Modulation of excessive neuronal activity by fibroblasts: Potential use in treatment of Parkinson's disease

Abstract

A number of neurological disorders are marked by increased or aberrant frequency of neuronal discharge in specific parts of the brain. Administration of drugs such as antiepileptic compounds results in the depression of neuronal activity in the whole brain, with the potential for serious side-effects. In the search for additional therapies to reduce the unphysiological electrical activity of over-active brain foci, we have examined the effect of fibroblasts transplanted to areas responsible for motor dysfunction in hemi-parkinsonian rats, since bursting synchronous discharges in internal segment of globus pallidus (GPi) are thought to be partially responsible for the movement disorders of PD. Fibroblasts express gap junctions and ion channels, and so, when transplanted to brain tissue, can potentially modulate excessive electrical activity. Neonatal cortical neurons were cultured on multi-electrode arrays, and their electrical activity was evaluated before and after fibroblast seeding. Unilateral 6-hydroxydopamine (6-OHDA) lesion was carried out in Fischer rats. Lesioned or control rats were transplanted with either syngeneic dermal fibroblasts, microfine glass beads, ibotenic acid, or physiological saline, in the entopeduncular nucleus (EP). Apomorphine-induced rotational behavior and L-dopa-induced dyskinetic movements were evaluated before transplantation (baseline) and 2, 4, 8, 12, and 24 weeks following transplantation. Following behavioral experiments, rats were perfused with 4% formaldehyde in PBS for immunohistochemical study of the brain. We demonstrate in vitro that the introduction of fibroblasts into a network of neurons does not interfere with overall functional measures of activity, while moderately altering the characteristics of synchronous neuronal discharge. In rats with unilateral 6-hydroxydopamine lesions of the nigro-striatal dopaminergic pathway, apomorphine-induced rotations were reduced by more than 60% following ipsilateral transplantation of fibroblasts to the EP. L-Dopa-induced dyskinesia was also significantly reduced. Transplantation of inert microspheres, or chemical lesion of the same area with ibotenic acid, did not produce beneficial effects on parkinsonian symptomatology. Fibroblast transplantation could be an alternative treatment strategy for the parkinsonian patient.