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Speranza L, di Porzio U, Viggiano D, de Donato A, Volpicelli F. Dopamine: The Neuromodulator of Long-Term Synaptic Plasticity, Reward and Movement Control. Cells 2021; 10:735. [PMID: 33810328 PMCID: PMC8066851 DOI: 10.3390/cells10040735] [Citation(s) in RCA: 93] [Impact Index Per Article: 31.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Revised: 03/20/2021] [Accepted: 03/23/2021] [Indexed: 01/11/2023] Open
Abstract
Dopamine (DA) is a key neurotransmitter involved in multiple physiological functions including motor control, modulation of affective and emotional states, reward mechanisms, reinforcement of behavior, and selected higher cognitive functions. Dysfunction in dopaminergic transmission is recognized as a core alteration in several devastating neurological and psychiatric disorders, including Parkinson's disease (PD), schizophrenia, bipolar disorder, attention deficit hyperactivity disorder (ADHD) and addiction. Here we will discuss the current insights on the role of DA in motor control and reward learning mechanisms and its involvement in the modulation of synaptic dynamics through different pathways. In particular, we will consider the role of DA as neuromodulator of two forms of synaptic plasticity, known as long-term potentiation (LTP) and long-term depression (LTD) in several cortical and subcortical areas. Finally, we will delineate how the effect of DA on dendritic spines places this molecule at the interface between the motor and the cognitive systems. Specifically, we will be focusing on PD, vascular dementia, and schizophrenia.
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Affiliation(s)
- Luisa Speranza
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA;
| | - Umberto di Porzio
- Institute of Genetics and Biophysics “Adriano Buzzati Traverso”, CNR, 80131 Naples, Italy
| | - Davide Viggiano
- Department of Translational Medical Sciences, Genetic Research Institute “Gaetano Salvatore”, University of Campania “L. Vanvitelli”, IT and Biogem S.c.a.r.l., 83031 Ariano Irpino, Italy; (D.V.); (A.d.D.)
| | - Antonio de Donato
- Department of Translational Medical Sciences, Genetic Research Institute “Gaetano Salvatore”, University of Campania “L. Vanvitelli”, IT and Biogem S.c.a.r.l., 83031 Ariano Irpino, Italy; (D.V.); (A.d.D.)
| | - Floriana Volpicelli
- Department of Pharmacy, School of Medicine and Surgery, University of Naples Federico II, 80131 Naples, Italy;
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Grant AH, Terminel MA, Ramos J, Alatorre LF, Castañeda E. Electrical Stimulation Evokes Rotational Behavior In Tandem with Exocytotic-like Increases in Dopamine Measured by In Vivo Intracerebral Microdialysis. J Neurosci Methods 2020; 346:108894. [PMID: 32771372 PMCID: PMC7606747 DOI: 10.1016/j.jneumeth.2020.108894] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Revised: 07/31/2020] [Accepted: 08/02/2020] [Indexed: 11/22/2022]
Abstract
BACKGROUND Electrical Stimulation is a traditional tool in neuroscience and is commonly used in vivo to evoke behavior and in vitro to study neural mechanisms. In vivo intracerebral microdialysis, also a traditional technique, is used to assay neurotransmitter release. However, the combination of these techniques is highly limited to studies using anesthetized animals; therefore, evoking and measuring exocytotic neurotransmitter release in awake models is lacking. Combining these techniques in an awake animal preparation is presented here with evidence to support the mechanistic action of electrical stimulation in vivo. NEW METHODS This report presents converging evidence to validate the combination of intracerebral electrical stimulation with microdialysis as a novel procedure to study exocytotic-like dopamine release in behaving animals. RESULTS It is shown that electrical stimulation of the medial forebrain bundle can be used to evoke frequency- and intensity-dependent exocytotic-like dopamine overflow and rotational behavior that are sensitive to Na+ channel blockade and Ca++ availability. COMPARISON WITH EXISTING METHODS Studies using modern techniques to evoke neurotransmitter release, combined with in vivo intracerebral microdialysis, and measured behavioral output are scarce. In contrast, commonly used pharmacological methods often are less precise and inefficient to evoke exocytotic dopamine release and behavior. Here we demonstrate, the combination of in vivo intracerebral microdialysis with electrical stimulation as a simple approach to simultaneously assess physiologically relevant neurotransmitter 'release' and behavior. CONCLUSIONS Research that aims to understand how dopamine neurotransmission is altered in behavioral disorders can utilize this innovative combination of electrical stimulation with in vivo intracerebral microdialysis.
