Neural grafting in a rat model of Huntington's disease: striosomal-like organization of striatal grafts as revealed by acetylcholinesterase histochemistry, immunocytochemistry and receptor autoradiography

Reduction of voluntary alcohol consumption in the rat by transplantation of hypothalamic grafts

Stimulation of the peripheral renin-angiotensin system has been shown previously to decrease the voluntary intake of ethanol in the rat. The existence of a separate brain renin-angiotensin system, independent from that of the periphery, has been widely demonstrated. The brain renin-angiotensin system plays an important role in the regulation of water and electrolyte balance and neuroendocrine function. However, the role played by this system in the regulation of voluntary alcohol consumption has not yet been studied. The goal of the present work was to assess the feasibility of decreasing the voluntary alcohol intake in a strain of rats (Rapp SS/Jr rats) that have a genetic deficiency responsible for a low activity of the renin-angiotensin system and elevated alcohol intake. Adult Rapp SS/Jr rats received intraventricular transplants of fetal hypothalamic grafts (from normal donors), known to contain angiotensin-immunoreactive cell bodies. Our studies revealed that angiotensin-immunoreactivity in the cell bodies and fibres in the paraventricular, supraoptic and suprachiasmatic nuclei of the hypothalamus in Rapp SS/Jr rats was markedly reduced. Animals that had surviving grafts containing angiotensin-immunoreactive cell bodies in the dorsal third ventricle--but not in the ventral third ventricle, in the lateral ventricles, or sham operated animals--had a 40% decrease of their voluntary alcohol intake, when compared to their intake before surgery, or to the control group. However, water consumption was not reduced in both the sham and transplanted animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamic acid decarboxylase gene expression in thalamic reticular neurons transplanted as a cell suspension in the adult thalamus

The goal of the present study was to determine whether alterations in neuronal morphology and connections in thalamic grafts were accompanied by changes in the expression of mRNA encoding glutamic acid decarboxylase (GAD), the key enzyme in the synthesis of GABA, the normal neurotransmitter of neurons of the thalamic reticular nucleus. Cell suspensions of rat fetal tissue containing both thalamic reticular nucleus and ventrobasal primordia were transplanted into the excitotoxically lesioned somatosensory thalamus of adult rats. Levels of messenger RNA (mRNA) encoding GAD (Mr 67,000; GAD67) were measured 7 days to 4 months following transplantation via quantitative in situ hybridization with 35S-radiolabeled antisense RNAs. Expression of GAD67 mRNA in the thalamic reticular nucleus was analyzed in parallel in rat pups between 0 and 30 days postnatally, and in adult animals. As already observed with immunohistochemistry, transplanted neurons of the thalamic reticular nucleus did not group in specific clusters but rather mingled with unlabeled (putatively ventrobasal) neurons. Levels of labelling for GAD67 mRNA per neuron increased over time and reached adult levels during the third week post-grafting, i.e. 2 weeks after the theoretical birthdate of the neurons (grafted at embryonic days 15-16). Similar values were observed and a plateau was reached at similar time points during normal ontogeny. The results suggest that, in contrast to morphology and size of the neuronal cell bodies, gene expression of GAD67 develops normally despite the ectopic location of neurons of the thalamic reticular nucleus in the somatosensory thalamus, the abnormal connectivity and the lack of segregation from non-GABAergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Schwann cells transplanted into the CNS

A small volume of purified Schwann cells, cultured from early postnatal rat sciatic nerve, was injected into the hippocampus or fimbria of syngeneic adult hosts. The procedure caused minimal structural disturbance at the transplantation site, with close graft-host contact and maximal opportunity for integration. The donor Schwann cells were identified by a combination of light and electron microscopic features (which include characteristic deep and complex infoldings of a well marked nuclear envelope), antigenic profile (especially low affinity nerve growth factor receptor immunoreactivity), uptake of fluorescent latex microspheres and autoradiography of [3H]thymidine-labelled dividing cells. The donor Schwann cells adopted a distinctive elongated form, with a central, ovoid nucleus flanked by processes which were up to 300 microns long, and which ranged from swollen segments with a diameter as large as 12 microns down to thread-like fibres of 1 microns or less with growth cone-like expansions. Transplanted cells migrated from the graft, particularly along blood vessels and could permeate all cytoarchitectonic regions of the adjacent host hippocampal neuropil. Donor Schwann cells also migrated along the longitudinal axis of the fimbria, where they were interspersed in parallel with the interfascicular glial rows and axons. The grafted cells induced a transient but marked host astrocytic hypertrophy, which did not appear to impede the migration of the donor Schwann cells. The transplanted Schwann cells did not form peripheral myelin (as detected by P0 immunoreactivity), and it is not clear whether they survive beyond the period at which we detect them.

Huntington's disease: animal models and transplantation repair

Recent identification of the gene for Huntington's disease is currently attracting widespread attention. While having importance for predictive testing and the potential of elucidating the underlying disease process, this discovery does not yet provide any advances for therapeutic intervention. Here we review recent advances in the development of improved animal models of Huntington's disease and strategies for its repair. Novel toxins may better mimic the neuropathology, and provide important clues about the underlying metabolic disorder, of the human disease. In addition, recent experiments into the cellular morphology, development and function of striatal cell transplants in both rats and monkeys are now indicating the prospect of viable strategies for structural repair in this disorder.

Intrastriatal grafts derived from fetal striatal primordia--IV. Host and donor neurons are not intermixed

Embryonic striatal grafts transplanted into excitotoxin-damaged host striatum develop a heterogeneous structure in which some regions resemble striatum but others do not. In the experiments reported here, we tested for the possibility that the regions resembling striatum were actually derived from host neurons that migrated into the grafts, rather than being derived from donor cells. We placed embryonic striatal grafts into host brains in which striatal cells had been multiply pulse-labeled with [3H]thymidine. Four groups of host rats were exposed to [3H]thymidine at embryonic days 12 and 13-15, 15-18, 16-19, or 20 to postnatal day 1, and were allowed to reach maturity. One week prior to grafting, lesions of the caudoputamen were made unilaterally in each host rat by injecting ibotenic acid. At grafting, dissociated cells from embryonic days 14-16 rat striatal primordia were injected bilaterally into the host caudoputamen. The locations of [3H]thymidine-labeled neurons were analysed by autoradiography eight to 16.5 months post-grafting. Despite the presence of many intensely labeled neurons in the host striatum of rats in all four groups, intensely labeled neurons were rarely found in the cores of grafts. A few weakly labeled small cells appeared in the graft cores, and occasional strongly or weakly labeled medium-sized cells appeared at the margins of the graft zones. Some perivascular cells associated with blood vessels in the grafts were also weakly labeled, but the gliotic tissue surrounding the graft zones was not labeled. These results suggest that very few host striatal neurons migrate into the cores of intrastriatal grafts, or that, if they do, such neurons return to the host striatum or do not survive. At most, surviving host striatal neurons have limited spatial interactions with donor cells at the margins of the grafts, both in the damaged and in the intact host striatal environment. These observations, combined with our previous finding that [3H]thymidine-labeled cells derived from embryonic day 15 striatal primordia do not appear in the host striatum, indicate that no extensive mutual migrations of striatal donor neurons and host neurons occur in the zones of grafting.

Synaptic relationships between cortical and dopaminergic inputs and intrinsic GABAergic systems within intrastriatal striatal grafts

Synaptic relationships between gamma-aminobutyric acid-ergic systems intrinsic to intrastriatal striatal grafts and inputs from host adult rat neocortex and substantia nigra were investigated using a variety of neuroanatomical techniques. The input from host frontal cortex was demonstrated using an anterograde degeneration technique, whilst a double immunocytochemical procedure, using the chromogens diaminobenzidine and benzidine dihydrochloride was utilized to visualize the tyrosine hydroxylase (TH)- and glutamate decarboxylase (GAD)-immunoreactive systems. Only areas receiving dense TH-immunoreactive innervation were examined for synaptic interactions since these areas were judged as being striatal in origin. Examples of synaptic interactions were observed between cortical and TH-immunoreactive inputs; between cortical input and GAD-immunoreactive neuronal elements within TH-immunoreactive inputs and a variety of GAD-immunoreactive neuronal elements within the striatal grafts. No interactions were seen between cortical input and GAD-immunoreactive neuronal perikarya or dendrites, possibly because of technical limitations since the GAD-immunoreactivity did not extend into the distal dendrites where cortical input is predominantly located, nor between all three systems. The results suggest that the formation of new synaptic connections in a pattern reminiscent of that seen in control neostriatum may be responsible, in part at least, for the behavioural recovery in motor skills seen in rats following intrastriatal striatal transplants. They also demonstrate that the host adult brain retains sufficient plasticity and may play an important role in the control of synaptic output from the transplant.

