Electrophysiological analysis reinnervation of transplants in the anterior chamber of the eye by the autonomic ground plexus of the iris

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.

Global scientific trends on the islet transplantation in the 21st century: A bibliometric and visualized analysis

BACKGROUND

Islet transplantation (IT) has emerged as a significant research area for the treatment of diabetes mellitus and has witnessed a surge in scholarly attention. Despite its growing importance, there is a lack of bibliometric analyses that encapsulate the evolution and scientific underpinnings of this field. This study aims to fill this gap by conducting a comprehensive bibliometric analysis to delineate current research hotspots and forecast future trajectories within the IT domain with a particular focus on evidence-based medicine practices.

METHODS

This analysis scrutinized literature from January 1, 2000, to October 1, 2023, using the Web of Science Core Collection (WoSCC). Employing bibliometric tools such as VOSviewer, CiteSpace, and the R package "bibliometrix," we systematically evaluated the literature to uncover scientific trends and collaboration networks in IT research.

RESULTS

The analysis revealed 8388 publications from 82 countries, predominantly the United States and China. However, global cross-institutional collaboration in IT research requires further strengthening. The number of IT-related publications has increased annually. Leading research institutions in this field include Harvard University, the University of Alberta, the University of Miami, and the University of Minnesota. "Transplantation" emerges as the most frequently cited journal in this area. Shapiro and Ricordi were the most prolific authors, with 126 and 121 publications, respectively. Shapiro also led to co-citations, totaling 4808. Key research focuses on IT sites and procedures as well as novel therapies in IT. Emerging research hotspots are identified by terms like "xenotransplantation," "apoptosis," "stem cells," "immunosuppression," and "microencapsulation."

CONCLUSIONS

The findings underscore a mounting anticipation for future IT research, which is expected to delve deeper into evidence-based methodologies for IT sites, procedures, and novel therapeutic interventions. This shift toward evidence-based medicine underscores the field's commitment to enhancing the efficacy and safety of IT for diabetes treatment, signaling a promising direction for future investigations aimed at optimizing patient outcomes.

Biomaterial-assisted strategies to improve islet graft revascularization and transplant outcomes

Islet transplantation holds significant promise as a curative approach for type 1 diabetes (T1D). However, the transition of islet transplantation from the experimental phase to widespread clinical implementation has not occurred yet. One major hurdle in this field is the challenge of insufficient vascularization and subsequent early loss of transplanted islets, especially in non-intraportal transplantation sites. The establishment of a fully functional vascular system following transplantation is crucial for the survival and secretion function of islet grafts. This vascular network not only ensures the delivery of oxygen and nutrients, but also plays a critical role in insulin release and the timely removal of metabolic waste from the grafts. This review summarizes recent advances in effective strategies to improve graft revascularization and enhance islet survival. These advancements include the local release and regulation of angiogenic factors (e.g., vascular endothelial growth factor, VEGF), co-transplantation of vascular fragments, and pre-vascularization of the graft site. These innovative approaches pave the way for the development of effective islet transplantation therapies for individuals with T1D.

Uncommon Transplantation Sites: Transplantation of Islets and Islet Organoids in the Anterior Chamber of the Eye of Rodents and Monkeys

The anterior chamber of the eye is a highly vascularized and innervated location that is also particularly rich in oxygen and immune privileged. This uncommon transplantation site offers unique possibilities for the observation of the transplanted material as well as for local pharmacological intervention. Transplantation of islets and islet organoids to the anterior chamber of the eye of mice and monkeys facilitates a multitude of new approaches for research into islet physiology and pathophysiology and for the treatment of diabetes. We now present a short overview of the experimental possibilities and describe an updated protocol for transplantation of islets and islet organoids into mice and monkeys.

