Michael F Salvatore

University of North Texas HSC at Fort Worth | UNTHSC · Department of Pharmacology and Neuroscience

Reduced movement frequency or physical activity (bradykinesia) occurs with high prevalence in the elderly. However, loss of striatal tyrosine hydroxylase (TH) in aging humans, non-human primates, or rodents does not reach the ~ 80% loss threshold associated with bradykinesia onset in Parkinson’s disease. Moderate striatal dopamine (DA) loss, either...

Identifying neurobiological mechanisms of aging-related parkinsonism, and lifestyle interventions that mitigate them, remain critical knowledge gaps. No aging study, from rodent to human, has reported loss of any dopamine (DA) signaling marker near the magnitude associated with onset of parkinsonian signs in Parkinson's disease (PD). However, in su...

Compensatory mechanisms that augment dopamine (DA) signaling are thought to mitigate onset of hypokinesia prior to major loss of tyrosine hydroxylase (TH) in striatum that occurs in Parkinson's disease. However, the identity of such mechanisms remains elusive. In the present study, the rat nigrostriatal pathway was unilaterally-lesioned with 6-hydr...

The mechanistic influences of dopamine (DA) signaling and impact on motor function are nearly always interpreted from changes in nigrostriatal neuron terminals in striatum. This is a standard practice in studies of human Parkinson's disease (PD) and aging and related animal models of PD and aging-related parkinsonism. However, despite dozens of stu...

Alleviation of motor impairment by aerobic exercise (AE) in Parkinson's disease (PD) patients points to activation of neurobiological mechanisms that may be targetable by therapeutic approaches. However, evidence for AE-related recovery of striatal dopamine (DA) signaling or tyrosine hydroxylase (TH) loss has been inconsistent in rodent studies. Th...

Cognitive decline in Parkinson’s disease (PD) is a critical premotor sign that may occur in approximately 40% of PD patients up to 10 years prior to clinical recognition and diagnosis. Delineating the mechanisms and specific behavioral signs of cognitive decline associated with PD prior to motor impairment is a critical unmet need. Rodent PD models...

Parkinson's disease (PD) rodent models provide insight into the relationship between nigrostriatal dopamine (DA) signaling and locomotor function. Although toxin-based rat models produce frank nigrostriatal neuron loss and eventual motor decline characteristic of PD, the rapid nature of neuronal loss may not adequately translate premotor traits, su...

Parkinsons disease (PD) rodent models provide insight into the relationship between nigrostriatal dopamine (DA) signaling and locomotor function. Although toxin-based rat models produce frank nigrostriatal neuron loss and eventual motor decline characteristic of PD, the rapid nature of neuronal loss may not adequately translate premotor traits, suc...

Cognitive decline in Parkinsons disease (PD) emerges up to 10 years before clinical recognition. Neurobiological mechanisms underlying premotor cognitive impairment in PD can potentially be examined in the PINK1 / rat, which exhibits a protracted motor onset. To enhance translation to human PD cognitive assessments, we tested a modified multiple T-...

The mechanistic influences of dopamine (DA) signaling and impact on motor function is nearly always interpreted from changes in nigrostriatal neuron terminals in striatum. This is a standard practice in studies of human Parkinson’s disease (PD) and aging, and related animal models of PD and aging-related parkinsonism. However, despite dozens of stu...

Background Alleviation of motor impairment by aerobic exercise (AE) in Parkinson’s disease (PD) points to a CNS response that could be targeted by therapeutic approaches, but recovery of striatal dopamine (DA) or tyrosine hydroxylase (TH) has been inconsistent in rodent studies. Objective To increase translation of AE, 3 components were implemente...

Although glial cell line-derived neurotrophic factor (GDNF) showed efficacy in preclinical and early clinical studies to alleviate parkinsonian signs in Parkinson's disease (PD), later trials did not meet primary endpoints, giving pause to consider further investigation. While GDNF dose and delivery methods may have contributed to diminished effica...