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Affiliation(s)
- Alice H Grant
- Department of Psychology, University of Texas at El Paso, 500 W. University Ave, El Paso, TX, USA.
| | - Mabel A Terminel
- Department of Psychology, University of Texas at El Paso, 500 W. University Ave, El Paso, TX, USA.
| | - Jeremiah Ramos
- Department of Psychology, University of Texas at El Paso, 500 W. University Ave, El Paso, TX, USA.
| | - Luisa F Alatorre
- Department of Psychology, University of Texas at El Paso, 500 W. University Ave, El Paso, TX, USA.
| | - Edward Castañeda
- Department of Psychology, University of Texas at El Paso, 500 W. University Ave, El Paso, TX, USA; Department of Psychology, Arizona State University, Tempe, AZ, USA.
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Creed RB, Menalled L, Casey B, Dave KD, Janssens HB, Veinbergs I, van der Hart M, Rassoulpour A, Goldberg MS. Basal and Evoked Neurotransmitter Levels in Parkin, DJ-1, PINK1 and LRRK2 Knockout Rat Striatum. Neuroscience 2019; 409:169-179. [PMID: 31029729 DOI: 10.1016/j.neuroscience.2019.04.033] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Revised: 04/12/2019] [Accepted: 04/15/2019] [Indexed: 02/06/2023]
Abstract
Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized by the loss of neurons in the substantia nigra that project to the striatum and release dopamine (DA), which is required for normal movement. Common non-motor symptoms likely involve abnormalities with other neurotransmitters, such as serotonin, norepinephrine, acetylcholine, glycine, glutamate and gamma-aminobutyric acid (GABA). As part of a broad effort to provide better PD research tools, the Michael J. Fox Foundation for Parkinson's Research funded the generation and characterization of knockout (KO) rats for genes with PD-linked mutations, including PINK1, Parkin, DJ-1 and LRRK2. Here we extend the phenotypic characterization of these lines of KO rats to include in vivo microdialysis to measure both basal and potassium-induced release of the above neurotransmitters and their metabolites in the striatum of awake and freely moving rats at ages 4, 8 and 12 months compared to wild-type (WT) rats. We found age-dependent abnormalities in basal DA, glutamate and acetylcholine in PINK1 KO rats and age-dependent abnormalities in basal DA metabolites in Parkin and LRRK2 KO rats. Parkin KO rats had increased glycine release while DJ-1 KO rats had decreased glutamate release and increased acetylcholine release compared to WT rats. All lines except DJ-1 KO rats showed age-dependent changes in release of one or more neurotransmitters. Our data suggest these rats may be useful for studies of PD-related synaptic dysfunction and neurotransmitter dynamics as well as studies of the normal and pathogenic functions of these genes with PD-linked mutations.
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Affiliation(s)
- Rose B Creed
- Center for Neurodegeneration and Experimental Therapeutics, The University of Alabama at Birmingham, Birmingham, Alabama 35294; Department of Neurology, The University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Liliana Menalled
- The Michael J. Fox Foundation for Parkinson's Research, 111 West 33(rd) Street, 10(th) Floor, New York, NY 10001
| | - Bradford Casey
- The Michael J. Fox Foundation for Parkinson's Research, 111 West 33(rd) Street, 10(th) Floor, New York, NY 10001
| | - Kuldip D Dave
- The Michael J. Fox Foundation for Parkinson's Research, 111 West 33(rd) Street, 10(th) Floor, New York, NY 10001
| | | | - Isaac Veinbergs
- Brains On-Line, 7000 Shoreline Court, South San Francisco, CA 94080
| | | | | | - Matthew S Goldberg
- Center for Neurodegeneration and Experimental Therapeutics, The University of Alabama at Birmingham, Birmingham, Alabama 35294; Department of Neurology, The University of Alabama at Birmingham, Birmingham, Alabama 35294; Department of Neurobiology, The University of Alabama at Birmingham, Birmingham, Alabama 35294.