The Eye as a Transplantation Site to Monitor Pancreatic Islet Cell Plasticity

The endocrine cells confined in the islets of Langerhans are responsible for the maintenance of blood glucose homeostasis. In particular, beta cells produce and secrete insulin, an essential hormone regulating glucose uptake and metabolism. An insufficient amount of beta cells or defects in the molecular mechanisms leading to glucose-induced insulin secretion trigger the development of diabetes, a severe disease with epidemic spreading throughout the world. A comprehensive appreciation of the diverse adaptive procedures regulating beta cell mass and function is thus of paramount importance for the understanding of diabetes pathogenesis and for the development of effective therapeutic strategies. While significant findings were obtained by the use of islets isolated from the pancreas, in vitro studies are inherently limited since they lack the many factors influencing pancreatic islet cell function in vivo and do not allow for longitudinal monitoring of islet cell plasticity in the living organism. In this respect a number of imaging methodologies have been developed over the years for the study of islets in situ in the pancreas, a challenging task due to the relatively small size of the islets and their location, scattered throughout the organ. To increase imaging resolution and allow for longitudinal studies in individual islets, another strategy is based on the transplantation of islets into other sites that are more accessible for imaging. In this review we present the anterior chamber of the eye as a transplantation and imaging site for the study of pancreatic islet cell plasticity, and summarize the major research outcomes facilitated by this technological platform.

Advances in Pancreatic Islet Transplantation Sites for the Treatment of Diabetes

Diabetes is a complex disease that affects over 400 million people worldwide. The life-long insulin injections and continuous blood glucose monitoring required in type 1 diabetes (T1D) represent a tremendous clinical and economic burdens that urges the need for a medical solution. Pancreatic islet transplantation holds great promise in the treatment of T1D; however, the difficulty in regulating post-transplantation immune reactions to avoid both allogenic and autoimmune graft rejection represent a bottleneck in the field of islet transplantation. Cell replacement strategies have been performed in hepatic, intramuscular, omentum, and subcutaneous sites, and have been performed in both animal models and human patients. However more optimal transplantation sites and methods of improving islet graft survival are needed to successfully translate these studies to a clinical relevant therapy. In this review, we summarize the current progress in the field as well as methods and sites of islet transplantation, including stem cell-derived functional human islets. We also discuss the contribution of immune cells, vessel formation, extracellular matrix, and nutritional supply on islet graft survival. Developing new transplantation sites with emerging technologies to improve islet graft survival and simplify immune regulation will greatly benefit the future success of islet cell therapy in the treatment of diabetes.

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.

Intraocular in vivo imaging of pancreatic islet cell physiology/pathology

BACKGROUND

Diabetes mellitus has reached epidemic proportions and requires new strategies for treatment. Unfortunately, the efficacy of treatment regimens on maintaining/re-gaining functional beta cell mass can, at the present, only be determined indirectly. Direct monitoring of beta cell mass is complicated by the anatomy of the endocrine pancreas, which consists of thousands to a million of discrete micro-organs, i.e. islets of Langerhans, which are scattered throughout the pancreas.

SCOPE OF REVIEW

Here, we review the progress made over the last years using the anterior chamber of the eye as a transplantation site for functional imaging of pancreatic islet cells in the living organism. Islets engrafted on the iris are vascularized and innervated and the cornea, serving as a natural body-window, allows for microscopic, non-invasive, longitudinal evaluation of islet/beta cell function and survival with single-cell resolution in health and disease.

MAJOR CONCLUSIONS

Data provided by us and others demonstrate the high versatility of this imaging platform. The use of 'reporter islets' engrafted in the eye, reporting on the status of in situ endogenous islets in the pancreas of the same animal, allows the identification of key-events in the development and progression of diabetes. This will not only serve as a versatile research tool but will also lay the foundation for a personalized medicine approach and will serve as a screening platform for new drugs and/or treatment protocols. 'Metabolic' islet transplantation, in which islets engrafted in the eye replace the endogenous beta cells, will allow for the establishment of islet-specific transgenic models and 'humanized' mouse models as well as serving as the basis for a new clinical transplantation site for the cure of diabetes.

