Effect of neurotoxic lesion of pedunculopontine nucleus in nigral and striatal redox balance and motor performance in rats

Cholinergic modulation of sensory processing in awake mouse cortex

Cholinergic modulation of brain activity is fundamental for awareness and conscious sensorimotor behaviours, but deciphering the timing and significance of acetylcholine actions for these behaviours is challenging. The widespread nature of cholinergic projections to the cortex means that new insights require access to specific neuronal populations, and on a time-scale that matches behaviourally relevant cholinergic actions. Here, we use fast, voltage imaging of L2/3 cortical pyramidal neurons exclusively expressing the genetically-encoded voltage indicator Butterfly 1.2, in awake, head-fixed mice, receiving sensory stimulation, whilst manipulating the cholinergic system. Altering muscarinic acetylcholine function re-shaped sensory-evoked fast depolarisation and subsequent slow hyperpolarisation of L2/3 pyramidal neurons. A consequence of this re-shaping was disrupted adaptation of the sensory-evoked responses, suggesting a critical role for acetylcholine during sensory discrimination behaviour. Our findings provide new insights into how the cortex processes sensory information and how loss of acetylcholine, for example in Alzheimer's Disease, disrupts sensory behaviours.

Balance alterations and reduction of pedunculopontine cholinergic neurons in early stages of parkinsonism in middle-aged rats

The purpose of the present study was to investigate balance alterations and the possible role of the cholinergic neurons in the pedunculopontine nucleus (PPN) in the early stages of a progressive animal model of Parkinson's disease (PD). Twenty-eight middle-aged (8-9 months) male Wistar rats received 4 or 10 subcutaneous vehicle (control, CTL) or reserpine (RES) injections (0.1 mg/kg). The animals were submitted to different behavioral tests. Forty-eight hours after the 4th injection, half of the animals of each group (n = 7) were perfused and submitted to immunohistochemical analysis for tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT). The remaining animals (n = 7 per group) were killed 48 h after the 10th injection. RES group presented motor deficits in the catalepsy and open field tests starting at days 12 and 20 of treatment, respectively (only for the animals that received 10 injections). On the other hand, dynamic and static balance changes were observed at earlier stages of RES treatment, starting at days 6 and 4, respectively. At this point of the treatment, there was no decrease in the number of TH immunoreactivity neurons in the substantia nigra pars compacta (SNpc), ventral tegmental area (VTA) and dorsal striatum (DS). However, a decrease was observed in SNpc and dorsal striatum of animals that received 10 injections. In contrast, there was a decrease in the number of ChAT immunoreactive cells in PPN concomitantly to the balance alterations at the early stages of treatment (after 4 RES injections). Thus, by mimicking the progressiveness of PD, the reserpine model made it possible to identify static and dynamic balance impairments prior to the motor alterations in the catalepsy and open field tests. In addition, changes in balance were accompanied by a reduction in the number of ChAT immunoreactive cells in NPP in the early stages of treatment.

JM-20 protects against 6-hydroxydopamine-induced neurotoxicity in models of Parkinson's disease: Mitochondrial protection and antioxidant properties

We have previously shown that JM-20, a new chemical entity consisting of 1,5-benzodiazepine fused to a dihydropyridine moiety, protects against rotenone-induced neurotoxicity in an experimental model of Parkinson's disease (PD). The aim of this study was to investigate the effect of a novel hybrid molecule, named JM-20, in in vitro and in vivo models of PD induced by 6-hydroxydopamine (6-OHDA). PC-12 cells were exposed to 6-OHDA and treated with JM-20. Protection against mitochondrial damage induced by 6-OHDA was also investigated using isolated rat brain mitochondria. We found that JM-20 protected PC-12 cells against cytotoxicity induced by 6-OHDA and inhibited hydrogen peroxide generation, mitochondrial swelling and membrane potential dissipation. For in vivo experiments, adult male Wistar rats were lesioned in the substantia nigra pars compacta (SNpc) by 6-OHDA administration. JM-20 was orally administered (10, 20 or 40 mg/kg), intragastric via gavage, 24 h after surgery and daily for seven days. Treatment with JM-20 significantly reduced the percentage of motor asymmetry and increased vertical exploration. It improved the redox state of the SNpc and the striatal tissue of these animals. Also, JM-20 reduced glial fibrillary acidic protein overexpression and increased tyrosine hydroxylase-positive cell number, both in SNpc. Altogether, these results demonstrate that JM-20 is a potential neuroprotective agent against 6-OHDA-induced damage in both in vitro and in vivo models. The mechanism underlying JM-20 neuroprotection against 6-OHDA appears to be associated with the control of oxidative injury and mitochondrial impairment.

