Hemiparkinsonian rat models: different sensitivity of dopaminergic neurotoxins

Identifying candidate genes associated with hippocampal dysfunction in a hemiparkinsonian rat model by transcriptomic profiling

Parkinson's disease (PD) often results in hippocampal dysfunction, which leads to cognitive and emotional challenges and synaptic irregularities. This study attempted to assess behavioral anomalies and identify differentially expressed genes (DEGs) within the hippocampus of a hemiparkinsonian rat model to potentially uncover novel genetic candidates linked to hippocampal dysfunction. Striatal 6-hydroxydopamine (6-OHDA) infusions were performed unilaterally in the brains of adult SD rats, while dopaminergic impairments were verified in rats with 6-OHDA-lesioned striata. RNA sequencing and gene expression analysis unveiled 1018 DEGs in the ipsilateral rat hippocampus following 6-OHDA infusion: 631 genes exhibited upregulation, while 387 genes were downregulated (with FDR-adjusted p-value < 0.05 and absolute fold-change > 1.5). Gene ontology analysis of DEGs indicated that alterations in the hippocampi of 6-OHDA-lesioned rats were primarily associated with synaptic signaling, axon development, behavior, postsynaptic membrane, synaptic membrane, neurotransmitter receptor activity, and peptide receptor activity. The Kyoto Encyclopedia of Genes and Genomes analysis of DEGs demonstrated significant enrichment of the neuroactive ligand-receptor interaction, calcium signaling pathway, cAMP signaling pathway, axon guidance, and notch signaling pathway in rat hippocampi that had been subjected to striatal 6-OHDA infusion. STRING analysis confirmed a notable upregulation of eight hub genes (Notch3, Gng4, Itga3, Grin2d, Hgf, Fgf11, Htr3a, and Col6a2), along with a significant downregulation of two hub genes (Itga11 and Plp1), as validated by reverse transcription-quantitative polymerase chain reaction. This study provides a comprehensive transcriptomic profile of the hippocampi in a hemiparkinsonian rat model, thereby offering insights into the signaling pathways underlying hippocampal dysfunction.

The significance of rotational behavior and sensitivity of striatal dopamine receptors in hemiparkinsonian rats: A comparative study of lactacystin and 6-OHDA

A growing body of evidence indicates that impairment of the ubiquitin-proteasome (UPS) system in the substantia nigra (SN) plays an important role in the pathogenesis of Parkinson's disease (PD). The aim of our study was to compare two unilateral rat models, one produced by intranigral administration of the UPS inhibitor lactacystin or the other induced by 6-OHDA, in terms of their effect on the amphetamine- and apomorphine-induced rotational behavior, striatal dopamine (DA) D1 and D2 receptor sensitivity and tissue levels of DA and its metabolites. We found that these models did not differ in the intensity of ipsilateral rotations induced by amphetamine. In contrast, apomorphine produced contralateral rotations only in 6-OHDA-lesioned rats, and, depending on the dose, it induced either no or moderate ipsilateral rotations in the lactacystin-lesioned group. In addition, lactacystin induced a strong reduction in the tissue DA level and its metabolites in the lesioned striatum and SN when measured three weeks after the administration which was aggravated six weeks post-lesion, reaching the level comparable to the 6-OHDA group. Binding of [3H]raclopride to D2 receptors was increased in the lesioned striatum in both investigated (PD) models six weeks after lesion. In turn, binding of [3H]SCH23390 to the striatal D1 receptors was not changed in the lactacystin group but was increased bilaterally in the 6-OHDA group. The present results add a new value to the study of DA receptor sensitivity and are discussed in the context of the validity of the lactacystin model as a suitable model of Parkinson's disease.

Early increase in dopamine release in the ipsilateral striatum after unilateral intranigral administration of lactacystin produces spontaneous contralateral rotations in rats

Since the discovery of the role of the ubiquitin-proteasome system (UPS) in the pathogenesis of Parkinson's disease, UPS inhibitors, such as lactacystin have been used to investigate the relationship between UPS impairment and degeneration of dopamine (DA) neurons. However, mostly long-term neurotoxic effects of lactacystin have been studied in animal models. Therefore, the aim of our study was to investigate behavioral and biochemical changes related to the DA system during the first week following unilateral intranigral injection of lactacystin to rats. We found that lactacystin produced early spontaneous contralateral rotations which were inhibited by combined administration of DA D1 and D2 receptor antagonists. Simultaneously, an increase in the extracellular level of DA and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA) was found in the ipsilateral striatum. In contrast, one week after lesion, when turning behavior was no longer visible, a decrease in the extracellular level of DA, DOPAC and HVA was demonstrated. It was accompanied by a substantial reduction in the tissue levels of DA and its metabolites in the lesioned substantia nigra and striatum. We concluded that unilateral intranigral administration of lactacystin produces an early increase in DA neurotransmission which precedes a decrease in the striatal and nigral tissue DA content. It is manifested by the appearance of spontaneous contralateral rotations and an elevation of the extracellular DA level in the ipsilateral striatum. Since similar behavior was previously observed after intranigral administration of rotenone and MPP(+) but not 6-hydroxydopamine (6-OHDA), it may indicate a common mechanism of action shared by these neurotoxins.

