Intracerebral grafting of neuronal cell suspensions. VI. Survival and growth of intrahippocampal implants of septal cell suspensions

The survival and growth of intrahippocampal septal suspension grafts were investigated by acetylcholine esterase (AChE) histochemistry in animals with lesions of the intrinsic septohippocampal cholinergic pathways. AChE was demonstrable in the grafts after the first postoperative week, and AChE-positive fibres were seen to extend into the host hippocampus by 3 weeks. Rapid fibre outgrowth occurred between 3 weeks and 3 months after grafting, and continued at a slower rate thereafter. By 6 months a fairly complete reinnervation of the initially denervated hippocampus was achieved in most specimens, and this persisted at 14 months, the longest postoperative time analysed. A comparison between the development of the AChE-positive neurones in the suspension grafts with that seen during ontogeny in situ suggested that the grafted neurones lagged behind normal development by at least 1 week. Similar to our previous observations on septal grafts implanted as solid tissue pieces, the pattern of the newly-formed AChE-positive innervation in the host hippocampal formation, established from the septal suspension grafts, was remarkably similar to that of the normal AChE-positive septal innervation. This pattern became established as soon as the graft-derived fibres first grew in, suggesting that the ingrowing axons extended and ramified preferentially into those hippocampal subfields which normally receive an AChE-positive innervation from the septal-diagonal band area

Intracerebral grafting of neuronal cell suspensions. VIII. Cell survival and axonal outgrcwth of dcpaminergic and cholinergic cells in the aged brain.

Neuronal cell suspensions prepared from the ventral mesencephalon and the septal-diagonal band area of rat embryos were implanted into the depth of the intact neostriatum or hippocampus of 21-23 month old female rats. Graft survival, assessed 3-4 months after grafting, was comparable to that seen in our previous studies of young adult recipients. Fibre outgrowth into the host brain was evaluated in animals which were subjected to lesions of the intrinsic nigrostriatal or septohippocampal system 6-10 days before killing. Dense dopamine fibre outgrowth was seen within a zone of up to about 1 mm radius around the nigral implants, and dense growth of acetylcholine esterase (AChE) positive fibres occurred up to about 2 mm away from the septal implants. The overall magnitude of fibre outgrowth was less than that generally seen in previously denervated targets in young adult recipients, but it appeared to be as extensive as in young recipients when the grafts are placed in non-denervated targets. The distribution of the AChE-positive fibres from the septal implants in the host hippocampus suggested that the pattern found in the non-denervated target of the aged recipients was more diffuse, and partly different, from normal, and that age-dependent synapse loss in intrinsic connections may influence the patterning of the graft-derived innervation

Intracerebral grafting of neuronal cell suspensions. V. Behavioural recovery in rats with bilateral 6-OHDA lesions following implantation of nigral cell suspensions.

Bilateral 6-hydroxydopamine-induced lesions of the ascending forebrain dopamine neurones induce a behavioural syndrome in rats which includes profound aphagia, adipsia, akinesia and bilateral sensorimotor neglect. Such animals will die unless maintained by intragastric feeding. Three experiments are reported in which we have attempted to ameliorate this syndrome with single or multiple placements of nigral cell suspensions into the forebrains of rats with bilateral dopamine depletions. Although the grafts were efficient in reversing the sensorimotor and akinetic impairments, and produced a significant increase in eating, the grafted rats remained hypophagic and adipsic. The results indicate that although many components of the bilateral dopamine denervation syndrome can be reversed by intrastriatal nigral suspension grafts, the severe eating and drinking deficits remain unameliorated

Intracerebral grafting of neuronal cell suspensions. III. Activaty of intrastriatal nigral suspension implants as assessed by measurements of dopamine synthesis and metabolism

The activity of intrastriatal grafts of nigral cell suspensions has been monitored biochemically, using radioenzymatic assays of dopamine, its major acidic metabolite, DOPAC, and DOPA accumulation after DOPA-decarboxylase inhibition. Implants of 4-9 microliter of nigral cell suspension restored striatal DA levels by an average of 13-18%, with the highest individual values reaching about 50% of control. DOPAC was restored from about 5% in the lesioned controls to about 20% of normal in the grafted animals. The DOPAC: DA ratios and the DOPA accumulation measures indicated that the grafted DA neurons were spontaneously active and that the transmitter turnover rate was on the average some 50-100% higher than the intact intrinsic nigrostriatal DA neurones. These results thus provide evidence that the intrastriatal nigral suspension grafts are capable of restoring dopaminergic neurotransmission in the previously denervated striatum

Intracerebral grafting of neuronal cell suspensions. II. Survival and growth of nigral cells implanted in different brain sites

Dissociated dopamine-rich cell suspensions were prepared from the ventral mesencephalon of rat embryos and injected in one or several sites in striatal and non-striatal regions in the dopaminergically denervated brain of adult rats. While the grafts survived well in all sites, the dopamine fibre outgrowth was markedly different depending on whether the grafts occurred in an area normally innervated by the mesencephalic dopamine neurones (i.e. neostriatum or nc. accumbens) or in areas not normally innervated by these neurones (i.e. parietal cortex, lateral hypothalamus or substantia nigra). Moreover, in grafts placed at different sites along the trajectory of the nigrostriatal pathway the outgrowing fibres remained confined to the graft, and there was little evidence that the implanted neurones could elongate their axons along the pathway of the nigrostriatal tract to reach the striatum from a distance. Thus, the intracerebral suspension grafts provided efficient reinnervation of a denervated target only when placed in the immediate vicinity of the target area. The results of multiple graft placements indicate that a relatively complete restoration of a lost innervation should be possible to achieve in large areas of the brain, such as the striatal complex, with the suspension grafting technique

Grafts of embryonic substantia nigra reinnervating the ventrolateral striatum ameliorate sensorimotor impairments and akinesia in rats with 6-OHDA lesions of the nigrostriatal pathway.

Previous studies have shown that transplants of embryonic substantia nigra, which reinnervate the dorsal neostriatum, can compensate for certain, but not all, behavioural deficits induced by unilateral or bilateral destruction of the nigrostriatal dopamine pathways in adult rats. The present study shows the nigral transplants which are placed in the lateral cortex so as to reinnervate ventral and lateral parts of the neostriatum, give an entirely different pattern of behavioural recovery. Thus, the laterally placed grafts were more efficient than the previous dorsally placed ones in compensating for the sensorimotor asymmetry in unilaterally lesioned animals, and the akinesia seen after bilateral lesions. Conversely, the drug-induced motor asymmetry which was completely abolished by the dorsal grafts was not significantly affected in the present animals. These results support the idea of topographic heterogeneity with respect to striatal functions, and suggest that the technique can be used as a tool for more detailed analysis of the functional organization of the meso-telencephalic dopamine systems and the functional heterogeneity of the dopaminergically innervated striatal-based forebrain regions