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Brodnik ZD, Double M, España RA, Jaskiw GE. L-Tyrosine availability affects basal and stimulated catecholamine indices in prefrontal cortex and striatum of the rat. Neuropharmacology 2017; 123:159-174. [PMID: 28571714 DOI: 10.1016/j.neuropharm.2017.05.030] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Revised: 05/22/2017] [Accepted: 05/26/2017] [Indexed: 12/15/2022]
Abstract
We previously found that L-tyrosine (L-TYR) but not D-TYR administered by reverse dialysis elevated catecholamine synthesis in vivo in medial prefrontal cortex (MPFC) and striatum of the rat (Brodnik et al., 2012). We now report L-TYR effects on extracellular levels of catecholamines and their metabolites. In MPFC, reverse dialysis of L-TYR elevated in vivo levels of dihydroxyphenylacetic acid (DOPAC) (L-TYR 250-1000 μM), homovanillic acid (HVA) (L-TYR 1000 μM) and 3-methoxy-4-hydroxyphenylglycol (MHPG) (L-TYR 500-1000 μM). In striatum L-TYR 250 μM elevated DOPAC. We also examined L-TYR effects on extracellular dopamine (DA) and norepinephrine (NE) levels during two 30 min pulses (P2 and P1) of K+ (37.5 mM) separated by t = 2.0 h. L-TYR significantly elevated the ratio P2/P1 for DA (L-TYR 125 μM) and NE (L-TYR 125-250 μM) in MPFC but lowered P2/P1 for DA (L-TYR 250 μM) in striatum. Finally, we measured DA levels in brain slices using ex-vivo voltammetry. Perfusion with L-TYR (12.5-50 μM) dose-dependently elevated stimulated DA levels in striatum. In all the above studies, D-TYR had no effect. We conclude that acute increases within the physiological range of L-TYR levels can increase catecholamine metabolism and efflux in MPFC and striatum. Chronically, such repeated increases in L-TYR availability could induce adaptive changes in catecholamine transmission while amplifying the metabolic cost of catecholamine synthesis and degradation. This has implications for neuropsychiatric conditions in which neurotoxicity and/or disordered L-TYR transport have been implicated.
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Affiliation(s)
- Zachary D Brodnik
- Drexel University College of Medicine, Department of Neurobiology and Anatomy, 2900 W. Queen Lane, Philadelphia, PA 19129, United States
| | - Manda Double
- Medical Research Service, Louis Stokes Cleveland DVAMC, 10701 East Blvd., Cleveland, OH 44106, United States
| | - Rodrigo A España
- Drexel University College of Medicine, Department of Neurobiology and Anatomy, 2900 W. Queen Lane, Philadelphia, PA 19129, United States
| | - George E Jaskiw
- Medical Research Service, Louis Stokes Cleveland DVAMC, 10701 East Blvd., Cleveland, OH 44106, United States; Dept. of Psychiatry, Case Western University Medical Center at W.O. Walker 10524 Euclid Ave, Cleveland, OH 44133, United States.
