Musa V. Mabandla

Voluntary Running Provides Neuroprotection in Rats After 6-Hydroxydopamine Injection into the Medial Forebrain Bundle

Neurotoxic drugs such as 6-hydroxydopamine (6-OHDA) have been used to mimic a Parkinsonian state in a rat model. The toxic effect of 6-OHDA has been shown to be reduced in rats that were forced to use the impaired limb immediately after unilateral 6-OHDA injection. The aim of this study was to determine whether dopamine neurons in the substantia nigra are spared in rats that exercise voluntary. Two groups of rats were placed in cages with attached running wheels 7 days prior to injection of 6-OHDA (10 μg/4 μL saline) into the medial forebrain bundle. The running wheels of the control group were immobilized for the duration of the study. After 6-OHDA injection, the rats were returned to their respective cages where they remained for a further period of 14 days. Wheel revolutions during free running were recorded daily in the experimental group. At the end of this period the rats were injected with apomorphine (0.5 mg/kg, s.c.) and the number and direction of rotations was recorded. Rats that exercised in the running wheels did not rotate contralaterally in response to apomorphine injection, suggesting that dopamine neurons had been spared sufficiently from the toxic effects of 6-OHDA injection to prevent upregulation of postsynaptic dopamine receptors in the striatum.

Stress reduces the neuroprotective effect of exercise in a rat model for Parkinson's disease.

Parkinsons disease (PD) is a progressive neurodegenerative disease of nigrostriatal dopamine (DA) neurons that project from the substantia nigra pars compacta (SNc) to the striatum. To further understand PD, researchers have developed standardized animal models of PD. In this study, Long Evans (LE) rats were unilaterally lesioned by injection of the neurotoxin, 6-hydroxydopamine (6-OHDA), into the medial forebrain bundle (MFB) of the left hemisphere. The rats were divided into three groups randomly; group 1 (runners) were housed in individual cages with attached running wheels, group 2 (stressed-runners) had access to individual free running wheels, except post-lesion when the rats were subjected to immobilization of the running wheel for 1 h per day for 14 days, as well as one session of 24-h food deprivation and a 7-h shift in the light/dark cycle. Group 3 (non-runnners) were housed individually in cages with attached running wheels that were permanently immobilized. Subcutaneous injection of the DA agonist, apomorphine, caused stressed-runners and non-runners to rotate vigorously away from the side of the lesion (contralaterally). Apomorphine-induced rotations provide a behavioural measure of the extent of the lesion, a depletion of more than 80% of DA neurons is required to produce vigorous contralateral rotations in response to apomorphine injection. Runners rotated significantly less than non-runners and stressed-runners. The number of rotations performed by stressed-runners was not significantly different from non-runners, suggesting that stress had cancelled the neuroprotective effect of running. Immunohistochemical staining for tyrosine hydroxylase in the SNc revealed slightly less destruction of DA neurons in the runners than in stressed-runners or non-runners, although these differences did not achieve statistical significance. The behavioural results confirm a previous finding suggesting that voluntary exercise is neuroprotective. A novel finding is that mild stressors cancel the neuroprotection afforded by voluntary exercise.

The effect of electromagnetic radiation in the mobile phone range on the behaviour of the rat.

Electromagnetic radiation (EMR) is emitted from electromagnetic fields that surround power lines, household appliances and mobile phones. Research has shown that there are connections between EMR exposure and cancer and also that exposure to EMR may result in structural damage to neurons. In a study by Salford et al. (Environ Health Perspect 111:881–883, 2003) the authors demonstrated the presence of strongly stained areas in the brains of rats that were exposed to mobile phone EMR. These darker neurons were particularly prevalent in the hippocampal area of the brain. The aim of our study was to further investigate the effects of EMR. Since the hippocampus is involved in learning and memory and emotional states, we hypothesised that EMR will have a negative impact on the subject’s mood and ability to learn. We subsequently performed behavioural, histological and biochemical tests on exposed and unexposed male and female rats to determine the effects of EMR on learning and memory, emotional states and corticosterone levels. We found no significant differences in the spatial memory test, and morphological assessment of the brain also yielded non-significant differences between the groups. However, in some exposed animals there were decreased locomotor activity, increased grooming and a tendency of increased basal corticosterone levels. These findings suggested that EMR exposure may lead to abnormal brain functioning.

