmortem had neuronal electrical properties, including an average resting membrane potential of -48 mV, voltage-sensitive currents, and action potentials. Neuron-like cells were immunoreactive for neuron-specific enolase, neurofilament 200, glutamate, MAP2, and tau after 2 weeks in culture. These experiments show that neuron-like cells can be reliably cultured from adult rat cortex up to 6 hr postmortem when stored at 22 degrees C and up to 24 hr postmortem when stored at 4 degrees C. These findings should encourage donation of human postmortem brain neurons for studies on ischemia, adult pharmacology, and neurological disease.

Effects of short- and long-term Schwann cell denervation on peripheral nerve regeneration, myelination, and size

Poor functional recovery after peripheral nerve injury has been generally attributed to inability of denervated muscles to accept reinnervation and recover from denervation atrophy. However, deterioration of the Schwann cell environment may play a more vital role. This study was undertaken to evaluate the effects of chronic denervation on the capacity of Schwann cells in the distal nerve stump to support axonal regeneration and to remyelinate regenerated axons. We used a delayed cross-suture anastomosis technique in which the common peroneal (CP) nerve in the rat was denervated for 0-24 weeks before cross-suture of the freshly axotomized tibial (TIB) and chronically denervated CP nerve stumps. Motor neurons were backlabeled with either fluoro-ruby or fluorogold 12 months later, to identify and count TIB motor neurons that regenerated axons into chronically denervated CP nerve stumps. Number, size, and myelination of regenerated sensory and motor axons were determined using light and electron microscopy. We found that short-term denervation of < or =4 weeks did not affect axonal regeneration but more prolonged denervation profoundly reduced the numbers of backlabeled motor neurons and axons in the distal nerve stump. Yet, atrophic Schwann cells retained their capacity to remyelinate regenerated axons. In fact, the axons were larger and well myelinated by long-term chronically denervated Schwann cells. These findings demonstrate a progressive inability of chronically denervated Schwann cells to support axonal regeneration and yet a sustained capacity to remyelinate the axons which do regenerate. Thus, axonal interaction can effectively switch the nonmyelinating phenotype of atrophic Schwann cells back into the myelinating phenotype.

Regeneration of a central synapse restores nonassociative learning

Sensitization is a form of nonassociative learning in which a strong or noxious stimulus persistently enhances the response produced by a weaker stimulus. In the leech Hirudo medicinalis, the S-interneuron is required for sensitization of the shortening response. A single S-cell axon was surgically separated from its sole synaptic partner, the neighboring S-cell. This consistently eliminated sensitization without impairing reflexive shortening itself, as measured in semi-intact specimens. Sensitization of the shortening reflex returned after 3 weeks when the severed axon grew and regenerated its specific electrical synapse within the nerve cord, as shown by restored conduction of impulses between S-cells. This confirms the essential role of one neuron, the S-cell, in sensitization, and it demonstrates that regeneration of the synapse between S-cells restores this example of nonassociative learning.

Culture of neurons from postmortem rat brain

Live neurons from pathological postmortem brains may provide a better model to study the molecular and cellular events associated with neurodegenerative disease. The aim of this study was to culture neurons from adult rat brain, 1 and 2 h postmortem, in typical normothermic autopsy conditions. We reliably cultured cells up to 2 h postmortem, in high yield, with neuron morphology, staining for neuronal markers (microtubule-associated protein 2, tau, and neurofilament 200). These neuron-like cells lacked glial marker staining (OX42 and glial fibrillary acidic protein). Our results suggest that neurons may be cultured from autopsy donors who have died either with or without a neurodegenerative disease such as Alzheimer or Parkinson disease.