Although glial cell line-derived neurotrophic factor (GDNF) showed efficacy in preclinical and early clinical studies to alleviate parkinsonian signs in Parkinson’s disease (PD), later trials did not meet primary endpoints, giving pause to consider further investigation. While GDNF dose and delivery methods may have contributed to diminished effica...

Mechanisms that augment dopamine (DA) signaling to compensate for tyrosine hydroxylase (TH) loss and delay motor impairment in Parkinson’s disease remain unidentified. The rat nigrostriatal pathway was unilaterally-lesioned by 6-OHDA to determine whether differences in DA content, TH protein, TH phosphorylation, or D 1 receptor expression in striat...

Background: Rodent Parkinson's disease (PD) models are valuable to interrogate neurobiological mechanisms of exercise that mitigate motor impairment. Translating these mechanisms to human PD must account for physical capabilities of the patient. Objective: To establish cardiovascular parameters as a common metric for cross-species translation of...

Preservation of motor capabilities is vital to maintaining independent daily living throughout a person's lifespan and may mitigate aging-related parkinsonism, a progressive and prevalent motor impairment. Physically active lifestyles can mitigate aging-related motor impairment. However, the metrics of physical activity necessary for mitigating par...

Importance Epidemiologists report a 56% increased risk of veterans with (+) mild traumatic brain injury (mTBI) developing Parkinson’s disease (PD) within 12-years post-injury. The most relevant contributors to this high risk of PD in veterans (+) mTBI is unknown. As cognitive problems often precede PD diagnosis, identifying specific domains most in...

Up to 23% of newly diagnosed, non-demented, Parkinson’s disease (PD) patients experience deficits in executive functioning (EF). In fact, EF deficits may occur up to 39-months prior to the onset of motor decline. Optimal EF requires working memory, attention, cognitive flexibility, and response inhibition underlying appropriate decision-making. The...

Glial cell line-derived neurotrophic factor (GDNF) improved motor function in Parkinson’s disease (PD) patients in Phase I clinical trials, and these effects persisted months after GDNF discontinuation. Conversely, phase II clinical trials reported no significant effects on motor improvement vs placebo. Disease duration, the quantity, infusion appr...

Parkinson's disease (PD) is the second most common neurodegenerative disease and there are no effective treatments that either slow or reverse the degeneration of the dopamine (DA) pathway. Using a 4-week progressive MPTP (1-methyl-1,2,3,6-tetrahydropyridine) neurotoxin model of PD, which is characterized by neuroinflammation, loss of nigrostriatal...

Methamphetamine (MA) exposure may increase the risk of motor or cognitive impairments similar to Parkinson’s disease (PD) by middle age. Although damage to nigrostriatal or mesoaccumbens dopamine (DA) neurons may occur during or early after MA exposure, overt PD-like symptoms at a younger age may not manifest due to compensatory mechanisms to maint...

Parkinson's disease (PD) is a common neurodegenerative disease worldwide. While the typical motor symptoms of PD are well known, the lesser known non-motor symptoms can also greatly impact the patient's quality of life. These symptoms often appear before motor impairment, therefore identifying biomarkers that may predict PD risk or pathology has be...

Identifying lifestyle strategies and allied neurobiological mechanisms that reduce aging-related motor impairment is imperative, given the accelerating number of retirees and increased life expectancy. A physically active lifestyle prior to old age can reduce risk of debilitating motor decline. However, if exercise is initiated after motor decline...

Body weight changes during acclimation to exercise regimen and during treadmill exercise initiation at 18 months (A,C) or 24 months old (B,D). Results are expressed as percent change in body weight, with respect to each individual’s baseline body weight, during each acclimation period. Data are presented as mean ± SEM. A. Percent change in body wei...

Exercise impact at 18 or 24 months on DA tissue content. Striatum (A,B). A. 18 months. DA tissue content was not significantly affected by the exercise regimen in 18 month old rats (t = 1.38, p = 0.19). B. 24 months DA tissue content was not significantly affected by the exercise regimen in 24 month old rats (t = 0.86, p = 0.41). Substantia nigra (...