Cholecystokinin-dependent regulation of host dopamine inputs to striatal grafts

Intrastriatal infusions of cholecystokinin-8-sulphate in the rat exerts a dose-dependent inhibition of dopamine-release from nigrostriatal terminals in the neostriatum, as measured by push-pull perfusion. This effect is abolished by excitotoxic lesions of the neostriatum, which, along with behavioural, electrophysiological and receptor binding studies, suggests that cholecystokinin exerts its action indirectly on dopamine release via receptors located on intrinsic striatal neurons. Grafts of embryonic striatum implanted in the lesioned striatum become innervated by host-derived dopamine axons and restore the response of those host neurons to cholecystokinin infusion. This suggests that the innervation of the grafts by dopaminergic axons of the host brain does not simply provide a tonic input to the grafts, but rather represents a phasic input that is under dynamic local regulation by graft-host feedback influences from the transplanted neurons themselves.

Long distance directed axonal growth from human dopaminergic mesencephalic neuroblasts implanted along the nigrostriatal pathway in 6-hydroxydopamine lesioned adult rats

Dissociated ventral mesencephalon of 6 to 8-week-old human embryos were implanted by stereotaxic injection at different sites along the nigrostriatal pathway in adult rats, previously subjected to a 6-hydroxydopamine lesion of the intrinsic mesotelencephalic dopamine pathways. The recipients were immunosuppressed by daily injections of cyclosporin A to prevent rejection. At 13-20 weeks after transplantation, the implanted human neurons and their associated fiber outgrowths were visualized with a species-specific antibody recognizing human, but not rat, intermediary neurofilaments (HNF). From implants placed in the host rostral mesencephalic region, HNF-positive axonal projections were seen to extend in large numbers rostrally along the medial forebrain bundle and the internal capsule, and ramify within the caudate putamen, the ventral striatum and the amygdaloid nuclei (a distance of about 5-6 mm), and more sparsely in the frontal cortex and the olfactory bulb (a distance of about 10 mm). From implants placed in the internal capsule, abundant HNF-positive axons extended in the rostral, but not caudal, direction along the myelinated fiber bundles into the caudate putamen and the ventral striatum. Tyrosine hydroxylase (TH) immunohistochemistry revealed that the vast majority of the rostrally projecting HNF-positive axons were also TH-positive, and that the graft-derived axons gave rise to dense TH-positive terminal networks, above all in large areas of the previously denervated caudate putamen. From control implants of cortical neuroblasts, axonal projections were seen along the medial forebrain bundle and the internal capsule, but the axons were TH-negative and showed only sparse projections to the striatal areas. Instead, dense projections were seen, e.g., in the frontal cortex. The results demonstrate a remarkable ability of human mesencephalic neuroblasts to extend axons along the trajectories of the nigrostriatal and mesolimbocortical pathways to reach and innervate the principal striatal and limbic target areas in the forebrain. This shows that the basic requirements for the formation of long axonal pathways may be present in the adult mammalian central nervous system (CNS) at least for certain types of projection neurons. Furthermore, it implies that the developing human neuroblasts can escape the inhibitory features known to be present along myelinated growth trajectories in the adult mammalian brain. In addition, the present approach may offer new possibilities for functional neural grafting in the rat Parkinson model, since transplanted nigral neurons placed in their natural position within the rostral mesencephalon could provide an anatomically and functionally more integrated system than the standard model with ectopically placed intrastriatal nigral grafts.

Differential regulation of neuropeptide mRNA expression in intrastriatal striatal transplants by host dopaminergic afferents

The effects of dopamine-specific manipulations on neuropeptide gene expression in intrastriatal grafts of fetal striatal tissue were studied by quantitative in situ hybridization histochemistry, using 35S-labeled oligonucleotide probes. Messenger RNA transcripts for the striatal neuropeptides preproenkephalin (PPE) and preprotachykinin (PPT) were detected in neurons forming discrete patches in the striatal grafts. The relative abundance of PPE and PPT mRNA-expressing neurons within the graft patches (51-54%) was similar to that found in normal caudate-putamen. In specimens with intact dopamine afferents the expression of PPE mRNA in grafted neurons was similar to that found in normal caudate putamen, whereas the hybridization signal for PPT mRNA was 27% higher in the graft neurons than in the normal caudate-putamen. Removal of host dopaminergic afferents by 6-hydroxydopamine lesions of the ipsilateral mesostriatal dopamine pathway increased the hybridization signal for PPE mRNA both in the grafts (+84%) and in the spared ipsilateral host caudate-putamen (+125%), whereas the PPT signal was reduced by 53% in the grafts and by 51% in the remaining host caudate-putamen. Similarly, chronic treatment of grafted animals with the dopamine receptor antagonist haloperidol (2 mg/kg per day for 10 days) produced a 146% increase in the PPE signal in the grafts and a 175% increase in the intact contralateral caudate-putamen, whereas the signal for PPT mRNA was again decreased by 52% and 51% in the grafts and host caudate-putamen, respectively. These results show that the host nigrostriatal dopamine pathway differentially regulates enkephalin and substance P gene expression within striatal grafts and thereby exerts a tonic functional influence over grafted striatal neurons.

Descriptive morphology of developing fetal neostriatal allografts in the rhesus monkey: a correlated light and electron microscopic Golgi study

Primate fetal striatal neurons were transplanted into the ibotenic acid lesioned rhesus monkey striatum. Ten weeks after transplantation the monkeys were transcardially perfused and graft tissue was histologically stained. Golgi impregnated, and processed for electron microscopy. The monkeys received magnetic resonance imaging (MRI) scans before lesioning, after lesioning, and ten weeks after transplantation to noninvasively study the striatal grafts. The study demonstrated that fetal striatal grafts, measuring up to 0.4 x 0.8 cm, can survive for extended periods of time in the non-human primate. Hematoxylin-eosin stained sections of the transplant demonstrated that neuronal, glial, vascular, and lymphocytic cells were present in the graft. The majority of the neurons had somatic diameters between 8 and 20 microns and were characterized by nuclei containing multiple nucleoli. A few neurons within the graft had somatic diameters up to 40 microns. These larger neurons exhibited more mature cytoplasm containing a moderate amount of Nissl substance. Some of the blood vessels within the graft were surrounded by a large number of plasma cells, but there was no evidence of hemorrhage or necrosis. Bielschowsky staining and Golgi impregnation of the transplanted tissue demonstrated that there were neurons at various degrees of differentiation. Some of the neurons had varicose dendrites, growth cones, and filopodia, which are all characteristics of immature neurons, while others had a much more mature appearance, including a moderate number of dendritic spines. Some of these neurons had an appearance typical of differentiating "medium spiny" neurons of the normal striatum. Electron microscopic analysis of the transplanted tissue and individual Golgi-impregnated neurons within the transplant confirmed that there were developing neurons within the graft. These neurons had an increased nuclear-to-cytoplasmic ratio and had nuclei containing multiple nucleoli. The neuropil surrounding these neurons was loosely organized and contained large areas of extracellular space. The neuropil exhibited developing dendrites, numerous growth cones, and mature synapses. In summary, the study demonstrated that fetal striatal allografts can survive for up to three months in the rhesus monkey and undergo normal differentiation as assessed by Golgi impregnation and electron microscopy.

