Showing papers by "Anders Björklund published in 1990"

Reformation of long axon pathways in adult rat central nervous system by human forebrain neuroblasts.

Abstract: THE failure of lesioned axons to regenerate over long distances in the mammalian central nervous system (CNS) is not due to an inability of central neurons to regenerate, but rather to the non-permissive nature of the CNS tissue environment1–4. Regenerating CNS axons, which grow well within a peripheral nerve, for example, fail to penetrate mature CNS tissue by more than about 1 mm1,5,6. Recent evidence indicates that this may be due to inhibitory membrane proteins associated with CNS oligodendrocytes and myelin2–4,7,8. We report here that human telencephalic neuroblasts implanted into the excitotoxically lesioned striatum of adult rats can escape or neutralize this inhibitory influence of the adult CNS environment and extend axons along major myelinated fibre tracts for distances of up to ∼20 mm. The axons were seen to elongate along the paths of the striato-nigral and cortico-spinal tracts to reach the substantia nigra, the pontine nuclei and the cervical spinal cord, which are the normal targets for the striatal and cortical projection neurons likely to be present in these implants.

The Importance of Graft Placement and Task Complexity for Transplant‐Induced Recovery of Simple and Complex Sensorimotor Deficits in Dopamine Denervated Rats

Abstract: The present study examined the role of graft placement and behavioural task complexity in determining the functional efficacy of intrastriatal grafts of dopamine-rich fetal ventral mesencephalon (VM) placed in the dopamine (DA) depleted striatum. The functional effects of two different striatal placements of VM grafts were evaluated using tests of drug-induced motor asymmetry, simple sensorimotor orienting response, and a more complex sensorimotor integrative task (disengage behaviour), in which the rat has to perform the orienting response while in the act of eating. Rats with complete unilateral 6-hydroxydopamine (6-OHDA) lesions of the mesostriatal DA pathway, received either implants of dissociated fetal VM in the central or ventrolateral portions of the denervated striatum. Nongrafted lesioned rats served as controls. Nine weeks after grafting, the rats were tested on separate days for disengage behaviour, sensorimotor orientation, and amphetamine-induced rotational behaviour. Consistent with previous findings, the two graft placements had differential effects on drug-induced motor asymmetry and sensorimotor responses: the centrally placed VM grafts reversed amphetamine-induced rotational asymmetry but had little effect on the sensorimotor deficit, whereas the ventrolaterally placed grafts reversed the sensorimotor orientation deficits without any effect on the drug-induced rotation. In contrast, fetal VM grafts, regardless of their placement, did not ameliorate the observed deficits in disengage behaviour; that is the grafted rats that had recovered their sensorimotor response in the absence of food were unable to perform the same orienting response while eating. These results provide evidence that functional intrastriatal VM grafts which are capable of restoring sensorimotor responses or motor asymmetry fail to affect lesion-induced deficits in a task that requires more complex sensorimotor integration. It is suggested that the degree of anatomical integration of the grafted DA neurons into the host circuitry will determine the efficacy of the grafts to influence more complex sensorimotor integrative deficits in the DA lesion model.

Acetylcholine release from intrahippocampal septal grafts is under control of the host brain.

Abstract: The activity of intrahippocampal transplants of cholinergic neurons was monitored by microdialysis in awake, freely moving rats. Fetal septal-diagonal band tissue was implanted into rats with a complete transection of the fimbria-fornix cholinergic pathway either as a cell suspension injected into the hippocampus or as a solid graft implanted in the lesion cavity. The grafts restored baseline acetylcholine release in the graft-reinnervated hippocampus to normal or supranormal levels. The graft-derived acetylcholine release was dependent on intact axonal impulse flow, and it was markedly increased during behavioral activation by sensory stimulation or by electrical stimulation of the lateral habenula. The results demonstrate that the septal grafts, despite their ectopic location, can become functionally integrated with the host brain and that the activity of the transplanted cholinergic neurons can be modulated from the host brain during ongoing behavior. Anatomical observations, using immunohistochemistry and retrograde tracing, indicate that direct or indirect brainstem afferents to the graft could mediate this functional integration. Host afferent control of the graft may thus play a role in the recovery of lesion-induced functional deficits seen with these types of transplants.