Synapsin I in Intraocular Hippocampal Transplants during Maturation and Aging: Effects of Brainstem Cografts

The role of target innervation for maintenance of synaptic proteins in the hippocampal formation during aging was investigated. Fetal CA1 tissue and brainstem tissue containing the nucleus locus coeruleus was dissected from albino rats and grafted sequentially into the anterior chamber of the eye of adult rat recipients. Synapsin protein distribution and levels were evaluated by immunohistochemistry and quantitative immunolabeling in single hippocampal grafts or brainstem-hippocampal double grafts at 6,12, or 24 mo postgrafting. The synapsin levels in 6-mo-old single hippocampal transplants were significantly lower than those in situ, and remained at these lower levels at 12 and 24 mo. On the contrary, synapsin levels were close to normal in the hippocampal portion of double grafts in the 6- and the 12-mo-group. However, in the 24-mo-old double transplants the levels had declined significantly, approaching levels seen in single hippocampal grafts. The immunoblot results were supported by morphological observations with synapsin antibodies and immunohistochemistry. The present data demonstrate that hippocampal tissue maintained near normal synapsin levels when grafted together with brainstem tissue, as compared to the lower levels seen in single hippocampal grafts. This normalization of synapsin levels was, however, not seen in the aged hippocampal-brainstem double grafts.

Comparison of Fetal Rabbit Brain Xenografts to Three Different Strains of Athymic Nude Rats: Electrophysiological and Immunohistochemical Studies of Intraocular Grafts

Interest in the use of neural tissue transplantation for the study of CNS development and maturation and the potential use of this technique for the treatment of certain degenerative CNS disorders has led to our use of transplantation of neural tissue across species lines. Prior to extensive transplantation studies using athymic rats as recipients, we wished to evaluate the currently available strains of athymic rat for their suitability as host animals for xenografts of neural tissue. Fetal cerebellar and cerebral cortex tissue from rabbit brain of gestational age 20-25 days was dissected and transplanted to the anterior chamber of the eye of Harlan Wisconsin, Fisher 344 Jnu, or NCI-Harlan athymic nude rat strains. The brain tissue grafts were allowed to mature for 3 mo during which time the size and vascularity of each graft was monitored through the cornea of anesthetized hosts. In each group all of the transplants survived and grew to varying extents in the anterior chamber of the eye. Following the growth study in vivo extracellular recording of single neuronal activity was performed. Spontaneous neural activity was found in most transplants in all three groups with no difference in the viability or discharge rates of neurons between the groups. Illumination of the ipsilateral eye increased the firing rate of neurons in all three groups, suggesting excitatory cholinergic innervation of the grafted neurons from the host parasympathetic iris ground plexus. Antibodies directed against neurofilament protein, glial fibrillary acidic protein, synapsin, and tyrosine hydroxylase were used to characterize the transplants immunocytochemically and revealed no differences between the grafts in the three groups of recipients. All transplants contained significant numbers of glial and neuronal elements with the distribution resembling that in adult brain tissue. Some of the transplants contained a sparse innervation of tyrosine hydroxylase–positive fibers from the sympathetic plexus of the host iris. Furthermore, synapsin-immunoreactivity suggested that synaptogenesis had taken place within the grafts. Histological examination of the grafts revealed that 67% of the grafts had been infiltrated, to varying extents, by lymphocytes which led to areas of cell lysis and necrosis. All host animals had populations of T-cell receptor positive cells, most of which also expressed the T-cell surface antigens CD4 and CD8. However, no transplants were overtly rejected over the 15 wk period of study. Our investigation demonstrates that all of the athymic strains used in this study are able to mount an immune response against grafted fetal tissue, despite the absence of rejection, and that none of these strains is superior to the others with respect to suitability as a host for the long-term study of fetal CNS xenografts in oculo.

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.

Novel approaches to studying the role of innervation in the biology of pancreatic islets

The autonomic nervous system helps regulate glucose homeostasis by acting on pancreatic islets of Langerhans. Despite decades of research on the innervation of the pancreatic islet, the mechanisms used by the autonomic nervous input to influence islet cell biology have not been elucidated. This article discusses how these barriers can be overcome to study the role of the autonomic innervation of the pancreatic islet in glucose metabolism. It describes recent advances in microscopy and novel approaches to studying the effects of nervous input that may help clarify how autonomic axons regulate islet biology.

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.