Growth of dorsal spinocerebellar axons through a lesion of their spinal pathway during early development in the North American opossum, Didelphis virginiana

Supraspinal axons grow around or through lesions of their spinal pathway during specific critical periods of mammalian development, but comparable plasticity has not been documented for axons which form ascending tracts. In the present study, we asked whether axons of the dorsal spinocerebellar tract (DSCT) are capable of such growth. The spinal cord of the North American opossum, Didelphis virginiana, was hemisected at mid-thoracic levels between postnatal day (PD) 5 and 68 and after varying survival times, bilateral injections of Fluoro-Gold or Fast Blue were made into the anterior lobe of the cerebellum, the major target of DSCT axons. Seven days later, the pups were sacrificed and their spinal cord processed for fluorescence microscopy. In animals lesioned between PD5 and 9, and allowed to survive for 37-269 days, neurons were labeled bilaterally in Clarke's nucleus (CN) caudal to the lesion, but they were fewest in number and smallest in size on the lesioned side. Since the DSCT originates almost entirely within CN on the ipsilateral side, we conclude that the neurons labeled ipsilateral and caudal to the lesion supported axons which grew around or through it. Histological examination revealed that recognizable spinal cord was present at the lesion site and that labeled spinocerebellar axons were located in their normal position ipsilateral to the lesion. It appears, therefore, that growth occurred through the lesion. In animals lesioned between PD13 and 68, labeled neurons were not found in CN caudal and ipsilateral to the lesion although they were present on the contralateral (control) side. We conclude that DSCT axons, like axons which form descending tracts, grow through a lesion of their spinal pathway if it is made early in development.

The effects of raphe grafts on hippocampal electrophysiology in aged rats

In previous studies we have demonstrated that raphe grafts, implanted into serotonin-depleted rat hippocampus can restore behavioral and physiological functions impaired by serotonin depletion. Since aging is associated with a reduction in serotonergic functions, we explored the possibility that grafting embryonic raphe tissue will ameliorate age-associated reduction of serotonergic functions in the hippocampus. Aged rats were implanted with E14 embryonic neural tissue, containing the raphe, or part of the parietal cerebral cortex. Three months later, the rats were anesthetized, and the responses of the dentate gyrus to perforant-path stimulation were measured. Serotonin-containing neurons were found in the raphe-grafted hippocampi. No differences were found between the two groups in the volume of the graft in the host brain. Raphe-grafted rats were not different from the cortex-grafted rats in reactivity to perforant path stimulation or in the response to a second of a pair of stimuli to the perforant path. They did, however, express a pronounced commissural inhibition, unlike the cortex-grafted rats. These results are similar to those found previously with a pharmacological enhancement of serotonergic neurotransmission. It is suggested that a graft of serotonergic neurons can ameliorate age-associated reduction in serotonergic functions in the hippocampus.

Models of delayed recovery

After a biologic insult has impaired function of the developing central nervous system, recovery may not become apparent for years. Probability models adopted from the carcinogenesis, developmental neurobiology, learning decay, and stochastic process literatures are presented so that assumptions about apparent delays in the recovery process can be tested with data from longitudinal studies after a temporally circumscribed adverse event/exposure. This process of evaluating multiple models is exemplified with one data set. Nonlinear models of recovery are important because some children with early deficits first show improvement months to years later.

Concurrent immediate early gene induction by epileptic seizures in heterotopic cortical grafts and neocortex

Cortical primordia of rat fetuses (gestation day 14) were stereotactically grafted into the rostral striatum of adult recipient rats. After 8 weeks, the transplants had developed into a highly differentiated population of mature neuroectodermal cells. Host rats were then subjected to 15 min of bicuculline-induced epileptic seizures or served as controls. Seizure-elicited immediate early gene (IEG) expression was investigated after various postictal survival times (up to 24 h), using immunocytochemistry with specific antisera against seven IEG encoded proteins (c-FOS, FOS B, c-JUN, JUN B, JUN D, KROX-24, KROX-20). Constitutive IEG expression in intra striatum grafted neocortical neurons was identical to that in the corresponding host neocortex. In particular, abundant KROX-24 and lack of c-JUN expression implies the establishment of synaptic contacts within the graft or with the host circuitry. Postictal expression kinetics of individual IEG encoded proteins within the transplants were strikingly similar to those seen in the neocortex in situ. c-FOS and KROX-24 were most rapidly induced, followed by c-JUN and JUN B, and a more delayed induction of FOS B, JUN D and KROX-20. Apart from a slightly prolonged c-FOS expression in grafts, individual transcription factors remained elevated for different time periods and showed a concurrent decline in transplants and in neocortex in situ. In conclusion, IEG induction in grafts closely paralleled that in the host neocortex but differed from the adjacent striatum which exhibited no c-JUN induction at any time point investigated. These results indicate that following an appropriate differentiation period, heterotopically grafted embryonic cortical neurons respond to extracellular stimuli with changes of gene expression that closely resemble the normal host cortex. This suggests development of a similar molecular phenotype, including proper acquisition and intracellular processing of information.