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Engel M, Snikeris P, Jenner A, Karl T, Huang XF, Frank E. Neuregulin 1 Prevents Phencyclidine-Induced Behavioral Impairments and Disruptions to GABAergic Signaling in Mice. Int J Neuropsychopharmacol 2015; 18:pyu114. [PMID: 26478928 PMCID: PMC4540095 DOI: 10.1093/ijnp/pyu114] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND Substantial evidence from human post-mortem and genetic studies has linked the neurotrophic factor neuregulin 1 (NRG1) to the pathophysiology of schizophrenia. Genetic animal models and in vitro experiments have suggested that altered NRG1 signaling, rather than protein changes, contributes to the symptomatology of schizophrenia. However, little is known about the effect of NRG1 on schizophrenia-relevant behavior and neurotransmission (particularly GABAergic and glutamatergic) in adult animals. METHOD To address this question, we treated adult mice with the extracellular signaling domain of NRG1 and assessed spontaneous locomotor activity and acoustic startle response, as well as extracellular GABA, glutamate, and glycine levels in the prefrontal cortex and hippocampus via microdialysis. Furthermore, we asked whether the effect of NRG1 would differ under schizophrenia-relevant impairments in mice and therefore co-treated mice with NRG1 and phencyclidine (PCP) (3 mg/kg). RESULTS Acute intraventricularly- or systemically-injected NRG1 did not affect spontaneous behavior, but prevented PCP induced hyperlocomotion and deficits of prepulse inhibition. NRG1 retrodialysis (10 nM) reduced extracellular glutamate and glycine levels in the prefrontal cortex and hippocampus, and prevented PCP-induced increase in extracellular GABA levels in the hippocampus. CONCLUSION With these results, we provide the first compelling in vivo evidence for the involvement of NRG1 signaling in schizophrenia-relevant behavior and neurotransmission in the adult nervous system, which highlight its treatment potential. Furthermore, the ability of NRG1 treatment to alter GABA, glutamate, and glycine levels in the presence of PCP also suggests that NRG1 signaling has the potential to alter disrupted neurotransmission in patients with schizophrenia.
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Ortega JE, Katner J, Davis R, Wade M, Nisenbaum L, Nomikos GG, Svensson KA, Perry KW. Modulation of neurotransmitter release in orexin/hypocretin-2 receptor knockout mice: a microdialysis study. J Neurosci Res 2011; 90:588-96. [PMID: 22038504 DOI: 10.1002/jnr.22781] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Revised: 07/13/2011] [Accepted: 08/04/2011] [Indexed: 11/09/2022]
Abstract
Orexinergic neurons are discretely localized within the lateral hypothalamus and have widespread projections to the whole brain. Here, the role of orexin/hypocretin-2 receptors (OX2) in modulating extracellular concentrations of neurotransmitters was evaluated in the hypothalamus and the prefrontal cortex (PFC) of OX2 knockout (KO) mice by using a microdialysis technique. In the hypothalamus, basal concentrations of norephinephrine (NE), acetylcholine (ACh), and histamine (Hist) were significantly higher in KO mice, whereas KCl perfusion (147 mM) resulted in significantly lesser increases in NE, ACh, and Hist release in KO compared with wild-type (WT) mice. No differences in basal concentrations or evoked release of serotonin (5-HT) or dopamine (DA) were found in the hypothalamus between genotypes. In the PFC, no differences in the basal concentrations of the studied neurotransmitters were found between genotypes. After KCl perfusion, significantly higher increases in NE, 5-HT, and DA release were found in KO compared with WT mice. No differences in the evoked release of ACh and Hist in the PFC were found between genotypes. The present results demonstrate that genetic deletion of OX2 receptors differentially modulates extracellular concentrations of distinct neurotransmitters in the somatodendritic region vs. a nerve terminal region of the orexinergic neurons. In the hypothalamus, an inhibitory role of the OX2 receptors in modulating basal concentrations of NE, ACh, and Hist was revealed, which probably accounts for the reduced responsiveness to KCl as well. In the PFC, the evoked release of the monoamines NE, 5-HT, and DA seems to be controlled negatively by OX2 receptors.
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Affiliation(s)
- Jorge E Ortega
- Eli Lilly and Co., Indianapolis, Indiana 46240-0510, USA.
