Connectivities of the striatal grafts and laminin guiding

Excitochemical-Induced Trophic Bridging Directs Axonal Growth of Transplanted Neurons to Distal Target

Brain grafts directly placed in their target regions often lack proper connections and normal regulation. When brain grafts are placed in their ontogenetic normal area, the axonal outgrowth of grafts to distal target regions is a major obstacle. We previously demonstrated that directional axonal growth of grafts can be facilitated by laminin. In this study we demonstrated that excitochemicals induced trophic environment can be strategically used as a bridge to guide transplanted neurons to innervate a distal target of millimeter distance, and has a unique effect on fiber expansion in the target region. To distinguish dopamine (DA) growth from that of transplants, 6-hydroxydopamine was unilaterally injected into medial forebrain bundle to remove dopamine innervation to the striatum. Ibotenic acid (IB), kainic acid (KA), or phosphate buffer (vehicle) were micro-injected through a glass-pipet to make a 7 mm long tract between the substantia nigra and the striatum in Sprague-Dawley rats. Gestational 14-15 days brainstem slurry was transplanted either in the same or a separate tract into nigra at the bottom of the bridge. All transplants survived with abundant serotonin (5-HT) and DA neurons. Traceable DA fibers formed distinct bundles from grafts along the length of IB/KA tracts. Upon arrival at their major target regions, fibers from bundles were capable of leaving the tracts, and reinnervating the DA-vacated striatum. The 5-HT fibers formed bundles similar to DA fibers but left the tract earlier upon arrival at their major target the globus pallidus and when arriving at the striatum and cortex. Fibers from grafts with vehicle tracts grew randomly and not into the tract. These results indicate that the trophic effects of chemical lesioning serves as a remarkably effective axonal guidance for more than one type of fetal neuron to innervate distal brain regions. This method has great potential in directing fibers in many transplant models.

Establishment of a Stable Glutamate Decarboxylase (Gad) Expressing Cell-Line by Transfection

We have constructed a recombinant DNA clone containing the gene encoding glutamic acid decarboxylase (GAD), which catalyzes the synthesis of γ-amino-butyric acid (GABA). This recombinant DNA was then transfected into mouse NIH-3T3 fibroblast cells for transplantation into Swiss-Web mice. In order to construct a plasmid capable of transcribing the DNA insert in the eucaryotic cells, the GAD gene was removed from pSP65-13, and was ligated into the vector pSV2neo, which contains the SV40 early promoter, and the neomycin resistance gene. The pSV2GAD was then transfected into NIH-3T3 fibroblasts by calcium phosphate precipitation, or by electroporation. The transfected fibroblasts were then selected with antibiotic G418 for amplification. The transient expression of GAD in the transfected fibroblasts was detected by immunocytochemical staining using anti-GAD antibody. A small population of GAD immunoreactive cells were clearly stained, and were easily distinguished from the majority of unstained background cells. These GAD-immunoreactive cells were not seen in either mock-transfected, or pSV2neo-transfected cells (vector-alone control). The transfected fibroblasts were continuously selected with antibiotic G418. Six out of 35 subcultures that had GAD-positive immunostaining in the cell lines were selected. Granular GAD-positive staining was observed in the cytoplasm and fiber extensions of the transfected cell lines in varying densities. The GAD-mRNA was also detected in the subcultures by in situ hybridization using a 35S-labeled 369-nucleotide riboprobe in pBluescript. The GAD-transfected NIH-3T3 cells were then transplanted into Swiss-Web mice. Fifteen to 30 days later, transplanted animals were perfused for identification. These cells were first identified with anti-fibronectin antibody, and the adjacent sections with anti-GAD or anti-GABA antibodies. All the transplants are fibronectin-positive. Both GAD- and GABA-positive cells were observed in the transplant.

Functional and anatomical reconstruction of the 6-hydroxydopamine lesioned nigrostriatal system of the adult rat

In an attempt to reconstruct the 6-hydroxydopamine lesioned nigrostriatal system of the adult rat we have combined homotopic grafting of embryonic ventral mesencephalon suspensions with the implantation of long oblique "bridge" grafts of fibroblast growth factor-4-transfected RN-22 schwannoma cells stretching from the site of the neuronal grafts to the striatum. At seven weeks after receiving both grafts, animals were killed and processed for immunohistochemistry against tyrosine hydroxylase. Tyrosine hydroxylase-immunoreactive axons were seen to extend from the nigral grafts, along the bridge graft to the striatum where terminal arborizations could be seen. The retrograde tracer Fluoro-gold was injected intrastriatally in some of the experimental animals and was taken up by grafted neurons confirming their projection to the striatum. In parallel to the anatomical reconstruction of the system, a decrease in amphetamine-induced rotation was demonstrated in those animals receiving both grafts which had received > 98% complete lesions. This decrease was greatest in those animals with the most tyrosine hydroxylase-immunoreactive axons in their bridge grafts. The presence of the bridge graft also led to an increase in neuronal graft survival with twice as many tyrosine hydroxylase-immunoreactive neurons being found in the grafts of those animals that had received both grafts compared to those that had received a neuronal graft but no bridge graft.

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.