Voluntary exercise reduces the neurotoxic effects of 6-hydroxydopamine in maternally separated rats

Maternal separation has been associated with development of anxiety-like behaviour and learning impairments in adult rats. This has been linked to changes in brain morphology observed after exposure to high levels of circulating glucocorticoids during the stress-hyporesponsive period (P4-P14). In the present study, adult rats that had been subjected to maternal separation (180 min/day for 14 days) during the stress-hyporesponsive period, received unilateral infusions of a small dose of 6-hydroxydopamine (6-OHDA, 5 microg/4 microl saline) into the medial forebrain bundle. The results showed that voluntary exercise had a neuroprotective effect in both non-stressed and maternally separated rats in that there was a decrease in forelimb akinesia (step test) and limb use asymmetry (cylinder test). Maternal separation increased forelimb akinesia and forelimb use asymmetry and reduced the beneficial effect of exercise on forelimb akinesia. It also reduced exploratory behaviour, consistent with anxiety-like behaviour normally associated with maternal separation. Exercise appeared to reduce dopamine neuron destruction in the lesioned substantia nigra when expressed as a percentage of the non-lesioned hemisphere. However, this appeared to be due to a compensatory decrease in completely stained tyrosine hydroxylase-positive neurons in the contralateral, non-lesioned substantia nigra. In agreement with reports that maternal separation increases the 6-OHDA-induced loss of dopamine terminals in the striatum, there was a small increase in dopamine neuron destruction when expressed as a percentage of the non-lesioned hemisphere but there was no difference in dopamine cell number, suggesting that exposure to maternal separation did not exacerbate dopamine cell loss.

The effects of vasopressin and oxytocin on methamphetamine-induced place preference behaviour in rats.

Methamphetamine is a highly addictive stimulant drug whose illicit use and resultant addiction has become an alarming global phenomenon. The mesolimbic dopaminergic pathway has been shown to be fundamental to the establishment of addictive behaviour. This pathway, as part of the reward system of the brain, has also been shown to be important in classical conditioning, which is a learnt response. Within the modulation of learning and memory, the neurohypophyseal hormones vasopressin and oxytocin have been reported to play a vital role, with vasopressin exerting a long- term facilitatory effect and oxytocin exerting an inhibitory effect. Therefore we adopted a conditioned place preference model to investigate whether vasopressin V1b receptor antagonist SSR 149415 or oxytocin treatment would cause a decrease in the seeking behaviour in a reinstatement paradigm. Behavioural findings indicated that methamphetamine induced a change in the place preference in the majority of our animals. This change in place preference was not seen when vasopressin was administered during the extinction phase. On the other hand the methamphetamine-induced change in place preference was enhanced during the reinstatement phase in the animals that were treated with oxytocin. Striatal dopamine levels were determined, as methamphetamine is known to increase dopamine transmission in this area. Significant changes in dopamine levels were observed in some of our animals. Rats that received both methamphetamine and oxytocin had significantly higher striatal dopamine than those that received oxytocin alone. Western blot analysis for hippocampal cyclic AMP response element binding protein (CREB) was also conducted as a possible indicator of glutamatergic NMDA receptor activity, a pathway that is important for learning and memory. The Western blot analysis showed no changes in hippocampal pCREB expression. Overall our data led us to conclude that methamphetamine treatment can change place preference behaviour in rats and that this change may be partially restored by vasopressin antagonism, but exaggerated by oxytocin.

The interaction between stress and exercise, and its impact on brain function

In response to acute adversity, emotional signals shift the body into a state that permits rapid detection, identification, and appropriate response to a potential threat. The stress response involves the release of a variety of substances, including neurotransmitters, neurotrophic factors, hormones, and cytokines, that enable the body to deal with the challenges of daily life. The subsequent activation of various physiological systems can be both protective and damaging to the individual, depending on timing, intensity, and duration of the stressor. Successful recovery from stressful challenges during early life leads to strengthening of synaptic connections in health-promoting neural networks and reduced vulnerability to subsequent stressors that can be protective in later life. In contrast, chronic intense uncontrollable stress can be pathogenic and lead to disorders such as depression, anxiety, hypertension, Alzheimer’s disease, Parkinson’s disease, and an increased toxic response to additional stressors such as traumatic brain injury and stroke. This review briefly explores the interaction between stress experienced at different stages of development and exercise later in life.

