Paradoxical lower sensitivity of Locus Coeruleus than Substantia Nigra pars compacta neurons to acute actions of rotenone

Baicalein attenuates rotenone-induced SH-SY5Y cell apoptosis through binding to SUR1 and activating ATP-sensitive potassium channels

Dopaminergic neurons in the substantia nigra (SN) expressing SUR1/Kir6.2 type ATP-sensitive potassium channels (K-ATP) are more vulnerable to rotenone or metabolic stress, which may be an important reason for the selective degeneration of neurons in Parkinson's disease (PD). Baicalein has shown neuroprotective effects in PD animal models. In this study, we investigated the effect of baicalein on K-ATP channels and the underlying mechanisms in rotenone-induced apoptosis of SH-SY5Y cells. K-ATP currents were recorded from SH-SY5Y cells using whole-cell voltage-clamp recording. Drugs dissolved in the external solution at the final concentration were directly pipetted onto the cells. We showed that rotenone and baicalein opened K-ATP channels and increased the current amplitudes with EC50 values of 0.438 μM and 6.159 μM, respectively. K-ATP channel blockers glibenclamide (50 μM) or 5-hydroxydecanoate (5-HD, 250 μM) attenuated the protective effects of baicalein in reducing reactive oxygen species (ROS) content and increasing mitochondrial membrane potential and ATP levels in rotenone-injured SH-SY5Y cells, suggesting that baicalein protected against the apoptosis of SH-SY5Y cells by regulating the effect of rotenone on opening K-ATP channels. Administration of baicalein (150, 300 mg·kg-1·d-1, i.g.) significantly inhibited rotenone-induced overexpression of SUR1 in SN and striatum of rats. We conducted surface plasmon resonance assay and molecular docking, and found that baicalein had a higher affinity with SUR1 protein (KD = 10.39 μM) than glibenclamide (KD = 24.32 μM), thus reducing the sensitivity of K-ATP channels to rotenone. Knockdown of SUR1 subunit reduced rotenone-induced apoptosis and damage of SH-SY5Y cells, confirming that SUR1 was an important target for slowing dopaminergic neuronal degeneration in PD. Taken together, we demonstrate for the first time that baicalein attenuates rotenone-induced SH-SY5Y cell apoptosis through binding to SUR1 and activating K-ATP channels.

Enhanced firing of locus coeruleus neurons and SK channel dysfunction are conserved in distinct models of prodromal Parkinson's disease

Parkinson's disease (PD) is clinically defined by the presence of the cardinal motor symptoms, which are associated with a loss of dopaminergic nigrostriatal neurons in the substantia nigra pars compacta (SNpc). While SNpc neurons serve as the prototypical cell-type to study cellular vulnerability in PD, there is an unmet need to extent our efforts to other neurons at risk. The noradrenergic locus coeruleus (LC) represents one of the first brain structures affected in Parkinson's disease (PD) and plays not only a crucial role for the evolving non-motor symptomatology, but it is also believed to contribute to disease progression by efferent noradrenergic deficiency. Therefore, we sought to characterize the electrophysiological properties of LC neurons in two distinct PD models: (1) in an in vivo mouse model of focal α-synuclein overexpression; and (2) in an in vitro rotenone-induced PD model. Despite the fundamental differences of these two PD models, α-synuclein overexpression as well as rotenone exposure led to an accelerated autonomous pacemaker frequency of LC neurons, accompanied by severe alterations of the afterhyperpolarization amplitude. On the mechanistic side, we suggest that Ca²⁺-activated K⁺ (SK) channels are mediators of the increased LC neuronal excitability, as pharmacological activation of these channels is sufficient to prevent increased LC pacemaking and subsequent neuronal loss in the LC following in vitro rotenone exposure. These findings suggest a role of SK channels in PD by linking α-synuclein- and rotenone-induced changes in LC firing rate to SK channel dysfunction.

