Kir6.2 oligoantisense administered into the globus pallidus reduces apomorphine-induced turning in 6-OHDA hemiparkinsonian rats

Potassium channels and their emerging role in parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, which is associated with a selective loss of dopaminergic neurons in the substantia nigra (SN) and a reduction of dopamine in the striatum. Recently, ion channel dysfunction has been considered a reason for the pathogenesis of PD. Potassium (K⁺) channels are widespread in the central nervous system, and play key roles in modulating cellular excitability, synaptic transmission, and neurotransmitter release. Based on recent studies and data, we propose that K⁺ channels may be new therapeutic targets for PD that slow the progressive loss of dopaminergic neurons and attenuate motor and non-motor symptoms. In this review, we mainly focus on: delayed rectifier, inwardly rectifying, and double-pore K⁺ channels. We summarize the expression and function of these channels in PD-related brain regions. We also discuss the effects of pharmacological blockade or activation of K⁺ channels in the progression and treatment of PD.

Sulfonylurea Receptor 1, Transient Receptor Potential Cation Channel Subfamily M Member 4, and KIR6.2:Role in Hemorrhagic Progression of Contusion

In severe traumatic brain injury (TBI), contusions often are worsened by contusion expansion or hemorrhagic progression of contusion (HPC), which may double the original contusion volume and worsen outcome. In humans and rodents with contusion-TBI, sulfonylurea receptor 1 (SUR1) is upregulated in microvessels and astrocytes, and in rodent models, blockade of SUR1 with glibenclamide reduces HPC. SUR1 does not function by itself, but must co-assemble with either KIR6.2 or transient receptor potential cation channel subfamily M member 4 (TRPM4) to form K_ATP (SUR1-KIR6.2) or SUR1-TRPM4 channels, with the two having opposite effects on membrane potential. Both KIR6.2 and TRPM4 are reportedly upregulated in TBI, especially in astrocytes, but the identity and function of SUR1-regulated channels post-TBI is unknown. Here, we analyzed human and rat brain tissues after contusion-TBI to characterize SUR1, TRPM4, and KIR6.2 expression, and in the rat model, to examine the effects on HPC of inhibiting expression of the three subunits using intravenous antisense oligodeoxynucleotides (AS-ODN). Glial fibrillary acidic protein (GFAP) immunoreactivity was used to operationally define core versus penumbral tissues. In humans and rats, GFAP-negative core tissues contained microvessels that expressed SUR1 and TRPM4, whereas GFAP-positive penumbral tissues contained astrocytes that expressed all three subunits. Förster resonance energy transfer imaging demonstrated SUR1-TRPM4 heteromers in endothelium, and SUR1-TRPM4 and SUR1-KIR6.2 heteromers in astrocytes. In rats, glibenclamide as well as AS-ODN targeting SUR1 and TRPM4, but not KIR6.2, reduced HPC at 24 h post-TBI. Our findings demonstrate upregulation of SUR1-TRPM4 and K_ATP after contusion-TBI, identify SUR1-TRPM4 as the primary molecular mechanism that accounts for HPC, and indicate that SUR1-TRPM4 is a crucial target of glibenclamide.

Da-bu-yin-wan and qian-zheng-san to neuroprotect the mouse model of Parkinson's disease

Da-Bu-Yin-Wan (DBYW) and Qian-Zheng-San (QZS), two classic traditional Chinese medicinal formulas, were clinically employed to treat Parkinson's disease (PD). Our previous studies demonstrated neuroprotective effects of them on mitochondrial function in PD mice induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The purpose of this research was to investigate their possible mechanisms in the light of mitochondrial ATP-sensitive potassium (mitoK_ATP) channels. The neuroprotective effect of DBYW and QZS on dopamine (DA) neurons in substantia nigra (SN) in the MPTP-induced PD mice was investigated by behavioral test (pole test) and immunohistochemistry. Adenosine triphosphate (ATP) level in the midbrain tissue was detected by firefly luciferase method. MitoK_ATP channel subunits SUR1 and Kir6.2 mRNA and protein expressions were tested by real-time PCR (RT-PCR) and Western blot. It was observed that DBYW and/or QZS served to ameliorate MPTP-induced behavioral impairment and prevent the loss of substantia nigra dopamine neurons, as well as increase ATP level in the midbrain tissue and downregulate SUR1 expression at mRNA and protein levels with no marked influence on Kir6.2. We concluded that DBYW and QZS exhibit neuroprotective effects probably through the regulation of ATP level and mitoK_ATP channel subunit expressions.