Differential recovery of inhibitory avoidance learning by striatal, cortical, and mesencephalic fetal grafts

Four groups of male Wistar rats showing disrupted inhibitory avoidance conditioning due to striatal lesions were studied. Three groups received striatal, cortical, or ventral mesencephalic brain grafts and the fourth group remained as a lesioned control. Sixty days postgraft the animals were retrained in an inhibitory avoidance task. The striatal-grafted animals were the only group that significantly improved in the ability to acquire the inhibitory avoidance task. Acetylcholinesterase histochemistry revealed positive patches of cells in the striatal grafts. Cortical grafts showed less reactivity, without patches. Immunocytochemical analyses for tyrosine hydroxylase revealed positive cell reactivity in the mesencephalic grafts and few positive fibers were detected in the border between the striatal grafts and the host tissue. These results demonstrate that striatal but not cortical or mesencephalic brain grafts can promote the restoration of the ability to acquire an inhibitory avoidance task and suggest that the acetylcholine tissue content is involved in the behavioral recovery.

Effects of fetal forebrain transplants in ibotenic-injured nucleus basalis: an anatomical investigation

Survival of fetal basal forebrain transplant (TP) into ibotenic-injured nucleus basalis of rats was examined after a delay lesion and TP (1 or 2 weeks) and a delay between harvest and TP (1-4.5 hours). Optimal TP survival occurred for TP made 2 weeks postlesion and less than 2 hours after harvesting. In these cases large, healthy TP-neurons displayed robust cytochrome oxidase (CO) activity and sent cholinergic processes throughout the TP and occasionally into host tissue. A mild astrocytic reaction was observed within the TP and at the host-TP interface. Surviving TPs increased choline acetyltransferase innervation and CO activity within the ipsilateral frontoparietal cortex. Therefore data suggest that fetal cholinergic TPs into the damaged NBM reduced neuronal degeneration within the NBM and stimulated remaining neurons spared by the lesion.

Pathological left-handedness and preserved function associated with a slowly evolving brain tumor

The authors report the serial neuropsychological evaluations of a patient with acquired left-handedness who had a massive brain tumor that infiltrated the entire temporal and posterior parietal lobes of the left hemisphere. Although the patient had pre-operative impairment of non-verbal memory, follow-up assessment 31 and 66 months after the tumor was resected revealed cognitive functions to be in the high-average to superior range. This case demonstrates the sparing of neuropsychological functions that can be seen with a slowly evolving lesion. The authors suggest that such functional sparing may be due to transfer of function rather than to the residual function of tumor-infiltrated neuronal tissue. Possible mediators of functional preservation include slow lesion growth, the patient's youth at disease onset and the large size of the lesion.

Dopamine release and dopaminergic inhibition of acetylcholine release in rat striatal slices after nigro-striatal hemitransection and parenteral ganglioside administration

Hemitransection of the nigro-striatal bundle in adult rats reduced [3H]dopamine ([3H]DA) uptake into striatal slices from the lesioned side to about 20% of that in the contralateral side 5 days after surgery. Spontaneous recovery of [3H]DA uptake was observed at days 8 and 15 post-lesion (42 and 67% of the unoperated side, respectively). After a short treatment (3 days) with the GM1 ganglioside inner ester (AGF2, 30 mg/kg i.p., daily, starting on day 2 after surgery) [3H]DA uptake amounted to 52% of that in the unoperated side. The electrically evoked fractional overflow of [3H]DA was increased by 500% in slices prepared from the lesioned side 5 days after injury, largely due to the reduced re-uptake by the DA axon terminals. The increase on day 5 was only about 350% in AGF2-treated animals. The DA D2 receptor antagonist, (-)-sulpiride, potentiated the stimulus-evoked overflow of [14C]acetylcholine in slices from the unoperated side prelabelled with [14C]choline. The effect of (-)-sulpiride was much reduced (by about 80%) in the lesioned striata at days 5 and 8 after surgery. Partial recovery was seen at day 15. The lesion did not modify the (-)-sulpiride effect in animals treated with AGF2 from the 2nd to the 5th day post-lesion. Thus early ganglioside administration slows the loss of endogenous dopaminergic control of acetylcholine release caused by partial hemitransection of the nigro-striatal bundle.

