Electrophysiological and cytological studies of brain homografts in the anterior chamber of the eye: maturation of cerebellar cortex in oculo

The anterior chamber of the eye technology and its anatomical, optical, and immunological bases

The anterior chamber of the eye (ACE) is distinct in its anatomy, optics, and immunology. This guarantees that the eye perceives visual information in the context of physiology even when encountering adverse incidents like inflammation. In addition, this endows the ACE with the special nursery bed iris enriched in vasculatures and nerves. The ACE constitutes a confined space enclosing an oxygen/nutrient-rich, immune-privileged, and less stressful milieu as well as an optically transparent medium. Therefore, aside from visual perception, the ACE unexpectedly serves as an excellent transplantation site for different body parts and a unique platform for noninvasive, longitudinal, and intravital microimaging of different grafts. On the basis of these merits, the ACE technology has evolved from the prototypical through the conventional to the advanced version. Studies using this technology as a versatile biomedical research platform have led to a diverse range of basic knowledge and in-depth understanding of a variety of cells, tissues, and organs as well as artificial biomaterials, pharmaceuticals, and abiotic substances. Remarkably, the technology turns in vivo dynamic imaging of the morphological characteristics, organotypic features, developmental fates, and specific functions of intracameral grafts into reality under physiological and pathological conditions. Here we review the anatomical, optical, and immunological bases as well as technical details of the ACE technology. Moreover, we discuss major achievements obtained and potential prospective avenues for this technology.

Use of Embryonic Heart Grafted In Oculo to Assess Neurohumoral Controls of Cardiac Development*

Culture of embryonic heart in the anterior eye chamber allows neurohumoral and genetic controls of cardiac development to be separated from the influence of hemodynamic load. Hearts from 12-day gestation rat embryos grafted into the anterior eye chamber of an adult host rat attach to the iris and become vascularized and innervated by collaterals from the host iris. The spontaneous beating of grafts is pacemaker-driven and under functional neural control. Grafts do not beat against a pressure load, allowing the influence of neurohumoral factors to be separated from altered hemodynamic load. In oculo, embryonic heart differentiates into mature myocardium by most morphologic and biochemical criteria. Mature intercalated disks and myofibrils with well-defined Z-lines and M-lines are observed. Mature grafts express the high levels of α-myosin heavy chain characteristic of young adult myocardium. Surgical sympathetic denervation of the anterior eye chamber prior to grafting of embryonic hearts compromises growth and increases the intrinsic pacemaker rate. Since the grafts are perfused by the host circulation, the hormonal milieu of the graft can be altered by treatment of the host. Thus, the interaction between hormones and innervation of grafts can be studied using the in oculo model system.

Organotypic cultures of cerebellar slices as a model to investigate demyelinating disorders

INTRODUCTION

Demyelinating disorders, characterized by a chronic or episodic destruction of the myelin sheath, are a leading cause of neurological disability in young adults in western countries. Studying the complex mechanisms involved in axon myelination, demyelination and remyelination requires an experimental model preserving the neuronal networks and neuro-glial interactions. Organotypic cerebellar slice cultures appear to be the best alternative to in vivo experiments and the most commonly used model for investigating etiology or novel therapeutic strategies in multiple sclerosis. Areas covered: This review gives an overview of slice culture techniques and focuses on the use of organotypic cerebellar slice cultures on semi-permeable membranes for studying many aspects of axon myelination and cerebellar functions. Expert opinion: Cerebellar slice cultures are probably the easiest way to faithfully reproduce all stages of axon myelination/demyelination/remyelination in a three-dimensional neuronal network. However, in the cerebellum, neurological disability in multiple sclerosis also results from channelopathies which induce changes in Purkinje cell excitability. Cerebellar cultures offer easy access to electrophysiological approaches which are largely untapped and we believe that these cultures might be of great interest when studying changes in neuronal excitability, axonal conduction or synaptic properties that likely occur during multiple sclerosis.

Neural Repair Strategies for Parkinson's Disease: Insights from Primate Models

Nonhuman primate models of Parkinson's disease (PD) have been invaluable to our understanding of the human disease and in the advancement of novel therapies for its treatment. In this review, we attempt to give a brief overview of the animal models of PD currently used, with a more comprehensive focus on the advantages and disadvantages presented by their use in the nonhuman primate. In particular, discussion addresses the 6-hydroxydopamine (6-OHDA), 1-methyl-1,2,3,6-tetrahydopyridine (MPTP), rotenone, paraquat, and maneb parkinsonian models. Additionally, the role of primate PD models in the development of novel therapies, such as trophic factor delivery, grafting, and deep brain stimulation, are described. Finally, the contribution of primate PD models to our understanding of the etiology and pathology of human PD is discussed.

Organotypic brain slice cultures: A review

In vitro cell cultures are an important tool for obtaining insights into cellular processes in an isolated system and a supplement to in vivo animal experiments. While primary dissociated cultures permit a single homogeneous cell population to be studied, there is a clear need to explore the function of brain cells in a three-dimensional system where the main architecture of the cells is preserved. Thus, organotypic brain slice cultures have proven to be very useful in investigating cellular and molecular processes of the brain in vitro. This review summarizes (1) the historical development of organotypic brain slices focusing on the membrane technology, (2) methodological aspects regarding culturing procedures, age of donors or media, (3) whether the cholinergic neurons serve as a model of neurodegeneration in Alzheimer’s disease, (4) or the nigrostriatal dopaminergic neurons as a model of Parkinson’s disease and (5) how the vascular network can be studied, especially with regard to a synthetic blood–brain barrier. This review will also highlight some limits of the model and give an outlook on future applications.

Neural control of the endocrine pancreas

The autonomic nervous system affects glucose metabolism partly through its connection to the pancreatic islet. Since its discovery by Paul Langerhans, the precise innervation patterns of the islet has remained elusive, mainly because of technical limitations. Using 3-dimensional reconstructions of axonal terminal fields, recent studies have determined the innervation patterns of mouse and human islets. In contrast to the mouse islet, endocrine cells within the human islet are sparsely contacted by autonomic axons. Instead, the invading sympathetic axons preferentially innervate smooth muscle cells of blood vessels. This innervation pattern suggests that, rather than acting directly on endocrine cells, sympathetic nerves may control hormone secretion by modulating blood flow in human islets. In addition to autonomic efferent axons, islets also receive sensory innervation. These axons transmit sensory information to the brain but also have the ability to locally release neuroactive substances that have been suggested to promote diabetes pathogenesis. We discuss recent findings on islet innervation, the connections of the islet with the brain, and the role islet innervation plays during the progression of diabetes.