Motor Coordination Disorders Evaluated through the Grid Test and Changes in the Nigral Nrf2 mRNA Expression in Rats with Pedunculopontine Lesion

Neurotoxic lesion of the pedunculopontine nucleus (PPN) is known to cause subtle motor dysfunctions. However, motor coordination during advance on a discontinuous and elevated surface has not been studied. It is also not known whether there are changes in the mRNA expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in nigral tissue. Methods: The effects of the unilateral neurotoxic lesion of the PPN in motor coordination evaluated through grid test and Nrf2 mRNA expression in nigral tissue were evaluated. Two experimental designs (ED) were organized: ED#1 behavioral study (7 and 30 days after PPN lesion) and ED#2 molecular biology study (24 h, 48 h and 7 days) after PPN lesion. Results: ED#1—The number of faults made with left limbs, were significant higher in the lesioned groups (p < 0.01) both 7 and 30 days post-lesion. The number of failures made by the right limbs, was also significantly higher (p < 0.05) vs. control groups. ED#2—Nrf2 mRNA expression showed an increase 24 h after PPN injury (p < 0.01), followed by a peak of expression 48 h post injury (p < 0.001). Conclusions: Disorders of motor coordination associated with PPN injury are bilateral. The increased Nrf2 mRNA expression could represent an adaptive response to oxidative stress in the nigral tissue following pontine injury.

Nurr1, Pitx3, and α7 nAChRs mRNA Expression in Nigral Tissue of Rats with Pedunculopontine Neurotoxic Lesion

Background and Objectives: The knowledge that the cholinergic neurons from pedunculopontine nucleus (PPN) are vulnerable to the degeneration in early stages of the Parkinson disease progression has opened new perspectives to the development of experimental model focused in pontine lesions that could increase the risk of nigral degeneration. In this context it is known that PPN lesioned rats exhibit early changes in the gene expression of proteins responsible for dopaminergic homeostasis. At the same time, it is known that nicotinic cholinergic receptors (nAChRs) mediate the excitatory influence of pontine-nigral projection. However, the effect of PPN injury on the expression of transcription factors that modulate dopaminergic neurotransmission in the adult brain as well as the α7 nAChRs gene expression has not been studied. The main objective of the present work was the study of the effects of the unilateral neurotoxic lesion of PPN in nuclear receptor-related factor 1 (Nurr1), paired-like homeodomain transcription factor 3 (Pitx3), and α7 nAChRs mRNA expression in nigral tissue. Materials and Methods: The molecular biology studies were performed by means of RT-PCR. The following experimental groups were organized: Non-treated rats, N-methyl-D-aspartate (NMDA)-lesioned rats, and Sham operated rats. Experimental subjects were sacrificed 24 h, 48 h and seven days after PPN lesion. Results: Nurr1 mRNA expression, showed a significant increase both 24 h (p < 0.001) and 48 h (p < 0.01) after PPN injury. Pitx3 mRNA expression evidenced a significant increase 24 h (p < 0.001) followed by a significant decrease 48 h and seven days after PPN lesion (p < 0.01). Finally, the α7 nAChRs nigral mRNA expression remained significantly diminished 24 h, 48 h (p < 0.001), and 7 days (p < 0.01) after PPN neurotoxic injury. Conclusion: Taking together these modifications could represent early warning signals and could be the preamble to nigral neurodegeneration events.