Non-invasive in vivo imaging of pancreatic β-cell function and survival - a perspective

A major problem in medical research is to translate in vitro observations into the living organism. In this perspective, we discuss ongoing efforts to non-invasively image pancreatic islets/β-cells by techniques, such as magnetic resonance imaging and positron emission tomography, and present an experimental platform, which allows in vivo imaging of pancreatic β-cell mass and function longitudinally and at the single-cell level. Following transplantation of pancreatic islets into the anterior chamber of the eye of mice and rats, these islets are studied by functional microscopic imaging. This imaging platform can be utilized to address fundamental aspects of pancreatic islet cell biology in vivo in health and disease. These include the dynamics of pancreatic islet vascularization, islet cell innervation, signal-transduction, change in functional β-cell mass and immune responses. Moreover, we discuss the feasibility of studying human islet cell physiology and pathology in vivo as well as the potential of using the anterior chamber of the eye as a site for therapeutic transplantation in type 1 diabetes mellitus.

Reinnervation of transplanted vas deferens by cholinergic nerves normally supplying skeletal muscle

The rat vas deferens was removed and either transplanted alongside the soleus muscle or into the bed of the soleus muscle that had previously been removed, and in this case the soleus nerve was connected to the transplant. The vas deferens reinnervated by the somatomotor nerve recovered the best. Contractions to transmural electrical stimulation could not be elicited from the denervated vas deferens, although noradrenaline and acetylcholine elicited contractions. The reinnervated vas deferens produced good contractile responses to transmural stimulation, and these were substantially reduced by a cholinergic muscarinic blocking agent, hyoscine, as compared to only a small reduction in the control vas deferens. Neostigmine potentiated the contraction of the transplanted vas deferens to a greater extent than that of the control. This indicated that a substantial component of the contractile response was produced by cholinergic fibres. Consistent with this was the finding that, while guanethidine blocked a greater proportion of the contraction in the control vas deferens, the contraction of the reinnervated transplant was less affected. Acetylcholine elicited a strong contraction in control vas deferens, but only a small response was obtained in the reinnervated transplant. However, the response to noradrenaline was greater in the transplant than in the control vas deferens. These results indicate that cholinergic nerves normally supplying skeletal muscle can reinnervate smooth muscle and that the alien somatomotor innervation altered the responsiveness of the smooth muscle of the vas deferens. Morphological studies confirm the shift from adrenergic to cholinergic fibres in the reinnervated vas deferens.

Factors regulating growth of catecholamine-containing nerves, as revealed by transplantation and explantation studies

Intraocular grafting of various types of neuron and target tissue shows that peripheral and central noradrenergic neurons may substitute morphologically and functionally for each other in certain, but not all, target tissues. The morphology of growing adrenergic nerve terminals, their patterning, and the number of fibres are completely determined by the target tissues. Thus, the sympathetic adrenergic neuron of an adult organism is a highly plastic unit which may, for instance, double or even triple its terminal field in response to new demands from the environment. Several differences exist between central and peripheral adrenergic nerves: locus coeruleus will not innervate heart grafts; sympathetic fibres will not innervate the spinal cord; and central adrenergic neurons are not sensitive to nerve growth factor (NGF). Chromaffin cells can be made to innervate peripheral and central targets. No NGF is detected in normal adult iris. The iris responds to grafting, explantation, and to sensory or sympathetic denervation with rapid production of NGF as shown by bioassays on chick embryonic ganglia. This iris also contains a potent stimulatory factor for the ciliary ganglion. Trauma to the iris or to the anterior eye chamber may cause it to become hyperinnervated. Heavy metals have characteristic and different effects on the sympathetic nerves of the iris: lead and manganese causes hyperinnervation; cadmium does not change the number of nerves; while mercury causes severe terminal degeneration followed by regeneration.