Restoration of serotonergic innervation underlies the behavioral effects of raphe grafts

It has been previously demonstrated that an embryonic raphe grafted into a serotonin-depleted hippocampus restores normal serotonin innervation of the hippocampus and behaviors associated with serotonin. To test the possibility that the behavioral effects of these grafts result from non-specific actions of the grafted tissue or the grafting procedure itself, we compared raphe grafts with septal grafts, in serotonin-depleted rats. We also compared the effects of a serotonin synthesis inhibitor, p-chlorophenylalanine, on the behavior of normal, serotonin-depleted and raphe-grafted rats. The results indicate that the bulk of behavioral effects of raphe grafts are due to the serotonergic nature of the graft.

Sparing and recovery of function in spinal larval frogs (Rana catesbeiana): effect of level of transection

Bullfrog tadpoles with cervical or midthoracic transection of the spinal cord were allowed to recover for 5 weeks, at which time axonal growth across the transection site was assessed by transport of horseradish peroxidase. Weekly behavioral tests included those for posture, spontaneous locomotion, cutaneously elicited swimming, and intersegmental coordination. Behavioral and electrophysiological assessments suggest that behavioral recovery depends, at least in part, on the growth of fibers across the transection site. Anatomical and behavioral recovery does not appear to differ with the level of spinal transection, but there was greater sparing of posture, spontaneous locomotion, and stimulus-induced locomotion in tadpoles with thoracic transection of the spinal cords.

Immature type-1 astrocytes suppress glial scar formation, are motile and interact with blood vessels

Previous studies have shown that immature but not mature astrocytes have the capacity to suppress glial scar formation and enhance axon outgrowth when transplanted into the adult mouse brain. We report here that glial scar formation is suppressed following transplantation of purified immature but not mature cultured type-1 rat cortical astrocytes into the adult rat brain. To examine the fate of transplanted cells, cultured astrocytes were labeled with either fluorescent beads or BSA-conjugated colloidal gold and traced after transplantation using both light and electron microscopy. While both immature and mature astrocytes survived transplantation, mature astrocytes appeared more susceptible to phagocytosis by cells of the immune system than immature astrocytes. Furthermore, while mature astrocytes were restricted to the region of the implant, immature astrocytes migrated into the surrounding CNS and became closely associated with host blood vessels. Such blood vessels were impermeable to the diffusion of systematically applied Evans blue dye. To determine whether immature astrocytes were intrinsically more motile than mature astrocytes, their rate of translocation was compared in vitro. Immature astrocytes translocated more than twice as fast as mature astrocytes. This ability of immature astrocytes to translocate throughout the host CNS and become associated with blood vessels may be a major factor in their ability to suppress glial scar formation in the adult animal.

Sprouting of peripherally regenerating primary sensory neurones in the adult central nervous system

We have studied the ability of primary afferent neurones to proliferate within the grey matter of the dorsal horn following the degeneration of other, nearby, afferent fibres. The peripheral branches of primary afferents have the capacity to regenerate successfully over long distances, and we have examined the possibility that when they are so doing, the neurones' status changes to facilitate greatly the sprouting of afferent fibres within the dorsal horn. "Spared root" preparations (rhizotomies of L3, L4, L6, S1, and the caudal half of L5, sparing the rostral half of the L5 dorsal root) were made in adult rats. In some animals (acute preparations) the distribution of the central terminals of the spared root was assessed by labelling the sciatic nerve with WGA-HRP at the time of the rhizotomies. In other animals (chronic preparations), symmetrical bilateral spared roots were made and the sciatic nerve on one side was concomitantly crushed to trigger regrowth of the peripheral branches of these axons. Eight to 10 weeks later the sciatic nerves on both sides were labelled with HRP-WGA. In the acute preparations the reaction product was found in a limited rostrocaudal and mediolateral region of the dorsal horn. In lamina II (the lamina of densest labelling) the labelled terminals occupied an average of 1.17 +/- 0.21 mm2. In chronic preparations, the area of labelled terminals on the side of the uncrushed sciatic nerve was 1.34 +/- 0.28 mm2 (not significantly different from acute animals). However, the labelled area on the side of the crushed sciatic nerve was significantly greater, averaging 2.17 +/- 0.14 mm2.(ABSTRACT TRUNCATED AT 250 WORDS)