Fos expression in intrastriatal striatal grafts: regulation by host dopaminergic afferents

Previous studies have shown that transplants of fetal striatum, implanted into the ibotenic acid-lesioned striatum of adult rats, become innervated from the host nigrostriatal dopamine (DA) pathway. In the present study we have used DA-receptor-mediated expression of the Fos protein (i.e. the product of the immediate-early c-fos gene) as a cellular marker for functional dopaminergic host-graft interactions in the striatal grafts. Amphetamine (5 mg/kg; 2 h) induced Fos-like immunoreactivity in clusters of cells located mainly within the DARPP-32-positive areas within the transplants, i.e. within the striatum-like graft compartment which is preferentially innervated by the host DA afferents. As in the normal striatum, this effect was largely, although not completely, abolished by a 6-hydroxydopamine lesion of the ipsilateral nigrostriatal DA pathway. Apomorphine (0.25 mg/kg; 2 h) had no detectable effect in grafts with an intact host DA system. Two to 3 weeks after a 6-OHDA lesion of the host DA pathway (i.e. a time sufficient for DA receptor supersensitivity to develop), apomorphine-induced extensive Fos-activation selectively within the DARPP-32-positive areas of the graft. The magnitude of the response was similar to that seen in the DA-denervated host striatum. Dual Fos/DARPP-32 immunostaining revealed that the activated graft neurons were, at least in part, DARPP-32-positive. In intrastriatal grafts of fetal neocortical tissue, which were studied for comparison, the amphetamine- and apomorphine-induced effects on Fos expression were much smaller and similar to that seen in the DARPP-32-negative, non-striatal compartment within the striatal grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Host dopaminergic afferents affect the development of DARPP-32 immunoreactivity in transplanted embryonic striatal neurons

Homotopic transplantation provides an interesting way to observe the relationships between developing cells and ingrowing host afferents. We have performed a complete and selective elimination of the mesostriatal dopaminergic system in adult rats to observe the influence of its absence on the development and chemical differentiation of embryonic striatal cells. Cell suspensions from striatal primordia of 14-15-day-old embryos were transplanted into host striata that were (i) neuron-depleted by kainic acid (control group) or (ii) deprived of dopamine by 6-hydroxydopamine prior to the neuronal depletion by kainic acid (experimental group). The expression of dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein (DARPP-32) by transplanted cells was observed in correlation with their innervation by host dopaminergic afferents which in turn were identified by tyrosine hydroxylase immunohistochemistry. Observations were made between four days and three months after transplantation. Four days after transplantation, no immunoreactivity for DARPP-32 was observed in transplants of control animals despite the presence of tyrosine hydroxylase-immunopositive fibers growing from the host to discrete cell clusters in the transplant. DARPP-32-labeled cells appeared soon afterwards. Six days after transplantation they displayed varying intensities of immunoreaction, ranging from just detectable to normal levels and were specifically targeted by developing tyrosine hydroxylase-immunopositive fibers. The number of DARPP-32-labeled cells increased rapidly and they formed increasingly compact clusters. Fourteen days after transplantation and afterwards, all the DARPP-32-labeled cells displayed an intensity of immunoreaction and a distribution comparable to that observed in long-term transplants. Transplants in the experimental hosts displayed the same organization and developmental features as the control transplants with the exception of DARPP-32 labeling which was not detected before eight days after transplantation. Ten days after transplantation, the distribution and intensity of DARPP-32 labeling was similar to that observed at six days in the control group. The evolution of DARPP-32 labeling after 10 days in the experimental group paralleled that observed six days post-transplantation and beyond in the control group. Dopaminergic mesostriatal host afferents are able to provide developing cells in grafted striatal tissues with normal innervation very rapidly. Despite this rapidity, the innervation does not seem to have any trophic influence on the general development of the transplant but does affect the onset time of the expression of neurochemical markers that are directly related to its synaptic function.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphology of intracellularly stained spiny neurons in rat striatal grafts

Two to six months after implantation of fetal striatal primordia into the kainic acid-lesioned neostriatum of adult rats, spiny neurons in the grafts were stained intracellularly with biocytin. To determine whether the spiny neurons in the grafts differentiate morphologically as in the host neostriatum, the intracellularly stained spiny neurons in the grafts were studied with light and electron microscopy and compared with that of spiny neurons in the host neostriatum. The spiny neurons in the grafts had ovoid or polygonal cell bodies with dendrites radiating in all directions. The somata were smooth and the dendrites, except for their most proximal portions, were rich in spines. All these features resembled the appearance of spiny neurons in the intact neostriatum. However, quantitative studies showed that the somata of spiny neurons in the grafts were larger than those in the host neostriatum (projected cross-sectional areas of 230 +/- 64.6 microns 2 in the grafts and 158 +/- 28.9 microns 2 in the host) and the spine density of graft neurons was lower than that of host neurons. Cells near the border of the grafts had dendrites extending both into the graft and into the host neostriatum. In these cells, the dendrites in the grafts had fewer spines than the dendrites in the host tissue. The axons of spiny neurons in the grafts had very large and dense intrastriatal collateral arborizations, which occupied a much larger volume than that of the dendritic domain of the parent cells. The local axonal arborizations of each of these cells filled almost the entire graft. In some cells, axonal branches were traced outside the grafts and were seen to enter the internal capsule fascicles. Unlike spiny neurons in the normal adult neostriatum, the spiny cells of the graft could have nuclear indentations. With this exception, the ultrastructural features of spiny neurons in the grafts were very similar to those in the hosts. Many unlabeled boutons made synapses on identified spiny neurons in the grafts. Terminals with small round vesicles made synaptic contacts on dendritic shafts and dendritic spines, while terminals with flattened or pleomorphic vesicles contacted somata, dendrites, and dendritic spines. Labeled axon collaterals of graft neurons made symmetrical synapses on somata, dendrites and spines in the grafts and in the host neostriatum. In the grafts, more than 60% of the axon terminals contacted dendritic shafts. The proportion of axosomatic and axospinous synapses varied substantially from cell to cell.(ABSTRACT TRUNCATED AT 250 WORDS)

A simplified approach to retrograde/anterograde axonal labeling using combined injections of horseradish peroxidase and ibotenic acid

Combined injections of ibotenic acid and horseradish peroxidase (HRP) were made into the region of the mouse ventrobasal thalamus that is related to the large mystacial vibrissae. Examination 4 and 5 days later of the corresponding area of the primary somatosensory cortex (i.e., barrel cortex), in thick and in thin sections, showed it to contain numerous corticothalamic projection cells the somata, dendrites and axons of which were densely labeled by the retrograde transport of HRP. Analysis of serial thin sections showed that thalamocortical axon terminals, which had degenerated in response to the injection of ibotenic acid, formed approximately 20% of the asymmetrical synapses in barrel cortex. The fine structure and distribution in cortex of degenerating thalamocortical axon terminals and of intrinsic HRP-labeled corticothalamic axon terminals were identical to those reported in previous studies in which the injection of HRP into the thalamus was combined with the making of electrolytic lesions. This indicates that injecting ibotenic acid is an effective replacement for electrolytic lesioning of the thalamus. The combined injection of ibotenic acid and HRP represents a new and efficient approach for studying reciprocal projection pathways.

Choline acetyltransferase- and substance P-like immunoreactive elements in fetal striatal grafts in the rat: a correlated light and electron microscopic study

Fetal striatal neurons were transplanted into the ibotenic acid-lesioned rat striatum. Three months after transplantation, the graft tissue was processed for choline acetyltransferase- and substance P-like immunoreactivity and was subsequently examined at the light and electron microscopic levels. The study demonstrated that choline acetyltransferase- and substance P-like-immunoreactive neurons were homogenously present throughout fetal striatal grafts, although in decreased numbers compared with those in the normal rat striatum. The majority of the choline acetyltransferase-immunoreactive neurons had fusiform, oval, or polygonal somata with somatic diameters greater than 20 microns and contained deeply invaginated nuclei surrounded by copious cytoplasm. In addition, choline acetyltransferase-immunoreactive neurons with somatic diameters between 10 and 20 microns were also demonstrated. The grafts' substance P-like-immunoreactive neurons, which had somatic diameters between 10 and 25 microns and had oval or polygonal perikarya, could be classified into two types based on their ultrastructural characteristics. Type I neurons contained an unindented nucleus which was surrounded by a thin rim or moderate amount of cytoplasm, whereas Type II immunoreactive neurons contained an indented nucleus which was surrounded by copious cytoplasm. Choline acetyltransferase- and substance P-like-immunoreactive dendrites in the grafts' neuropil were contacted by multiple unlabeled axon terminals. In addition, choline acetyltransferase- and substance P-like-immunoreactive axon terminals forming symmetric contacts with unlabeled dendrites were present within the graft. The study demonstrated that many of the neuroanatomical features of choline acetyltransferase- and substance P-like-immunoreactive elements found in the normal rat striatum are present in mature fetal striatal grafts.