Noninvasive in vivo model demonstrating the effects of autonomic innervation on pancreatic islet function

The autonomic nervous system is thought to modulate blood glucose homeostasis by regulating endocrine cell activity in the pancreatic islets of Langerhans. The role of islet innervation, however, has remained elusive because the direct effects of autonomic nervous input on islet cell physiology cannot be studied in the pancreas. Here, we used an in vivo model to study the role of islet nervous input in glucose homeostasis. We transplanted islets into the anterior chamber of the eye and found that islet grafts became densely innervated by the rich parasympathetic and sympathetic nervous supply of the iris. Parasympathetic innervation was imaged intravitally by using transgenic mice expressing GFP in cholinergic axons. To manipulate selectively the islet nervous input, we increased the ambient illumination to increase the parasympathetic input to the islet grafts via the pupillary light reflex. This reduced fasting glycemia and improved glucose tolerance. These effects could be blocked by topical application of the muscarinic antagonist atropine to the eye, indicating that local cholinergic innervation had a direct effect on islet function in vivo. By using this approach, we found that parasympathetic innervation influences islet function in C57BL/6 mice but not in 129X1 mice, which reflected differences in innervation densities and may explain major strain differences in glucose homeostasis. This study directly demonstrates that autonomic axons innervating the islet modulate glucose homeostasis.

Cell transplantation and gene therapy in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disorder affecting, in part, dopaminergic motor neurons of the ventral midbrain and their terminal projections that course to the striatum. Symptomatic strategies focused on dopamine replacement have proven effective at remediating some motor symptoms during the course of disease but ultimately fail to deliver long-term disease modification and lose effectiveness due to the emergence of side effects. Several strategies have been experimentally tested as alternatives for Parkinson's disease, including direct cell replacement and gene transfer through viral vectors. Cellular transplantation of dopamine-secreting cells was hypothesized as a substitute for pharmacotherapy to directly provide dopamine, whereas gene therapy has primarily focused on restoration of dopamine synthesis or neuroprotection and restoration of spared host dopaminergic circuitry through trophic factors as a means to enhance sustained controlled dopamine transmission. This seems now to have been verified in numerous studies in rodents and nonhuman primates, which have shown that grafts of fetal dopamine neurons or gene transfer through viral vector delivery can lead to improvements in biochemical and behavioral indices of dopamine deficiency. However, in clinical studies, the improvements in parkinsonism have been rather modest and variable and have been plagued by graft-induced dyskinesias. New developments in stem-cell transplantation and induced patient-derived cells have opened the doors for the advancement of cell-based therapeutics. In addition, viral-vector-derived therapies have been developed preclinically with excellent safety and efficacy profiles, showing promise in clinical trials thus far. Further progress and optimization of these therapies will be necessary to ensure safety and efficacy before widespread clinical use is deemed appropriate.

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.

Noninvasive high-resolution in vivo imaging of cell biology in the anterior chamber of the mouse eye

There is clearly a demand for an experimental platform that enables cell biology to be studied in intact vascularized and innervated tissue in vivo. This platform should allow observations of cells noninvasively and longitudinally at single-cell resolution. For this purpose, we use the anterior chamber of the mouse eye in combination with laser scanning microscopy (LSM). Tissue transplanted to the anterior chamber of the eye is rapidly vascularized, innervated and regains function. After transplantation, LSM through the cornea allows repetitive and noninvasive in vivo imaging at cellular resolution. Morphology, vascularization, cell function and cell survival are monitored longitudinally using fluorescent proteins and dyes. We have used this system to study pancreatic islets, but the platform can easily be adapted for studying a variety of tissues and additional biological parameters. Transplantation to the anterior chamber of the eye takes 25 min, and in vivo imaging 1-5 h, depending on the features monitored.

Noninvasive in vivo imaging of pancreatic islet cell biology

Advanced imaging techniques have become a valuable tool in the study of complex biological processes at the cellular level in biomedical research. Here, we introduce a new technical platform for noninvasive in vivo fluorescence imaging of pancreatic islets using the anterior chamber of the eye as a natural body window. Islets transplanted into the mouse eye engrafted on the iris, became vascularized, retained cellular composition, responded to stimulation and reverted diabetes. Laser-scanning microscopy allowed repetitive in vivo imaging of islet vascularization, beta cell function and death at cellular resolution. Our results thus establish the basis for noninvasive in vivo investigations of complex cellular processes, like beta cell stimulus-response coupling, which can be performed longitudinally under both physiological and pathological conditions.

Cerebellar grafting in the oculomotor system as a model to study target influence on adult neurons

In the last decades, there have been many efforts directed to gain a better understanding on adult neuron-target cell relationships. Embryonic grafts have been used for the study of neural circuit rewiring. Thus, using several donor neuronal tissues, such as cerebellum or striatum, developing grafted cells have been shown to have the capability of substituting neural cell populations and establishing reciprocal connections with the host. In addition, different lesion paradigms have also led to a better understanding of target dependence in neuronal cells. Thus, for example, axotomy induces profound morphofunctional changes in adult neurons, including the loss of synaptic inputs and discharge alterations. These alterations are probably due to trophic factor loss in response to target disconnection. In this review, we summarize the different strategies performed to disconnect neurons from their targets, and the effects of target substitution, performed by tissue grafting, upon neural properties. Using the oculomotor system-and more precisely the abducens internuclear neurons-as a model, we describe herein the effects of disconnecting a population of central neurons from its natural target (i.e., the medial rectus motoneurons at the mesencephalic oculomotor nucleus). We also analyze target-derived influences in the structure and physiology of these neurons by using cerebellar embryonic grafts as a new target for the axotomized abducens internuclear neurons.

Cellular replacement therapy for Parkinson's disease--where we are today?

The concept of replacing lost dopamine neurons in Parkinson's disease using mesencephalic brain cells from fetal cadavers has been supported by over 20 years of research in animals and over a decade of clinical studies. The ambitious goal of these studies was no less than a molecular and cellular "cure" for Parkinson's disease, other neurodegenerative diseases, and spinal cord injury. Much research has been done in rodents, and a few studies have been done in nonhuman primate models. Early uncontrolled clinical reports were enthusiastic, but the outcome of the first randomized, double blind, controlled study challenged the idea that dopamine replacement cells can cure Parkinson's disease, although there were some significant positive findings. Were the earlier animal studies and clinical reports wrong? Should we give up on the goal? Some aspects of the trial design and implantation methods may have led to lack of effects and to some side effects such as dyskinesias. But a detailed review of clinical neural transplants published to date still suggests that neural transplantation variably reverses some aspects of Parkinson's disease, although differing methods make exact comparisons difficult. While the randomized clinical studies have been in progress, new methods have shown promise for increasing transplant survival and distribution, reconstructing the circuits to provide dopamine to the appropriate targets and with normal regulation. Selected promising new strategies are reviewed that block apoptosis induced by tissue dissection, promote vascularization of grafts, reduce oxidant stress, provide key growth factors, and counteract adverse effects of increased age. New sources of replacement cells and stem cells may provide additional advantages for the future. Full recovery from parkinsonism appears not only to be possible, but a reliable cell replacement treatment may finally be near.