ATP-sensitive potassium channels: novel potential roles in Parkinson's disease

The ATP-sensitive potassium (K(ATP)) channels which extensively distribute in diverse tissues (e.g. vascular smooth muscle, cardiac cells, and pancreas) are well-established for characteristics like vasodilatation, myocardial protection against ischemia, and insulin secretion. The aim of this review is to get insight into the novel roles of K(ATP) channels in Parkinson's disease (PD), with consideration of the specificities K(ATP) channels in the central nervous system (CNS), such as the control of neuronal excitability, action potential, mitochondrial function and neurotransmitter release.

A role for eukaryotic translation initiation factor 2B (eIF2B) in taste memory consolidation and in thermal control establishment during the critical period for sensory development

All species exhibit critical periods for sensory development, yet very little is known about the molecules involved in the changes in the network wiring that underlies this process. Here the role of transcription regulation of the translation machinery was determined by evaluating the expression of eIF2Bepsilon, an essential component of translation initiation, in both taste-preference development and thermal control establishment in chicks. Analysis of the expression pattern of this gene after passive-avoidance training revealed clear induction of eIF2Bepsilon in both the mesopallium intermediomediale (IMM) and in the striatum mediale (StM). In addition, a correlation was found between the concentration of methylanthranilate (MeA), which was the malaise substrate in the passive-avoidance training procedure, the duration of memory, and the expression level of eIF2Bepsilon. Training chicks on a low concentration of MeA induced short-term memory and low expression level of eIF2Bepsilon, whereas a high concentration of MeA induced long-term memory and a high expression level of eIF2Bepsilon in both the IMM and StM. Furthermore, eIF2Bepsilon-antisense "knock-down" not only reduced the amount of eIF2Bepsilon but also attenuated taste memory formation. In order to determine whether induction of eIF2Bepsilon is a general feature of neuronal plasticity, we checked whether it was induced in other forms of neuronal plasticity, with particular attention to its role in temperature control establishment, which represents hypothalamic-related plasticity. It was established that eIF2Bepsilon-mRNA was induced in the preopotic anterior hypothalamus during heat conditioning. Taken together, these results correlate eIF2Bepsilon with sensory development.

Brain-derived neurotrophic factor is critically involved in thermal-experience-dependent developmental plasticity

All species exhibit critical period for sensory development, yet very little is known about the molecules involved in the changes in the network wiring that underlies this process. Here the role of brain-derived neurotrophic factor (BDNF) in the critical period of thermal control establishment in chicks was investigated. Neuroanatomically, the body temperature is balanced by the preoptic anterior hypothalamus (PO/AH) and controlled by thermosensitive neurons. Exposure to hot or cold conditions during the critical period of temperature control development causes a plastic change in the ratio between heat- and cold-sensitive cells and can modulate temperature tolerance. It was found that expression of BDNF mRNA but not of NGF or neurotrophin-3 was induced in the PO/AH of 3-d-old chicks during both heat and cold exposure. The peak of BDNF induction in both heat and cold exposure occurred after 6 h, with, respectively, threefold and sevenfold increases in its mRNA expression. To prove the concept that BDNF activation is a critical step in thermal-experience-dependent plasticity, BDNF was "knocked down" using antisense. It was found that, when BDNF in the PO/AH was inhibited by 80% during the third postnatal day, thermal establishment was impaired, and, after 1 week, the chicks' body temperature was reduced by 0.5 degrees C. Furthermore, later in life, their reaction to thermal challenge was altered, and they exhibited a pronounced reduction in their ability to maintain their body temperature and body weight under harsh conditions. Together, these results prove that BDNF is critically involved in thermal-experience-dependent development.