Factors influencing survival of transplanted embryonic motoneurones in the spinal cord of adult rats

The survival of transplanted embryonic motoneurones in the initially intact spinal cord of adult rats was studied and compared to that previously observed in the motoneurone-depleted cord. Embryonic (ED 11-12) spinal grafts prelabeled with 5-bromo-2'-deoxyuridine (BrDUr) were placed in the intact lumbar cord of the hosts. To provide a target for grafted embryonic motoneurones and to guide their axons to it, the contralateral extensor hallucis longus (EHL) muscle with its nerve attached was transferred paravertebrally. The nerve stump was implanted in the cord at the site of transplantation. Eight to 14 weeks later BrDUr-labeled motoneurone-like cells had migrated outside the grafts into the host's neuropil, preferentially into the anterior horn. Following injection of HRP into the implanted EHL muscle 6-17 weeks after transplantation a few retrogradely labeled motoneurones were seen in the host's anterior horn around the grafts. The lumbar cord of the rats with neuromuscular implants but without embryonic grafts had no retrogradely labeled cells. However, most animals, both with and without embryonic grafts, had retrogradely labeled motoneurones in the thoracic cord, which may contribute to the reinnervation of the implanted muscle. Thus, although some embryonic motoneurones can survive, migrate into the proper location, and probably innervate a host muscle when transplanted into the intact spinal cord, their number was significantly fewer than that in the motoneurone-depleted cord. The results show that reduction of the host's motoneurone pool increases chances of their survival.

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

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

Striatal, ventral mesencephalic and cortical transplants into the intact rat striatum: a neuroanatomical study

Intrastriatal transplantation of fetal striatal (STR), cortical (CTX), or ventral mesencephalic (VM) tissue into the normal striatum has been shown to produce behavioral deficits (38). Here, we have examined the cellular elements of the transplants and their connectivity with the host using histochemistry for cytochrome oxidase (CO) and acetylcholinesterase (AChE), immunocytochemistry for glial fibrillary acidic protein (GFAP), OX42, tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), serotonin (5-HT), and cholecystokinin (CCK). Autoradiography for dopamine D1 and D2, muscarinic cholinergic, and serotonin 5-HT1 and 5-HT2 receptors at 5-15 months after transplantation was also investigated. CO staining showed that all transplants were metabolically active. The STR and VM transplants contained AChE-positive neurons and fibers. The CTX transplants exhibited AChE terminals with an appearance similar to that of the host cortex. AChE staining within the STR transplants was patchy. 5-HT-, TH-, and DBH-immunoreactive (IR) fibers were found in the STR and CTX transplants. In two of six CTX transplants, many TH-IR neurons were present. The VM transplants contained many TH-IR, 5-HT-IR, and DBH-IR cell bodies and fibers. CCK-IR stain was found in the VM transplant and was coextensive with regions containing TH-IR cell bodies. Fibers stained by all markers crossed the transplant and host border. Receptor autoradiography revealed that muscarinic cholinergic and 5-HT2 receptors were present in the STR, CTX, and VM transplants. In addition, dopamine D1 and D2 receptors were present in the STR transplants. Intermittent heavy staining for GFAP and OX42 were observed along the border of most transplants and the hosts. It was noted that high densities and hypertrophy of GFAP- or OX42-stained astrocytes or microglia, respectively, were present in the transplants and adjacent host. OX42-stained macrophages were found in many transplants. The present results indicate that intrastriatal transplants into the intact normal brain express numerous histochemical, immunocytochemical, and receptor features characteristic of the appropriate adult tissues. The afferents from the host extend into the STR and CTX transplants, and neural fibers from the VM transplants grew into surrounding host tissue, suggesting possible anatomical connection. Ultrastructural evidence is needed to determine if these fibers form synaptic connections. The results from GFAP and OX42 immunocytochemical staining support the possibility suggested by behavioral studies that damage to the host brain is induced by neural transplantation.

Fetal neocortical transplants into the medial forebrain bundle attract ingrowth of catecholaminergic fibers in adult rat brain

The hypothesis that fetal tissue grafts may exert a trophic influence on damaged catecholaminergic fibers was examined. Ascending dopamine and norepinephrine axons normally innervate frontal cortex targets in the intact rat brain. These and other ascending catecholaminergic fibers were disrupted with stereotaxic injections of 6-hydroxydopamine into the medial forebrain bundle (mfb), followed after 1 or 14 days by grafts of fetal neocortical tissue placed into the injection site, or by sham grafts. Glyoxylic acid histofluorescence techniques were then used to examine catecholaminergic fiber distribution. When such lesions were made without subsequent grafting, virtually no growth of catecholaminergic fibers occurred beyond the injection site and frontal cortex norepinephrine levels were depleted to 15% of control levels. However, when grafts of fetal neocortical tissue were made into the lesion site and animals examined 3 months later, catecholaminergic fibers grew through the lesion site to ramify within the graft tissue. Catecholaminergic fibers were seen in all portions of most grafts, though they were most dense on the caudal and ventral edges of the graft, close to the path of the mfb. Similar densities of graft innervation were seen 3 months after animals received grafts placed into the same site without prior lesioning of catecholaminergic fibers. Fetal neocortical grafts thus induce collateral sprouting from intact host catecholaminergic axons and may also promote regenerative sprouting when such fibers are otherwise irreparably damaged.

Restoration of thalamostriatal projections in rat neostriatal grafts: an electron microscopic analysis

The thalamostriatal projections to rat neostriatal grafts were studied by using the Phaseolus vulgaris-leucoagglutinin (PHA-L) axonal tracing technique. Two to 6 months after implantation of striatal primordia into adult neostriata, PHA-L was injected into two different portions of the intralaminar nuclear complex of the thalamus. In the host neostriatum, labeled fibers from the parafascicular nucleus (PF) arborized in a large region in the neostriatum, but avoided small patchlike areas. Most of the fibers from PF had irregular curved trajectories with short side branches that formed boutons. Labeled fibers from the centromedial and paracentral nuclei (CeM-PC) projected to a similarly large area within the neostriatum but did not show any nonuniformity. CeM-PC axons had relatively straight trajectories and formed boutons en passant. Both sets of thalamostriatal projection fibers were found in the grafts. Some of the labeled fibers in the grafts formed dense, focal arborizations. Compared to the host neostriatum, the distribution of postsynaptic elements in the grafts was altered dramatically. In the host neostriatum, 89% of the terminals from PF terminated onto dendritic shafts; 93% of the CeM-PC terminals contacted dendritic spines. However, only 47% of the PF terminals in the grafts contacted dendritic shafts; 53% of them terminated on dendritic spines. In grafts, 81% of the terminals from CeM-PC region contacted dendritic spines; 19% of them made synapses on dendritic shafts. The shift of postsynaptic elements in the grafts suggests a loss of pathway specificity in the induction of dendritic spines on neostriatal neurons in grafts.