Firing properties of axotomized central nervous system neurons recover after graft reinnervation

Axotomy produces changes in the electrical properties of neurons and in their synaptic inputs, leading to alterations in firing pattern. We have considered the possibility that these changes occur as a result of the target deprivation induced by the lesion. Thus, we have provided a novel target to axotomized central neurons by grafting embryonic tissue at the lesion site to study the target dependence of discharge characteristics. The extracellular single-unit electrical activity of abducens internuclear neurons was recorded in the alert behaving cat in control, after axotomy, and after axotomy plus the implantation of cerebellar primordium. As recently characterized (de la Cruz et al. [2000] J. Comp. Neurol. 427:391-404), firing alterations induced by axotomy included an overall decrease in firing rate and a loss of eye-related signals, i.e., eye position and velocity neuronal sensitivities, that do not resume to normality with time. The grafting of a novel target to the injured abducens internuclear neurons restored the normal firing and sensitivities as recorded in the majority of units. To study the reinnervation of the implant, we performed anterograde labeling with biocytin combined with electron microscopy visualization. Axons of abducens internuclear neurons grew into the transplant sprouting into granule cell and molecular layers, as characterized by the immunostaining for gamma-aminobutyric acid and calbindin D-28k. Ultrastructural examination of labeled axons and boutons revealed the establishment of synaptic contacts, mainly axodendritic, with different cell types of the grafted cerebellar cortex. Therefore, these data indicate that axotomized central neurons resume to normal firing after the reinnervation of a novel target.

Survival of grafted fetal neural cells in kainic acid lesioned CA3 region of adult hippocampus depends upon cell specificity

We hypothesize that the degree of graft cell survival within the damaged CNS correlates with the specificity of donor cells to the region of grafting. We investigated graft cell survival following transplantation of fetal micrografts into the CA3 region of the adult rat hippocampus at a time-point of 4 days after an intracerebroventricular administration of kainic acid (KA). Grafts consisted of 5'-bromodeoxyuridine (BrdU) labeled embryonic day (E) 19 cells from hippocampal fields CA3 and CA1 and E15 and E19 cells from the striatum. Absolute cell survival in these grafts was quantitatively analyzed at 1 month postgrafting, using BrdU immunostaining of serial sections and three-dimensional reconstruction of grafts. Absolute graft cell survival in lesioned CA3 was dramatically greater for cells having hippocampal origin (CA3 cells, 69% cell survival; CA1 cells, 42% cell survival) than those having nonhippocampal origin, such as striatal cells (E15 cells, 12% cell survival; E19 cells, 4% cell survival). This difference is in sharp contrast to survival of these cells in culture, where E19 cells from both hippocampal and nonhippocampal origins exhibited similar survival. Comparison of survival among hippocampal cell types indicated significantly greater survival for cells that are specific to the lesioned area (i.e., CA3 cells) than for those that are nonspecific to the lesioned area (i.e., CA1 cells). Graft cell survival in the intact CA3 region (contralateral to KA administration), however, did not differ either between cells having hippocampal and nonhippocampal origins or between CA3 and CA1 cells (CA3 cells, 26% cell survival; CA1 cells, 33% cell survival; and E15 striatal cells, 20% cell survival). These results underscore the finding that enhanced survival of fetal cell grafts in the lesioned CNS is critically dependent upon the specificity of donor fetal cells to the region of transplantation. Thus, grafting of cells that are specific to the lesioned area is a prerequisite for achieving maximal graft cell survival and integration in the lesioned host CNS.

Prospects for the clinical application of neural transplantation with the use of conditionally immortalized neuroepithelial stem cells

Although neural transplantation has made a relatively successful transition from the animal laboratory to human neurosurgery for the treatment of Parkinson's disease, the use of human embryonic brain tissue as the source of transplants raises difficult ethical and practical problems. These are likely to impede the widespread use of this otherwise promising therapy across the range of types of brain damage to which the results of animal experiments suggest its potential applicability. Various alternative approaches are reviewed briefly, aimed at developing sources of tissue for transplantation that can be maintained in vitro until needed, so obviating the requirement for fresh embryonic tissue at each occasion of surgery. Particularly promising are conditionally immortalized neuroepithelial stem cell lines in which the immortalizing gene is downregulated upon transplantation into a host brain. We describe experiments from our laboratory with the use of cells of this kind, the multipotent MHP clonal cell lines, derived from the developing hippocampus of a transgenic mouse harbouring a temperature-sensitive oncogene. Implanted into the hippocampus of rats and marmosets with damage to the CA1 cell field, the MHP36 line gave rise to healthy surviving grafts and to essentially complete recovery of cognitive function. Postmortem study of the implanted rat brains indicated that MHP36 cells migrate to the region of damage, adopt both neuronal (pyramidal) and glial phenotypes in vivo, and reconstitute the normal laminated appearance of the CA1 cell field. We have previously shown that, when primary differentiated foetal tissue is used as the source of grafts in rats with CA1 damage, there is a stringent requirement for replacement with homotypic CA1 cells. We interpret our results as showing that the MHP36 cell line responds to putative signals associated with damage to the hippocampus and takes up a phenotype appropriate for the repair of this damage; they therefore open the way to the development of a novel strategy with widespread applicability to the treatment of the diseased or damaged human brain.

Path and target finding of afferents in cerebellar anlagen grafted in the cerebellum of adult rats: a Phaseolus vulgaris leucoagglutinin study

Cerebellar anlagen from rat embryos were grafted into the cerebellum of intact adult rats. Most of the grafts survived and formed 'minicerebella'. The location of the grafts were varied, which provided various types of host/graft interface in laminar configuration: Hw/Gg, Hw/Gp, Hw/Gm, Hg/Gw, Hg/Gg, Hm/Gw, Hm/Gg, Hm/Gp, and Hm/Gm that comprised of the granule cell layer (g), the Purkinje cell layer (p), the molecular layer (m), or the white matter (w) of the host (H) or graft (G). The manner of entrance of mossy and climbing fibers through the host/graft interface and their outgrowth in the graft which has various subset of laminar organization of the cerebellum were examined 28-158 days after grafting by means of anterograde Phaseolus vulgaris leucoagglutinin (PHA-L) labeling. Each cerebellar afferent entered the graft through specific types of interface and grew in specific layers. Mossy fibers passed through Hg/Gg and Hw/Gg, grew in Gg, and mostly terminated there like normal fibers. Fibers in Gg, though rarely, grew further outside Gg like in development. Climbing fibers passed through Hm/Gg, Hw/Gg, and Hw/Gm, proceeded in cortical layers, and terminated in Gm. The outgrowth of climbing fibers in Gm showed selectivity for the direction of Gm with respect to the polarity of Purkinje cells; they permeated Gm to form terminal arbors similar to normal in the direction from the side of Purkinje cell somata to dendrites but not in the reverse direction. Occasionally a single fiber innervated neighboring multiple Purkinje cells. These results indicate that mature cerebellar afferents have potential to regrow and innervate the extraneous cerebellar anlage by finding paths and targets in a manner similar to normal ontogenesis.