Development of synapsin I and synapsin II in intraocular hippocampal transplants

Previous studies have indicated that the appearance of synaptic vesicle-associated proteins known as the synapsins is one indicator of synapse formation. In this study, the levels and morphological distribution of synapsin I and synapsin IIa and IIb were studied in intraocular hippocampal transplants and in situ in the intact hippocampus. No detectable levels of either synapsin I or synapsin II were found in the fetal brain. The in situ levels of the synapsins exhibited parallel increases rapidly after birth, reaching peak levels at 8 weeks, after which a slight decline was noted in synapsin I and synapsin IIb. In hippocampal transplants, a comparable increase in the synapsins was seen during the first 8 weeks in oculo. It is likely that the synapse formation in the hippocampal transplants represents synapses from neurons within the transplant, as well as from various peripheral ganglia that send collaterals into the graft. Peripheral and central synapses express different synapsin I: synapsin IIa and IIb ratios. When the ratios of the synapsin proteins in hippocampal transplants were examined ratios essentially identical to those seen in the normal hippocampus were found, despite the numerous peripheral neurites innervating the grafts. Immunohistochemical studies supported the immunoblot data, showing no detectable immunofluorescence with synapsin antibodies in fetal or newborn hippocampal formation. The density of immunoreactive profiles increased substantially both in transplants and in the hippocampal formation in situ during the first 2 postnatal months. In conclusion, the present data demonstrate that hippocampal transplants in oculo can develop significant levels of the synapsins and that there is no time lag in development in these levels compared to the hippocampal formation in situ.

Tyrosine hydroxylase and neuropeptide-Y immunoreactivity in pineal glands developing in situ and in pineal grafts

Postnatal development of the innervation of the pineal gland in situ as well as the reinnervation of pineal grafts by tyrosine hydroxylase (TH)- and neuropeptide Y (NPY)-immunoreactive nerve fibers were examined using the avidin-biotin-peroxidase immunohistochemical technique. TH-immunoreactive nerve fibers appeared in the pineal gland on the second postnatal day (P2) in both hamsters and gerbils. NPY-immunoreactive nerve fibers first appeared in the pineal gland of gerbils on P2 and in the hamsters on P3. By the seventh postnatal day (P7), the pineal glands of both hamsters and gerbils were richly innervated by TH- and NPY-fibers that appeared as smooth fibers or fibers with sporadic varicosities. By the age of 4 weeks, the innervation of the pineal glands of hamsters and gerbils by TH- and NPY-fibers was fully developed. Abundant TH- and NPY-fibers formed a dense meshwork in the parenchyma of the superficial and deep pineals. The great majority of the fibers bore a large number of varicosities. More NPY-fibers were found in the pineal glands of gerbils than hamsters. NPY fibers were distributed evenly throughout the pineal glands of the gerbil, but they were more often located in the central region of the superficial pineal of the hamster. For the pineal grafts, superficial pineals from neonatal and 4-week-old hamsters were transplanted to different sites in the third cerebral ventricle (infundibular recess, posterior third ventricle) or beneath the renal capsule. The pineal grafts from 4-week-old donors appeared to undergo severe degeneration and eventually disappeared. The pineal grafts from neonatal hamsters, however, successfully survived and became well integrated into their new locations. Abundant TH- and NPY-fibers in the host brain were found surrounding the pineal grafts placed in the third cerebral ventricle, but were only rarely seen entering the parenchyma of the grafts. A few TH-fibers were demonstrated in the renal grafts 4 weeks after transplantation. These studies describe the postnatal development of the innervation of the pineal glands in situ by TH- and NPY-nerve fibers, and demonstrate a lack of reinnervation of cerebroventricular pineal grafts by TH and NPY fibers from adjacent host brain.

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)

Role of sympathetic innervation in cardiac development in oculo

Embryonic heart cultured in oculo differentiates into adult-like heart tissue, increases in size, and maintains spontaneous activity driven by a defined pacemaker. The growth and beating rate of embryonic heart maturing in oculo are modulated by its neural milieu. Culture in a sympathetically denervated eye chamber compromised growth and increased intrinsic beating rate. Exposure to an additional source of sympathetic neurons increased parasympathetic control of heart rate but did not alter growth or intrinsic beating rate. Because eye chamber sympathectomy alters neurotransmitter expression in parasympathetic and sensory neurons, it is possible that the growth inhibition observed in heart grafts is not a direct consequence of preventing sympathetic innervation. This possibility is being tested in additional experiments.

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.