Development of intrastriatal striatal grafts and their afferent innervation from the host

The morphological maturation of cell suspension grafts of fetal striatal tissue (obtained from 14-15-day-old rat fetuses) was followed from two days to eight weeks after implantation into intact and ibotenic acid-lesioned striata of adult rats. The development of host afferent innervation of the grafts from the substantia nigra (tyrosine hydroxylase immunoreactive), mesencephalic raphe (serotonin immunoreactive), and the frontal cortex (anterogradely labelled with Phaseolus vulgaris leucoagglutinin) were revealed by immunohistochemistry. During the first weeks post-grafting, the striatal implants consisted of a mixture of mature- and immature-looking cell clusters. Grafts implanted into ibotenic acid-lesioned striatum grew rapidly (about five-fold) in volume over the first week. The areas of immature (probably proliferating) cells gradually disappeared, and by six to eight weeks the grafts had a fully mature appearance with patches of neurons which stained densely for DARPP-32 (i.e. were striatum-like) embedded within areas of essentially DARPP-32-negative (i.e. non-striatum-like) tissue. Peripheral clusters of grafted cells gradually intermingled with nearby areas of the surrounding lesioned host, and already by two to four days after implantation, coarse and densely immunoreactive host fibres from the substantia nigra, mesencephalic raphe and frontal cortex were present within the grafts. By four to five days the first DARPP-32-immunoreactive neurons appeared in patches within the mature portions of the grafts, and one to two days later the tyrosine hydroxylase-positive fibres began to sprout thin axons selectively within the DARPP-32-positive patches. Similarly, the serotonergic and cortical fibres in the grafts increased in number over the next two weeks, but they showed no preference for the DARPP-32-positive regions. Rich terminal networks were established by two to three weeks post-grafting, and by six to eight weeks the nigral, raphe and cortical afferents had reached terminal densities similar to those seen previously in long-term surviving grafts. Grafts implanted into dopamine-denervated hosts showed a normal morphological maturation of both DARPP-32-positive and -negative areas, although no tyrosine hydroxylase-positive innervation appeared within the grafts. Grafts implanted into non-lesioned striata did not grow beyond their initial size. The implanted cells showed less intermingling with the surrounding host striatum, thus resulting in sharply delineated graft-host borders. DARPP-32-positive patches developed, but they were smaller in size and generally present only in the most peripheral graft portions.(ABSTRACT TRUNCATED AT 400 WORDS)

Long-term survival of GABA-, enkephalin-, NADPH-diaphorase- and calbindin-d28k-containing neurons in fetal striatal grafts

Neurons in long-term striatal grafts were examined to determine if they retain the neurotransmitter characteristics of cells in younger grafts. In addition, calbindin-d28k, a ubiquitous marker of medium spiny neurons, was used to examine the overall frequency and ultrastructural characteristics of spiny neurons in the older grafts. Grafts from 17-day fetal striata were injected into the quinolinic acid-lesioned caudate nucleus in 5 adult rats. After 16 months, the neostriatum was processed for the localization of immunoreactive GABA, calbindin, enkephalin and NADPH-diaphorase (-d) activity. The proportions of GABA-, enkephalin- and NADPH-d-labeled neurons to total Nissl-stained neurons in the 16-month-old grafts (25 +/- 6, 13 +/- 4, and 3 +/- 3, respectively) were similar to findings in 2-month-old grafts. Calbindin-positive cells formed the highest proportion (36.3 +/- 3) of labeled neurons in the older grafts. Nuclear and spine morphology of immunoreactive calbindin cells varied more in the grafts than in host caudate. Results show that there is long-term survival and stability of GABA, enkephalin and NADPH-d cell populations in the grafts and that some grafted spiny neurons may exhibit altered phenotype from those of host striatum.

Haloperidol induces Fos and related molecules in intrastriatal grafts derived from fetal striatal primordia

Haloperidol induces Fos and related molecules (Fos-related antigens, FRAs) in adult striatal neurons. We tested whether a similar induction of Fos and FRAs by haloperidol injection would occur in fetal striatal neurons transplanted into adult quinolinic acid-lesioned striatum. We found that Fos and FRAs were induced in striatal neurons after haloperidol. This induction had a time course in transplanted neurons that was identical to the time course of induction in normal adult striatum. Furthermore, the relative numbers of Fos- and FRA-immunopositive neurons induced by haloperidol were identical for both transplanted and normal striatal neurons. These results provide the first demonstration that neurons in intrastriatal grafts derived from fetal striatal primordia have similar intracellular biochemical characteristics to normal adult striatal neurons.

Intrastriatal grafts derived from fetal striatal primordia: II. Reconstitution of cholinergic and dopaminergic systems

Reconstitution of striatal cholinergic and dopaminergic systems was studied in intrastriatal grafts derived from embryonic day 15 rat striatal primordia and implanted into adult host rats in which unilateral ibotenic acid lesions had previously been made in the striatum. Histochemical, immunohistochemical, and ligand binding autoradiographic techniques were applied to analyze different constituents of these two systems and to study their locations relative to each other in grafts allowed to grow for 9-17 months following transplantation. For the cholinergic system, a modular organization was found in the striatal grafts with stains for choline acetyltransferase and acetylcholinesterase, respectively the synthetic and degradative enzymes for cholinergic neurons; by autoradiographic [3H]hemicholinium binding, specific for high affinity choline uptake sites associated with cholinergic terminals; and by autoradiographic [3H]pirenzepine binding, selective for M1 receptors. For the dopaminergic system, a comparable modular organization was found in the grafts by immunostaining for tyrosine hydroxylase, the catecholamine synthetic enzyme; by autoradiographic [3H]mazindol binding for dopamine uptake sites; and by [3H]SCH23390 binding for dopamine D1 receptors and [3H]sulpiride binding for dopamine D2 receptors. The results indicate that the distributions of the cholinergic and dopaminergic markers in striatal grafts are in close anatomical register. These markers for intracellular and membrane-associated components of the cholinergic and dopaminergic systems were preferentially localized in the acetylcholesterase-rich patches of the grafts in which cortical and thalamic fibers have also been found in striatal grafts, and in which output neurons projecting to the pallidum are located. This anatomical correlation suggests that the substrates for cholinergic-dopaminergic interactions typical of the normal striatum may be reinstated in the grafts both in relation to efferent neurons establishing connections with the host brain that are typical of normal striatofugal connections, and in relation to major afferent fiber systems from the host brain originating in regions known to project densely to the normal striatum. Accordingly, the cholinergic and dopaminergic systems in such grafts may regulate the functional influence of the grafts on the behavior of host animals.

Modulation by muscarine and opioid receptors of acetylcholine release in slices from striato-striatal grafts in the rat

The accumulation of tritium during incubation with [3H]choline and the subsequent efflux of tritium were studied in striatal slices from non-operated rats, in striatal slices from animals which had received a contralateral striatal ibotenic acid lesion, and in slices from striato-striatal suspension grafts, 16-31 weeks after implantation into previously lesioned striata. In graft slices, the accumulation of tritium as well as the overflow of tritium evoked by electrical stimulation (360 pulses, 3 Hz) was much smaller than in slices from non-operated controls. The muscarine receptor agonist oxotremorine (0.1-1 micromol/l) inhibited the stimulation-evoked overflow, and this effect was blocked by the muscarine receptor antagonists atropine (0.1 micromol/l) and pirenzepine (1 micromol/l) in all experimental groups to the same extent. The delta-receptor selective opioid peptide [D-Pen2, D-Pen5]enkephalin (0.3 micromol/l) inhibited [3H]acetylcholine release in all groups, although its effect was smaller in grafts than in normal tissue. The preferential mu-receptor agonist [D-Ala2,N-methyl-Phe4,Gly-ol5]enkephalin also reduced [3H]acetylcholine release in all groups, but only at the high concentration of 10 micromols/l. The effect of both drugs was antagonized by naloxone (1 micromol/l). The preferential kappa-receptor agonist ethylketocyclazocine enhanced the stimulation-evoked overflow in non-operated animals, an effect abolished by naloxone and also by sulpiride. In grafts, ethylketocyclazocine caused no change. It is concluded that acetylcholine release in striato-striatal grafts can be modulated by muscarine autoreceptors and by opioid delta receptors. The enhancement by kappa-receptor activation of [3H]acetylcholine release in non-operated striata depends on a dopaminergic input to the cholinergic cells which does not exist in grafts.

Autoradiographic localisation of D1 and D2 dopamine receptors in primordial striatal tissue grafts in rats

Using in vitro autoradiography the study examined the binding of the dopamine (DA) D1 receptor and D2 receptor radiolabelled ligands, [125I]SCH 23982 and [125I]sulpiride, respectively, to striatal sections of control rats, those with unilateral ibotenic acid (IA) lesions of the striatum and those with grafts of primordial striatal tissue implanted into the IA-lesioned striatum. In animals with IA-lesions, there was almost total degeneration of striatal neurones and a complete disappearance of both D1 and D2 receptors in the lesioned striatum. Within the striatal grafts, dense 'patches' of both D1 and D2 receptors were observed with densities comparable to those in the intact neostriatum. These data indicate that both D1 and D2 receptors are localized on the soma of intrinsic striatal neurones. Moreover, the specific localisation of D1 and D2 receptors in the grafts provides the neurochemical basis for the mechanisms by which the host nigrostriatal DA system can regulate the functional capacity of striatal grafts.