The cerebellar model of neural grafting: structural integration and functional recovery

A synopsis is presented of the recent history of cerebellar tissue transplantation over the past 25 years. The properties of growth and differentiation of cerebellar grafts placed intraocularly or intracranially are reviewed, as well as the interaction of heterotopic and orthotopic grafts with the host brain. Particular emphasis is placed on the use of ataxic mouse mutants as recipients of donor cerebellar tissue for the correction of their structural deficits and the functional recovery of behavioural responses.

Intrastriatal cerebellar grafts: differentiation of cerebellar anlage and sprouting of Purkinje cell axons

Pieces of cerebellar primordia were obtained from G16 (day 16 of gestation) rat fetuses and stereotaxically injected into the striatum of adult Wistar rats. The transplants were allowed to integrate with the host brain for 2 h up to 6 months after implantation. Ninety four out of 105 transplants perfectly integrated with the host brain (90%) and established the typical trilaminar histoarchitecture of cerebellar cortex. The transplants were sufficiently vascularized. Vessels seen within the grafts provided all ultrastructural elements of a blood-brain barrier. Light microscopic evaluation of graft development showed no considerable retardation of cerebellar histogenesis. Electron microscopic examination disclosed normal ultrastructure of cerebellar neurons, as well as elements of regular synaptic organization. The topic of efferent graft-to-host projections was investigated 2.5 months after transplantation using the monoclonal Purkinje cell marker anti-Leu-4 (CD3). This method allowed us to detect immunoreactive, morphologically intact axons of grafted Purkinje cells running over long distances (at least 500 microns) within the host striatum. Whilst afferent but in no case efferent connections of heterotopic cerebellar transplants had been demonstrated elsewhere, we could now prove the reciprocal modus of graft-host interaction with heterotopic cerebellar grafts.

Effects of ethanol on development of dorsal raphe transplants in oculo: a morphological and electrophysiological study

The purpose of this project was to investigate ethanol influence on the development of serotonin-containing (5-HT) neurons of the dorsal raphe nucleus in rat. Fetal tissue of embryonic day 17 from the dorsal brainstem was grafted to the anterior chamber of the eye of adult albino rats. The experimental group was exposed to 16% ethanol in the drinking water, and the control group received water ad libitum. After 4 weeks, morphological and electrophysiological evaluations were performed. Immunohistochemical analysis showed that 5-HT-immunoreactive fibers from ethanol-treated transplants had a disturbed outgrowth pattern into the host iris as compared to the control group. Furthermore, the outgrowth area and axon bundle formation was significantly greater in the control group than in the ethanol group. Electrophysiological recordings revealed a dose-dependent biphasic effect of locally applied ethanol on transplanted monoaminergic neurons. Low doses of ethanol (0.5-3 mM) induced an increase in basal firing rate of control neurons, while higher doses (10-100 mM) caused inhibition. However, monoaminergic neurons in the ethanol group showed a decreased neuronal sensitivity to locally applied ethanol. The same dose of locally applied ethanol which produced an excitation of neuronal activity in the ethanol transplants produced an inhibition in the control grafts. The dose-response curve was shifted to the right. The present results suggest that chronic ethanol exposure during early development leads to altered axonal outgrowth from brainstem 5-HT neurons, as well as decreased sensitivity of these neurons to locally applied ethanol.

Noradrenergic agents into the cerebellar anterior vermis modify the gain of vestibulospinal reflexes in the cat

The noradrenergic (NA) afferent projection to the cerebellar cortex, which originates mainly from the locus coeruleus (LC), may act on the target neurons by utilizing both alpha- and beta-adrenoceptors. Experiments performed in decerebrate cats have shown that unilateral injection into the vermal cortex of the cerebellar anterior lobe of 0.25 microliter of the alpha 1-adrenergic agonist metoxamine or the alpha 2-agonist clonidine (at 2-8 micrograms/microliters of saline) as well as of the non-selective beta-agonist isoproterenol (at 8-16 micrograms/microliters) decreased the postural activity in the ipsilateral forelimb, while the extensor tonus either remained unmodified or slightly increased on the contralateral side. The same agents also increased the gain of the vestibulospinal (VS) reflexes elicited by recording the multiunit EMG responses of the ipsilateral and the contralateral triceps brachii to roll tilt of the animal (at 0.15 Hz, +/- 10 degrees), leading to sinusoidal stimulation of labyrinth receptors. The crossed effects were more prominent for the alpha 2- than for the alpha 1- and beta-agonists. Only slight changes in the phase angle of the responses were observed. The effects described above appeared 5-10 min after the injection, reached the peak values after 15-30 min and disappeared within 2 h. The effective area was located within the third and/or the fourth folium of the culmen rostral to the fissura prima, 1.4-1.8 mm lateral to the midline. This area corresponded to zone B of the cerebellar cortex, which projects to the ipsilateral lateral vestibular nucleus (LVN), on which it exerts a prominent inhibitory influence. In fact, monopolar stimulation of this area with three negative pulses (at 300/sec) performed prior to the local injection inhibited the spontaneous EMG activity of the ipsilateral triceps brachii. The effects described above were dose-dependent; injection of an equal volume of saline was ineffective. All changes in posture and reflexes elicited by metoxamine or clonidine were impaired by previous injection into the same corticocerebellar area of the corresponding alpha 1- or alpha 2-adrenergic antagonist prazosin or yohimbine, respectively (0.25 microliters at 8-16 micrograms/microliters). However, cross-interactions between alpha 1- and alpha 2-adrenergic agonists and antagonists were also observed. In fact, injection of the alpha 2-adrenergic antagonist yohimbine prevented the occurrence of all the metoxamine effects, while administration of the alpha 1-adrenergic antagonist prazosin prevented the occurrence of the ipsilateral, but not of the contralateral effects induced by clonidine injection.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxic effects of lead on neuronal development and function

