New Insights into Dose-Dependent Effects of Curcumin on ARPE-19 Cells.

Opposing dose-dependent effects of curcumin (Cur) have been documented in Retinal Pigment Epithelium (RPE); therefore, to shed the light on the mechanisms of action is crucial for ophthalmic applications. On this basis we explored new insights about the dose-dependent mechanisms triggered by Cur in human retinal pigment epithelial cells (ARPE-19). Three concentrations (0.01 mM; 0.05 mM; 0.1 mM) of Cur were tested, followed by morphological, molecular, and functional analysis of the cells. Cur 0.01 mM promotes a significant increase in cell proliferation, not affecting cell cycle progression and apoptosis; by contrast, Cur 0.05 mM and 0.1 mM block cellular proliferation and trigger S-phase cell cycle arrest without inducing apoptosis. The observation of neuronal-like morphological changes in Cur 0.05 mM and 0.1 mM were not associated with neuronal differentiation, as observed by the quantification of Neurofilament-200 and by the analysis of voltage-dependent currents by patch clamp. Evaluation of autophagic markers LC3BII and p62 revealed significant modulations, suggesting an important activation of autophagy in ARPE-19 cells treated with Cur 0.05 mM and Cur 0.1 mM; conversely, Cur 0.01 mM did not affect autophagy. Altogether, our findings show new dose-dependent mechanisms of action of Cur that suggest a wide therapeutic application in ocular diseases with different pathogenesis (i.e., proliferative vitreoretinopathy or Age-Related Macular Degeneration).

The pedunculopontine tegmental nucleus: implications for a role in modulating spinal cord motoneuron excitability.

There is evidence that deep brain stimulation (DBS) of the pedunculopontine tegmental nucleus (PPTg) improves parkinsonian motor signs. The mechanisms that mediate these effects and the modifications that occur in the PPTg in Parkinson's disease (PD) are not fully known and are the object of current debate. The aim of this paper was to critically review available data with respect to (1) the presence of PPTg neurons linked to reticulospinal projections, (2) the involvement of these neurons in modulating spinal reflexes, and (3) the participation of fibers close to or within the PPTg region in such modulation. The PPTg neurons are distributed in a large pontotegmental region, stimulation of which can evoke activity in hindlimb, shoulder and neck muscles, and potentiate motor responses evoked by stimulation of dorsal roots. This influence seems to be carried out by fast-conducting descending fibers, which likely run in the medial reticulospinal pathway. It is yet unclear which neurotransmitters are involved and on which elements of the gray matter of the spinal cord PPTg fibers synapse. The modulation of spinal cord activity which can be achieved by stimulating the PPTg region seems to be mediated not only by PPTg neurons, but also by tecto-reticular fibers which run in the pontotegmental area, and which likely are activated during PPTg-DBS. The importance of these fibers is discussed taking into account the degeneration of PPTg neurons in PD and the benefits in gait and postural control that PPTg-DBS exerts in PD. The potential usefulness of PPTg-DBS in other neurodegenerative disorders characterized by neuronal loss in the brainstem is also considered.

Pedunculopontine tegmental Nucleus-evoked prepulse inhibition of the blink reflex in Parkinson's disease.

OBJECTIVE: To investigate the effects on the blink reflex (BR) of single stimuli applied to the pedunculopontine tegmental nucleus (PPTg). METHODS: The BR was evoked by stimulating the supraorbital nerve (SON) in fifteen patients suffering from idiopathic Parkinson's disease (PD) who had electrodes monolaterally or bilaterally implanted in the PPTg for deep brain stimulation (DBS). Single stimuli were delivered to the PPTg through externalized electrode connection wires 3-4 days following PPTg implantation. RESULTS: PPTg stimuli increased the latency and reduced duration, amplitude and area of the R2 component of the BR in comparison to the response recorded in the absence of PPTg stimulation. These effects were independent of the side of SON stimulation and were stable for interstimulus interval (ISI) between PPTg prepulse and SON stimulus from 0 to 110 ms. The PPTg-induced prepulse inhibition of the BR was bilaterally present in the brainstem. The R1 component was unaffected. CONCLUSIONS: The prepulse inhibition of the R2 component may be modulated by the PPTg. SIGNIFICANCE: These findings suggest that abnormalities of BR occurring in PD may be ascribed to a reduction of basal ganglia-mediated inhibition of brainstem excitability.