BMSC and CoQ10 improve behavioural recovery and histological outcome in rat model of Parkinson's disease

OBJECTIVE

This study assessed the ability of a combination treatment of bone marrow stromal cell (BMSC) graft and oral coenzyme (CoQ10) in a rat model of Parkinson's disease (PD) as an appropriate substitute for current Parkinson treatments. The combination treatment was compared to sole treatments of BMSC and CoQ10.

MATERIALS AND METHODS

In this experimental study, there were six groups of male Wistar rats: control, sham, lesion, CoQ10, graft BMSC and graft BMSC plus CoQ10. Oral administration of CoQ10 began 1 week before the PD and continued during the entire treatment period. To simulate PD, we injected 6 hydroxydopamine (6OHDA) in rats. BMSC were labelled by 5-bromo-2'-deoxyuridine (Brdu) before transplantation. We assessed behaviour before PD, 2 weeks after PD and 8 weeks after cell transplantation. At the end of the second month of treatment, immunohistochemistry, histology and molecular studies were performed.

RESULTS

Behavioural assessment of the CoQ10 group and BMSC group indicated equal recovery in comparison with the lesion group (P<0.01), while the combined treatment of BMSC and CoQ10 showed considerably better recovery compared with the lesion group (P<0.001). There were no signs of gliosis and graft rejection. Immunohistochemistry analysis of Brdu indicated that cells were alive after 2 months of application in host tissue. Cell counts showed significantly greater numbers of neural cells in the combination treatment of BMSC and CoQ10 compared to the other groups. Tyrosine hydroxylase (TH) gene expression levels in the combined therapy group was significantly more than the other experimental groups (P<0.001).

CONCLUSION

The combined use of two neuroprotective treatments and cell replacement therapy can be effective in the treatment of PD, at least in experimental settings.

Rats with unilateral median forebrain bundle, but not striatal or nigral, lesions by the neurotoxins MPP+ or rotenone display differential sensitivity to amphetamine and apomorphine

Rotenone and 1-methyl-4-phenyl pyridinium (MPP+) are two mitochondrial neurotoxins known to produce Parkinson's disease (PD) in experimental animals. In the present study, we compared drug-induced rotational asymmetry in rats lesioned using these neurotoxins at three distinct basal ganglia sites, the striatum, substantia nigra pars compacta (SNpc) and median forebrain bundle (MFB). The levels of dopamine (DA) in the ipsilateral striata of these hemiparkinsonian animals were assayed employing an HPLC-electrochemical procedure 2 days after the final rotational study. Rats infused with rotenone or MPP+ into the SNpc, but not into the striatum or MFB, exhibited contralateral rotations immediately after recovery from anesthesia. Irrespective of the lesion site or the toxin used, all the animals exhibited ipsilateral rotations when challenged with D-amphetamine. Apomorphine administration caused contralateral circling behavior in MFB-lesioned animals, but ipsilateral rotations in rats that received rotenone or MPP+ in the striatum or SNpc. Stereotaxic administration of rotenone into the MFB, SNpc or striatum caused a significant loss of DA in the ipsilateral striatum to varying degrees (96%, 62% and 30%, respectively, as compared to the contralateral side). However, unilateral MPP+ administration into the MFB, SNpc or striatum caused respectively about 98%, 74% and 59% loss of striatal DA. Behavioural observations and the neurochemical results indicate that, among the three anatomically distinct loci-lesioned, MFB-lesioned animals mimicked behavioral aberrations similar to nigral lesions caused by 6-hydroxydopamine, a classical parkinsonian neurotoxin. Moreover, the results point out that while both d-amphetamine and apomorphine-induced rotations could be considered as valuable behavioral indices to test novel drugs against PD, yet apomorphine-induced contralateral bias proves to be a more reliable indicator of specific destruction in the nigrostriatal pathway and development of post-synaptic DA receptor supersensitivity.

Neuroprotective and neurorescue effect of black tea extract in 6-hydroxydopamine-lesioned rat model of Parkinson's disease

In the present study, an attempt has been made to explore the neuroprotective and neuroreparative (neurorescue) effect of black tea extract (BTE) in 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease (PD). In the neuroprotective (BTE + 6-OHDA) and neurorescue (6-OHDA + BTE) experiments, the rats were given 1.5% BTE orally prior to and after intrastriatal 6-OHDA lesion respectively. A significant recovery in d-amphetamine induced circling behavior (stereotypy), spontaneous locomotor activity, dopamine (DA)-D2 receptor binding, striatal DA and 3-4 dihydroxy phenyl acetic acid (DOPAC) level, nigral glutathione level, lipid peroxidation, striatal superoxide dismutase and catalase activity, antiapoptotic and proapoptotic protein level was evident in BTE + 6-OHDA and 6-OHDA + BTE groups, as compared to lesioned animals. BTE treatment, either before or after 6-OHDA administration protected the dopaminergic neurons, as evident by significantly higher number of surviving tyrosine hydroxylase immunoreactive (TH-ir) neurons, increased TH protein level and TH mRNA expression in substantia nigra. However, the degree of improvement in motor and neurochemical deficits was more prominent in rats receiving BTE before 6-OHDA. Results suggest that BTE exerts both neuroprotective and neurorescue effects against 6-OHDA-induced degeneration of the nigrostriatal dopaminergic system, suggesting that possibly daily intake of BTE may slow down the PD progression as well as delay the onset of neurodegenerative processes in PD.