Spinal cord grafts in oculo: survival, growth, histological organization and electrophysiological characteristics

Fetal spinal cord tissue was grafted to the anterior chamber of the eye of adult recipients. Transverse segments from the cervical and high thoracic levels were divided in halves which were grafted directly or further divided into ventral horn and dorsal horn parts before grafting. Survival and intraocular growth was monitored through the cornea. Grafts from E14 to E16 grew to final sizes several times the initial size. The final size of E17 grafts was approximately similar to the initial size, while the final size of E18 and E19 grafts was considerably smaller than the size at grafting. All grafts were well vascularized from the host iris. Grafts from younger donors contained several neurons typical of spinal cord including alpha-moto-neuron-type cells. Cells were found in clusters in gray matter areas surrounded by white matter. Extracellular recording revealed many spontaneously active cells. Several had high sustained discharge (10-25 Hz) and large amplitudes. Many cells could be excited by stimulation of the graft surface via activation of local afferents. It is concluded that the capacity of fetal spinal cord tissue to survive grafting to the eye chamber is inversely related to the donor age. Before E17, large grafts retaining several morphological and electrophysiological characteristics of spinal cord are obtained. The intraocular spinal cord graft provides a useful model for studies of spinal cord development and, using co-grafting techniques, a model for spinal cord regeneration and functional connectivity.

Gustatory trophic action of arterial chemosensory neurones in the cat

The proximal stump of the carotid sinus nerve (c.s.n.) branch of the IXth cranial nerve was surgically cross-anastomosed to the distal stump of the lingual nerve (l.n.) branch of the same cranial nerve to test the ability of regenerating c.s.n. axons to reinnervate and induce taste buds on cat circumvallate papillae. The l.n. branch of the IXth nerve, which normally innervates circumvallate papillae, was directed away from the tongue by suturing it to the distal stump of the c.s.n. Animals with normal and re-anastomosed (cut, then resutured) l.n. served as control preparations. 2-19 months following cross-anastomosis, circumvallate papillae contained 59.8 +/- 9.1% (mean +/- S.E. of mean) of the normal incidence of taste buds, indicating that axons possessing specific gustatory trophic properties had reinnervated the epithelium. Further experimentation was concerned with confirming the identity of the putative foreign axons which reinnervated the taste buds. Radiolabelled axoplasmic transport and autoradiography showed that 89 +/- 4.4% of the taste buds in cross-anastomosed, and 97 +/- 2.1% in normal preparations were innervated by axons from the principal sensory ganglion (petrosal) of the IXth nerve (P greater than 0.05). Whole-nerve recordings in cross-anastomosed preparations demonstrated gustatory activity in the transposed c.s.n., which was similar to responses present in normal and re-anastomosed l.n. preparations. The largest response was evoked by 4 M-NaCl, followed by 1 M-NH4Cl and 0.02 M-quinine HCl. Sucrose (0.5 M) elicited insignificant nerve activity. In normal animals, gustatory or mechanical stimulation did not alter cardiopulmonary function, but in bilaterally cross-anastomosed preparations, gustatory stimuli produced respiratory excitation while mechanical stimulation resulted in reductions in blood pressure and respiratory inhibition. These data suggest that following cross-anastomosis, arterial chemosensory axons innervate taste buds and barosensory axons innervate tongue mechanoreceptors (which normally evoke cardiopulmonary reflexes from the carotid body and carotid sinus, respectively). We conclude that arterial chemosensory neurones share with gustatory chemosensory neurones a trophic function essential for the development and maintenance of taste buds.

Effect of dopamine agonists and antagonists on the electrical activity of substantia nigra neurons transplanted into the lateral ventricle of the rat

Pieces of fetal rat mesencephalon containing the substantia nigra were transplanted into the lateral ventricle of rats pretreated with 6-OHDA injections into the ipsilateral substantia nigra. Extracellular recordings from these grafts revealed spontaneously active neurons with action potential waveforms and firing rates similar to those found in substantia nigra zona compacta in situ. Furthermore, local application of dopamine agonists inhibited, while dopamine antagonists increased zona compacta activity, both in situ and of cells from nigral grafts. We conclude that substantia nigra grafts contain spontaneously active neurons similar to those of zona compacta in situ, and that some of the mechanisms regulating nigral neuronal activity in situ are also present in this preparation.