Is it possible to repair the damaged prefrontal cortex by neural tissue transplantation?

The techniques are now well established for the viable transplantation of cortical and other neural tissues into the neonatal and adult cortex, at least in the laboratory rat. Under appropriate conditions such grafts survive well and can establish reciprocal connections with the host brain. On this basis, neural transplantation has become a powerful technique for the study of mechanisms involved in the development of the central nervous system and its capacity for regeneration after injury. Moreover, a variety of anatomical, electrophysiological and behavioural techniques suggest that grafted neural tissue may sustain functional interactions with the host brain. However, the extent and duration of recovery using present techniques is extremely limited. It remains undetermined whether such experimental observations may ever acquire therapeutic application.

Effects of intraventricular substantia nigra allografts as a function of donor age

Transplantation of fetal substantia nigra into the brain can alleviate some of the manifestations of animal models of Parkinson's disease. The purpose of the present experiment was to determine the optimal embryonic donor age for solid tissue substantia nigra grafts. Rats with unilateral substantia nigra lesions were tested for rotational behavior in response to apomorphine. Animals then received intraventricular grafts of ventral mesencephalon from fetal donors of 11, 13, 15, 17, or 19 days gestational age, and were tested for rotational behavior 6 and 12 weeks after transplantation. After 12 weeks, animals receiving grafts from donors of 11 through 17 days gestation showed similar decreases (means = 42-58%) in rotation. All 4 groups showed greater decreases in rotation than the 19 day group (17%). In both the 11 and 13 day groups, however, there were substantial decreases in rotational behavior from the 6th to the 12th week testing periods. This study confirms that during a critical period of rat fetal development, between 17 and 19 days gestational age, the substantia nigra loses much of its ability to produce functional effects after transplantation. Grafts from very immature donors did not, however, produce markedly greater effects, and the youngest grafts required more time for the development of maximal effects.

Anatomical and functional recovery following spinal cord transection in the chick embryo

Following complete transection of the thoracic spinal cord at various times during embryonic development, chick embryos and posthatched animals exhibited various degrees of anatomical and functional recovery depending upon the age of injury. Transection on embryonic day 2 (E2), when neurogenesis is still occurring and before descending or ascending fiber tracts have formed, produced no noticeable behavioral or anatomical deficits. Embryos hatched on their own and were behaviorally indistinguishable from control hatchlings. Similar results were found following transection on E5, an age when neurogenesis is complete and when ascending and descending fiber tracts have begun to project through the thoracic region. Within 48 h following injury on E5, large numbers of nerve fibers were observed growing across the site of transection. By E8, injections of horse-radish peroxidase (HRP) administered caudal to the lesion, retrogradely labelled rostral spinal and brainstem neurons. Embryos transected on E5 were able to hatch and could stand and locomote posthatching in a manner that was indistinguishable from controls. Following spinal cord transections on E10, anatomical recovery of the spinal cord at the site of injury was not quite as complete as after E5 transection. Nonetheless, anatomical continuity was restored at the site of injury, axons projected across this region, and rostral spinal and brainstem neurons could be retrogradely labelled following HRP injections administered caudal to the lesion. At least part of this anatomical recovery may be mediated by the regeneration or regrowth of lesioned axons. Although none of the embryos transected on E10 that survived to hatching were able to hatch on their own, because several sham-operated embryos were also unable to hatch, we do not attribute this deficit to the spinal transection. When E10-transected embryos were aided in escaping from the shell, they were able to support their own weight, could stand, and locomote, and were generally comparable, behaviorally, to control hatchlings. Repair of the spinal cord following transection on E15 was considerably less complete compared to embryos transected on E2, E5, or E10. However, in some cases, a degree of anatomical continuity was eventually restored and a few spinal neurons rostral to the lesion could be retrogradely labelled with HRP. By contrast, labelled brainstem neurons were never observed following E15 transection. E15 transected embryos were never able to hatch on their own, and when aided in escaping from the shell, the hatchlings were never able to stand, support their own weight or locomote.(ABSTRACT TRUNCATED AT 400 WORDS)

