The Effects of Deep Brain Stimulation of the Subthalamic Nucleus on Vascular Endothelial Growth Factor, Brain-Derived Neurotrophic Factor, and Glial Cell Line-Derived Neurotrophic Factor in a Rat Model of Parkinson's Disease.

OBJECTIVE: Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has evolved as a powerful therapeutic alternative for the treatment of Parkinson's disease (PD). Despite its clinical efficacy, the mechanisms of action have remained poorly understood. In addition to the immediate symptomatic effects, long-term neuroprotective effects have been suggested. Those may be mediated through neurotrophic factors (NFs) like vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF), and glial cell line-derived neurotrophic factor (GDNF). Here, the impact of DBS on the expression of NFs was analysed in a rat model of PD. METHODS: Unilateral 6-hydroxydopamine (6-OHDA) lesioned rats received DBS in the STN using an implantable microstimulation system, sham DBS in the STN, or no electrode placement. Continuous unilateral STN-DBS (current intensity 50 µA, frequency 130 Hz, and pulse width 52 µs) was conducted for 14 days. Rats were then sacrificed and brains shock frozen. Striata and motor cortices were dissected with a cryostat. Levels of VEGF, BDNF, and GDNF were analysed, both by quantitative PCR and colorimetric ELISA. RESULTS: PCR revealed a significant upregulation of only BDNF mRNA in the ipsilateral striata of the DBS group, when compared to the sham-stimulated group. There was no significant increase in VEGF mRNA or GDNF mRNA. ELISA analysis showed augmentations of BDNF, VEGF, as well as GDNF protein in the ipsilateral striata after DBS compared to sham stimulation. In the motor cortex, significant increases after DBS were observed for BDNF only, not for the other 2 NFs. CONCLUSIONS: The upregulation of trophic factors induced by STN-DBS may participate in its long-term therapeutic efficacy and potentially neuroprotective effects.

Subthalamic beta oscillations correlate with dopaminergic degeneration in experimental parkinsonism.

Excessive beta activity has been shown in local field potential recordings from the cortico-basal ganglia loop of Parkinson's disease patients and in its various animal models. Recent evidence suggests that enhanced beta oscillations may play a central role in the pathophysiology of the disorder and that beta activity may be directly linked to the motor impairment. However, the temporal evolution of exaggerated beta oscillations during the ongoing dopaminergic neurodegeneration and its relation to the motor impairment and histological changes are still unknown. We investigated motor behavioral, in-vivo electrophysiological (subthalamic nucleus, motor cortex) and histological changes (striatum, substantia nigra compacta) 2, 5, 10 and 20-30 days after a 6-hydroxydopamine injection into the medial forebrain bundle in Wistar rats. We found strong correlations between subthalamic beta power and motor impairment. No correlation was found for beta power in the primary motor cortex. Only subthalamic but not cortical beta power was strongly correlated with the histological markers of the dopaminergic neurodegeneration. Significantly increased subthalamic beta oscillations could be detected before this increase was found in primary motor cortex. At the latest observation time point, a significantly higher percentage of long beta bursts was found. Our study is the first to show a strong relation between subthalamic beta power and the dopaminergic neurodegeneration. Thus, we provide additional evidence for an important pathophysiological role of subthalamic beta oscillations and prolonged beta bursts in Parkinson's disease.

Topological Causality in Dynamical Systems.

Determination of causal relations among observables is of fundamental interest in many fields dealing with complex systems. Since nonlinear systems generically behave as wholes, classical notions of causality assuming separability of subsystems often turn out inadequate. Still lacking is a mathematically transparent measure of the magnitude of effective causal influences in cyclic systems. For deterministic systems we found that the expansions of mappings among time-delay state space reconstructions from different observables not only reflect the directed coupling strengths, but also the dependency of effective influences on the system's temporally varying state. Estimation of the expansions from pairs of time series is straightforward and used to define novel causality indices. Mathematical and numerical analysis demonstrate that they reveal the asymmetry of causal influences including their time dependence, as well as provide measures for the effective strengths of causal links in complex systems.

Stability of Neuronal Networks with Homeostatic Regulation.