Progressive and extensive dopaminergic degeneration induced by convection-enhanced delivery of 6-hydroxydopamine into the rat striatum: a novel rodent model of Parkinson disease

OBJECT

A striatal dopamine lesion induces progressive nigral degeneration in rodents; however, intrastriatal injection of 6-hydroxydopamine (6-OHDA) causes only limited lesions due to spontaneous regeneration of the neurons that survive. To make an extensive lesion, the authors used a convection-enhanced delivery (CED) method for intrastriatal infusion of 6-OHDA and evaluated the animals for a model of Parkinson disease (PD).

METHODS

Different doses of 6-OHDA were infused into the unilateral striatum in rats by using the CED method. The dopaminergic neuronal degeneration was evaluated based on morphological, biochemical, and behavioral measurements until 8 weeks postlesion. Due to the wide distribution of the drug, CED of 20 microg of 6-OHDA into the striatum was sufficient to obtain a progressive and extensive nigrostriatal lesion as defined by morphological (> 80% cell loss in the substantia nigra [SN]) and biochemical (> 95% decrease in striatal dopamine) criteria. The extent of the lesion manifested as a stable turning behavior with amphetamine (> 6 turns/minute) and apomorphine (> 4 turns/minute). It also appeared that at I week postlesion the apoptotic markers were maximal in neurons of the SN.

CONCLUSIONS

A rat model of PD with a progressive and extensive dopamine lesion was successfully made by intrastriatal CED of 6-OHDA. In this model, the therapeutic value can be assessed using behavioral, biochemical, and histochemical measurements. The delay of nigral neuronal death with respect to the time of 6-OHDA administration may provide a therapeutic window for testing neuroprotective strategies.

D2-mediated modulation of N-type calcium currents in rat globus pallidus neurons following dopamine denervation

We have studied the effects of dopamine and the D2-like agonist quinpirole on calcium currents of neurons isolated from the striatum and the globus pallidus (GP). Experiments were performed in young adult rats, either in control conditions or following lesion of the nigrostriatal pathway by the unilateral injection of 6-hydroxydopamine (6-OHDA) in the substantia nigra. Apomorphine-driven contralateral turning, 15 days after lesioning, assessed the severity of the dopamine denervation. In addition, the loss of tyrosine hydroxylase immunohistochemistry confirmed the extent of the toxin-induced damage. In both striatal medium spiny (MS) and GP neurons of control animals dopamine and quinpirole promoted a very modest inhibition of calcium conductance. Following 6-OHDA, the inhibition was unaltered in MS (from 10 to 12%), but significantly augmented in GP neurons (21% vs. 9%). Interestingly, analogous inhibition was observed in GP neurons dissociated 20 h after reserpine treatment. Further features of the D2 response were thus studied only in neurons isolated from 6-OHDA-lesioned GP. The D2 modulation was G-protein-mediated but not strictly voltage-dependent. omega-Conotoxin-GVIA occluded the response implying the involvement of N-type calcium channels. The effect of quinpirole developed fast and was insensitive to alterations of cytosolic cAMP. The incubation in phorbol esters or OAG blocked the D2 effect, supporting the involvement of PKC. These findings suggest that postsynaptic D2-like receptors are functionally expressed on GP cell bodies and may supersensitize following dopamine-denervation. A direct D2 modulation of calcium conductance in GP may alter GP firing properties and GABA release onto pallidofugal targets.