Tyrosine hydroxylase (TH) catalyzes the conversion of L-tyrosine into L-Dopa, which is the rate-limiting step in the synthesis of catecholamines, particularly dopamine in dopaminergergic neurons. Low dopamine levels and death of the dopaminergic neurons are hallmarks of Parkinson's disease (PD), where α-synuclein is also a key player. TH is highly...

Background: Increased extracellular glutamate may contribute to l-dopa induced dyskinesia, a debilitating side effect faced by Parkinson's disease patients 5 to 10 years after l-dopa treatment. Therapeutic strategies targeting postsynaptic glutamate receptors to mitigate dyskinesia may have limited success because of significant side effects. Incre...

The escalating increase in retirees living beyond their 8th decade brings increased prevalence of aging-related impairments, including locomotor impairment (Parkinsonism) which may affect ~50% of those reaching age 80, but has no confirmed neurobiological mechanism. Lifestyle strategies that attenuate motor decline, and its allied mechanisms, must...

Tyrosine hydroxylase (TH) and dopamine transporters (DATs) regulate dopamine (DA) neurotransmission at the biosynthesis and reuptake steps, respectively. Dysfunction or loss of these proteins occurs in impaired locomotor or addictive behavior, but little is known about the influence of DAT expression on TH function. Differences in TH phosphorylatio...

Exercise may alleviate locomotor impairment in Parkinson's disease (PD) or aging. Identifying molecular responses immediately engaged by exercise in the nigrostriatal pathway and allied tissue may reveal critical targets associated with its long-term benefits. In aging, there is loss of tyrosine hydroxylase (TH) and the glial cell line-derived neur...

Aging-related bradykinesia affects ∼15% of those reaching age 65 and 50% of those reaching their 80s. Given this high risk and lack of pharmacologic therapeutics, noninvasive lifestyle strategies should be identified to diminish its risk and identify the neurobiological targets to reduce aging-related bradykinesia. Early-life, long-term calorie res...

Pharmacological dopamine (DA) replacement with Levodopa (L-DOPA) is the gold standard treatment for Parkinson's disease (PD). However, long term L-DOPA treatment is complicated by eventual debilitating abnormal involuntary movements termed L-DOPA induced dyskinesia (LID), a clinically significant obstacle for the majority of patients who rely on L-...

There is a major increase in the awareness of the positive impact of exercise on improving several disease states with neurobiological basis; these include improving cognitive function and physical performance. As a result, there is an increase in the number of animal studies employing exercise. It is argued that one intrinsic value of forced exerc...

Read the full article 'A vesicular sequestration - to - oxidative deamination shift in myocardial sympathetic nerves in Parkinson disease' on doi: 10.1111/jnc.12766.

Compensatory mechanisms in dopamine (DA) signaling have long been proposed to delay onset of locomotor symptoms during Parkinson's disease (PD) progression until ~80% loss of striatal DA occurs. Increased striatal dopamine turnover has been proposed to be a part of this compensatory response, but may occur after locomotor symptoms. Increased tyrosi...

Excess glutamatergic neurotransmission may contribute to excitotoxic loss of nigrostriatal neurons in Parkinson's disease (PD). Here, we determined if increasing glutamate uptake could reduce the extent of tyrosine hydroxylase (TH) loss in PD progression. The beta-lactam antibiotic, ceftriaxone, increases the expression of glutamate transporter 1 (...

Methamphetamine (METH) is a highly addictive and neurotoxic psychostimulant. Its use in humans is often associated with neurocognitive impairment. Whether this is due to long-term deficits in short-term memory and/or hippocampal plasticity remains unclear. Recently, we reported that METH increases baseline synaptic transmission and reduces LTP in a...

Delivery of exogenous glial cell line-derived neurotrophic factor (GDNF) increases locomotor activity in rodent models of aging and Parkinson's disease in conjunction with increased dopamine (DA) tissue content in substantia nigra (SN). Striatal GDNF infusion also increases expression of GDNF's cognate receptor, GFRα1, and tyrosine hydroxylase (TH)...