Theories on the promotion of CNS transplant integration by selective activation of presynaptic enzyme cascades: prospects for future clinical applications

It is hypothesized that multiple parallel presynaptic enzyme cascades act concertedly to regulate synaptic plasticity. These enzyme cascades include phospholipases A2 and C, protein kinase C, calcium/calmodulin and cAMP-dependent protein kinases and adenylate cyclase. New putative neurotrophic agents are postulated based on their ability to activate these enzymes. The artificial induction and amplification of multiple presynaptic enzymes in the fetal graft-mature host CNS tissue complex should maximally augment axon growth and synaptogenesis. In turn this would lead to enhanced transplant integration and hence maximal functional neurologic restoration. These enzyme cascades could be stimulated in-vivo by the intraventricular infusion of receptor-specific and/or lipophilic neurotrophic agents as well as by the application of external electric fields. A theoretical construct is formulated for developing future grafting experimentation with the hope of ultimately applying these concepts to the amelioration of human neurodegenerative diseases.

Maturation of astrocytes in vitro alters the extent and molecular basis of neurite outgrowth

In the developing mammalian central nervous system astrocytes have been proposed as an important substrate for axon growth. In the adult central nervous system following injury, astrocytes are a major component of the gliotic response which has been proposed to block axon growth. Experimental transplantation studies using cultured astrocytes have suggested that immature but not mature cultured astrocytes have the capacity to support axon outgrowth when transplanted into the adult rodent CNS. These observations suggest that astrocyte maturation is accompanied by changes in the functional capacity of these cells to support axon outgrowth. To determine whether this functional change reflects an intrisic astrocyte property, the extent and molecular bases of neurite outgrowth from embryonic rat cortical and chick retinal neurons on cultures of purified immature and mature astrocytes have been compared in vitro. The rate and extent of neurite outgrowth from both neuronal populations are consistently greater over the surface of immature than over the surface of mature astrocytes. Furthermore, antibodies to NCAM and G4/L1 significantly reduce neurite outgrowth on immature but not mature astrocytes, while antibodies to the integrin B1 receptor reduced outgrowth on both immature and, to a lesser extent, mature astrocytes. These results suggest that in vitro mature astrocytes have a reduced capacity and different molecular bases for supporting neurite outgrowth compared to immature astrocytes and are consistent with the proposal that functional changes during astrocyte maturation may partially contribute to regulating axon growth in the mammalian CNS.

Attenuation of nucleus basalis of Meynert lesion-induced cholinergic deficits by nerve growth factor

Nerve growth factor (NGF) was administered into either the lateral ventricle or into the basal forebrain of n. basalis of Meynert (nbM) lesioned rats. Rats received either continuous infusion of 5 micrograms of 7S NGF per day for 28 days, or 5 micrograms of 7S NGF on 4 occasions distributed evenly during the first two post-lesion weeks. The administration of NGF reduced lesion-induced cortical cholinergic marker deficits by approximately 50%, irrespective of the locus or mode of NGF administration. Thus NGF is able to attenuate lesion-induced cholinergic deficits across a range of treatment and lesion conditions.