Intranasal Administration of Rotenone Reduces GABAergic Inhibition in the Mouse Insular Cortex Leading to Impairment of LTD and Conditioned Taste Aversion Memory

The pesticide rotenone inhibits mitochondrial complex I and is thought to cause neurological disorders such as Parkinson’s disease and cognitive disorders. However, little is known about the effects of rotenone on conditioned taste aversion memory. In the present study, we investigated whether intranasal administration of rotenone affects conditioned taste aversion memory in mice. We also examined how the intranasal administration of rotenone modulates synaptic transmission and plasticity in layer V pyramidal neurons of the mouse insular cortex that is critical for conditioned taste aversion memory. We found that the intranasal administration of rotenone impaired conditioned taste aversion memory to bitter taste. Regarding its cellular mechanisms, long-term depression (LTD) but not long-term potentiation (LTP) was impaired in rotenone-treated mice. Furthermore, spontaneous inhibitory synaptic currents and tonic GABA currents were decreased in layer V pyramidal neurons of rotenone-treated mice compared to the control mice. The impaired LTD observed in pyramidal neurons of rotenone-treated mice was restored by a GABA_A receptor agonist muscimol. These results suggest that intranasal administration of rotenone decreases GABAergic synaptic transmission in layer V pyramidal neurons of the mouse insular cortex, the result of which leads to impairment of LTD and conditioned taste aversion memory.

Arginine promotes porcine type I muscle fibres formation through improvement of mitochondrial biogenesis

The present study aimed to investigate whether arginine (Arg) promotes porcine type I muscle fibres formation via improving mitochondrial biogenesis. In the in vivo study, a total of sixty Duroc × Landrace × Yorkshire weaning piglets with an average body weight of 6·55 (sd 0·36) kg were randomly divided into four treatments and fed with a basal diet or a basal diet supplemented with 0·5, 1·0 and 1·5 % l-Arg, respectively, in a 4-week trial. Results showed that dietary supplementation of 1·0 % Arg significantly enhanced the activity of succinate dehydrogenase, up-regulated the protein expression of myosin heavy chain I (MyHC I) and increased the mRNA levels of MyHC I, troponin I1, C1 and T1 (Tnni1, Tnnc1 and Tnnt1) in longissimus dorsi muscle compared with the control group. In addition, ATPase staining analysis indicated that 1·0 % Arg supplementation significantly increased the number of type I muscle fibres and significantly decreased the number of type II muscle fibres. Furthermore, 1·0 % Arg supplementation significantly up-regulated PPAR-γ coactivator-1α (PGC-1α), sirtuin 1 and cytochrome c (Cytc) protein expressions, increased PGC-1α, nuclear respiratory factor 1 (NRF1), mitochondria transcription factor B1 (TFB1M), Cytc and ATP synthase subunit C1 (ATP5G) mRNA levels and increased mitochondrial DNA content. In the in vitro study, mitochondrial complex I inhibitor rotenone (Rot) was used. We found that Rot annulled Arg-induced type I muscle fibres formation. Together, our results provide for the first time the evidence that Arg promotes porcine type I muscle fibres formation through improvement of mitochondrial biogenesis.

Action potential and calcium dependence of tonic somatodendritic dopamine release in the Substantia Nigra pars compacta

Despite the importance of somatodendritic dopamine (DA) release in the Substantia Nigra pars compacta (SNc), its mechanism remains poorly understood. Using a novel approach combining fast-scan controlled-adsorption voltammetry (FSCAV) and single-unit electrophysiology, we have investigated the mechanism of somatodendritic release by directly correlating basal (non-stimulated) extracellular DA concentration ([DA]_out ), with pharmacologically-induced changes of firing of nigral dopaminergic neurons in rat brain slices. FSCAV measurements indicated that basal [DA]_out in the SNc was 40.7 ± 2.0 nM (at 34 ± 0.5°C), which was enhanced by amphetamine, cocaine, and L-DOPA, and reduced by VMAT2 inhibitor, Ro4-1284. Complete inhibition of firing by TTX decreased basal [DA]_out , but this reduction was smaller than the effect of D₂ receptor agonist, quinpirole. Despite similar effects on neuronal firing, the larger decrease in [DA]_out evoked by quinpirole was attributed to cell membrane hyperpolarization and greater reduction in cytosolic free Ca²⁺ ([Ca²⁺ ]_in ). Decreasing extracellular Ca²⁺ also reduced basal [DA]_out , despite increasing firing frequency. Furthermore, inhibiting L-type Ca²⁺ channels decreased basal [DA]_out , although specific Ca_v 1.3 channel inhibition did not affect firing rate. Inhibition of sarcoplasmic/endoplasmic reticulum Ca²⁺ -ATPase (SERCA) also decreased [DA]_out , demonstrating the importance of intracellular Ca²⁺ stores for somatodendritic release. Finally, in vivo FSCAV measurements showed that basal [DA]_out in the SNc was 79.8 ± 10.9 nM in urethane-anesthetized rats, which was enhanced by amphetamine. Overall, our findings indicate that although tonic somatodendritic DA release is largely independent of action potentials, basal [DA]_out is strongly regulated by voltage-dependent Ca²⁺ influx and release of intracellular Ca²⁺ . OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Age-related accumulation of toxic metals in the human locus ceruleus