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Shin SS, Bray ER, Zhang CQ, Dixon CE. Traumatic brain injury reduces striatal tyrosine hydroxylase activity and potassium-evoked dopamine release in rats. Brain Res 2010; 1369:208-15. [PMID: 21047500 DOI: 10.1016/j.brainres.2010.10.096] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2010] [Revised: 10/21/2010] [Accepted: 10/26/2010] [Indexed: 11/28/2022]
Abstract
There is increasing evidence that traumatic brain injury (TBI) induces hypofunction of the striatal dopaminergic system, the mechanisms of which are unknown. In this study, we analyzed the activity of striatal tyrosine hydroxylase (TH) in rats at 1 day, 1 week, and 4 weeks after TBI using the controlled cortical impact model. There were no changes in the level of TH phosphorylated at serine 40 site (pser40TH) at 1 day or 4 weeks. At 1 week, injured animals showed decreased pser40TH to 73.9±7.3% (p≤0.05) of sham injured rats. The in vivo TH activity assay showed no significant difference between injured and sham rats at 1 day. However, there was a decreased activity in injured rats to 62.1±8.2% (p≤0.05) and 68.8±6.2% (p≤0.05) of sham injured rats at 1 and 4 weeks, respectively. Also, the activity of protein kinase A, which activates TH, decreased at 1 week (injured: 87.8±2.8%, sham: 100.0±4.2%, p≤0.05). To study the release activity of dopamine after injury, potassium (80 mM)-evoked dopamine release was measured by microdialysis in awake, freely moving rats. Dialysates were collected and analyzed by high-performance liquid chromatography. There were no significant differences in dopamine release at 1 day and 4 weeks between sham and injured groups. At 1 week, there was a significant decrease (injured: 0.067±0.015 μM, sham: 0.127±0.027 μM, p≤0.05). These results suggest that TBI-induced dopamine neurotransmission deficits are, at least in part, attributable to deficits in TH activity.
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Affiliation(s)
- Samuel S Shin
- Brain Trauma Research Center, Department of Neurosurgery, University of Pittsburgh, 3434 Fifth Ave, Suite 201, Pittsburgh, PA 15260, USA
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Rodriguez VM, Thiruchelvam M, Cory-Slechta DA. Sustained exposure to the widely used herbicide atrazine: altered function and loss of neurons in brain monoamine systems. ENVIRONMENTAL HEALTH PERSPECTIVES 2005; 113:708-15. [PMID: 15929893 PMCID: PMC1257595 DOI: 10.1289/ehp.7783] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The widespread use of atrazine (ATR) and its persistence in the environment have resulted in documented human exposure. Alterations in hypothalamic catecholamines have been suggested as the mechanistic basis of the toxicity of ATR to hormonal systems in females and the reproductive tract in males. Because multiple catecholamine systems are present in the brain, however, ATR could have far broader effects than are currently understood. Catecholaminergic systems such as the two major long-length dopaminergic tracts of the central nervous system play key roles in mediating a wide array of critical behavioral functions. In this study we examined the hypothesis that ATR would adversely affect these brain dopaminergic systems. Male rats chronically exposed to 5 or 10 mg/kg ATR in the diet for 6 months exhibited persistent hyperactivity and altered behavioral responsivity to amphetamine. Moreover, when measured 2 weeks after the end of exposure, the levels of various monoamines and the numbers of tyrosine hydroxylase-positive (TH+) and -negative (TH-) cells measured using unbiased stereology were reduced in both dopaminergic tracts. Acute exposures to 100 or 200 mg/kg ATR given intraperitoneally to evaluate potential mechanisms reduced both basal and potassium-evoked striatal dopamine release. Collectively, these studies demonstrate that ATR can produce neurotoxicity in dopaminergic systems that are critical to the mediation of movement as well as cognition and executive function. Therefore, ATR may be an environmental risk factor contributing to dopaminergic system disorders, underscoring the need for further investigation of its mechanism(s) of action and corresponding assessment of its associated human health risks.