The effects of lead on the development of the nervous system are of immediate concern to human health. While it is clear that lead can affect neuronal development at levels of exposure within the range found in the environment, the particular mechanism of the disruption is not readily ascertained. Lack of knowledge of the mechanisms of lead-induced damaged hampers its treatment and prevention. The goal of our research is to develop a model system in which the effects of lead on central nervous system development can be demonstrated. The complexity of the brain hampers such investigations because often it is not clear if apparent toxic effects represents changes secondary to somatic changes, such as endocrine or hematological defects, that could alter brain development, or even transneuronal effects caused by toxicity at a distal site that deprives a brain area of a synaptic input needed for its proper development. A related problem is the redundancy of compensatory systems in the brain. Such system may disguise the severity of the initial toxic insult and themselves can cause functional disturbances. To study neuronal development in a system that minimizes such difficulties, we have grafted discrete brain regions derived from rat fetuses into the anterior chamber of the eye of adult hosts. The brain pieces continue organotypic development of the eye, but are isolated from possible secondary changes due to alterations in the development of the endocrine and other somatic systems because the adult host has these systems already fully developed. Similarly, effects mediated by connecting brain areas are minimized since the transplant is isolated in the anterior chamber of the eye.(ABSTRACT TRUNCATED AT 250 WORDS)

Transplantation of cultured embryonic spinal cord grafts into the hemisected spinal cord of adult rabbits

Spinal cord fragments from 20-day-old rabbit embryos cultivated for 1 week were transplanted into the hemisected and intact spinal cord of adult rabbits. The morphological changes at the site of intervention were investigated by light and electron microscopy 3, 12, and 29 weeks following implantation. In 80% of the animals the procedure was successful. The implants grew in volume, the cells matured, and many new neural processes with myelinization and synapse formation appeared. The histological findings indicate the survival, maturation, and integration of transplanted cultured embryonic spinal cord tissue in the lesioned adult spinal cord.

Growth of brain tissue grafts is dependent upon host age

Growth of grafts of cortex cerebri, hippocampus, septum and cerebellum in oculo were significantly reduced in 16--17-month-old hosts as compared to growth in 3-month-old and 1.5-month-old rat hosts. (Host age is given as the age of the recipients at the time of grafting.) This growth difference was less pronounced in locus coeruleus grafts. The vascular network (as observed with laminin immunofluorescence) in cortex cerebri, hippocampus, cerebellum and septum grafts in 16--17-month-old hosts was abnormal with few thick-walled vessels in clusters as compared to the more 'normal' vascularization found in 1.5-month-old hosts with a high number of thin-walled blood vessels evenly distributed throughout the grafts. Grafts in the oldests hosts were markedly more gliotic than grafts in 1.5- and 3-month-old hosts as evaluated using immunofluorescence with antibodies against glial fibrillary acidic protein. Neurofilament immunoreactivity in the grafts seemed not to be influenced by host age. When a second cortex cerebri or hippocampus graft was placed into contact with a previously grafted locus coeruleus graft, the second graft grew less well in 16--17-month-old hosts as compared to 1.5-month-old hosts. When cortex cerebri was added to a previously grafted cortex cerebri graft, the second graft in both 16--17- and 3-month-old hosts grew to larger sizes than the corresponding single cortex grafts, although the growth differences between the two groups of hosts described above were still maintained. Thus, cortex grafts in 16--17-month-old hosts still have the ability to become trophically stimulated. The vascularization of the second graft in both groups was almost normalized and the gliotic reaction was less pronounced in the second grafts in both groups as compared to the single cortex grafts. In conclusion, the present results indicate that host age affects growth and morphology of intraocular single grafts from several brain regions. Using double grafts of cortex cerebri it was shown that grafts in 16-17-month-old hosts still had the capacity to become trophically stimulated. Data on brain transplants in older hosts are important in view of clinical possibilities to use transplantation strategies to counteract the symptoms of neurodegenerative diseases, which usually occur in old patients.

Multiple changes in noradrenergic mechanisms in the coeruleo-hippocampal pathway during aging. Structural and functional correlates in intraocular double grafts

Age-related changes of the coeruleo-hippocampal noradrenergic system were investigated using intraocular double transplants. Pieces of fetal hippocampus were grafted into the anterior chamber of the eye and placed into contact with previously inserted locus coeruleus grafts. Ages of both transplants and hosts were varied to enable studies of intrinsic versus extrinsic determinants of aging in an isolated neuronal circuit. Four different experimental groups, with the approximate age in months of grafts/hosts at the time of recording given in parentheses, were studied; young grafts in the eyes of young hosts (3/7), young grafts in the eyes of old hosts (3/23), mature transplants in adult host rats (8/12) and aged transplants in the eyes of aged rats (21/25). Extracellular recordings from the hippocampal part of the double grafts were performed. Superfusion with alpha-adrenergic antagonists and the alpha 2-agonist clonidine elicited significant increases in the discharge rate of the grafted hippocampal neurons in all groups except the aged transplants in the aged hosts (21/25), where a small excitation was elicited with clonidine and no effect at all was seen with alpha-adrenergic antagonists. The host age did not seem to be important since young transplants in the old hosts (3/23) showed a similar increase in discharge rate as transplants in the young and adult hosts. Tyrosine hydroxylase immunohistochemistry and high-performance liquid chromatography revealed that hippocampal transplants remaining in oculo for a minimum of 6-10 months became permanently hyperinnervated by noradrenergic fibers from the locus coeruleus grafts. The density of noradrenergic fibers was significantly lower in young transplants.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related alterations in noradrenergic input to the hippocampal formation: structural and functional studies in intraocular transplants

Intrinsic versus extrinsic determinants of age-related alterations in hippocampal noradrenergic transmission were investigated using intraocular allografts in rats. Three groups of animals were examined: young hippocampal transplants in young hosts, old transplants in old hosts and young transplants in old hosts. Postsynaptic sensitivity to noradrenaline (NA) was measured by extracellular recordings of spontaneous activity and superfusion with known concentrations of catecholamines in the anterior chamber of the eye. Hill plots demonstrated that the dose-response relationships of NA-induced depressions were linear and parallel in the 3 groups. Aged hippocampal grafts displayed a highly significant subsensitivity to NA of one order of magnitude. The EC50 for this group was 203.1 microM as compared to 29.2 in young grafts. Young intraocular grafts in old hosts responded similarly to transplants in young hosts, with an EC50 of 32.4 microM for the depressant actions of NA. Collaterals of the host iris sympathetic ground plexus invaded the hippocampal grafts. The density of this noradrenergic innervation was estimated by immunohistochemistry for tyrosine hydroxylase. A slightly increased density and fluorescence intensity of the noradrenergic fibers were observed in the old transplants as compared to the young transplants in young and old hosts. This was correlated with a significantly (P less than 0.01) increased content of NA in old transplants, as measured with high performance liquid chromatography. The old transplants also contained a large number of autofluorescent lipofuchsin granules, which were absent in the young transplants, regardless of the recipient age. Taken together, these results suggest the existence of alterations in pre- as well as postsynaptic noradrenergic mechanisms in the aging hippocampus. These changes were dependent on transplant age rather than host age, thus suggesting an involvement of intrinsic rather than extrinsic determinants in this model system.

