High-Frequency Stimulation of the Rat Entopeduncular Nucleus Does Not Provide Functional or Morphological Neuroprotection from 6-Hydroxydopamine.

Deep brain stimulation (DBS) is the most common neurosurgical treatment for Parkinson's disease (PD). Whereas the globus pallidus interna (GPi) has been less commonly targeted than the subthalamic nucleus (STN), a recent clinical trial suggests that GPi DBS may provide better outcomes for patients with psychiatric comorbidities. Several laboratories have demonstrated that DBS of the STN provides neuroprotection of substantia nigra pars compacta (SNpc) dopamine neurons in preclinical neurotoxin models of PD and increases brain-derived neurotrophic factor (BDNF). However, whether DBS of the entopeduncular nucleus (EP), the homologous structure to the GPi in the rat, has similar neuroprotective potential in preclinical models has not been investigated. We investigated the impact of EP DBS on forelimb use asymmetry and SNpc degeneration induced by 6-hydroxydopamine (6-OHDA) and on BDNF levels. EP DBS in male rats received unilateral, intrastriatal 6-OHDA and ACTIVE or INACTIVE stimulation continuously for two weeks. Outcome measures included quantification of contralateral forelimb use, stereological assessment of SNpc neurons and BDNF levels. EP DBS 1) did not ameliorate forelimb impairments induced by 6-OHDA, 2) did not provide neuroprotection for SNpc neurons and 3) did not significantly increase BDNF levels in any of the structures examined. These results are in sharp contrast to the functional improvement, neuroprotection and BDNF-enhancing effects of STN DBS under identical experimental parameters in the rat. The lack of functional response to EP DBS suggests that stimulation of the rat EP may not represent an accurate model of clinical GPi stimulation.

Recombinant adenoassociated virus 2/5-mediated gene transfer is reduced in the aged rat midbrain.

Clinical trials are examining the efficacy of viral vector-mediated gene delivery for treating Parkinson's disease. Although viral vector strategies have been successful in preclinical studies, to date clinical trials have disappointed. This may be because of the fact that preclinical studies fail to account for aging. Aging is the single greatest risk factor for developing Parkinson's disease and age alters cellular processes utilized by viral vectors. We hypothesized that the aged brain would be relatively resistant to transduction when compared with the young adult. We examined recombinant adeno-associated virus 2/5-mediated green fluorescent protein (rAAV2/5 GFP) expression in the young adult and aged rat nigrostriatal system. GFP overexpression was produced in both age groups. However, following rAAV2/5 GFP injection to the substantia nigra aged rats displayed 40%-60% less GFP protein in the striatum, regardless of rat strain or duration of expression. Furthermore, aged rats exhibited 40% fewer cells expressing GFP and 4-fold less GFP messenger RNA. rAAV2/5-mediated gene transfer is compromised in the aged rat midbrain, with deficiencies in early steps of transduction leading to significantly less messenger RNA and protein expression.

Striatal pleiotrophin overexpression provides functional and morphological neuroprotection in the 6-hydroxydopamine model.

Neurotrophic factors are integrally involved in the development of the nigrostriatal system and in combination with gene therapy, possess great therapeutic potential for Parkinson's disease (PD). Pleiotrophin (PTN) is involved in the development, maintenance, and repair of the nigrostriatal dopamine (DA) system. The present study examined the ability of striatal PTN overexpression, delivered via psueudotyped recombinant adeno-associated virus type 2/1 (rAAV2/1), to provide neuroprotection and functional restoration from 6-hydroxydopamine (6-OHDA). Striatal PTN overexpression led to significant neuroprotection of tyrosine hydroxylase immunoreactive (THir) neurons in the substantia nigra pars compacta (SNpc) and THir neurite density in the striatum, with long-term PTN overexpression producing recovery from 6-OHDA-induced deficits in contralateral forelimb use. Transduced striatal PTN levels were increased threefold compared to adult striatal PTN expression and approximated peak endogenous developmental levels (P1). rAAV2/1 vector exclusively transduced neurons within the striatum and SNpc with approximately half the total striatal volume routinely transduced using our injection parameters. Our results indicate that striatal PTN overexpression can provide neuroprotection for the 6-OHDA lesioned nigrostriatal system based upon morphological and functional measures and that striatal PTN levels similar in magnitude to those expressed in the striatum during development are sufficient to provide neuroprotection from Parkinsonian insult.

Subthalamic nucleus stimulation increases brain derived neurotrophic factor in the nigrostriatal system and primary motor cortex.

The mechanisms underlying the effects of long-term deep brain stimulation of the subthalamic nucleus (STN DBS) as a therapy for Parkinson's disease (PD) remain poorly understood. The present study examined whether functionally effective, long-term STN DBS modulates glial cell line-derived neurotrophic factor (GDNF) and/or brain-derived neurotrophic factor (BDNF) in both unlesioned and unilateral 6-hydroxydopamine lesioned rats. Lesioned rats that received two weeks of continuous unilateral STN DBS exhibited significant improvements in parkinsonian motor behaviors in tests of forelimb akinesia and rearing activity. Unilateral STN DBS did not increase GDNF in the nigrostriatal system, primary motor cortex (M1), or hippocampus of unlesioned rats. In contrast, unilateral STN DBS increased BDNF protein 2-3 fold bilaterally in the nigrostriatal system with the location (substantia nigra vs. striatum) dependent upon lesion status. Further, BDNF protein was bilaterally increased in M1 cortex by as much as 2 fold regardless of lesion status. STN DBS did not impact cortical regions that receive less input from the STN. STN DBS also was associated with bilateral increases in BDNF mRNA in the substantia nigra (SN) and internal globus pallidus (GPi). The increase observed in GPi was completely blocked by pretreatment with 5-Methyl-10,11-dihydro-5 H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), suggesting that the activation of N-methyl-D-aspartate (NMDA) receptors was involved in this phenomenon. The upregulation of BDNF associated with long term STN DBS suggest that this therapy may exert pronounced and underappreciated effects on plasticity in the basal ganglia circuitry that may play a role in the symptomatic effects of this therapy as well as support the neuroprotective effect of stimulation documented in this rat model.