Damage to the locus ceruleus has been implicated in the pathogenesis of a number of neurological conditions. Locus ceruleus neurons accumulate toxic metals such as mercury selectively, however, the presence of toxic metals in locus ceruleus neurons of people of different ages, and with a variety of disorders, is not known. To demonstrate at what age toxic metals are first detectable in the locus ceruleus, and to evaluate whether their presence is more common in certain clinicopathological conditions, we looked for these metals in 228 locus ceruleus samples. Samples were taken at coronial autopsies from individuals with a wide range of ages, pre-existing conditions and causes of death. Paraffin sections of pons containing the locus ceruleus were stained with silver nitrate autometallography, which indicates inorganic mercury, silver and bismuth within cells (termed autometallography-detected toxic metals, or AMG™). No locus ceruleus AMG neurons were seen in 38 individuals aged under 20 years. 47% of the 190 adults (ie, aged 20 years and over) had AMG locus ceruleus neurons. The proportion of adults with locus ceruleus AMG neurons increased during aging, except for a decreased proportion in the 90-plus years age group. No differences were found in the proportions of locus ceruleus AMG neurons between groups with different neurological, psychiatric, or other clinicopathological conditions, or among various causes of death. Elemental analysis with laser ablation-inductively coupled plasma-mass spectrometry was used to cross-validate the metals detected by AMG, by looking for silver, gold, bismuth, cadmium, chromium, iron, mercury, nickel, and lead in the locus ceruleus of ten individuals. This confirmed the presence of mercury in locus ceruleus samples containing AMG neurons, and showed cadmium, silver, lead, iron, and nickel in the locus ceruleus of some individuals. In conclusion, toxic metals stained by AMG (most likely inorganic mercury) appear in locus ceruleus neurons in early adult life. About half of adults in this study had locus ceruleus neurons containing inorganic mercury, and elemental analysis found a range of other toxic metals in the locus ceruleus. Locus ceruleus inorganic mercury increased during aging, except for a decrease in advanced age, but was not found more often in any single clinicopathological condition or cause of death.

Mitochondrial regulation by pyrroloquinoline quinone prevents rotenone-induced neurotoxicity in Parkinson's disease models

Pyrroloquinoline quinone (PQQ), a redox cofactor in the mitochondrial respiratory chain, has been reported to protect SH-SY5Y cells from cytotoxicity induced by rotenone, a mitochondrial complex I inhibitor. In this study, we aimed to investigate the mitochondrial mechanisms involved in the neuroprotection of PQQ both in vitro and in vivo. The cultured human SH-SY5Y neuroblastoma cells were exposed to different concentrations of PQQ after which the cells were treated with rotenone. Electron microscopy images showed that PQQ could prevent the mitochondrial morphology damage. The down-regulation of mitochondrial biogenesis related genes (PGC-1alpha and TFAM) and mitochondrial fission and fusion related genes (Drp1and Mfn2) in rotenone-injured SH-SY5Y cells could be inhibited by PQQ. PQQ could also promote the transposition of Drp1 and Mfn2 from cytosol to mitochondria. In addition, rotenone was injected into the left medial forebrain bundle of SD rats to establish a Parkinson's disease (PD) model in vivo, after which different doses of PQQ or Edaravone were given intraperitoneally once daily for 8 weeks. PQQ could up-regulate the mRNA levels of PGC-1alpha, TFAM, Drp-1 and Mfn2 in the midbrain of PD rats. Our findings indicated that PQQ could prevent mitochondrial dysfunction by promoting mitochondrial biogenesis and regulating mitochondrial fission and fusion, which might contribute to its neuroprotective effect in PD models.