Effect of Prior Dopamine Denervation on Survival and Fiber Outgrowth from Intrastriatal Fetal Mesencephalic Grafts

Abstract: [3H]Dopamine (DA) uptake radioautography and tyrosine hydroxylase (TH) immunocytochemistry were used to assess quantitatively the effects of the presence or absence of host mesostriatal DA afferents on the survival and fiber outgrowth from fetal ventral mesencephalic DA neurons grafted into the neostriatum of adult recipient rats. Rats received bilateral intrastriatal transplants of fetal ventral mesencephalic tissue 1 month after a unilateral injection of 6-hydroxydopamine (6-OHDA) into the right nigrostriatal bundle (denervated side). Five to six months later, some of the grafted rats received a second 6-OHDA injection in the left nigrostriatal bundle (acutely denervated or 'intact' side). After a further 7 days, slices of each hemisphere from the latter rats were incubated with [3H]DA and processed for film and high resolution radioautography. The density of the film radioautographs was measured with a computerized image analysis system and calibrated by silver grain cluster (i.e. DA terminal) counting over selected areas of the same sections in light microscope radioautographs. The brains of the remaining grafted rats were processed for TH immunoreactivity 6 - 12 months after graft surgery. Neither the size of the grafts, nor the number of surviving TH-positive graft neurons showed any significant difference between the nondenervated and the denervated sides. However, the size of the TH-positive cell bodies was significantly greater in the grafts on the denervated side. In the [3H]DA uptake radioautographs, considerable outgrowth of DA fibers was evident in the neostriatum on the 'intact' side in spite of the presence of an intact host DA innervation until 7 days before sacrifice. The overall DA fiber outgrowth was nevertheless almost two-fold greater on the denervated side, and extended deeper into the host neostriatum than on the 'intact' side; only 7% of the total neostriatal area, on average, was at background level compared to 30% on the 'intact' side, and the overall density of neostriatal DA innervation amounted to 36% of normal as compared to 20% on the 'intact' side. The correlation between the overall density of graft-derived DA innervation and the size of the grafts was linear on the 'intact' side, but reached a plateau with relatively small grafts on the denervated side. However, the ventral striatum on both sides was very poorly innervated by these grafts. These findings demonstrate that the mature neostriatal tissue can support axonal growth and innervation from grafted fetal DA neurons even in the presence of a normal complement of endogenous DA fibers. Prior removal of the host striatal DA innervation does not influence the overall size of the grafts nor the number of surviving DA neurons, but induces an increase in the cell body size and fiber outgrowth of the grafted DA neurons.

Practical aspects of the use of human fetal brain tissue for intracerebral grafting.

Abstract: Publisher Summary This chapter describes the current conditions for the acquisition and preparation of human fetal tissue for intracerebral grafting and to discuss possible optimization and perspectives for its future use. The chapter focuses on the transplantation of dopamine (DA) neurons in experimental and clinical Parkinsonism. The use of human fetal brain tissue for transplantation purposes inevitably brings up several basic medical ethical issues. Following the routine suction abortion procedure, it is possible to identify and dissect a ventral mesencephalo (VM) piece in 50–75% of cases. The search for fetal tissue and dissection of CNS is conducted in a sterile hood by an investigator dressed in full sterile gear. The aborted material, which includes other parts of uterine content in addition to the fetus, is transported from the operating theatre to the place of dissection in a sterile Petri dish. The material is inspected initially to find pieces of the fetus, without a microscope, typically by utilizing a large pair of forceps and by rinsing away blood using a syringe containing sterile saline. Xenografting experiments to rats have revealed some inherent properties of the human fetal neural cells that are useful to bear in mind also when considering the clinical scenario.

Chapter 83 Neural transplantation in Parkinson's disease: the Swedish experience

Abstract: Publisher Summary This chapter discusses the neural transplantation in Parkinson's disease (PD). The fetal nigral implants have provided a modest improvement in motor function in PD patients. This is consistent with the presence of small surviving grafts indicated by positron emission tomography (PET). Despite the lack of a therapeutically significant improvement in these patients, results together with the solid animal experimental data obtained with DA neuron grafting both in rodents and in non-human primates provide a strong rationale to pursue this approach. However, widespread clinical trials with neural transplantation in PD are probably not warranted at this time. From the observations made on the 2 patients reported in the chapter, the following conclusions are drawn: (1) ventral mesencephalic tissue obtained from routine elective abortions can be implanted into the brains of immunosuppressed PD patients without major complications; (2) no major graft-induced improvement of therapeutic value to the patients has been observed; (3) neurophysiological methods and the clinical test battery have detected significant but small post-operative improvements that could indicate a graft effect; and (4) PET provides an evidence of a slight increase of 18 F-dopa uptake in the transplanted striatum, suggesting that small grafts have survived.