Nerve growth factor can influence growth of cortex cerebri and hippocampus: evidence from intraocular grafts

The effects of nerve growth factor and antiserum against nerve growth factor on cortical cholinergic projection areas in the central nervous system and cerebellum were evaluated using intraocular grafts of cortex cerebri, hippocampus and cerebellum in rat hosts receiving injections into the anterior chamber of the eye of nerve growth factor (at transplantation, 5 and 10 days after transplantation) or antiserum to nerve growth factor (every 5 days). The controls received cytochrome c or preimmune serum. Growth of grafts was followed by repeated observations directly through the cornea of the host using a stereomicroscope. Nerve growth factor-treated grafts of cortex cerebri and hippocampus grew significantly smaller as compared to the corresponding control grafts. In one experiment, growth of cytochrome c and saline-treated cortex cerebri was compared and no difference in growth was found. Growth of nerve growth factor-treated cerebellar grafts did not differ significantly from growth of cytochrome c-treated grafts. Morphological analysis using Nissl-staining, antibodies to glial acidic fibrillary protein to evaluate the degree of gliosis and antiserum to neurofilament as a neuronal marker did not reveal any marked differences between nerve growth factor- and cytochrome c-treated grafts. Cortical grafts receiving anti-nerve growth factor antiserum by injection or by immunizing host rats against nerve growth factor showed similar growth to the controls. Similarly, grafts of fetal hippocampus to rats immunized with nerve growth factor were not significantly different from grafts to host rats immunized with cytochrome c. We conclude that exogenous nerve growth factor affects the development of grafted cortex cerebri and hippocampus. The fact that these cortical areas stop growing earlier in the presence of nerve growth factor without the grafts showing evidence of disturbed glial or neuronal populations compared to control grafts indicates that nerve growth factor acts to induce overall/premature differentiation and maturation. The mechanism for this whether or not it is receptor-mediated and which cells are primarily affected by nerve growth factor is not yet known.

Cryopreservation, culture, and transplantation of human fetal mesencephalic tissue into monkeys

Studies in animals suggest that fetal neural grafts might restore lost neurological function in Parkinson's disease. In monkeys, such grafts survive for many months and reverse signs of parkinsonism, without attendant graft rejection. The successful and reliable application of a similar transplantation procedure to human patients, however, will require neural tissue obtained from human fetal cadavers, with demonstrated cellular identity, viability, and biological safety. In this report, human fetal neural tissue was successfully grafted into the brains of monkeys. Neural tissue was collected from human fetal cadavers after 9 to 12 weeks of gestation and cryopreserved in liquid nitrogen. Viability after up to 2 months of storage was demonstrated by cell culture and by transplantation into monkeys. Cryopreservation and storage of human fetal neural tissue would allow formation of a tissue bank. The stored cells could then be specifically tested to assure their cellular identity, viability, and bacteriological and virological safety before clinical use. The capacity to collect and maintain viable human fetal neural tissue would also facilitate research efforts to understand the development and function of the human brain and provide opportunities to study neurological diseases.

Toluene exposure during maturation of intraocular brain tissue transplants: alterations of host and graft cerebellar Purkinje neuron function and sensitivity to norepinephrine

The effects of chronic toluene exposure on central neurons were examined using syngeneic grafts into the anterior chamber of the eye. Young adult albino rats with intraocular brain transplants inhaled toluene (1000 ppm) for 9 weeks starting at the time of transplantation, or from Week 8 to 17 after the graft was placed in oculo. Control animals were exposed to room air during the same intervals. Toluene treatment during development did not affect general growth or morphology of any of the brain areas examined. The distribution of neurofilament or glial fibrillary acidic protein immunoreactivity was similar in the experimental group and control group as well. Extracellular recordings of cerebellar Purkinje neurons showed a significantly reduced spontaneous firing rate, of 15-25%, both in intraocular transplants and in cerebellum in situ in toluene exposed animals. Postsynaptic sensitivity of intraocular and in situ Purkinje neurons to norepinephrine (NE) was evaluated. Purkinje neurons in transplants exposed to toluene during development were markedly supersensitive to superfused NE as compared to controls, while neither Purkinje neurons in mature cerebellar grafts nor cerebellum in situ showed any effects of the toluene treatment on NE sensitivity. The tissue content of NE in transplants exposed to toluene during maturation, evaluated with high-performance liquid chromatography coupled with electrochemical detection, was greater than that in the control grafts. Moreover, the content of free (3-methoxy-4-hydroxyphenyl) ethylene glycol (MHPG) was increased in both transplant and host cerebellum after toluene exposure. Taken together, these data indicate that toluene exposure during development of cerebellar grafts in oculo causes changes in postsynaptic noradrenergic sensitivity as well as decreased spontaneous activity of Purkinje neurons. Toluene exposure of adult cerebellum in situ or in oculo appears to decrease the Purkinje neuron discharge rate and increase NE turnover, but has no marked effect on postsynaptic NE sensitivity.

Electrophysiological effects of norepinephrine on Purkinje neurons in intraocular cerebellar grafts: alpha- vs beta-specificity

The present study investigates the receptor specificity of the electrophysiological effects of norepinephrine (NE) on cerebellar Purkinje neurons. Intraocular cerebellar grafts were utilized to allow both superfusion and local administration of selective adrenergic agonists and antagonists. Fetal cerebellar anlagen (E13-15) were homologously transplanted to the anterior chamber of the eye of adult recipient rats and allowed to mature in the eye for at least 5 weeks. Spontaneous activity of Purkinje neurons was recorded extracellularly in the intraocular grafts. Superfusion of 5 microM NE caused elevations of the spontaneous firing rate. Superfusion of 30 microM NE caused depressions, which were occasionally preceded by an excitation. Iontophoretic application of NE to grafted Purkinje neurons primarily caused depressions of the spontaneous discharge rate. Thus, the NE-induced excitations previously reported from in vitro slices are not anomalies of the in vitro slice preparation, but can be observed with superfusion of NE in our in vivo preparation as well. In general, the excitations caused by low doses of superfused NE were blocked by timolol, a specific beta-adrenergic antagonist, while the depressions caused by 30 microM superfused NE or iontophoretically applied NE were blocked by the specific alpha-adrenergic antagonist phentolamine. Large doses of sotalol were found to block both excitatory and depressant responses while lower doses only antagonized the NE-induced excitations. Taken together, these results suggest that the inhibitory effects of NE on PUrkinje neuron firing rate in intraocular cerebellar grafts in vivo are mediated via an alpha-adrenergic receptor mechanism, while the excitations caused by NE may be beta-mediated.