High Cervical Spinal Cord Stimulation: A One Year Follow-Up Study on Motor and Non-Motor Functions in Parkinson's Disease.

BACKGROUND: The present study investigated the effectiveness of stimulation applied at cervical levels on pain and Parkinson's disease (PD) symptoms using either tonic or burst stimulation mode. METHODS: Tonic high cervical spinal cord stimulation (T-HCSCS) was applied on six PD patients suffering from low back pain and failed back surgery syndrome, while burst HCSCS (B-HCSCS) was applied in twelve PD patients to treat primarily motor deficits. Stimulation was applied percutaneously with quadripolar or octapolar electrodes. Clinical evaluation was assessed by the Unified Parkinson's Disease Rating Scale (UPDRS) and the Hoehn and Yahr (H&Y) scale. Pain was evaluated by a visual analog scale. Evaluations of gait and of performance in a cognitive motor task were performed in some patients subjected to B-HCSCS. One patient who also suffered from severe autonomic cardiovascular dysfunction was investigated to evaluate the effectiveness of B-HCSCS on autonomic functions. RESULTS: B-HCSCS was more effective and had more consistent effects than T-HCSCS in reducing pain. In addition, B-HCSCS improved UPDRS scores, including motor sub-items and tremor and H&Y score. Motor benefits appeared quickly after the beginning of B-HCSCS, in contrast to long latency improvements induced by T-HCSCS. A slight decrease of effectiveness was observed 12 months after implantation. B-HCSCS also improved gait and ability of patients to correctly perform a cognitive-motor task requiring inhibition of a prepared movement. Finally, B-HCSCS ameliorated autonomic control in the investigated patient. CONCLUSIONS: The results support a better usefulness of B-HCSCS compared to T-HCSCS in controlling pain and specific aspects of PD motor and non-motor deficits for at least one year.

Fluorescent light induces neurodegeneration in the rodent nigrostriatal system but near infrared LED light does not.

We investigated the effects of continuous artificial light exposure on the mouse substantia nigra (SN). A three month exposure of C57Bl/6J mice to white fluorescent light induced a 30% reduction in dopamine (DA) neurons in SN compared to controls, accompanied by a decrease of DA and its metabolites in the striatum. After six months of exposure, neurodegeneration progressed slightly, but the level of DA returned to the basal level, while the metabolites increased with respect to the control. Three month exposure to near infrared LED light (∼710nm) did not alter DA neurons in SN, nor did it decrease DA and its metabolites in the striatum. Furthermore mesencephalic cell viability, as tested by [3H]DA uptake, did not change. Finally, we observed that 710nm LED light, locally conveyed in the rat SN, could modulate the firing activity of extracellular-recorded DA neurons. These data suggest that light can be detrimental or beneficial to DA neurons in SN, depending on the source and wavelength.

Continuous stimulation of the pedunculopontine tegmental nucleus at 40 Hz affects preparative and executive control in a delayed sensorimotor task and reduces rotational movements induced by apomorphine in the 6-OHDA parkinsonian rat.

The pedunculopontine tegmental nucleus (PPTg) relays basal ganglia signals to the thalamus, lower brainstem and spinal cord. Using the 6-hydroxydopamine (6-OHDA) rat model of parkinsonism, we investigated whether deep brain stimulation (DBS) of the PPTg (40 Hz, 60 µs, 200-400 µA) may influence the preparative and executive phases in a conditioned behavioural task, and the motor asymmetries induced by apomorphine. In the conditioned task, rats had to press two levers according to a fixed delay paradigm. The 6-OHDA lesion was placed in the right medial forebrain bundle, i.e. contralaterally to the preferred forepaw used by rats to press levers in the adopted task. The stimulating electrode was implanted in the right PPTg, i.e. contralateral to left side, which was expected to be most affected. The lesion significantly reduced correct responses from 63.4% to 16.6%. PPTg-DBS effects were episodic; however, when rats successfully performed in the task (18.9%), reaction time (468.8 ± 36.5 ms) was significantly increased (589.9 ± 45.9 ms), but not improved by PPTg-DBS (646.7 ± 33.8 ms). Movement time was significantly increased following the lesion (649.2 ± 42.6 ms vs. 810.9 ± 53.0 ms), but significantly reduced by PPTg-DBS (820.4 ± 39.4 ms) compared to sham PPTg-DBS (979.8 ± 47.6 ms). In a second group of lesioned rats, rotations induced by apomorphine were significantly reduced by PPTg-DBS compared to sham PPTg-DBS (12.2 ± 0.6 vs. 9.5 ± 0.4 mean turns/min). Thus, it appears that specific aspects of motor deficits in 6-OHDA-lesioned rats may be modulated by PPTg-DBS.