Dissimilar responses of adult thalamic monoaminergic and somatosensory afferent fibers to implantation of thalamic fetal cells

It is generally accepted that transplanted fetal neurons can, after several weeks to months, establish connections with the host CNS. Host afferent systems seem, however, to show different types of responses to the presence of grafted fetal neurons. The present study is a preliminary step to identify mechanisms involved in the reactions of adult axons to transplanted fetal neurons. The right ventrobasal thalamus of adult rats was depleted of neurons by in-situ injection of kainic acid and cell suspensions from homotopic thalamic embryonic primordia which were injected into the lesioned area. After various post-implantation delays, ranging from five to 30 days, two types of experiments were performed: (i) noradrenaline and serotonin immunohistochemistry with specific antibodies on alternate sections; and (ii) anterograde tracing using wheat germ agglutinin conjugated to horseradish peroxidase from the dorsal column nuclei and the principal sensory trigeminal nucleus. Five days after transplantation, host monoaminergic fibers (either noradrenergic or serotoninergic) had already grown into the transplants. Ingrowing fibers were thin and poorly varicose, exhibiting endings morphologically similar to the growth cones observed during axogenesis. Seven days after grafting, growth cones were no longer visible and monoaminergic fibers exhibited either normal-sized or very large varicosities. Large varicosities progressively decreased in number and, after three weeks, the fibers displayed a normal adult morphology, forming a dense network all over the transplants. In contrast, host somatosensory afferents, labeled by anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, did not grow into the transplants. Intermingling of somatosensory afferents and transplanted cells was observed only after 10 days, when grafted neurons extended outside the original transplantation site into the neuron-depleted area containing the somatosensory afferents. The present results demonstrate that adult monoaminergic and somatosensory afferents, when deprived of their usual target, do not react in a similar way to the addition of fetal neurons. It is proposed that adult monaminergic fibers have the ability to regain morphological (and probably functional) immature forms which were considered to be restricted to the period of axogenesis or to lesion-induced regeneration. In contrast, fetal transplants do not seem to induce, by themselves, a similar alteration of genetic expression in adult somatosensory neurons. It has been proposed that "diffuse" and "point-to-point" axonal systems may be differentiated in the CNS on anatomical bases. The present results add to the identification of two different systems by demonstrating that, in the thalamus, they present dissimilar responses to the implantation of fetal cells.

Fetal neostriatal transplants in the rat: a light and electron microscopic Golgi study

Fetal striatal neurons were transplanted into the ibotenic acid lesioned rat striatum. Three months after transplantation the grafted tissue was Golgi-impregnated and examined at the light microscopic level to determine the morphological characteristics of the transplanted neurons. Golgi-impregnated neurons were then gold-toned and examined at the electron microscopic level. The transplanted neurons were classified by both somatic size and somatic and dendritic morphology, which demonstrated that at least seven distinct cell types are present in striatal grafts. Type I large neurons had aspinous somata, sparsely spined dendrites, and indented nuclei, whereas type II large neurons displayed somatic spines, sparsely spined dendrites, and indented nuclei. Type I medium neurons exhibited aspinous somata and proximal dendrites, heavily spined distal dendrites, and unindented nuclei. Type II medium neurons had somatic spines, sparsely spined dendrites, and indented nuclei. Type III medium neurons had aspinous somata, poorly branched and sparsely spined dendrites, and indented nuclei, while type IV medium neurons had aspinous somata, highly branched and sparsely spined dendrites, and indented nuclei. Type V medium neurons displayed aspinous somata, varicose dendrites, and indented nuclei. These results demonstrate that transplanted fetal striatal neurons differentiate into morphologically and ultrastructurally distinct striatal cell types.

Gene expression in striatal grafts--I. Cellular localization of neurotransmitter mRNAs

This study utilized the technique of in situ hybridization histochemistry to identify cells expressing neurotransmitter mRNAs in embryonic striatal tissue grafts implanted into the ibotenic acid-lesioned rat neostriatum. Synthetic 32P- or 35S-labelled oligodeoxyribonucleotide probes specific for prosomatostatin, proneuropeptide Y. proenkephalin, prodynorphin and preprotachykinin mRNAs and a 32P-labelled cRNA probe specific for glutamate decarboxylase mRNA were used to study the regional and cellular changes in these mRNA levels in the normal, lesioned and grafted neostriatum. The levels of neuropeptide Y mRNA and somatostatin mRNA were substantially increased in the striatal grafts compared with the intact control striata. The levels of glutamate decarboxylase mRNA in the grafts also appeared to be slightly elevated over those in the control striata. However, the levels of proenkephalin mRNA, prodynorphin mRNA and preprotachykinin mRNA were significantly lower in the grafts. The increased levels of neuropeptide Y mRNA and somatostatin mRNA in the grafts were due both to an increase in the number of labelled cells and to an increase in the cellular levels of each neuropeptide mRNA. In contrast, the cellular levels of proenkephalin mRNA, prodynorphin mRNA and preprotachykinin mRNA in the grafts were comparable, or elevated relative, to those in the intact striata but the density of cells expressing each of these mRNAs was reduced. Since neuropeptide Y and somatostatin are known to be present in medium to large aspiny striatal neurons (interneurons) and enkephalin, dynorphin and tachykinin peptides and GABA are localized in medium spiny striatal projection neurons, the above findings would indicate that there is a divergence in the levels of activity between these two neuronal populations in the striatal grafts. Our data suggest that the levels of gene expression and hence the functional neurotransmitter-synthesizing and releasing activity in the grafted neuron are different from those in the normal mature striatum.

Synaptic connections formed by grafts of different types of cholinergic neurons in the host hippocampus

The present experiment was performed to determine whether different types of grafted central cholinergic neurons are able to form synaptic contacts with host hippocampal neurons. Grafts from the septal-diagonal band area, which contain the neurons that normally innervate the hippocampal formation, were compared to those from the nucleus basalis magnocellularis region (NBM), the striatum, the pontomesencephalic tegmentum of the brain stem, and the spinal cord. The regions were dissected from 14- to 16-day-old rat fetuses, and the same number of viable cells (35 x 10(4] from each of the different regions was stereotaxically injected as a cell suspension into the hippocampus of rats subjected to a complete fimbria-fornix lesion, transecting the intrinsic septohippocampal pathways. At 14 to 17 weeks after transplantation, the brains were processed for choline acetyltransferase (ChAT) immunocytochemistry at the light and electron microscopic levels and acetylcholinesterase (AChE) histochemistry at the light microscopic level. There was a great variation in the number of surviving ChAT-positive cells among the different graft types. The septal grafts contained the highest number of ChAT-positive cells, and the striatal grafts showed the lowest numbers. The NBM, brain stem, and spinal cord grafts were in between. The differences in the number of ChAT-positive neurons between the groups matched, in general, the differences found in the magnitude of graft-derived AChE-positive fiber growth into the host hippocampal formation. At the electron microscopical level, all types of grafts were capable of forming synaptic contacts with host elements, however, with vast differences in the number of synapses found. The septal grafts produced the highest number of contacts, whereas the striatal and spinal cord grafts produced very few contacts. The ultrastructure of the cholinergic fibers from grafts obtained from the forebrain areas, i.e., septum, NBM, and striatum all appeared normal, whereas brain stem and spinal cord grafts produced different types of anomalies. The results show that grafted cholinergic neurons, that normally do not innervate the hippocampus, can send axons and form synaptic contacts in the host hippocampus. The ability to reinnervate the denervated hippocampal target appears to be shared by the embryologically closely related forebrain cholinergic neuron types, i.e., the septal, NBM, and striatal neurons. The marked differences in overall fiber ingrowth and number of synapses observed between these different types of grafts could be explained largely on the basis of differences in survivability of each grafted neuron type. By contrast, the reinnervation obtained from the grafted brain stem and spinal cord neurons were both quantitatively and qualitatively abnormal.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of a retroviral vector to identify foetal striatal neurones transplanted into the adult striatum

A retrovirus which encodes beta-galactosidase was used to infect embryonic rat striatal cells before grafting these cells into the lesioned adult rat striatum. Examination of the grafts after long term survival (8 months) revealed that a few small and large cells expressed large amounts of bacterial beta-galactosidase activity. The larger diameter cells were identified as neurones by their size, shape and presence of neuronal processes. The identity of the small diameter cell types was not established.