Transplantation of B16/C3 melanoma cells into the brains of rats and mice

The B16/C3 mouse melanoma cell line produces L-DOPA, catecholamines and melanin in tissue culture. Growth and development of these cells after transplantation into the rat and mouse brain were studied by immunocytochemical and histological techniques. The implanted cells were localized by prelabelling the cell nuclei with bisbenzimide, a fluorescent marker which binds to DNA. Following transplantation into rats, B16/C3 melanoma cells were found to survive for at least 4-6 weeks. These cells initially expressed tyrosinase and tyrosine hydroxylase immunoreactivity and in some cases contained catecholamines. After 3 weeks, the cytoplasm of the transplanted cells began to accumulate melanin; catecholamines and tyrosinase immunoreactivity were no longer detected. Ultimately the cells became round in shape and densely pigmented. Growth of the tumor in the rats was restricted and the implant was encapsulated within a glial sheath. There was evidence of an immune reaction to the tumor in that cells with Ia antigen immunoreactivity were present surrounding the graft. The rat hosts were not adversely affected by the presence of the tumor, nor did the tumor cell grafts alter rotational behavior consequent to unilateral substantia nigra lesions. In mouse hosts, however, the melanoma grew rapidly, was not encapsulated by glia and led to death of all animals. These data suggest that the tumor was not rapidly destroyed in rats, even though its growth was controlled through immunological mechanisms. Both trophic and immunological mechanisms may therefore be involved in the regulation of survival and differentiation of intracerebral grafts of tumor cells.

Neurite extension on dibutyryl cyclic AMP-stimulated astrocytes

Although both central and peripheral neurons successfully regenerate cut axons along peripheral nerve and other suitable substrates, axonal elongation through the mature central nervous system (CNS) is limited. It has been proposed that the presence of reactive astrocytes formed in response to CNS injury act as a barrier to axonal regeneration. In contrast, in vitro, astrocytes in a flat or unstimulated state have been shown to be a preferred substrate for neurite extension. We have investigated whether induced modifications of astrocytes alter the capacity of these cells to act as a substrate for axonal elongation. Treatment with dibutyryl cyclic AMP (dBcAMP) results in a marked morphological and biochemical change in astrocytes, considered by some to be a model of reactive astrocytosis. Retinal and dorsal root ganglia explants from embryonic mice were cultured on top of untreated glial monolayers and those treated with dBcAMP. The subsequent neuritic growth was measured at 48 h. No difference was found between the groups, indicating that astrocytes are an excellent substrate for axonal growth, even after they develop a stellate shape and high levels of glial fibrillary acidic protein.

Studies of the early stages of optic axon regeneration in the goldfish

We have studied the early stages (4-14 days) of axonal regeneration following intraorbital optic nerve crush in the goldfish. We used 3H-proline autoradiography to anterogradely label and visualize the growing axons and wheat germ agglutinin-conjugated horseradish peroxidase (WGA:HRP) for retrograde labeling to determine the cells of origin of the earliest projections. The first retinal ganglion cells (RGCs) that could be retrogradely filled from the optic tract, following optic nerve crush, were in the central retina and were seen at 8 days postoperative. More peripheral cells were only labeled with longer postcrush survival periods. Thus, the first axons to regenerate past the lesion were from central RGCs. The axons of these cells extended into the cranial nerve stump between 4 and 5 days postcrush and entered the nerve as a fascicle, which travelled just beneath its surface. Studies of nerve cross sections from animals at 5-8 days postoperative demonstrated that initial outgrowth was not confined to any particular locale within the nerve although the early fibers appeared to avoid its temporal aspect. When the regenerating axons reached the optic tract they remained in fascicles but left the surface to run along the medial, deep portion of the tract, immediately adjacent to the diencephalon and pretectum. The positions occupied by the earliest-regenerating axons in the optic nerve were variable and not always appropriate for their central retinal origin. However, the abrupt change in growth trajectory as the fibers entered the optic tract brought them into the areas of the visual paths that are occupied by central axons in intact animals. We suggest that this change in position is related to both changes in the structural organization of the intracranial visual paths and to possible axon guidance signals in the region of the nerve-tract juncture.

Topographical distribution in the adult rat brain of neurotrophic activities directed to central nervous system targets

Cortex, hippocampus, septum and striatum of day 18 rat embryos were grafted to several brain regions of young adult rats which had been lesioned in the chosen area 4 days earlier. Thirty days after transplantation, the grafts were fixed and morphometrically analysed under light microscope. The volumes, neuronal densities and total number of neurons of the transplants were compared. Each graft survived best when transplanted to its original region. Good survival was also achieved by heterotopic grafts between regions that are anatomically related. Striatal grafts showed reasonable survival only when transplanted to their original site. In a second series of experiences, the neurons from the same embryonic brain regions were cultured in a defined medium, to which was added tissue extracts from the lesioned regions of the adult brain. The neuronal survival was estimated. The in vitro results are closely related to those obtained in vivo. This experimental evidence agrees with the theory of the existence of a retrograde transport of NGF from the hippocampus to the septum, sustaining the survival of the latter. On the other hand, our results demonstrate the existence of other unidentified neurotrophic factors in the central nervous system which differ from one region to another.