The temporal context of certainty-uncertainty modulates the subthalamic nucleus-mediated anticipatory responding.

Lesions of the subthalamic nucleus (STN) in the rat are known to induce anticipatory responses in the preparatory period preceding conditioned movements. This study aimed to investigate how the temporal context in which a stimulus is presented affects the anticipatory responding caused by a unilateral STN lesion. A reaction-time task was employed in which a trigger signal starting a bar-pressing movement was presented at either side of the head in two temporal contexts. In the first, the trigger was presented at a fixed delay (FD paradigm) of 1s following an instruction signal. In the second, the 1s delay was randomly distributed (RD paradigm) among other delays. Reaction time was faster in the FD paradigm with respect to the RD paradigm. An increased readiness to move was observed in animals engaged in the RD paradigm as the delay period shortened, and this function was not abolished by the STN lesion. Anticipatory responding in general was less pronounced than in other paradigms previously reported in the literature, and predominated in the RD paradigm with respect to the FD paradigm. The destruction of the STN worsened the anticipatory responding only in the FD paradigm. A major consequence of the STN lesion was an increase of unconditioned responses to the instruction signal starting each trial. This attention deficit was more pronounced in the RD paradigm with respect to the FD paradigm, and was subsequently worsened by the lesion in both paradigms. The results suggest that the anticipatory responding may depend on the level of uncertainty implicit in each behavioural paradigm whereas inappropriate responding to the behavioural cue starting a trial may be independent from this factor, and highlight the importance of the behavioural paradigms employed when dealing with STN functions.

Low frequency stimulation of the pedunculopontine nucleus modulates electrical activity of subthalamic neurons in the rat.

Electrical stimulation of the rat pedunculopontine nucleus (PPTg) (<25 Hz) synchronized firing of subthalamic neurons (STN) with each stimulus, and a continuous irregular activity often preceded recovery of burst discharges in control as well as in 6-hydroxydopamine lesioned animals. Firing was blocked both by increasing frequency of stimulation (>50 Hz) and current intensity (>500 microA). The data suggest that clinically relevant frequencies for PPTg deep brain stimulation in Parkinson's disease modulate burst discharges in STN neurons.

Behavioural learning-induced increase in spontaneous GABAA-dependent synaptic activity in rat striatal cholinergic interneurons.

Cholinergic striatal interneurons play a crucial role in cognitive aspects of context-dependent motor behaviours. They are considered to correspond to the tonically active neurons (TANs) of the primate striatum, which phasically decrease their discharge at the presentation of reward-related sensory stimuli. The origin of this response is still poorly understood. Therefore, in the present paper, we have investigated whether synaptic changes establish in cholinergic interneurons from young rats that have learned a rewarded, externally cued sensorimotor task. Corticostriatal slices were prepared from both control and trained rats. No significant change in intrinsic membrane properties and evoked synaptic activity was observed in cholinergic interneurons, nor the responsiveness to exogenously applied dopaminergic and glutamatergic agonists was modified. Conversely, an increased occurrence of spontaneous bicuculline-sensitive depolarizing postsynaptic potentials (sDPSP) was recorded. The frequency of the GABAA-mediated sDPSP was increased in comparison to not-conditioned rats. Overall, these results suggest that after learning a rewarded sensorimotor paradigm an increased GABA influence develops on cholinergic interneurons. The origin of this effect might be searched in collaterals of GABAergic output spiny neurons as well as in GABAergic striatal interneurons impinging onto cholinergic interneurons. This intrastriatal mechanism might be involved in the phasic suppression of discharge of TANs at the presentation of reward-related sensory stimuli.