Functional organization of striatum as studied with neural grafts

The function of the striatum has proved elusive. A structure which, at the gross microscopic level, appears homogeneous is now revealed to be heterogeneous in terms of its afferent and efferent relationships with cortex, limbic system and mid brain. Cerebral cortex projects topographically to caudate/putamen. Lesions to different cortical areas result in different behavioural impairments which are mirrored by selective neuronal or neurochemical lesions to the sectors of striatum receiving input from the cortex. Foetal neurones prepared from substantia nigra or striatum grafted to a damaged area of adult striatum reverse the lesion-induced behavioural impairments. Within different sectors of striatum the neurones and their afferent and efferent connections are defined to striosomes and matrix representing a finer grain of intrastriatal organization, the functional significance of which is unclear. It remains a challenge within such complex anatomical circuitry to discover the full extent of anatomical reintegration and functional compensation that can be achieved with grafts of foetal neurones.

Connectivities of the striatal grafts in adult rat brain: a rich afference and scant striatonigral efference

Previous reports from this laboratory have indicated that fetal rat striatal grafts have the major types of neuronal and glial components known to be involved in Huntington's chorea. In this study a number of major afferent and efferent innervations seen in normal striatum were examined in the striatal grafts and were compared with embryonic striatal afferents. First, using immunocytochemistry and histochemistry, the host serotonergic (5-HT), dopaminergic (DA, stained with anti-tyrosine hydroxylase (TH) antiserum), and acetylcholinesterase (AChE) fibers exhibited vigorous growth into the grafts implanted in neostriatum, lateral ventricle, globus pallidus or substantia nigra within a period of 6 and 10 weeks. Individual characteristic terminal patterns formed in striatal grafts: 5-HT fibers were diffused; TH fibers became heavily packed, and AChE fibers were patchy. This peculiar patternization of 5-HT and TH growth into striatal graft appeared to be a recapitulation of the normal 5-HT and TH ingrowth into striatum in the embryonic stage. However, a significantly slow (6 week) onset of adult 5-HT and TH ingrowth into the fetal graft was noted, as compared with that of normal embryonic development (5-6 days from the appearance of 5-HT and TH neurons). With the anterograde-transport marker Phaseolus vulgaris agglutinin leuca method, host cortical neurons also projected to the graft, but in limited numbers. Finally, with the retrograde-transport marker (horseradish peroxidase method, the grafts implanted in neostriatum were found incapable of sending fibers to a major, distal target, substantia nigra. In a current evaluation of striatal transplants, it is shown that major input to the graft can be achieved over time, but output to the distal nigra seems an unrealistic expectation. These data suggest that: (1) the fetal brain tissue was found to be a strong stimulant for sprouting or regeneration of adult nerve fibers; (2) a number of functional recoveries reported on the tested behavior paradigm in this grafting model could be due to the survival of striatal graft and the establishment of input circuitries; further, (3) the data illustrate the necessity of seeking a bridge from the striatal transplant to the host nigra. If a proper functional recovery in Huntington's chorea requires complete striatonigral circuitry, then such a bridge is worthy of a major investigation.

Fetal striatal tissue grafts into excitotoxin-lesioned striatum: pharmacological and behavioral aspects

In an excitotoxin animal model of Huntington's disease (HD), fetal striatal tissue transplants survive and grow in the host brain and reverse the behavioral, and, hence, functional deficits produced by the lesion. In the present study we found recovery of apomorphine-induced rotation behavior in unilateral excitotoxin-lesioned rats indicating that the transplant reverses this functional pharmacologic deficit induced by the lesion. It might, therefore, by expected that the transplanted fetal striatal tissue would possess similar pharmacological characteristics as the host striatum. However, autoradiographic localization of D1 and D2 dopamine receptors demonstrated that the transplanted tissue expressed relatively small numbers of these receptor subtypes. Furthermore, there was a relative deficit of [3H]forskolin binding to the stimulatory guanine nucleotide regulatory subunit/adenylate cyclase complex in the fetal striatal tissue transplants. Therefore, transplanted tissue which is neurochemically dissimilar to the host striatum is capable of reversing deficits in both drug-induced and spontaneous locomotor activity.

Cellular localisation of somatostatin mRNA and neuropeptide Y mRNA in foetal striatal tissue grafts

Using in situ nucleic acid hybridisation histochemistry, we have studied the expression of somatostatin mRNA and neuropeptide Y mRNA in grafts of embryonic striatal neurones implanted into the ibotenic acid-lesioned rat neostriatum. Tissue sections of the grafted striatum were incubated with either 32P- or 35S-labelled complementary oligodeoxyribonucleotide probes specific for somatostatin mRNA and neuropeptide Y mRNA, exposed with X-ray film and dipped in Ilford K-5 emulsion. Neither somatostatin mRNA nor neuropeptide Y mRNA was detectable in the ibotenic acid-lesioned striatum indicating a pronounced degeneration of somatostatin- and neuropeptide Y-containing neurones. However, in the striatal grafts the levels of somatostatin mRNA and neuropeptide Y mRNA were substantially increased over those in the control intact striata. The results suggest that in the grafts, somatostatin mRNA and neuropeptide Y mRNA were expressed in a higher proportion of primordial striatal neurones and there was also an increased level of expression of each neuropeptide gene per individual neurone (reflecting a higher synthetic activity of such neurones) compared to the intact mature striatum. These data demonstrate the sensitivity of the in situ hybridisation technique to study patterns of gene expression in developing neuronal tissues after transplantation.

Abnormal expression of tyrosine hydroxylase-like immunoreactivity in intraocular transplants of rat caudate nucleus

The purpose of the present study was to examine tyrosine hydroxylase (TH)-like immunoreactivity in single intraocular grafts of caudate nucleus, and in caudate grafts which were co-grafted with substantia nigra. Grafts of caudate obtained from fetal rats (crown-rump length: 15-17 mm) were placed into the anterior chamber of eye of adult female Sprague-Dawley rats, and were allowed to survive from 6 to 20 months. The host rats were then perfused with fixative and the tissue was prepared for immunocytochemistry for TH. In 7 out of 8 surviving caudate grafts, including those containing no substantia nigra, tyrosine TH-like immunoreactive (THLI) cell bodies were present. The results of our study suggest that TH is inappropriately expressed in caudate grafts placed in the anterior chamber of the eye.

Restoration of the corticostriatal projection in rat neostriatal grafts: electron microscopic analysis

The corticostriatal projection in rat neostriatal grafts was studied by using the axonal transport of Phaseolus vulgaris-leucoagglutinin. The neostriatal primodia from 15-18-day embryos were used to make a cell suspension which was implanted unilaterally into the rat neostriatum 3-5 days after kainic acid lesion. Two to four months later, regions of the frontal cortex ipsilateral to the grafts were injected iontophoretically with Phaseolus vulgaris-leucoagglutinin. There were many Phaseolus vulgaris-leucoagglutinin labeled cortical fibers in the host neostriatum. Although the density of labeled fibers in the grafts was much lower than that in the surrounding host tissue, some fibers could be seen to enter the grafts and form terminal arborizations. The morphology of labeled fibers in the graft differed from that of corticostriatal fibers from the same injection but distributing in the host neostriatum. The labeled fibers in the host neostriatum arborized in an extended pattern, branching infrequently and making most of their synapses en passant at varicosities along their courses. The labeled fibers in the grafts made more dense arborizations with many short branches that formed clusters of terminals confined to small foci along their courses. The cellular composition and the structure of the neuropil in the neostriatal grafts were similar to that of the neostriatum. As those in the host, labeled corticostriatal terminals in the grafts contained densely packed round vesicles and made asymmetric synapses on dendritic spines, dendritic shafts and somata. A quantitative analysis, however, revealed that the distribution of postsynaptic elements of labeled boutons in the grafts was different from that in the hosts. More than 90% of the labeled cortical terminals in the host neostriatum contacted dendritic spines whereas only 47% of the labeled terminals in the grafts contacted spines, and 50% of them terminated on the dendritic shafts. The present study provides direct anatomic evidence to demonstrate the restoration of the corticostriatal projection in grafts. The difference in the distribution of postsynaptic elements in the grafts and the hosts may represent a response to the decreased innervation density of cortical inputs to the graft tissue, and may contribute to the recovery of corticostriatal responses by increasing the effectiveness of transmission by the fibers that do grow into the graft and form contacts there.