Early use of oleanolic acid provides protection against 6-hydroxydopamine induced dopamine neurodegeneration

Oleanolic acid is a triterpenoid that has been shown to possess antioxidant properties. In this study we investigated the effects of oleanolic acid in a parkinsonian rat model. Unilateral 6-hydroxydopamine (6-OHDA) lesions were carried out on postnatal day (PND) 60 in 4 groups viz. (1) Rats that started oleanolic acid treatment 7 days prior to lesion. (2) Rats not treated with oleanolic acid. (3) Rats that started oleanolic acid treatment 1 day post-lesion. (4) Rats treated with oleanolic acid 7 days post-lesion. The degree of forelimb impairment was assessed using limb use asymmetry and forelimb akinesia tests. Neurochemical changes were assessed using a Dopamine ELISA kit and mitochondrial apoptosis was measured using a mitochondrial apoptosis detection kit. In this study, animals injected with 6-OHDA displayed forelimb use asymmetry that was ameliorated by treatment with oleanolic acid 7 days pre- and 1 day post-lesion. In the cylinder test, rats injected with 6-OHDA favored using the forelimb ipsilateral (unimpaired) to the lesioned hemisphere while rats treated with oleanolic acid used the forelimb contralateral (impaired) to the lesioned hemisphere significantly more. Rats treated with oleanolic acid 7 days pre- and 1 day post-lesion had more dopamine in the striatum than the non-treated or the 7 days after lesion rats. Similarly, 6-OHDA-induced membrane depolarization was decreased in rats that received oleanolic acid treatment pre- or immediately post-lesion. This suggests that early treatment with oleanolic acid protects dopamine neurons from the toxic effects of 6-OHDA.

Exposure to Early Life Stress Results in Epigenetic Changes in Neurotrophic Factor Gene Expression in a Parkinsonian Rat Model

Early life adversity increases the risk of mental disorders later in life. Chronic early life stress may alter neurotrophic factor gene expression including those for brain derived neurotrophic factor (BDNF) and glial cell derived neurotrophic factor (GDNF) that are important in neuronal growth, survival, and maintenance. Maternal separation was used in this study to model early life stress. Following unilateral injection of a mild dose of 6-hydroxydopamine (6-OHDA), we measured corticosterone (CORT) in the blood and striatum of stressed and nonstressed rats; we also measured DNA methylation and BDNF and GDNF gene expression in the striatum using real time PCR. In the presence of stress, we found that there was increased corticosterone concentration in both blood and striatal tissue. Further to this, we found higher DNA methylation and decreased neurotrophic factor gene expression. 6-OHDA lesion increased neurotrophic factor gene expression in both stressed and nonstressed rats but this increase was higher in the nonstressed rats. Our results suggest that exposure to early postnatal stress increases corticosterone concentration which leads to increased DNA methylation. This effect results in decreased BDNF and GDNF gene expression in the striatum leading to decreased protection against subsequent insults later in life.

Inhibition of HIV-1 tat-induced transactivation and apoptosis by the divalent metal chelators, fusaric acid and picolinic acid—Implications for HIV-1 dementia

The HIV-1 transactivator protein tat is pivotal to the pathogenesis of AIDS, exerting its effects on both viral and cellular gene expression. The basic structure of tat protein allows it to be secreted by HIV-1 infected cells and penetrate uninfected cells where it elicits its multifunctional biochemical effects. The main function of tat protein is viral transactivation which leads to the upregulation of transcription through complex interactions with RNA and host cell factors. Since HIV-1 has been widely implicated as a causative agent of HIV-1 dementia, the aim of our study was to investigate the ability of two novel metal chelators, fusaric acid (FA) and picolinic acid (PA) to firstly inhibit HIV-1 tat induced transcription and secondly, to minimize its cytotoxic effects as mediated via apoptosis. Biologically active tat protein is not freely available commercially. We therefore had to produce, isolate and purify our own protein. A cell culture system and flow cytometric techniques were used in our study. Exposure of CEM-GFP cells to exogenous recombinant tat protein induced transcription and apoptosis, and both processes were inhibited by FA and PA at concentrations that alone did not induce any cytotoxicity. Our data suggest that FA and PA may have therapeutic potential in the management of HIV-1 dementia.

Epigenetics: a link between addiction and social environment

The detrimental effects of drug abuse are apparently not limited to individuals but may also impact the vulnerability of their progenies to develop addictive behaviours. Epigenetic signatures, early life experience and environmental factors, converge to influence gene expression patterns in addiction phenotypes and consequently may serve as mediators of behavioural trait transmission between generations. The majority of studies investigating the role of epigenetics in addiction do not consider the influence of social interactions. This shortcoming in current experimental approaches necessitates developing social models that reflect the addictive behaviour in a free-living social environment. Furthermore, this review also reports on the advancement of interventions for drug addiction and takes into account the emerging roles of histone deacetylase (HDAC) inhibitors in the etiology of drug addiction and that HDAC may be a potential therapeutic target at nucleosomal level to improve treatment outcomes.