Behavioral differences in a rotenone-induced hemiparkinsonian rat model developed following intranigral or median forebrain bundle infusion

A mitochondrial complex-I inhibitor, rotenone was unilaterally infused into the substantia nigra pars compacta (SNpc) or median forebrain bundle (MFB) to create hemiparkinsonian animal models and investigated spontaneous and drug-induced stereotypic rotations, as well as certain postural behaviors in Sprague-Dawley rats. Animals infused intranigrally, but not intra-MFB, with rotenone exhibited spontaneous contralateral rotations immediately after recovery from anesthesia. Head position bias and elevated body swing test showed insignificant contralateral bias in animals with nigral damage but a significant ipsilateral bias in MFB-lesioned rats. General motor activity of the animals was reduced in both the groups as indicated by reduced performance on a Plus-Maze. Intranigrally, rotenone-infused animals exhibited progressive ipsilateral rotations when challenged with d-amphetamine on the 7th, 14th, 21st, and 28th days or with apomorphine on 9th, 16th, 23rd, and 30th days. However, animals that received rotenone in MFB exhibited ipsilateral or contralateral rotations when challenged respectively with d-amphetamine or apomorphine only in the 5th week (28th and 30th days). Stereotaxic administration of rotenone into SNpc or MFB caused a significant loss of dopamine in the ipsilateral striatum (>80% in SNpc; >95% in MFB), when assayed employing an HPLC equipped with electrochemical detector on the 32nd day. Neuronal loss in SNpc was confirmed in coronal sections stained with cresyl violet and revealed extension of lesion towards SN pars reticulata, in SNpc-infused animals. Our results demonstrate that rotenone-induced neurodegeneration is a slow, yet progressive process similar to that in idiopathic Parkinson's disease and unlike that observed in other classical neurotoxin-mediated lesions which are abrupt and developed in few hours to days. Thus, intranigral or intra-MFB infusion of rotenone could be used for producing hemiparkinsonian animal models in rats. These findings further suggest that, while both d-amphetamine and apomorphine-induced stereotypic rotations could be used as a valuable behavioral assay procedure to test novel drugs against Parkinson's disease, yet apomorpine-induced contralateral bias in turning is a reliable indicator of specific destruction in nigrostriatal pathway and development of postsynaptic dopamine receptor supersensitivity.

Restorative potential of dopaminergic grafts in presence of antioxidants in rat model of Parkinson's disease

Free radical mediated damage has been reported to contribute significantly towards low survival (5-10%) of grafted dopaminergic neurons, post transplantation. In the present study, an attempt has been made to explore the neuroprotective potential of the combination of two major antioxidants ascorbic acid (AA) and glutathione (GSH) on ventral mesencephalic cells (VMC) and nigral dopamine (DA) neurons when co-transplanted together with VMC in rat model of Parkinson's disease (PD). GSH and AA have been reported to act co-operatively in the conditions of oxidative stress thereby helping in maintaining the cellular GSH/GSSG redox status. Functional recovery was assessed 12 weeks post transplantation, where a significant restoration (p<0.001) in d-amphetamine induced circling behavior (62%), spontaneous locomotor activity (SLA; 64%), dopamine-D2 receptor binding (63%), dopamine (65%) and 3,4-dihydroxy phenyl acetic acid (DOPAC) level (64%) was observed in co-transplanted animals as compared to lesioned and VMC alone grafted rats. VMC and GSH+AA co-transplanted animals exhibited a significantly higher surviving TH-immunoreactive (TH-ir) neurons number (p<0.01), TH-ir fibers outgrowth (p<0.05) in striatal graft and TH-ir neurons in substantia nigra pars compacta (SNpc) (p<0.01), as compared to VMC alone transplanted rats. An attempt was made to further confirm our in vivo observations through in vitro experiments where following in vitro exposure to 6-OHDA, a higher cell survival (p<0.01), TH-ir cell counts (p<0.001) and DA and DOPAC levels (p<0.01) were also observed in 8-day-old VMC culture in presence of GSH+AA as compared to VMC cultured in absence of antioxidants. The results suggest that GSH+AA when co-transplanted with VMC provide higher restoration probably by increasing the survival of grafted VMC and simultaneously supporting nigral TH-immunopositive neurons in rat model of PD.