Cerebellar noradrenergic systems in aging: studies in situ and in in oculo grafts

Age-related changes in noradrenergic function in the rat cerebellum were examined using electrophysiological and electrochemical techniques. Sprague-Dawley and Fischer 344 rats showed subsensitivity to norepinephrine (NE) locally applied onto cerebellar Purkinje neurons. The modulatory actions of NE on Purkinje cell-evoked activity was also examined. In young rats NE preferentially inhibits spontaneous activity more than evoked excitations when compared to control. These modulatory actions of NE are not seen in senescent Fischer 344 rats. The intrinsic vs. extrinsic influences determining the loss of efficacy to NE were examined using three groups of rats with in oculo cerebellar grafts. The first group had young grafts grown in young hosts and these grafts showed a potent response to perfused NE. The second group, old grafts in old hosts, showed a diminished responsiveness to NE with respect to the first group. The third group consisted of young grafts in old hosts. These grafts demonstrated a responsiveness to NE that was indistinguishable from those in the first group. The integrity of the presynaptic NE fibers was examined in the grafts using electrochemical techniques. No difference in the release of NE was observed in the old grafts. Taken together, these results suggest a loss of postsynaptic NE function that is intrinsically determined. The change in NE modulation could influence information processing within the aged cerebellar cortex. This deficit could underlie behavioral changes seen in senescence.

Survival and development of embryonic and postnatal cerebellum transplanted into adult rat hosts: effect of growth as explants in culture prior to transplantation

The survival and organization of embryonic and postnatal cerebellum transplanted into intracephalic cavities in adult rat hosts was studied before and after growth as explants in tissue culture. It is well known that embryonic cerebellum survives transplantation and develops a typical cerebellar cytoarchitecture. This study demonstrates that early postnatal cerebellum survives transplantation poorly if at all using the intracephalic transplant paradigm. Postnatal cerebellum is capable of extensive growth and organization in explant culture; however, prior growth in explant culture did not enhance survival in the transplant situation. On the other hand, embryonic cerebellum grown in explant culture for as long as two weeks, to an age comparable to the postnatal cerebellar transplants, survives transplantation and develops similar cytoarchitectural features to directly transplanted embryonic cerebellum.

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

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

Morphological study of cerebellar transplant cocultivated with cerebral cortical graft in the anterior eye chamber. II. Purkinje cells and molecular layer

Morphological organization of Purkinje cells and of molecular layer of the cerebellar cortex cocultivated intraocularly with cerebral cortex for two months was studied. It was found, that while numerous spines on the main dendritic branches of Purkinje cells in single cerebellar grafts were "vacant" and non-synaptic, dendritic spines of thick Purkinje dendrites in double grafts were covered by large presynaptic bags. The resulting complex synaptic arrangement was strikingly similar although not identical to climbing terminals in normal ("in situ") cerebellar cortex. Three distinct types of large presynaptic climbing-fibre like terminals were distinguished: (a) bouton with dense matrix and small round synaptic vesicles, (b) with large round vesicles and (c) containing ovoid synaptic vesicles. The spines of the thin, presumably tertiary dendritic branches were contacted mostly by one parallel axon varicosity, or--as a contrast to normal conditions--by axon terminal, containing ovoid synaptic vesicles. Irrespective of the shape of synaptic vesicles in the presynaptic terminal, all spine-synapses were of asymmetric type; in contrast, synapses on the dendritic shafts were always symmetric. GABA-immunogold reaction has revealed the presence of this inhibitory transmitter in most axon terminals containing ovoid-pleomorphic vesicles within the molecular layer, including those resembling climbing fiber-terminals. This shows a plasticity of the Purkinje cell dendrites to receive non-specific, "foreign" axons in the absence of specific afferents. Also, the type of synaptic junctions, i.e. whether symmetric or asymmetric, is determined exclusively by the postsynaptic neuron and is independent of the transmitter content of the presynaptic terminal.

Morphological study of cerebellar transplant cocultivated with cerebral cortical graft in the anterior eye chamber. I. Granular layer

Fetal cerebral cortex and cerebellar anlage from rat fetuses of 15-16 gestational day were grafted simultaneously to the anterior eye chamber of adult female albino rat recipients. Two months after transplantation the cerebellar portion of the double graft consisted of foliated cerebellar cortex surrounding a well-defined cerebellar nucleus. In the absence of pia mater or glial scar the cerebral and cerebellar grafts were observed to establish direct contact with each other. Although much thinner than in the normal cerebellum, the overall morphological organization of the granular layer in the transplant was similar to that described for "in situ" normal cerebellum, with some remarkable differences, though. In normal cerebellum all mossy terminals contain spheroid synaptic vesicles, a characteristic morphological feature of excitatory endings. In the transplant, however, although the majority of mossy terminals contained (small or large) spheroid synaptic vesicles, numerous mossy terminals were filled with ovoid, or pleomorphic synaptic vesicles, a morphological marker of inhibitory terminals. GABA-immunogold reaction, revealed, indeed, the presence of this inhibitory transmitter in mossy terminals containing ovoid synaptic vesicles. Both GABA (-) and GABA (+) mossy terminals formed asymmetric (Gray I-type) synaptic junctions with the surrounding dendritic digits of granule cells. It is suggested that GABA-ergic fibers as well as most non-GABA-ergic axons (originating either from the cerebral cortical graft, or from the cerebellar nucleus) may develop to mossy terminal-like structures as a consequence of the hugh deficit in "natural" mossy fibers in this model.

Age-related changes in cerebellar noradrenergic pre- and postsynaptic mechanisms: intrinsic vs extrinsic determinants evaluated with brain grafts in oculo

Intrinsic versus extrinsic determinants of changes in cerebellar noradrenergic transmission during senescence in the rat were measured using homologous cerebellar grafts in oculo. Postsynaptic sensitivity of Purkinje neurons to catecholamines was determined by perfusing the anterior eye chamber with known concentrations of norepinephrine (NE) dissolved in a balanced salt solution. NE elicited a dose-dependent slowing of spontaneous Purkinje neuron discharge in both young (3-6 months) and aged (20-22 months) cerebellar grafts. Hill plots demonstrated that the dose-response relationships in both age-groups were linear and parallel to one another. Aged transplant Purkinje neurons manifested a marked and highly significant subsensitivity to NE with an EC50 of 583 microM, as compared with an EC50 of only 15.9 microM in the young grafts. Young grafts in 15-21-month-old hosts manifested an EC50 of 20 microM for the depressant actions of NE. Collaterals of host iris sympathetic fibers innervate the grafts. Activity of these fibers can be reflexly altered by changing illumination of the retina. The dynamics of presynaptic NE release from these fibers was evaluated using in vivo electrochemistry with Nafion-coated graphite epoxy capillary electrodes, which are highly selective for the monoamine neurotransmitters. As illumination of the ipsilateral retina is increased, the release of catecholamine in the cerebellar graft decreases. A mean change in the extracellular electroactive species of 4.2 +/- 0.6 microM was found in young cerebellar grafts. Equivalent stimuli induced a mean change of 2.3 +/- 0.8 microM in aged grafts. However, this diminished release was not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Human fetal cerebellar and cortical tissue transplanted to the anterior eye chamber of athymic rats: electrophysiological and structural studies