A new in vivo model to study the influence of the microenvironment in the regeneration of the central nervous system

In order to study the 'in vivo' regenerative capacity of the central nervous system, a semipermeable tube was placed in the axis of the lesioned nigrostriatal pathway of adult rats. In spite of a correct positioning of the tube, no growing central nervous processes were observed within the tube after 3 to 6 weeks when it was left empty. However, when the lumen of the tube was previously filled with a pre-degenerated sciatic nerve, unmyelinated and myelinated fibers were observed growing in the peripheral graft. Since the content of the tube can be modified, it appears that this model can be used to test the capability of cellular or acellular microenvironments to promote the 'in vivo' regeneration of the mammalian central nervous system fibers.

Fetal tectal or cortical tissue transplanted into brachial lesion cavities in rats: influence on the regrowth of host retinal axons

Fetal neural tissue was transplanted into suction lesions of the left brachium and pretectal region in young rats. Tectal tissue was grafted into 6-18-day-old rats and cortical tissue was transplanted into 17-20-day-old animals. The aim was to determine whether grafts could potentiate the regrowth of damaged retinal axons and, as a consequence, stimulate the axons to reenter their host target, the superior colliculus (SC). Fifteen to 581 days after transplantation, host retinal projections were traced by injecting the right eye with horseradish peroxidase (HRP). Parallel series of frozen brain sections were stained for HRP histochemistry, acetylcholinesterase, Nissl, or neurofibrils. At all ages studied, grafts survived and grew within the wound cavity; survival was better in the older animals. Most cortical grafts and a small number of tectal grafts filled the wound cavity and formed complete tissue bridges across the lesion. The majority of tectal grafts were attached to one or the other side of the lesion and were connected to the opposite lesion face by glial and connective tissue membranes that formed over the lesion site. In many animals that received tectal transplants, host retinal axons were traced growing into the grafts. Regenerating axons innervated specific, localized areas within the grafts, and it appeared that the axons retained the ability to recognize their appropriate target cells within the graft neuropil. Comparable ingrowth into cortical grafts was not observed. Optic axons were occasionally seen reentering the superficial layers of the host SC; however, compared to fetal tectal grafts, the density of host SC innervation was sparse. The implications of these data are discussed with regard to the possible use of fetal neural tissue grafts as reconstructive tissue bridges in the mammalian central nervous system.

Identification of acetylcholinesterase-reactive neurons and neuropil in neostriatal transplants

To identify and describe neurons in neostriatal transplants that synthesize acetylcholinesterase (AChE), the present study has utilized the irreversible AChE inhibitor diisopropylfluorophosphate (DFP) combined with AChE histochemistry. Dissociated suspensions of tissue taken from the striatal ridge of embryos at 14 days of gestation were transplanted into the neostriatum of adult rats 5 days after intrastriatal kainic acid lesions. Two types of AChE neurons have been identified in transplants treated with DFP. One type resembled the large intensely reactive AChE neuron that is thought to be a cholinergic interneuron of the normal neostriatum. The other type resembled smaller, less reactive AChE neurons of the neostriatum, as well as medium-sized, lightly reactive AChE neurons of the globus pallidus. Qualitative observations suggest that these less reactive AChE neurons were more numerous in transplants compared to the normal neostriatum. Both AChE neuronal types were found in segregated clusters throughout the grafts. Transplants processed for AChE histochemistry without DFP treatment contained two types of AChE neuropil. Dark areas of AChE neuropil similar in intensity to the normal neostriatum were found between larger areas of lighter AChE neuropil. These results demonstrate that neostriatal transplants contain AChE neurons and suggest that these neurons contribute to the AChE reactivity within the graft.