Chapter 44 Extensive efferent projections of intra-striatally transplanted striatal neurons as revealed by a species-specific neurofilament marker and anterograde axonal tracing

Abstract: Publisher Summary The human neurofilaments (HNF) antibody reveals a remarkably extensive graft-to-host projection from the human fetal striatal tissue grafts. As revealed by the Phaseolus vulgaris leucoagglutinin (PHA-L) experiment described in the chapter, the axons growing out from the striatal grafts to the globus pallidus were myelinated and formed the normal types of symmetrical synapses with the host pallidal neurons. In contrast to the monoaminergic types of neurons, which have been seen to grow preferentially within grey matter to reach distant target sites, the axons of the striatal neurons grew within white matter pathways, such as the internal capsule, the pyramidal tract, and the corpus callosum. Indeed, both in the PHAL labeled rat-to-rat grafts and the HNF labeled human-to-rat grafts, the labeled axons ran intermingled with the host myelinated fibers, both within and on the surface of the myelinated fiber bundles. Within the internal capsule and the cerebral peduncle, the HNF labeled axons formed a well-defined bundle that occupied a position very similar to that of the striato-nigral pathway and the cortico-ponto-spinal axons. Axons appeared to branch off from this descending bundle specifically into those nuclei that normally receive prominent projections from either the striato-fugal or the cortico-fugal axonal pathways—that is, the globus pallidus, the subthalamic nucleus, the substantia nigra pars reticulate, and the pontine nuclei. This indicates a remarkable precision in the ability of the outgrowing axons to find their way over extended distances, up to about 10 mm to reach the pontine nuclei and about 20 mm for the most advanced axons to reach the cervical spinal cord.

Intrastriatal implants of mesencephalic cell suspensions in weaver mutant mice: ultrastructural relationships of dopaminergic dendrites and axons issued from the graft.

Abstract: Dissociated cell suspensions were prepared from the ventral midbrain of normal mouse foetuses and stereotaxically implanted into the neostriatum of 2–3 months old homozygous weaver mutant mice, which are severely deficient in dopamine. In tests of amphetamine-induced turning behaviour 60 days after grafting, recipient animals displayed a rotational bias opposite to the grafted side. Prior to perfusion, which was carried out at 80 days after transplantation surgery, the grafted striata of the weaver recipients were deprived of their intrinsic mesostriatal dopamine input by local injections of 6-hydroxydopamine into the ipsilateral substantia nigra in order to selectively study the innervation derived from the graft. Grafts were found to contain an estimated 100–700 tyrosine hydroxylase immunoreactive neurones. An ultrastructural analysis demonstrated that both axons and dendrites immunoreactive for tyrosine hydroxylase extended from the graft into the recipient striatum. In the host striatum proximal to the graft (i.e. at a distance of 0.0–0.5 mm from the graft) the proportion of dendrites to axons was about 1∶2, whereas distal to the graft (i.e. at a distance of 0.5–1.0 mm) it was 1∶20. Graft-derived tyrosine hydroxylase immunoreactive axons were primarily found in apposition with unlabelled dendrites or spines of the recipient striatum (>90%). Graftderived dopaminergic dendrites received synaptic input from unlabelled axon terminals and were opposed to the unlabelled somata of striatal neurones in a few instances. In conclusion, this study shows that mesencephalic cell suspensions survive in the weaver striatum and provide a functional dopamine innervation which comprises both axonal and dendritic processes.

Reafferentation of the subcortically denervated hippocampus as a model for transplant-induced functional recovery in the CNS.

Abstract: Subcortical deafferentation of the hippocampal formation is known to induce profound behavioural deficits. Transplants of fetal septal or brainstem tissue are capable of restoring some aspects of normal physiological and behavioural function in subcortically deafferented (i.e. fimbria-fornix or septal lesioned) rats. Such grafts have been shown to re-establish extensive new afferent inputs to the denervated hippocampal formation. As shown for grafted cholinergic and noradrenergic neurons, the ingrowing axons form laminar innervation patterns which closely mimic those of the normal cholinergic and noradrenergic innervations. The ingrowth appears to be very precisely regulated by the denervated target: each neuron type produces distinctly different innervation patterns; the growth is inhibited by the presence of an intact innervation of the same type; and it is stimulated by additional denervating lesions. Both ultrastructually and electrophysiologically the graft-derived fibres have been seen to form extensive functional synaptic contacts. Biochemically, cholinergic septal grafts and noradrenergic locus coeruleus grafts restore transmitter synthesis and turnover in the reinnervated hippocampus. Intracerebral microdialysis has revealed that acetylcholine and noradrenaline release is restored to normal or supranormal levels in the graft-reinnervated hippocampus, and that the grafted neurons can be activated in a normal way from the host through behavioural activation induced by sensory stimulation or electrical stimulation of the lateral habenula. These results indicate that the grafted monoaminergic neurons can restore tonic regulatory neurotransmission at previously denervated synaptic sites even when they are implanted into the ectopic brain sites. Such functional reafferentation may be sufficient for at least partial restoration of function in the subcortically deafferented hippocampus.