Human fetal tissue fragments from cortex cerebri and cerebellum were grafted to the anterior chamber of the eye of adult athymic nude rats. The grafts were obtained from tissue fragments recovered after elective routine abortions, performed in weeks 8-11 of gestation. Both cerebellar and cortex cerebri grafts survived and developed in the anterior chamber of the eye for 1-4 months. The transplants slowly became vascularized from the host iris. The grafts developed blood vessels with laminin-immunoreactive walls and contained relatively high amounts of glial fibrillary acidic protein- and neurofilament-immunoreactivity in the neuropil after 4 months in oculo. Recordings of extracellular action potentials from the grafts revealed spontaneously active neurons with action-potential waveforms similar to those observed in immature rodents. Morphologically, the grafts showed no signs of rejection. Clusters and bands of large neurons resembling Purkinje cells and dense aggregates of smaller granule-like cells could be found in the cerebellar grafts. Large neurons were also seen in the cortex grafts. Taken together, these data suggest that the athymic rat may serve as a useful tool for studies of central nervous system tissue from otherwise immunologically incompatible species.

Human fetal tissues grafted to rodent hosts: structural and functional observations of brain, adrenal and heart tissues in oculo

The potential for growth and development of human tissue grafts was explored by transplantation to the anterior chamber of the eye of rats and mice. Tissues were obtained from therapeutic abortions, performed in the eighth to twelfth week of gestation, using a slight modification of routine vacuum aspirations. Recipients were either adult rats immunosuppressed with cyclosporin A and protected with antibiotics, or nude immunodeficient Balb C mice. Catecholamine-rich tissues such as chromaffin cells from the adrenal medulla, sympathetic ganglia, central dopamine neuroblasts from the substantia nigra, and noradrenaline neuroblasts from the locus coeruleus all survived grafting, and in many cases formed nerve fibers that invaded the host iris. Similarly, central serotonin neurons from developing raphe nuclei grafts were able to innervate host irides. Human fetal cerebellar and cerebral cortical transplants continued their development in rat host eyes. Extracellular recordings from such cerebellar and cortical grafts revealed spontaneously active cells with immature action potential waveforms. Spinal cord grafts also survived and contained substance P-immunoreactive neurons. Dorsal root ganglia were able to form nerve fibers invading the host iris, as evidenced by neurofilament immunohistochemistry. Heart tissue survived and manifested spontaneous rhythmic contractions in oculo. Both human cortex cerebri and heart tissue grafts became innervated by sympathetic adrenergic nerve fibers from the rat host iris. Thus both graft-to-host and host-to-graft neuronal connections may be established between man and rat. Taken together, these data suggest that transplantation of human fetal nervous tissues to the anterior chamber of immunosuppressed or immunodeficient rodent hosts yields a unique model system for studies of human brain development, developmental disturbances, connectivity, and the action of drugs.

Myocardium and cortex cerebri xenografts transplanted into the anterior chamber of the eye of athymic rats: a morphologic and electrophysiologic profile

Heart atria and cortex cerebri from fetal rabbits (E14 and E18, respectively) were grafted into the anterior eye chamber of anesthetized athymic nude rats and allowed to mature for 2-11 weeks. All grafts received a rich vascular supply from the host iris. Atrial transplants survived well but showed no significant growth while cortex grafts increased in size an average of 320%. Spontaneous action potentials were recorded from cellular elements in both tissues and, in the case of the atria, were accompanied by observable contractions. Functional cholinergic innervation from the autonomic ground plexus of the iris was elicited in both types of grafts by phasic retinal illumination. No evidence of immunologic rejection was found by histological analysis. Taken together, these data suggest that athymic rats may provide an appropriate host environment to study transplants of the central nervous and peripheral tissue from immunologically otherwise incompatible mammalian species.

Differentiation of the suprachiasmatic nucleus in fetal rat anterior hypothalamic transplants in oculo

The capacity of the rat anterior hypothalamus, and particularly the suprachiasmatic nucleus (SCN), to develop and differentiate when removed from its normal environment was examined in this study using light and electron microscopy. The hypothalamus from fetuses ranging in age from embryonic day 12 (E 12) to E 16 was transplanted to the anterior chamber of the eye of adult rats. In initial experiments, we found that transplants from E 15 fetuses and older routinely differentiated into fields of neurons with extensive neuropil with an appearance similar to the anterior hypothalamic area. Groups of small, compactly organized neurons were observed only occasionally in this tissue. Ultrastructural analysis of these transplants typically revealed well-differentiated neuronal perikarya and neuropil with a complex synaptic organization similar in appearance to the normal rat anterior hypothalamic area. Occasionally both mature and immature tissue coexisted in some of the transplants. Tissue from young embryos (E 12-14) frequently showed development of a compact, small neuron nucleus with the cytoarchitectonic appearance of the SCN. At least 45 days were required after transplantation for the successful differentiation to occur in this situation. The SCN in these transplants displayed vasoactive intestinal polypeptide-immunoreactive cells and fibers surrounded by vasopressin-immunoreactive cells and fibers, similar to the pattern observed in the normal adult SCN. Our results indicate that the anterior hypothalamus will differentiate normally in oculo and that the phenotypic specification of the SCN occurs prior to the birthdate of its component neurons.

Anatomical predictors of behavioral recovery following fetal striatal transplants

The ability of fetal striatal transplants to reverse behavioral deficits produced by kainic acid striatal lesions was assessed in adult female rats. Three groups of animals, including a lesion-only, a lesion and transplant, and a control group were assessed on several measures, including rewarded alternation, a sensorimotor neurological examination and on spontaneous locomotor activity. Anterior-medial striatal lesions led to a decreased performance on the rewarded alternation and sensorimotor neurological examination and caused the animals to be hyperactive in horizontal and stereotypical movements. The transplants partially reversed the rewarded alternation and locomotor deficits, but had little effect on the sensorimotor neurological deficit. Histologically, the transplanted fetal tissue survived well within the kainate-treated striatal region, and partially reversed the lesion-induced cell loss. Neuronal cell counts successfully predicted outcome on several of the behavioral measures, suggesting that the extent of behavioral recovery depends partially on quantitative aspects of the transplantation methodology.