Neurons are equipped with homeostatic mechanisms that counteract long-term perturbations of their average activity and thereby keep neurons in a healthy and information-rich operating regime. While homeostasis is believed to be crucial for neural function, a systematic analysis of homeostatic control has largely been lacking. The analysis presented here analyses the necessary conditions for stable homeostatic control. We consider networks of neurons with homeostasis and show that homeostatic control that is stable for single neurons, can destabilize activity in otherwise stable recurrent networks leading to strong non-abating oscillations in the activity. This instability can be prevented by slowing down the homeostatic control. The stronger the network recurrence, the slower the homeostasis has to be. Next, we consider how non-linearities in the neural activation function affect these constraints. Finally, we consider the case that homeostatic feedback is mediated via a cascade of multiple intermediate stages. Counter-intuitively, the addition of extra stages in the homeostatic control loop further destabilizes activity in single neurons and networks. Our theoretical framework for homeostasis thus reveals previously unconsidered constraints on homeostasis in biological networks, and identifies conditions that require the slow time-constants of homeostatic regulation observed experimentally.

A model for attentional information routing through coherence predicts biased competition and multistable perception.

Selective attention allows to focus on relevant information and to ignore distracting features of a visual scene. These principles of information processing are reflected in response properties of neurons in visual area V4: if a neuron is presented with two stimuli in its receptive field, and one is attended, it responds as if the nonattended stimulus was absent (biased competition). In addition, when the luminance of the two stimuli is temporally and independently varied, local field potentials are correlated with the modulation of the attended stimulus and not, or much less, correlated with the nonattended stimulus (information routing). To explain these results in one coherent framework, we present a two-layer spiking cortical network model with distance-dependent lateral connectivity and converging feed-forward connections. With oscillations arising inherently from the network structure, our model reproduces both experimental observations. Hereby, lateral interactions and shifts of relative phases between sending and receiving layers (communication through coherence) are identified as the main mechanisms underlying both biased competition as well as selective routing. Exploring the parameter space, we show that the effects are robust and prevalent over a broad range of parameters. In addition, we identify the strength of lateral inhibition in the first model layer as crucial for determining the working regime of the system: increasing lateral inhibition allows a transition from a network configuration with mixed representations to one with bistable representations of the competing stimuli. The latter is discussed as a possible neural correlate of multistable perception phenomena such as binocular rivalry.

High frequency stimulation of the subthalamic nucleus leads to presynaptic GABA(B)-dependent depression of subthalamo-nigral afferents.

Patients with akinesia benefit from chronic high frequency stimulation (HFS) of the subthalamic nucleus (STN). Among the mechanisms contributing to the therapeutic success of HFS-STN might be a suppression of activity in the output region of the basal ganglia. Indeed, recordings in the substantia nigra pars reticulata (SNr) of fully adult mice revealed that HFS-STN consistently produced a reduction of compound glutamatergic excitatory postsynaptic currents at a time when the tetrodotoxin-sensitive components of the local field potentials had already recovered after the high frequency activation. These observations suggest that HFS-STN not only alters action potential conduction on the way towards the SNr but also modifies synaptic transmission within the SNr. A classical conditioning-test paradigm was then designed to better separate the causes from the indicators of synaptic depression. A bipolar platinum-iridium macroelectrode delivered conditioning HFS trains to a larger group of fibers in the STN, while a separate high-ohmic glass micropipette in the rostral SNr provided test stimuli at minimal intensity to single fibers. The conditioning-test interval was set to 100 ms, i.e. the time required to recover the excitability of subthalamo-nigral axons after HFS-STN. The continuity of STN axons passing from the conditioning to the test sites was examined by an action potential occlusion test. About two thirds of the subthalamo-nigral afferents were occlusion-negative, i.e. they were not among the fibers directly activated by the conditioning STN stimulation. Nonetheless, occlusion-negative afferents exhibited signs of presynaptic depression that could be eliminated by blocking GABA(B) receptors with CGP55845 (1 µM). Further analysis of single fiber-activated responses supported the proposal that the heterosynaptic depression of synaptic glutamate release during and after HFS-STN is mainly caused by the tonic release of GABA from co-activated striato-nigral afferents to the SNr. This mechanism would be consistent with a gain-of-function hypothesis of DBS.

Neurochemical characterization of the striatum and the nucleus accumbens in L-type Ca(v)1.3 channels knockout mice.