Thyroxin dependency of the developing locus coeruleus. Evidence from intraocular grafting experiments

Surgical thyroidectomies were used as means of altering the thyroid state of adult recipients to study the possible influence of thyroid hormones on fibre formation in irides by immature noradrenaline neurons of the locus coeruleus grafted to the eye. Whole-mount preparations of irides were analysed using fluorescence histochemistry according to Falck-Hillarp, subjectively estimating on a 'blind' basis the number of fibres, their pattern of distribution and individual morphology in the iris dilator plate. Neurones of the locus coeruleus formed nerve fibres in irides of thyroidectomized recipients to the same extent as in controls. Distribution and fine structure of these fibres, however, differed markedly. The numerous thick axon bundles from the attachment of the brain graft, normally seen to radiate out from locus coeruleus-neurones in oculo, were almost totally lacking in the thyroidectomized group. Also, the individual nerve fibres showed abundant peripheral accumulations of fluorescent material. This appearance of the outgrowth of fluorescent fibres in the experimental group, indicative of a disturbed formation of nerve fibres during development in oculo, was abolished by reversal of the thyroid hormone deficiency using daily injections of l-thyroxin to the recipients throughout the experiment. This strongly indicates a role for thyroxin in the process of formation of nerve fibres originating from the neurones of the locus coeruleus during perinatal development. The present paper is supportive of recent reports claiming that during the development of the CNS thyroxin plays a crucial role in tubulin assembly, and thus presumably for the ability of neurones to form processes.

Effect of cross-transplantation on normotensive and spontaneously hypertensive rat arterial muscle membrane

Transplantation of arteries into the anterior eye chamber of rats for 8 weeks was used to test the hypothesis that the neurohumoral environment is important in establishing the altered membrane potential (observable during electrogenic ion transport inhibition) of vascular muscle in hypertension. When caudal arteries from 12- to 16-week-old spontaneously hypertensive rats (SHR) or genetically matched Kyoto-Wistar normotensive rats (KNR) were transplanted into the opposite strain, there was no change in the transport inhibited membrane potential (Em) of the arterial muscle cells from that found in freshly excised donor arteries. However, when caudal arteries from 2-week-old animals were transplanted into the anterior eye chamber, the arteries always developed the appropriate Em for the host animal. In other words, a genetically KNR artery developed the Em of an SHR artery in an SHR host; conversely, a genetically SHR artery developed the Em of a KNR artery in the KNR host. These results provide evidence that: 1) the differences between th Em of caudal arteries from SHR and KNR are not inherent in those muscle cells; 2) the change in Em is triggered in young animals preceding development of hypertension, but not after hypertension is established; and 3) the Em alteration of the caudal artery is independent of structural changes that occur in the artery as a result of increased blood pressure (because KNR transplants were not connected in series with the host anterior eye chamber vasculature and subject to the elevated blood pressures). We conclude that the arterial muscle cells up to a certain age respond to an external factor that regulates their Em and presumably their sensitivity to vasopressor agents.

Conditions for adrenergic hyperinnervation in hippocampus: II. Electrophysiological evidence from intraocular double grafts

Following sequential intraocular transplantations of areas containing NE cell bodies (locus coeruleus or superior cervical ganglion) and of NE fiber target areas (hippocampus), both pieces mature in a manner analogous to that observed for individual transplants. NE-containing nerve fibers, derived from either LC or SCG transplants, can be seen to invade the hippocampal formation. When LC is used, the invading fibers markedly hyperinnervate the hippocampus while SCG-derived fiber densities approximate those seen with innervation from the adrenergic ground plexus of the iris. Electrophysiological recordings from neurons in the LC reveal an atropine-sensitive excitatory response to illumination, suggesting innervation of the LC by cholinergic nerve fibers from the iris. This is supported by the fact that dense cholinesterase-positive staining can be found in the LC piece. Application of an epileptogenic agent, such as penicillin, results in a marked excitation of neurons in the LC without inducing epileptiform activity in the hippocampus. In contrast, single hippocampal grafts seize readily after penicillin. Local application of the inhibitory agent GABA into the LC allows penicillin-induced epileptiform activity to generate in the hippocampus, suggesting that functional inhibitory innervation develops between NE fibers derived from LC and pyramidal neurons in the hippocampus. Supporting this, subsequent excitation of LC neurons by iontophoresis of glutamate terminates the hippocampal seizure. Prior administration of reserpine (2.5 mg/kg) disrupts the inhibitory influence of LC innervation on the hippocampal EEG following penicillin. After reserpine, the hippocampal portions of double grafts behave like single hippocampal transplants. It is concluded that sequential transplantations of cell body and target regions of the CNS to the anterior chamber of the eye creates a functional, yet isolated, neuronal pathway which can be utilized to study the development of neuronal connections.