Functional effect of adeno-associated virus mediated gene transfer of aromatic L-amino acid decarboxylase into the striatum of 6-OHDA-lesioned rats

In animal models of Parkinson's disease, gene transfer of aromatic L-amino acid decarboxylase (AADC) leads to an increase in the capacity of the striatum to decarboxylate exogenous L-DOPA. However, the functional effects of enhanced L-DOPA to dopamine conversion have not been explored. Here, we show that following adeno-associated virus (AAV)-AADC transduction, the transgenic AADC is able to decarboxylate exogenous L-DOPA more efficiently so that a dose of L-DOPA ineffective before gene transfer elicits a motor asymmetry (rotational behavior) following gene transfer. Furthermore, rotation scores showed a strong correlation with AADC activity in the lesioned striatum, thus allowing for behavioral screening of successful gene transfer in the brain. In animals receiving AAV2-AADC, dopamine production was restored to 50% of normal levels 12 weeks after the infusion. Microdialysis experiments demonstrated an in vivo enhanced conversion of L-DOPA to dopamine, but no storage capacity as dopamine was released to the extracellular space in a continuous, nonregulated fashion. In addition to the potential clinical benefit of improving decarboxylation efficiency in Parkinson's disease, our approach may be relevant for the treatment of AADC deficiency, a rare, autosomal recessive disorder causing a severe movement disorder and progressive cognitive impairment.

Protective role of ATP-sensitive potassium channels in hypoxia-induced generalized seizure

Adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels are activated by various metabolic stresses, including hypoxia. The substantia nigra pars reticulata (SNr), the area with the highest expression of K(ATP) channels in the brain, plays a pivotal role in the control of seizures. Mutant mice lacking the Kir6.2 subunit of K(ATP) channels [knockout (KO) mice] were susceptible to generalized seizures after brief hypoxia. In normal mice, SNr neuron activity was inactivated during hypoxia by the opening of the postsynaptic K(ATP) channels, whereas in KO mice, the activity of these neurons was enhanced. K(ATP) channels exert a depressant effect on SNr neuronal activity during hypoxia and may be involved in the nigral protection mechanism against generalized seizures.

3,4-Dihydroxyphenylacetaldehyde potentiates the toxic effects of metabolic stress in PC12 cells

3,4-Dihydroxyphenylacetaldehyde (DOPAL) is a toxic metabolite formed by the oxidative deamination of dopamine. This aldehyde is mainly oxidized to 3,4-dihydroxyphenylacetic acid (DOPAC) by aldehyde dehydrogenase (ALDH), but is also partly reduced to 3, 4-dihydroxyphenylethanol (DOPET) by aldehyde or aldose reductase (ARs). In a previous study, we found that rotenone, a complex I inhibitor, induced a rapid accumulation of DOPAL and DOPET in the medium of cultured PC12 cells. Here, we examined the potential role of DOPAL in the toxicity induced by complex I inhibition in PC12 cells and compared the effects of rotenone on concentrations of DOPAL and DOPET to those of MPP(+). DOPAL and DOPET levels were increased by rotenone but decreased by MPP(+). Inhibition of ALDH by daidzein reduced the formation of DOPAC and increased the accumulation of DOPAL. Inhibition of ARs (with AL1576) diminished DOPET formation and elevated DOPAL concentrations. Combined inhibition of ALDH and ARs markedly elevated DOPAL concentrations while diminishing DOPET and DOPAC levels. The elevation of DOPAL levels induced by combined inhibition of ALDH and ARs had no effect on cell viability. However, combined inhibition of ALDH and ARs potentiated rotenone-induced toxicity. Both the potentiation of toxicity and the increase in DOPAL levels were blocked by inhibition of monoamine oxidase with clorgyline indicating that accumulation of DOPAL was responsible for the potentiated rotenone-induced toxicity following combined inhibition of ALDH and ARs. Since complex I dysfunction is reported to be involved in the pathogenesis of Parkinson's disease, DOPAL potentiation of the deleterious effects of complex I inhibition may contribute to the specific vulnerability of dopaminergic neurons to injury.