L-type Ca(v)1.3 channels control the autonomous pacemaking of the substantia nigra (SN) dopamine (DA) neurons, which maintains the sustained release of DA in the striatum, its target structure. The persistent engagement of L-type channels during pacemaking might lead to increased vulnerability to environmental stressors or degenerative processes, providing a mechanism for the development of Parkinson's disease (PD). Interestingly, L-type channels are not necessary for pacemaking, opening the possible use of calcium channel antagonists as neuroprotective agents for PD without disturbing normal DA function. In this study we aimed to evaluate the consequences of Ca(v)1.3 channels deletion at the neurochemical level. For this purpose, tissue concentrations of DA and their respective metabolites were measured using high performance liquid chromatography (HPLC) in the striatum and the nucleus accumbens (NAcc) of mice lacking the gene for the Ca(v)1.3 channel subunit (CACNA1D) and compared to those in wild-type mice. Striatal DA level did not differ between the two groups. In contrast, the level of serotonin, glutamate, GABA, and taurine were increased by more than 50% in the striatum of Ca(v)1.3 null mice. Neurotransmitters levels in the NAcc did not differ between the different groups. In conclusion, our results neurochemically corroborate the robustness of the nigrostriatal DA neurons in the absence of Ca(v)1.3 channels, but suggest that complete deletion of this channel affected a variety of other transmitter systems.

Activity modulation of the globus pallidus and the nucleus entopeduncularis affects compulsive checking in rats.

Deep brain stimulation at high frequencies (HFS) is currently studied in the treatment of therapy-refractory obsessive-compulsive disorder (OCD). The diversity of targeted brain areas and the discrepancy in demonstrating beneficial effects, highlight the need for better mapping of brain regions in which HFS may yield anti-compulsive effects. This goal may be achieved by investigating the effects of HFS in appropriate animal models of OCD. The present study tested the effect of bilateral HFS or pharmacological inactivation (as induced by intracerebral administration of the GABA-agonist muscimol) of both the Globus pallidus (GP; rodent equivalent to human GP externus) and the Nucleus entopeduncularis (EP; rodent equivalent to human GP internus) on checking behaviour in the quinpirole rat model of OCD. We demonstrate that HFS of the GP does not and HFS of the EP only partially reduces OCD-like behaviour in rats. In contrast, pharmacological inactivation of both GP and EP significantly reduces OCD-like behaviour in the model. These data contrast previously derived data on the effectiveness of HFS of the subthalamic nucleus, nucleus accumbens, GP and EP in the same and other rat models of OCD. We conclude that (i) although GP and EP play an important role in the pathophysiology of OCD, these areas may not represent first choice target structures for HFS, (ii) the effectiveness of HFS may depend on different subtypes of OCD, represented in different animal models, and (iii) differential net mechanisms may subserve the effectiveness of HFS and pharmacological inactivation.

Development of an implantable microstimulation system for chronic DBS in rodents.

High frequency deep brain stimulation (DBS) of certain basal ganglia nuclei (e.g. subthalamic nucleus, STN) has emerged as a powerful neuromodulatory approach in the treatment of late stage Parkinson's disease patients. However, the underlying mechanisms of action are not fully understood. We have therefore established an implantable DBS device for small laboratory animals (e.g. rats) that allows the reliable and safe application of continuous DBS for at least 3 weeks. We could further show that miniaturized monopolar electrodes comprising activated iridium are suitable for continuous stimulation of small brain structures like the STN without inducing severe insertion or stimulation related injuries.

The impact of subthalamic deep brain stimulation on nigral neuroprotection-myth or reality?

OBJECTIVE: In the present review article we summarize available clinical and preclinical evidence, if modulation of the subthalamic nucleus (STN) could be a target for neuroprotection in Parkinson's disease (PD). BACKGROUND: Chronic deep brain stimulation (DBS) of the STN has emerged as a powerful therapeutic alternative for the treatment of PD, ensuring stable symptom control for up to five years despite the progressive nature PD. MATERIALS AND METHODS: Comparative review of literature in PuBMed available up to December 2008. RESULTS: The assessment of neuroprotection has been proven difficult in the clinical situation, as medical or surgical therapeutic options that improve PD symptoms could be erroneously considered to be neuroprotective because of the difficulty of differentiating between symptomatic effects and potential neuromodulative disease-related effects of various treatment options applied in PD. The methodological limitations of clinical trials underline the importance of putative neuroprotective compounds to be tested in clinically driven preclinical studies. Thus, animal models, mimicking progressive nigrostriatal cell death, are indispensable to further advance the important issue of neuroprotection or neuromodulation following DBS. CONCLUSION: Clear clinical evidence for STN-DBS-related neuroprotection in PD is missing. However, numerous preclinical studies show (and are discussed) that silencing of the STN via lesion or DBS may exert neuromodulative effects on nigral dopamine neurons.