The dopamine transporter (DAT) regulates synaptic dopamine (DA) in striatum and modulation of DAT can affect locomotor activity. Thus, in Parkinson's disease (PD), DAT loss could affect DA clearance and locomotor activity. The locomotor benefits of L-DOPA may be mediated by transport through monoamine transporters and conversion to DA. However, its...

Dopamine is a vigorously studied neurotransmitter in the CNS. Indeed, its involvement in locomotor activity and reward-related behaviour has fostered five decades of inquiry into the molecular deficiencies associated with dopamine regulation. The majority of these inquiries of dopamine regulation in the brain focus upon the molecular basis for its...

Measures of dopamine-regulating proteins in somatodendritic regions are often used only as static indicators of neuron viability, overlooking the possible impact of somatodendritic dopamine (DA) signaling on behavior and the potential autonomy of DA regulation between somatodendritic and terminal field compartments. DA reuptake capacity is less in...

Environmental enrichment has been shown to be both neuroprotective and neurorestorative in 1-methyl-2-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse models of Parkinson's disease (PD). However, whether social interaction or novel physical stimulation is responsible for this recovery is controversial. In the current study, we have investigated the e...

Methamphetamine (MA) increases extracellular dopamine (DA) and at chronic high doses induces toxicity as indicated by decreased expression of tyrosine hydroxylase (TH) and dopamine transporter (DAT). Notably, rats will self-administer MA in escalating quantities producing such toxicity. However, the impact of MA at sub-toxic doses on DA regulation...

J. Neurochem. (2010) 115, 707–715. We recently reported that age-related bradykinesia was associated with reduced dopamine (DA) tissue content, ser31 tyrosine hydroxylase (TH) phosphorylation, and total TH levels in substantia nigra (SN) only. In this study, we propose that these decreases result from reduced glial cell line-derived neurotrophic fa...

Correlation of movement number with other locomotor activity parameters. Data presented are means of individual locomotor tests conducted at 4 and 22 months and movement number correlated to horizontal activity (HAC) (p<0.0001; r = 0.982), total distance (cm/hr) (p<0.0001; r = 0.947), and time spent moving (p<0.0001; r = 0.937). No significant corr...

Dopamine content (expressed as total harvested in the dissections) in the SN. In Figure 5 in the main text, DA content is normalized to total protein. This figure shows that total DA tissue content is reduced in the 30 month group, overall. Note there is considerable overlap in nigral DA content between the two groups, and the DA levels from each o...

Critical supporting information for manuscript. (0.03 MB DOC)

Example of between-group differences and session-to-session variability total distance and movement number in two selected pairs of young and old test subjects. Test results are from the 12 and 30 month session. In young-1 vs. old-1, no difference in mean locomotor activity was seen in spite of the age difference, whereas in young-2 vs. old-2 a sig...

Habituation of locomotion. (0.04 MB DOC)

Phosphorylation-state specificity of ser31 antibody produced by 21st Century Biochemicals. Top row values are the quantity of total TH assayed to generate the phosphorylation-state specific immunoreactivity quantities for the ser31 phosphorylation site on TH (as listed in the bottom row). The relative stoichiometries of ser31 phosphorylation for th...

Correlation of total TH versus total DA in the substantia nigra (SN). Spearman r = 0.656, p = 0.011. All data points represent operationally-matched results from SN dissections from the subjects used in this locomotor correlation study. (0.01 MB TIF)

Mesoaccumbens pathway DA correlations (p-values). (0.05 MB DOC)

Background: Tyrosine hydroxylase (TH) regulates dopamine (DA) bioavailability. Its product, L-DOPA, is an established treatment for Parkinson's disease (PD), suggesting that TH regulation influences locomotion. Site-specific phosphorylation of TH at ser31 and ser40 regulates activity. No direct evidence shows that ser40 phosphorylation is the domi...

