ENCAPSULATED GENETICALLY-ENGINEERED FIBROBLASTS - RELEASE OF NERVE GROWTH-FACTOR AND EFFECTS IN-VIVO ON RECOVERY OF CHOLINERGIC MARKERS AFTER DEVASCULARIZING CORTICAL-LESIONS

Genetically engineered rat fibroblasts producing nerve growth factor ( NGF) were encapsulated in alginate-polylysine-alginate gels with the o bjective to produce viable ''minifactories'' continuously producing an d secreting NGF into the rat brain. Microencapsulated fibroblasts (NGF secretors and NGF non-secretors) were placed onto the surface of the lesioned rat cortex (unilateral devascularizing lesion) and animals we re sacrificed 30 days after surgery. Fibroblasts NGF-non secreters nor mally produce tumors after implantation, therefore, they were irradiat ed prior to encapsulation. Three other experimental groups were studie d in parallel: non-lesioned (controls), lesioned rats receiving ''empt y'' alginate spheres and lesioned animals without treatment and micros pheres. Biochemical analysis of microdissected brain tissues of lesion ed animals treated with encapsulated NGF-secretor fibroblasts showed a significant increase in choline acetyltransferase (ChAT) activity in cortices adjacent to the lesion but not far from it (entorhinal cortex ). This may indicate a gradient of concentration of the released NGF a nd/or differential responsivity of lesioned vs nonlesioned target tiss ue. ChAT enzymalic activity in the microdissected nucleus basalis magn ocellularis (NBM) was significantly decreased (P < 0.05) in all lesion ed animals treated with spheres without fibroblasts and those with fib roblasts not secreting NGF. Morphometric analysis of ChAT-IR and low a ffinity NGF-receptor IR cholinergic neurons in the middle portion of t he NBM shows a prevention of neuronal shrinkage and extensive neuropil in animals treated with microencapsulated NGF-secretor fibroblasts. T he results of this study demonstrate that NGF from encapsulated geneti cally engineered fibroblasts can be secreted for at least long enough to prevent degenerative changes of cholinergic neurons in the NBM.