A syndrome of the dentate nucleus mimicking psychogenic ataxia.

To date, cerebellar involvement in control of non-motor functions like cognition and emotion is increasingly well established. Current models suggest that motor and non-motor networks connecting the cerebellum with cortical areas operate independently in closed and segregated loops. Here, we report a 59-year-old female patient with a small cerebellar lesion that shows that cognitive activation can significantly influence cerebellar motor control. Surprisingly, this led to a clinical picture mimicking a psychogenic disorder. Similar to non-human primates, this case suggests that the human dentate nucleus consists of distinct cognitive and motor domains with additional somatotopical arrangement of the latter. Extending current models of cerebro-cerebellar interaction, this case further illustrates that there can be significant functional cross-talk between motor and cognitive cerebellar networks.

High-frequency stimulation of the nucleus accumbens core and shell reduces quinpirole-induced compulsive checking in rats.

Electrical deep brain stimulation (DBS) is currently studied in the treatment of therapy-refractory obsessive compulsive disorders (OCDs). The variety of targeted brain areas and the inconsistency in demonstrating anti-compulsive effects, however, highlight the need for better mapping of brain regions in which stimulation may produce beneficial effects in OCD. Such a goal may be advanced by the assessment of DBS in appropriate animal models of OCD. Currently available data on DBS of the nucleus accumbens (NAc) on OCD-like behavior in rat models of OCD are contradictory and partly in contrast to clinical data and theoretical hypotheses about how the NAc might be pathophysiologically involved in the manifestation of OCD. Consequently, the present study investigates the effects of DBS of the NAc core and shell in a quinpirole rat model of OCD. The study demonstrates that electrical modulation of NAc core and shell activity via DBS reduces quinpirole-induced compulsive checking behavior in rats. We therefore conclude that both, the NAc core and shell constitute potential target structures in the treatment of OCD.

Survival and functional recovery of transplanted human dopaminergic neurons into hemiparkinsonian rats depend on the cannula size of the implantation instrument.

Promising therapeutic strategies for neurodegenerative diseases such as Parkinson's disease include replacement of lost striatal dopaminergic neurons by grafting of embryonic mesencephalic cells. However, the poor survival of the transplanted tissue still limits transplantation of these cells into the human brain in a larger number of patients. We addressed the question, if the diameter of the transplantation cannulas has an effect on the number of surviving transplanted human embryonic mesencephalic cells into the striatum of 6-OHDA lesioned rats. We report a significantly higher number of surviving human cells using an ultrathin micropipette compared to cannulas with wider diameters. Importantly, higher numbers of surviving cells also correlated with a behavioral recovery of the hemiparkinsonian rats.

Subthalamic stimulation increases striatal tyrosine hydroxylase phosphorylation.

Subthalamic stimulation enhances striatal tyrosine hydroxylase activity, which is regulated by phosphorylation at different serine residues. Western blotting was performed to investigate phosphorylation at the serine residues 19, 31 and 40 in striatal tissue of rats that had received subthalamic stimulation or sham stimulation for 2 h. In animals that were killed directly after stimulation, the tyrosine hydroxylase protein content was unchanged, whereas phosphorylation at the serine residue 19 was increased and phosphorylation at the serine residues 31 and 40 tended to be higher compared with controls. By contrast, tyrosine hydroxylase protein content and phosphorylation were similar in rats that were killed 24 h after stimulation. Our results suggest that subthalamic stimulation may increase tyrosine hydroxylase activity via increased phosphorylation.

High frequency stimulation and temporary inactivation of the subthalamic nucleus reduce quinpirole-induced compulsive checking behavior in rats.

Obsessive-compulsive disorder (OCD) represents a highly prevalent and impairing psychiatric disorder. Functional and structural imaging studies implicate the involvement of basal ganglia-thalamo-cortical circuits in the pathophysiology of this disorder. In patients remaining resistant to pharmaco- and behavioral therapy, modulation of these circuits may consequently reverse clinical symptoms. High frequency stimulation (HFS) of the subthalamic nucleus (STN), an important station of the basal ganglia-thalamo-cortical circuits, has been reported to reduce obsessive-compulsive symptoms in a few Parkinson's disease patients with comorbid OCD. The present study tested the effects of bilateral HFS of the STN and of bilateral pharmacological inactivation of the STN (via intracranial administration of the GABA agonist muscimol) on checking behavior in the quinpirole rat model of OCD. We demonstrate that both HFS and pharmacological inactivation of the STN reduce quinpirole-induced compulsive checking behavior. We conclude that functional inhibition of the STN can alleviate compulsive checking, and suggest the STN as a potential target structure for HFS in the treatment of OCD.