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Affiliation(s)
- Veronica M Rodriguez
- Environmental and Occupational Health Sciences Institute, and Department of Environmental and Occupational Medicine, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854, USA
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Purdom MS, Stanford JA, Currier TD, Gerhardt GA. Microdialysis studies of D-amphetamine-evoked striatal dopamine overflow in young versus aged F344 rats: effects of concentration and order of administration. Brain Res 2003; 979:203-9. [PMID: 12850587 DOI: 10.1016/s0006-8993(03)02922-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
In order to measure the effects of different concentrations of D-amphetamine (D-AMPH) infusions on striatal dopamine (DA) overflow in young versus aged rats, and to determine the influence of preceding infusions on subsequent stimuli, two microdialysis studies were conducted. In the first study, D-AMPH (100, 200, and 2000 microM) was infused in ascending order of concentration, while in the second study the order of administration was reversed. The order of administration significantly affected DA overflow and extracellular levels of 3,4-dihydroxyphenylacetic acid (DOPAC). Generally, DA overflow was greater for a given concentration when it was administered first in a sequence than when it was administered later in a sequence. The two age groups did not differ on measures of DA overflow. The order of administration also significantly influenced the effect of D-AMPH on extracellular DOPAC, as the D-AMPH-related decreases in DOPAC were greater for a concentration when it was administered earlier versus later in the sequence. This effect was greater in the young rats than in the aged rats. D-AMPH also resulted in diminished levels of DOPAC in the aged rats compared to the young rats. These results suggest that between-groups studies may be more appropriate for determining the effects of different concentrations of D-AMPH on striatal DA overflow. They also demonstrate that while some measures of stimulus-evoked DA overflow may not differ between young and aged F344 rats, extracellular regulation of striatal DA (as measured by changes in DOPAC) may be altered. These alterations may contribute to age-related decreases in motor function.
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Affiliation(s)
- Matthew S Purdom
- Department of Anatomy and Neurobiology, University of Kentucky Chandler Medical Center, 306 Davis Mills Bldg., 40536-0098, Lexington, KY, USA
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Cass WA, Harned ME, Bailey SL. Enhanced effects of 6-hydroxydopamine on evoked overflow of striatal dopamine in aged rats. Brain Res 2002; 938:29-37. [PMID: 12031532 DOI: 10.1016/s0006-8993(02)02481-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Nigrostriatal dopamine neurons degenerate during aging, and the excessive loss of dopamine neurons that occurs with Parkinson's disease is usually confined to older individuals. Although 6-hydroxydopamine lesioning of the nigrostriatal dopamine system is a common method for producing animal models of dopamine neuron degeneration, there have been relatively few studies that have examined the effects of 6-hydroxydopamine on the dopamine systems of aged animals. The present experiments were designed to determine if nigrostriatal dopamine neurons in aged rats are more sensitive to the neurotoxic effects of 6-hydroxydopamine than those of younger rats. Young (4-month-old), middle-aged (14-month-old) and aged (24-month-old) Fischer-344 rats were given a single injection of vehicle, 50 or 100 microg 6-hydroxydopamine into the right lateral ventricle. Three to four weeks later in vivo electrochemistry was used to measure potassium-evoked overflow of dopamine in the striatum. In the young rats the 50-microg dose had no significant effect on evoked overflow of dopamine in the striatum or on post-mortem levels of dopamine in the striatum or substantia nigra. The higher dose in the young animals diminished evoked overflow of dopamine as well as tissue levels of dopamine. In the aged rats both doses of 6-hydroxydopamine led to significant decreases in evoked overflow of striatal dopamine and in tissue levels of dopamine in the striatum and substantia nigra. These results suggest that dopamine neurons of aged Fischer-344 rats are more susceptible to the toxic effects of 6-hydroxydopamine than those of younger animals.
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Affiliation(s)
- Wayne A Cass
- Department of Anatomy and Neurobiology, MN-225 Chandler Medical Center, University of Kentucky College of Medicine, Lexington, KY 40536-0298, USA.
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