Changing views of the pathophysiology of Parkinsonism

Studies of the pathophysiology of parkinsonism (specifically akinesia and bradykinesia) have a long history and primarily model the consequences of dopamine loss in the basal ganglia on the function of the basal ganglia/thalamocortical circuit(s). Changes of firing rates of individual nodes within these circuits were originally considered central to parkinsonism. However, this view has now given way to the belief that changes in firing patterns within the basal ganglia and related nuclei are more important, including the emergence of burst discharges, greater synchrony of firing between neighboring neurons, oscillatory activity patterns, and the excessive coupling of oscillatory activities at different frequencies. Primarily focusing on studies obtained in nonhuman primates and human patients with Parkinson's disease, this review summarizes the current state of this field and highlights several emerging areas of research, including studies of the impact of the heterogeneity of external pallidal neurons on parkinsonism, the importance of extrastriatal dopamine loss, parkinsonism-associated synaptic and morphologic plasticity, and the potential role(s) of the cerebellum and brainstem in the motor dysfunction of Parkinson's disease. © 2019 International Parkinson and Movement Disorder Society.

JM-20, a novel hybrid molecule, protects against rotenone-induced neurotoxicity in experimental model of Parkinson's disease

Oxidative stress and mitochondrial dysfunction are two pathophysiological factors often associated with the neurodegenerative process involved in Parkinson's disease (PD). The aim of this study was to investigate the effects of a novel hybrid molecule, named JM-20, in different in vitro and in vivo models of PD induced by rotenone. To perform in vitro studies, SHSY-5Y cells were exposed to rotenone and/or treated with JM-20. To perform in vivo studies male Wistar rats were intoxicated with rotenone (2.5 mg/kg) via intraperitoneal injection and/or treated with JM-20 (40 mg/kg) administered via oral (for 25 days, both treatment). Rats were evaluated for global motor activity by measurement of locomotor activity. In addition, the effects on mortality, general behavior and redox parameters were also investigated. JM-20 protected SHSY-5Y cells against rotenone-induced cytotoxicity, evidenced by a significant diminution of cell death. In in vivo studies, JM-20 prevented rotenone-induced vertical exploration and locomotion frequency reductions, moreover prevented body weight loss and mortality induced by rotenone. It also improved the redox state of rotenone-exposured animals by increasing superoxide dismutase and catalase activities, total tissue-SH levels and decreasing malondialdehyde concentrations. Finally, JM-20 inhibited spontaneous mitochondrial swelling and membrane potential dissipation in isolated rats brain mitochondria. These results demonstrate that JM-20 is a potential neuroprotective agent against rotenone-induced damage in both in vitro and in vivo models, resulting in reduced neuronal oxidative injury and protection of mitochondria from impairment.

Impairment in exploratory behavior is associated with arc gene overexpression in the dorsolateral striatum of rats with nigral injection of l-buthionine sulfoximine

The aims of the present work were to evaluate the exploratory activity in Sprague-Dawley rats, as well as to analyze the nigral and striatal mRNA expression of the plasticity-related genes bdnf and arc after L-buthionine sulfoximine (BSO) injection into substantia nigra compacta. Lesioned rats traveled less distance in open field but did not show a decline in the novel object recognition test. On the other hand, RT-PCR analysis showed overexpression of striatal arc 24 h post-lesion; no significant changes in bdnf expression were observed in nigral or striatal tissue. These results suggest that intranigral BSO injection causes impairment in exploratory behavior in these rats, by affecting locomotion, which is associated with changes in striatal synaptic plasticity.