Intrinsic Organization and Connectivity of Intrastriatal Striatal Transplants in Rats as Revealed by DARPP-32 Immunohistochemistry: Specificity of Connections with the Lesioned Host Brain

Intrastriatal grafts of tissue obtained from the striatal or neocortical primordia of rat fetuses have been studied with respect to their intrinsic organization and connectivity using antibodies to DARPP-32 in combination with acetylcholinesterase (AChE) histochemistry, tyrosine hydroxylase (TH) immunocytochemistry, and anterograde and retrograde axonal tracing techniques. The striatal grafts were characterized by distinct patches of DARPP-32-immunoreactive neurons, which were identical to the densely AChE-positive patches stained in adjacent sections from the same specimens. The non-patch areas possessed only few DARPP-32-positive neurons and contained only sparse AChE-positive fibres. The cortical grafts, by contrast, contained no neurons with clear-cut DARPP-32-positivity and they exhibited a sparse, evenly distributed AChE fibre network, similar to that seen in the non-patch areas of the striatal grafts. The host dopaminergic afferents, as revealed by TH immunostaining, had grown selectively into the DARPP-32-positive patches in the striatal grafts, where they formed a dense terminal network around the DARPP-32-positive cell bodies. The non-patch areas, as well as the cortical grafts, received only sparse TH innervation. By contrast, the host cortical afferents, labelled by Phaseolus vulgaris leucoagglutinin from the host frontal cortex, were seen to extend into both the patch and non-patch areas of the striatal grafts. Transplant neurons projecting into the host brain were labelled by Fluoro-Gold injections into the ipsilateral host globus pallidus. These injections labelled large numbers of medium-sized neurons within the striatal grafts and the vast majority of them (over 85%) were confined to the DARPP-32-positive patches. Similar Fluoro-Gold injections labelled only few graft neurons in the cortical grafts. The results indicate that the striatal grafts are composed of a mixture of striatal and non-striatal tissue, and that the striatal graft compartment selectively establishes afferent and efferent connections with the host nigro-pallidal system. These graft connections demonstrate a remarkable specificity in the formation of graft - host connectivity. The results, moreover, suggest that developmental properties of the grafted striatal primordium are retained and expressed in the implanted cell suspension, and that the neuronal systems of the lesioned adult host brain, at least to some extent, remain responsive to growth regulating mechanisms normally operating during ontogenetic development.

Neuronal and glial elements of fetal neostriatal grafts in the adult neostriatum

The cellular components of striatal grafts into the host striatum of rats were studied using [3H]thymidine autoradiography, histochemistry, immunocytochemistry and Golgi-staining. Autoradiography revealed that a layer of glial cells, somas smaller than 8 microns in diameter, stained positive with glial fibrillary acidic protein, and demarcating transplant from host, is derived mainly from the donor. Golgi studies revealed that many neuronal fibers fail to cross the glial layer to reach the host striatum. Migration of transplanted striatal cells into the host milieu was evident. The density of migrated cells decreased linearly as a function of distance from the transplant. Most of the far-migrated cells were glial cells. Neuronal migration was limited. In the transplant, donor cells marked by [3H]thymidine constituted at least 70% of the population. Neurons which stained positively for GABA, substance P, and acetylcholinesterase were identified in the transplant. Fibers of two of these three neuronal types, substance P and acetylcholinesterase, formed patchy patterns in the transplant. Detailed morphology on GABAergic fiber is not available to date, because of the limited antibodies or the method used. GABA is the highest population in the striatal transplant. Two types of GABA-positive cells were clearly distinguishable according to cell size. A majority resembled the medium-sized cell commonly found in striatum, while those of the other type resembled the larger GABA cells usually found in the globus pallidus.

Functional effects of fetal striatal transplants

Much interest has been generated in recent years by the finding that fetal brain tissue transplants into adult brain can survive and grow in the host brain. Most work has been done transplanting relatively homogeneous populations of dopaminergic nigral neurons. However, it is now clear that the more complex fetal striatal tissue, which contains multiple neuronal types, will also survive and grow when transplanted into excitotoxin-lesioned adult striatum. We review herein studies demonstrating that the fetal striatal transplants are functional in that they can elicit changes in behavior in the transplant recipients. The striatal transplants reverse the locomotor hyperactivity characteristic of bilateral excitotoxin lesions. However, there is some controversy about the reversal of the abnormal apomorphine- and amphetamine-induced locomotor responses by fetal striatal transplants into excitotoxin-lesioned striatum and the presence of absence of dopamine receptors within the transplanted tissue. We review the evidence for and against the existence of neuroanatomical connections between the host brain and the transplanted fetal striatal tissue. We also point out the possibility of neurotrophic factors mediating the recovery of spontaneous locomotor activity in light of recent evidence that neurotrophic factors may mediate the functional recovery following transplants of adrenal medulla tissue into dopaminergic deafferented striatum.

Release of acetylcholine and its dopaminergic control in slices from striatal grafts in the ibotenic acid-lesioned rat striatum

Tritium accumulation during incubation with 3H-choline, and the efflux as well as the electrically evoked overflow of tritium during subsequent superfusion, were investigated in slices from unilateral striatal suspension grafts 16 to 20 weeks after implantation into the previously ibotenic acid-lesioned rat striatum. Slices from non-operated animals, from striata contralateral to grafts, and from animals with acute ibotenic acid lesions of the striatum were studied in parallel. The accumulation of tritium and the overflow of tritium in response to electrical stimulation (2 min, 3 Hz) were markedly impaired in acutely lesioned striata. In graft slices, tritium accumulation and the subsequent electrically evoked overflow were greater than in slices obtained after acute lesions, but were still smaller than in non-operated animals or in the contralateral striata. The dopamine D2-receptor agonist quinpirole inhibited the electrically evoked overflow of tritium in grafts, but only to a small extent. The D2-receptor antagonist sulpiride increased, whereas the dopamine uptake inhibitor nomifensine and the dopamine releasing drug amphetamine decreased the evoked overflow in slices from non-operated rats and from striata contralateral to grafts, but had no significant effect in grafts. As in graft slices, the release of acetylcholine in striata from animals in which the mesostriatal dopamine pathway had been lesioned by 6-hydroxy-dopamine was not changed by sulpiride and amphetamine, and was only minimally decreased by nomifensine. Our data show that striato-striatal grafts can partly restore the impaired choline accumulation and acetylcholine release in excitotoxin-lesioned striata. Functional D2-receptors are present on graft cholinergic cells, but are not activated by endogenous dopamine under the present in vitro conditions.

Receptor characteristics and recovery of function following kainic acid lesions and fetal transplants of the striatum. II. Dopaminergic systems

This experiment reports the development of striosomal-like patches in fetal striatal transplants grafted either into the intact, or kainic acid-lesioned, striatum of adult female rat brain. Although D2 receptor density approached control levels in the area of the patches, otherwise the transplanted striatum was relatively empty of dopamine receptors, and overall D2 development of the graft was strikingly reduced from controls. Transplants reversed lesion-induced hyperactivity under saline, but not amphetamine/apomorphine conditions, and led to an increased sensitivity of lesion and grafted animals following haloperidol injection. Transplants into the intact brain led to a lesion-like effect. M1 muscarinic cholinergic/D2 receptor density inversely correlated with behavior following amphetamine/apomorphine injections, while striatal cross-sectional area inversely correlated with activity after saline injection. These results suggest that abnormal maturation of the grafted striatum correlates with deficits in activity in grafted animals, and suggests that abnormal transplant development significantly impacts on transplant-induced behavioral changes.