Dopamine (DA) affects GABA neuronal function in the striatum and together these neurotransmitters play a large role in locomotor function. We recently reported that unilateral striatal administration of GDNF, a growth factor that has neurotrophic effects on DA neurons and enhances DA release, bilaterally increased striatal neuron activity related t...

Neurodegenerative diseases involving neurofibrillary tangle pathology are pernicious. By expressing the microtubule-associated protein tau, a major component of tangles, with a viral vector, we induce neuropathological sequelae in rats that are similar to those seen in human tauopathies. We tested several variants of the adeno-associated virus (AAV...

Extracellular L-glutamate poses a severe excitotoxic threat to neurons and glia when unregulated, therefore low synaptic levels of this neurotransmitter must be maintained via a rapid and robust transport system. A recent study from our laboratory showed a reduced glutamate uptake rate in the striatum of the aged Fischer 344 (F344) rat, yet the mec...

AMPT (alpha-methyl-para-tyrosine) is an inhibitor of tyrosine hydroxylase, the rate-limiting enzyme in dopamine biosynthesis. In clinical settings, AMPT is approved to treat pheochromocytoma. Dystonias and dyskinesias seem to have their origin in inconsistent regulation of dopamine function in dopamine pathways. This paper presents case histories o...

In order to determine its effects on locomotor-related striatal electrophysiology in aged rats, glial cell line-derived neurotrophic factor (GDNF) was infused (vehicle or 30mug) into the right striatum of 24-25-month-old Fischer 344 (F344) rats. Multi-wire electrode arrays were then chronically implanted in striatum bilaterally. Thirty days later,...

Significant differences have been reported in results from three clinical trials evaluating intraputamenal infusion of glial cell line-derived neurotrophic factor (GDNF) for the treatment of Parkinson's disease. To determine if problems in drug bioavailability could have contributed to the discrepancies between studies, we have analyzed the distrib...

Abnormal iron accumulations are frequently observed in the brains of patients with Parkinson's disease and in normal aging. Iron metabolism is regulated in the CNS by iron regulatory proteins (IRP-1 and IRP-2). Mice engineered to lack IRP-2 develop abnormal motoric behaviors including tremors at rest, abnormal gait, and bradykinesia at middle to la...

Glial cell line-derived neurotrophic factor (GDNF) improves motor dysfunction associated with aging in rats and non-human primates, in animal models of Parkinson's disease, and may improve motoric function in patients with advanced Parkinson's disease. These improvements are associated with increased dopamine function in the nigrostriatal system, b...

The emerging profile for the effects of prenatal cocaine exposure presents two prominent features in the exposed offspring: cognitive/attention deficits and an age-associated trend toward motor/tone abnormalities up to 2 years of age. One candidate mechanism underlying these clinical features is long-lasting alterations to dopamine (DA) neuron func...

Aging in rodents, monkeys, and man is correlated with a reduction in dopamine transporter (DAT) ligand binding and DAT function. Using Western blot techniques, we investigated whether the source of these age-related changes in DAT was correlated with decreases in DAT protein levels in the striatum, substantia nigra (SN), nucleus accumbens (NAc), an...

This chapter is intended for those who wish to gain a general knowledge of the principles, materials, and approaches that underlie the current methodologies being used to study drug-abuse issues in central nervous system (CNS) tissues using electrochemical techniques, which are often termed “voltammetric recordings.” We have not tried to be compreh...

Depolarizing stimuli increase catecholamine (CA) biosynthesis, tyrosine hydroxylase (TH) activity, and TH phosphorylation at Ser19, Ser31, and Ser40 in a Ca2+-dependent manner. However, the identities of the protein kinases that phosphorylate TH under depolarizing conditions are not known. Furthermore, although increases in Ser31 or Ser40 phosphory...

Electrical stimulation of the medial forebrain bundle increases (32)P incorporation into striatal tyrosine hydroxylase (TH) at Ser (19), Ser(31), and Ser(40). In the present studies, the effects of acute haloperidol and related drugs on sitespecific TH phosphorylation stoichiometry (PS) in the nigrostriatal and mesolimbic systems were determined by...