Reciprocal interaction between monoaminergic systems and the pedunculopontine nucleus: Implication in the mechanism of L-DOPA

The pedunculopontine nucleus (PPN) is part of the mesencephalic locomotor region (MLR) and has been involved in the control of gait, posture, locomotion, sleep, and arousal. It likely participates in some motor and non-motor symptoms of Parkinson's disease and is regularly proposed as a surgical target to ameliorate gait, posture and sleep disorders in Parkinsonian patients. The PPN overlaps with the monoaminergic systems including dopamine, serotonin and noradrenaline in the modulation of the above-mentioned functions. All these systems are involved in Parkinson's disease and the mechanism of the anti-Parkinsonian agents, mostly L-DOPA. This suggests that PPN interacts with monoaminergic neurons and vice versa. Some evidence indicates that the PPN sends cholinergic, glutamatergic and even gabaergic inputs to mesencephalic dopaminergic cells, with the data regarding serotonergic or noradrenergic cells being less well known. Similarly, the control exerted by the PPN on dopaminergic neurons, is multiple and complex, and more extensively explored than the other monoaminergic systems. The data on the influence of monoaminergic systems on PPN neuron activity are rather scarce. While there is evidence that the PPN influences the therapeutic response of L-DOPA, it is still difficult to discerne the reciprocal action of the PPN and monoaminergic systems in this action. Additional data are required to better understand the functional organization of monoaminergic inputs to the MLR including the PPN to get a clearer picture of their interaction.

Tyrosine Hydroxylase, Vesicular Monoamine Transporter and Dopamine Transporter mRNA Expression in Nigrostriatal Tissue of Rats with Pedunculopontine Neurotoxic Lesion

BACKGROUND

The degeneration of the pedunculopontine nucleus (PPN) precedes the degeneration of the nigral cells in the pre-symptomatic stages of Parkinson's disease (PD). Although the literature recognizes that a lesion of the PPN increases the vulnerability of dopaminergic cells, it is unknown if this risk is associated with the loss of capability of handling the dopaminergic function.

METHODS

In this paper, the effects of a unilateral neurotoxic lesion of the PPN in tyrosine hydroxylase (TH), vesicular monoamine transporter 2 (VMAT2) and dopamine transporter (DAT) mRNA expression in nigrostriatal tissue were evaluated. Three experimental groups were organized: non-treated rats, NMDA-lesioned rats and Sham-operated rats.

RESULTS

Seven days after the PPN lesion, in nigral tissue, TH mRNA expression was higher in comparison with control groups (p < 0.05); in contrast, VMAT2 mRNA expression showed a significant decrease (p < 0.01). DAT mRNA expression showed a significant decrease (p < 0.001) in the striatal tissue. Comparing nigral neuronal density of injured and control rats revealed no significant difference seven days post-PPN injury.

CONCLUSIONS

Findings suggest that the PPN lesion modifies the mRNA expression of the proteins associated with dopaminergic homeostasis at nigrostriatal level. It could represent vulnerability signals for nigral dopaminergic cells and further increase the risk of degeneration of these cells.

Pedunculopontine glutamatergic neurons control spike patterning in substantia nigra dopaminergic neurons

Burst spiking in substantia nigra pars compacta (SNc) dopaminergic neurons is a key signaling event in the circuitry controlling goal-directed behavior. It is widely believed that this spiking mode depends upon an interaction between synaptic activation of N-methyl-D-aspartate receptors (NMDARs) and intrinsic oscillatory mechanisms. However, the role of specific neural networks in burst generation has not been defined. To begin filling this gap, SNc glutamatergic synapses arising from pedunculopotine nucleus (PPN) neurons were characterized using optical and electrophysiological approaches. These synapses were localized exclusively on the soma and proximal dendrites, placing them in a good location to influence spike generation. Indeed, optogenetic stimulation of PPN axons reliably evoked spiking in SNc dopaminergic neurons. Moreover, burst stimulation of PPN axons was faithfully followed, even in the presence of NMDAR antagonists. Thus, PPN-evoked burst spiking of SNc dopaminergic neurons in vivo may not only be extrinsically triggered, but extrinsically patterned as well.

