Transplantation of mesencephalic cell suspension in dopamine-denervated striatum of the rat. II. Effects on corticostriatal transmission

MPTP-induced deficits in striatal synaptic plasticity are prevented by glial cell line-derived neurotrophic factor expressed via an adeno-associated viral vector

This study determined the consequences of dopamine denervation of the striatum on synaptic plasticity and prevention of these changes with gene therapy using an adeno-associated viral vector (AAV) expressing glial cell line-derived neurotrophic factor (GDNF). C57BL6/J mice were injected with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP); long-term depression (LTD) or potentiation (LTP) were measured in vitro. Fast-scan cyclic voltammetry measured electrically released dopamine from a functionally relevant pool in these same striatal slices. After MPTP, dopamine release and uptake were greatly diminished, and LTP and LTD were blocked in the striatal slices. The loss of plasticity resulted directly from the loss of dopamine since its application rescued synaptic plasticity. Striatal GDNF expression via AAV, before MPTP, significantly protected against the loss of dopamine and prevented the blockade of corticostriatal LTP. These data demonstrate that dopamine plays a role in supporting several forms of striatal plasticity and that GDNF expression via AAV prevents the loss of dopamine and striatal plasticity caused by MPTP. We propose that impairment of striatal plasticity after dopamine denervation plays a role in the symptomology of Parkinson's disease and that AAV expression of neurotrophic factors represents a tenable approach to protecting against or slowing these neurobiological deficits.

Dopamine depletion causes fragmented clustering of neurons in the sensorimotor striatum: evidence of lasting reorganization of corticostriatal input

Firing during sensorimotor exam was used to categorize single neurons in the lateral striatum of awake, unrestrained rats. Five rats received unilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle to deplete striatal dopamine (DA; >98% depletion, postmortem assay). Three months after treatment, rats exhibited exaggerated rotational behavior induced by L-dihydroxyphenylalanine (L-DOPA) and contralateral sensory neglect. Electrode track "depth profiles" on the DA-depleted side showed fragmented clustering of neurons related to sensorimotor activity of single body parts (SBP neurons). Clusters were smaller than normal, and more SBP neurons were observed in isolation, outside of clusters. More body parts were represented per unit volume. No recovery in these measures was observed up to one year post lesion. Overall distributions of neurons related to different body parts were not altered. The fragmentation of SBP clusters after DA depletion indicates that a percentage of striatal SBP neurons switched responsiveness from one body part to one or more different body parts. Because the specific firing that characterizes striatal SBP neurons is mediated by corticostriatal inputs (Liles and Updyke [1985] Brain Res. 339:245-255), the data indicate that DA depletion resulted in a reorganization of corticostriatal connections, perhaps via unmasking or sprouting of connections to adjacent clusters of striatal neurons. After reorganization, sensory activity in a localized body part activates striatal neurons that have switched to that body part. In turn, switched signals sent from basal ganglia to premotor and motor neurons, which likely retain their original connections, would create mismatches in these normally precise topographic connections. Switched signals could partially explain parkinsonian deficits in motor functions involving somatosensory guidance and their intractability to L-DOPA therapy-particularly if the switching involves sprouting.