Continuous high-frequency stimulation in freely moving rats: development of an implantable microstimulation system.

High-frequency stimulation (HFS) of basal ganglia and thalamic nuclei is an established treatment for various movement disorders and has recently been extended to other neuro-psychiatric conditions. Numerous experimental studies in small laboratory animals provided important insights in the mode of action of HFS. However, the interpretation of the results is often limited by the use of short-term HFS, while patients receive continuous stimulation for many years. One reason is the lack of an established model for the application of long-term HFS in small animals. Therefore, we thought to develop an implantable microstimulation system for small laboratory animals and to establish a protocol for long-term HFS by defining non-damaging stimulus parameters with respect to brain integrity. For this purpose, we designed a miniaturized, microcontroller-based, and programmable microstimulator that allows the reliable application of continuous HFS for up to 5 weeks. Chronic HFS (total stimulation time: 3 weeks) of the subthalamic nucleus with up to 100 microA (5.2 nC/phase) through monopolar electrodes comprising activated iridium did not induce significant tissue damage as assessed by various histological techniques (Nissl's, hematoxylin and eosin, Klüver-Barrera, van Gieson's staining, NeuN and GFAP-immunoreactivity). In conclusion, chronic HFS with an implantable stimulator can be successfully applied in small animals.

High frequency stimulation of the subthalamic nucleus modulates neurotransmission in limbic brain regions of the rat.

Despite the benefit high frequency stimulation (HFS) of the subthalamic nucleus (STN) has on motor symptoms of Parkinson's Disease (PD), accumulating data also suggest effects of STN-HFS on non-motor behavior. This may be related to the involvement of the STN in the limbic basal ganglia-thalamocortical loops. In the present study we investigated the effect of acute STN-HFS on neurotransmission in associated structures of these pathways, i.e. the nucleus accumbens (NAc) core and shell as well as the ventral tegmental area (VTA) using in vivo microdialysis. Experiments were performed in anaesthetized naive rats and rats selectively lesioned in the substantia nigra pars compacta (SNc) or VTA. We demonstrate that: 1. STN-HFS leads to an increase in DA in the NAc, 2., these effects are more pronounced in the NAc shell than in the NAc core, 3. STN-HFS leads to a decrease in GABA in the VTA, 4. preceding lesion of the SNc does not seem to affect the effect of STN-HFS on accumbal DA transmission whereas 5. preceding lesion of the VTA seems to prohibit further detection of DA in the NAc. We conclude that STN-HFS significantly affects neurotransmission in the limbic system, which might contribute to explain the non-motor effects of STN-HFS.

Placebo-controlled chronic high-frequency stimulation of the subthalamic nucleus preserves dopaminergic nigral neurons in a rat model of progressive Parkinsonism.

Chronic high-frequency stimulation (HFS) of the subthalamic nucleus (STN) protects nigral dopaminergic neurons from neurodegeneration in animal models of Parkinson's disease (PD). However, these data are challenged by the lack of control for neuroprotective effects that might be related to tissue damage due to electrode insertion or STN-HFS. Here we report the first placebo-controlled study on continuous STN-HFS in a rat model of PD using an implantable microstimulation system. We found a significant increase of preserved dopaminergic nigral neurons on the lesioned side (expressed as ratio to the non-lesioned side) of approximately 50% in comparison to STN sham-stimulated and STN-naive rats. These data provide evidence for the phenotypic rescue of nigral dopamine neurons by long-term STN-HFS in this animal model of PD.

Dopamine transporters, D2 receptors, and glucose metabolism in corticobasal degeneration.

Alterations in presynaptic and postsynaptic dopaminergic system and cerebral glucose metabolism in corticobasal degeneration (CBD) were assessed to evaluate the potential usefulness of different imaging methods for CBD. (123)I-FP-CIT/(123)I-beta-CIT SPECT and (123)I-IBZM SPECT as well as (18)F-FDG PET were performed in eight CBD patients. Decreased presynaptic dopamine transporter binding was found in all CBD patients while D2 receptor binding was reduced in only one patient. (18)F-FDG PET displayed a contralateral hypometabolism in cortical and subcortical areas in seven out of eight patients. Our results demonstrate that glucose metabolism and DAT are reduced, while D2 receptors may be frequently preserved in CBD.