Garcinia kola seeds may prevent cognitive and motor dysfunctions in a type 1 diabetes mellitus rat model partly by mitigating neuroinflammation

Background We reported recently that extracts of seeds of Garcinia kola, a plant with established hypoglycemic properties, prevented the loss of inflammation-sensible neuronal populations like Purkinje cells in a rat model of type 1 diabetes mellitus (T1DM). Here, we assessed G. kola extract ability to prevent the early cognitive and motor dysfunctions observed in this model. Methods Rats made diabetic by single injection of streptozotocin were treated daily with either vehicle solution (diabetic control group), insulin, or G. kola extract from the first to the 6th week post-injection. Then, cognitive and motor functions were assessed using holeboard and vertical pole behavioral tests, and animals were sacrificed. Brains were dissected out, cut, and processed for Nissl staining and immunohistochemistry. Results Hyperglycemia (209.26 %), body weight loss (-12.37 %), and T1DM-like cognitive and motor dysfunctions revealed behavioral tests in diabetic control animals were not observed in insulin and extract-treated animals. Similar, expressions of inflammation markers tumor necrosis factor (TNF), iba1 (CD68), and Glial fibrillary acidic protein (GFAP), as well as decreases of neuronal density in regions involved in cognitive and motor functions (-49.56 % motor cortex, -33.24 % medial septal nucleus, -41.8 % /-37.34 % cerebellar Purkinje /granular cell layers) were observed in diabetic controls but not in animals treated with insulin or G. kola. Conclusions Our results indicate that T1DM-like functional alterations are mediated, at least partly, by neuroinflammation and neuronal loss in this model. The prevention of the development of such alterations by early treatment with G. kola confirms the neuroprotective properties of the plant and warrant further mechanistic studies, considering the potential for human disease.

Role of pedunculopontine cholinergic neurons in the vulnerability of nigral dopaminergic neurons in Parkinson's disease

Pedunculopontine nucleus (PPN) cholinergic neurons, which exert excitatory nicotinic control over substantia nigra dopaminergic neurons, degenerate in Parkinson's disease (PD). This finding and other studies showing that nicotine, the preferential agonist of nicotinic acetylcholine receptors, is neuroprotective in experimental models of PD suggest that a deficit in PPN excitatory cholinergic inputs might contribute to the death of nigral dopaminergic neurons in PD. To explore this possibility, we used lesion paradigms of dopaminergic and/or cholinergic systems in rats and monkeys. Consistent with our hypothesis, we observed that stereotaxic lesioning of PPN cholinergic neurons with diphtheria toxin coupled to urotensin II resulted in a significant loss of nigral dopaminergic neurons in rats and induced morphological changes in these neurons in macaques. Unexpectedly, a lesion of dopaminergic neurons induced by unilateral striatal injection of 6-hydroxydopamine (6-OHDA) in rats, or by repeated systemic injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in macaques, led to a 29% and 7% loss of PPN cholinergic neurons, respectively. Lastly, when the PPN cholinergic lesion was performed in rats in which the dopaminergic lesion induced by 6-OHDA was in progress, loss of cholinergic neurons was more drastic than when each neurotransmitter system was lesioned separately. Thus, our results suggest that strong PPN cholinergic and dopaminergic interactions may be an important mechanism in the pathophysiology of PD.

The effects of gestational and chronic atrazine exposure on motor behaviors and striatal dopamine in male Sprague-Dawley rats

This study sought to investigate the effects of environmentally relevant gestational followed by continued chronic exposure to the herbicide, atrazine, on motor function, cognition, and neurochemical indices of nigrostriatal dopamine (DA) activity in male rats. Dams were treated with 100 μg/kg atrazine, 10mg/kg atrazine, or vehicle on gestational day 1 through postnatal day 21. Upon weaning, male offspring continued daily vehicle or atrazine gavage treatments for an additional six months. Subjects were tested in a series of behavioral assays, and 24h after the last treatment, tissue samples from the striatum were analyzed for DA and 3,4-dihydroxyphenylacetic acid (DOPAC). At 10mg/kg, this herbicide was found to produce modest disruptions in motor functioning, and at both dose levels it significantly lowered striatal DA and DOPAC concentrations. These results suggest that exposures to atrazine have the potential to disrupt nigrostriatal DA neurons and behaviors associated with motor functioning.