Uridine as a Regulator of Functional and Ultrastructural Changes in the Brain of Rats in a Model of 6-OHDA-Induced Parkinson's Disease

Abstract

Using a model of Parkinson's disease (PD) induced by the bilateral injection of neurotoxin 6-hydroxydopamine (6-OHDA) into rat brain substantia nigra (SN), we showed uridine to exert a protective effect associated with activation of the mitochondrial ATP-dependent potassium (mitoK-ATP) channel. Injection of 4 µg neurotoxin evoked a 70% decrease in the time the experimental animal spent on the rod in the RotaRod test, an increase in the amount of lipid peroxides in blood serum and cerebral-cortex mitochondria and the rate of reactive oxygen species formation, and a decrease in Ca²⁺ retention in mitochondria. Herewith, lymphocytes featured an increase in the activity of lactate dehydrogenase, a cytosolic enzyme of glycolysis, without changes in succinate-dehydrogenase activity. Structural changes occurring in the SN and striatum manifested themselves in the destruction of mitochondria, degeneration of neurons and synapses, and stratification of myelin sheaths in them. Subcutaneous injections of 30 µg/kg uridine for 22 days restored the neurotoxin-induced changes in these parameters to levels close to the control. 5-Hydroxydecanoate (5 mg/kg), a specific mitoK-ATP channel inhibitor, eliminated the beneficial effect of uridine for almost all characteristics tested, indicating the involvement of the mitoK-ATP channel in the protective effect of uridine. The mechanism of the protective effect of uridine and its therapeutic applications for the prevention and treatment of PD are discussed.

Keywords: 6-hydroxydopamine; Parkinson’s disease; mitochondria; mitochondrial ATP-dependent potassium channel; neurons; oxidative stress; structure; synapses; uridine.

Figure 1

Effect of uridine on the motor function and ion exchange in rat brain mitochondria after the bilateral injection of 6-OHDA into the substantia nigra. (A) Estimation of the motor function on the 22nd day after the injection. y-axis: the time the animals move at a speed of 8 cm/s before falling from the RotaRod device. (B) Calcium retention capacity of rat brain mitochondria in the normal state and in a PD model. The results are presented as the mean ± SEM. * p < 0.05, relative to the control, # p < 0.05, relative to the 6-OHDA group.

Figure 2

Effect of uridine on the rate of hydrogen peroxide formation and MDA production in rat brain mitochondria and blood serum after the bilateral injection of 6-OHDA into the substantia nigra. (A) The rate of hydrogen peroxide formation by rat brain mitochondria on the 22nd day after the administration of 6-OHDA. (B) Concentration of lipid peroxidation products in rat brain mitochondria on the 22nd day after the injection of 6-OHDA. (C) Concentration of lipid peroxidation products in blood serum of rats on the 22nd day after the injection of 6-OHDA. (D) A correlation between the content of TBA-active products in the blood serum and the LDG activity in lymphocytes. The results are presented as the mean ± SEM. * p < 0.05, relative to the control, # p < 0.05, relative to the 6-OHDA group.

Figure 3

A region of a dopaminergic neuron from the substantia nigra in the control (A), in a model of parkinsonism (B), in the presence of uridine (C), and in the presence of uridine and 5-HD (D). N, nucleus; Gc, Golgi complex; M, mitochondrion; rer, endoplasmic reticulum. Scale bar = 1 µm.

Figure 4

Myelin sheaths of axons in the neuropil of substantia nigra neurons in the control (A), in a model of parkinsonism (B), in the presence of uridine (C), and in the presence of uridine and 5-HD (D). Myelin sheaths are shown by arrows. Scale bar = 0.5 µm.

Figure 5

A region of a neuron from the striatum in the control (A), in a model of parkinsonism (B), in the presence of uridine (C), in the presence of uridine and 5-HD (D). N, nucleus; Gc, Golgi complex; M, mitochondrion; rer, endoplasmic reticulum. Scale bar = 1 µm.

Figure 6

Regions of the neuropil of striatum neurons in the control (A), in a model of parkinsonism (B,C), and after the injection of uridine (D). Panel (B) shows a destroyed, swollen mitochondria and a large dark axon terminus, panel (C) shows synaptic endings with perforated multiple postsynaptic densities. AT, axon terminus; M, mitochondrion; az, active zone (asterisks). Scale bar = 1 µm.

Figure 7

Myelin sheaths of axons in the neuropil of the striatum in the control (A), in a model of parkinsonism (B), in the presence of uridine (C), and in the presence of uridine and 5-HD (D). Myelin sheaths are shown by arrows. M, mitochondrion. Scale bar = 0.5 µm.