Conditions for adrenergic hyperinnervation in hippocampus: I. Histochemical evidence from intraocular double grafts

The developing hippocampal anlage of rats was homologously grafted to the anterior chamber of the eye of adult recipients. After intraocular maturation of the hippocampal graft and removal of the sympathetic innervation of the eye by ipsilateral superior cervical ganglionectomy, four types of monoamine neurons were transplanted to the eye chamber: Peripheral sympathetic neurons, central adrenergic neurons of locus coeruleus, central dopaminergic neurons of substantia nigra, and central 5-hydroxytryptamine neurons of the lower raphe nuclei. All four classes of monoamine neurons were able to reinnervate the hippocampal graft, but the fiber ingrowth differed markedly. Although peripheral sympathetic neurons produced a pattern of adrenergic innervation in the hippocampal graft which resembled innervation of the hippocampus by the locus coeruleus in the brain, locus coeruleus neurons themselves produced an extremely dense plexus of fibers within the graft. This hyperinnervation remained intact for up to 9 months, the longest period of time studied. The locus coeruleus graft itself received fibers from the hippocampus graft, as demonstrated by the retrograde transport of horseradish peroxidase. We conclude that the hippocampal graft exerts a much stronger growth stimulation on the locus coeruleus neurons than on the peripheral sympathetic neurons. The difference between innervation patterns suggest that both presynaptic and postsynaptic influences determine fiber ingrowth in the central nervous system.

Cephalic-phase insulin secretion in normal and pancreatic islet-transplanted rats

The ability of saccharin, in comparison with glucose and tap water, to elicit glycemia-independent neurally mediated insulin secretion was investigated in chronically catheterized, freely moving rats. Plasma glucose and insulin concentrations were measured continuously from venous blood with a sampling resolution of one per minute. In normal rats, 1 ml of 0.15% saccharin caused a significant rapid rise in peripheral plasma insulin levels lasting up to 5 min, without significant changes in glycemia. Tap water alone also induced a transient elevation in insulinemia but was much smaller than the saccharin-induced response. In streptozotocin diabetic rats bearing intrahepatic, presumably denervated islet isografts, these rapid insulin responses to oral saccharin and tap water stimulation were completely abolished, whereas the early insulin response to intravenous glucose was decreased by only about 30%. These results are consistent with the concept of gustatory and other oral sensory signals acting as triggers for neurally mediated insulin release.

Seizures and related epileptiform activity in hippocampus transplanted to the anterior chamber of the eye: modulation by cholinergic and adrenergic input

Transplants of rat hippocampus into the anterior chamber of the eye of a host animal were used to assess the effects of cholinergic and adrenergic neuronal inputs on the generation and duration of seizure activity. Cholinomimetics initiated both seizures and hypersynchronous neuronal activity in the transplants. Cyclic guanosine monophosphate (GMP) derivatives and isobutyl methylxanthine elicited similar changes. Reflex activation of the cholinergic parasympathetic input to the iris and transplant by illumination of the ipsilateral retina also induced seizures or increased the rate of penicillin-induced interictal spike discharge. Application of beta-adrenergic agonists inhibited interictal spikes and paroxysmal depolarizing shifts induced by penicillin. Fluorescence histochemical studies showed that host sympathetic adrenergic fibers derived from the ground plexus of the iris invaded the transplant to form fine varicose nerve terminals. Activation of these adrenergic afferents to the transplant diminished both the amplitude and frequency of penicillin-induced epileptiform activity. Epileptiform activity in hippocampal occular transplants is strongly modulated by cholinergic and adrenergic neuronal inputs, with the former exerting a facilatory influence and the latter, an inhibitory effect.