Neuropeptides in the CNS

Abstract: I. Dynorphin-containing neurons (J.H. Fallon and P. Ciofi). II. Growth hormone releasing hormone (P.E. Sawchenko and L.W. Swanson). III. Angiotensin (R W. Lind and D. Ganten). IV. Pancreatic polypeptide, neuropeptide Y and peptide YY in central neurons (M.E. de Quidt, H. Kiyama and P.C. Emson). Neuropeptide receptors. V. Opioid peptide receptors (B. Adler, R.R. Goodman and G.W. Pasternak). VI. Tachykinin receptors in the central nervous system (T.L. O'Donohue, C.J. Helke, C.W. Shults, S.H. Buck and E. Burcher). VII. Neurotensin receptors (G.R. Uhl). VIII. Cholecystokinin receptors (T.H. Moran and P.R. McHugh). IX. TRH receptors (D.R. Burt and N.A. Sharif). X. Immunocytochemistry of neuronal phosphoproteins in dopaminoceptive brain regions (C.C. Ouimet and P. Greengard). Subject index.

Acetylcholine release from intrahippocampal septal grafts is under control by the host brain: a microdialysis study.

Abstract: Publisher Summary This chapter examines the acetylcholine release from intrahippocampal septal grafts. It discusses the dependency of acetylcholine release on axonal impulse flow and behavioral activation. By using the intracerebral microdialysis technique, it is possible to measure the extracellular levels of transmitter and study the effects of different manipulations. Two sets of manipulations are performed in unrestrained normal rats, FF-lesioned rats, and rats with lesions plus either septal suspension grafts in the hippocampus or solid septal grafts in the lesion cavity. A pharmacological characterization is made by changing the axonal membrane properties by high K + or by adding tetrodotoxin (TTX) to the perfusate. Behavioral activation is achieved either by handling the rats or by electrically stimulating the nucleus of the lateral habenula (LHb). The stimulation of the LHb, which has widespread projections to the brainstem reticular formation, causes sustained behavioral activation as well as release of noradrenaline and serotonin in the forebrain. To control for the effects of the LHb stimulation, a transection of the fasciculus retroflexus (FR), which is the outflow pathway from the LHb, is performed between two stimulations.

Evaluations of Swedish labor market policy

Abstract: Sweden has for a long time spent large resources on labor market policies targeted to the unemployed. In the Anglo-Saxon labor economics literature new methods have been developed for the purpose of estimating the effects of such policies. This paper presents the new methods in this field and describes the main studies of Swedish labor market policies. The conclusion is that in spite of new methodological insight there remains much uncertainty about the effects of the Swedish policy experiment.

Chapter 37 In vivo microdialysis: a new approach for the study of functional activity of grafted monoaminergic neurons and their interaction with the host brain

Abstract: Publisher Summary The microdialysis technique provides a useful tool for the study of the functional regulation of intracerebrally grafted monoaminergic neurons as well as for the analysis of graft–host interactions. Although the monoaminergc fiber and terminal density varied substantially from one graft to another, the extracellular levels of monoamines are maintained at near-normal levels, not only under baseline conditions but also during K + -induced depolarization, transmitter-selective uptake blockade, and tetrodotoxin (TTX). This suggests that the monoaminergic neurons possess important autoregulatory properties despite their ectopic location. The results also show that the monoamine release in the graft-reinnervated host target is impulse dependent and that the neurons are spontaneously functionally active at the synaptic level. An electrical stimulation of the lateral habenular nucleus (LHb) produces a virtually identical increase in noradrenaline (NA) release in the intact and grafted hippocampi. In contrast, in awake animals, a complex environmental stimulus, such as handling, induces inconsistent effects on NA output in the grafted hppocampi. These findings suggest that the grafted locus coeruleus (LC) neurons receive regulatory inputs from the host brain, but that the functional integration is incomplete as the LC grafts, in most cases, lack the ability to respond adequately to handling stimulation.