Dopaminergic Cells In Substantia Nigra Research Articles

Levodopa Rescues Retinal Function in the Transgenic A53T Alpha-Synuclein Model of Parkinson's Disease.

Loss of substantia nigra dopaminergic cells and alpha-synuclein (α-syn)-rich intraneuronal deposits within the central nervous system are key hallmarks of Parkinson's disease (PD). Levodopa (L-DOPA) is the current gold-standard treatment for PD. This study aimed to evaluate in vivo retinal changes in a transgenic PD model of α-syn overexpression and the effect of acute levodopa (L-DOPA) treatment. Anaesthetised 6-month-old mice expressing human A53T alpha-synuclein (HOM) and wildtype (WT) control littermates were intraperitoneally given 20 mg/kg L-DOPA (50 mg levodopa, 2.5 mg benserazide) or vehicle saline (n = 11-18 per group). In vivo retinal function (dark-adapted full-field ERG) and structure (optical coherence tomography, OCT) were recorded before and after drug treatment for 30 min. Ex vivo immunohistochemistry (IHC) on flat-mounted retina was conducted to assess tyrosine hydroxylase (TH) positive cell counts (n = 7-8 per group). We found that photoreceptor (a-wave) and bipolar cell (b-wave) ERG responses (p < 0.01) in A53T HOM mice treated with L-DOPA grew in amplitude more (47 ± 9%) than WT mice (16 ± 9%) treated with L-DOPA, which was similar to the vehicle group (A53T HOM 25 ± 9%; WT 19 ± 7%). While outer retinal thinning (outer nuclear layer, ONL, and outer plexiform layer, OPL) was confirmed in A53T HOM mice (p < 0.01), L-DOPA did not have an ameliorative effect on retinal layer thickness. These findings were observed in the absence of changes to the number of TH-positive amacrine cells across experiment groups. Acute L-DOPA treatment transiently improves visual dysfunction caused by abnormal alpha-synuclein accumulation. These findings deepen our understanding of dopamine and alpha-synuclein interactions in the retina and provide a high-throughput preclinical framework, primed for translation, through which novel therapeutic compounds can be objectively screened and assessed for fast-tracking PD drug discovery.

Trehalose Neuroprotective Effects on the Substantia Nigra Dopaminergic Cells by Activating Autophagy and Non-canonical Nrf2 Pathways.

Trehalose, as a natural disaccharide, is known as an autophagy inducer. The neuroprotective effects of trehalose in the rat model of Parkinson′s disease were the aim of the present study. Parkinson′s disease model was induced by injecting 6-hydroxydopamine (6-OHDA) in the striatum of male Wistar rats. Apomorphine-induced behavior and substantia nigra neuronal counts were applied to evaluate the neuroprotective effects of trehalose. The autophagy was studied using the expression of p62 and LC3II/LC3I ratio. In addition, the antioxidant effects of trehalose were assessed by analyzing the levels of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and also glutathione reductase (GR), glutathione peroxidase (GPx) and Catalase (CAT) enzymes. Moreover, the levels of 3, 4-dihydroxyphenylacetic acid (DOPAC) and dopamine (DA) were assessed.The behavioral test showed that trehalose in the treatment group reduced the damage to the substantial nigra dopaminergic neurons, which was characterized by improved motor and reduced rotations in the treatment group as compared with the lesion group. In the histological examinations of the treatment group, trehalose prevented the destruction of dopaminergic neurons. Trehalose treatments increased autophagy (high LC3II/LC3I ratio) and the expression of the p62 protein as well. Through p62-dependent manner, it led to increased nuclear translocation of Nrf2 transcription factor and elevated expression of downstream antioxidant enzymes, such as GR, GPx, and CAT, restoring DA and DOPAC contents of the cells. In the current study, trehalose simultaneously protects substantia nigra dopaminergic cells by activating both non-canonical p62/SQSTM1-Keap1-Nrf2 and autophagy pathways.

Therapeutic efficacy of olfactory stem cells in rotenone induced Parkinsonism in adult male albino rats

BackgroundOlfactory stem cells (OSCs) are found in the olfactory mucosa and olfactory bulb and have the capacity to proliferate and differentiate along multiple tissue lineages. Rotenone; widely used insecticide has a neurodegenerative effect on the dopaminergic cells of substantia nigra (SN) of midbrain producing Parkinsonism. The aim of this study is to isolate rat OSCs from olfactory mucosa and olfactory bulb, culture these OSCs in suitable medium to allow for their proliferation to be used in the treatment of Parkinsonism induced by rotenone. MethodsThe characteristics of OSCs, the effects of rotenone on the SN of midbrain and the curative effect of OSCs on the substantia nigra were determined morphologically, immunohistochemically, and by transmission electron microscopy. PKH 26; immunofluorescent dye was used as a cell tracer to locate the transplanted cells in host midbrain. ResultsOSCs were spindle shaped with irregular processes, and were positive for CD44 and Nestin and negative for CD34. Subcutaneous rotenone produced Parkinsonism through producing degeneration of the dopaminergic cells of SN of the midbrain. Transplantation of OSCs produced restoration of the normal structure of SN and dopaminergic cells and improves the clinical manifestations of Parkinsonism. ConclusionThese results indicate that, the isolated rat OSCs can proliferate and expand in vitro when culture in suitable medium and these cells can exert therapeutic effects in Parkinsonism by recruitment in SN and restoration of the structure and function of dopaminergic cells.

Cell survival and differentiation with nanocrystalline glass-like carbon using substantia nigra dopaminergic cells derived from transgenic mouse embryos.

Regenerative medicine requires, in many cases, physical supports to facilitate appropriate cellular architecture, cell polarization and the improvement of the correct differentiation processes of embryonic stem cells, induced pluripotent cells or adult cells. Because the interest in carbon nanomaterials has grown within the last decade in light of a wide variety of applications, the aim of this study was to test and evaluate the suitability and cytocompatibility of a particular nanometer-thin nanocrystalline glass-like carbon film (NGLC) composed of curved graphene flakes joined by an amorphous carbon matrix. This material is a disordered structure with high transparency and electrical conductivity. For this purpose, we used a cell line (SN4741) from substantia nigra dopaminergic cells derived from transgenic mouse embryos. Cells were cultured either in a powder of increasing concentrations of NGLC microflakes (82±37μm) in the medium or on top of nanometer-thin films bathed in the same culture medium. The metabolism activity of SN4741 cells in presence of NGLC was assessed using methylthiazolyldiphenyl-tetrazolium (MTT) and apoptosis/necrosis flow cytometry assay respectively. Growth and proliferation as well as senescence were demonstrated by western blot (WB) of proliferating cell nuclear antigen (PCNA), monoclonal phosphorylate Histone 3 (serine 10) (PH3) and SMP30 marker. Specific dopaminergic differentiation was confirmed by the WB analysis of tyrosine hydroxylase (TH). Cell maturation and neural capability were characterized using specific markers (SYP: synaptophysin and GIRK2: G-protein-regulated inward-rectifier potassium channel 2 protein) via immunofluorescence and coexistence measurements. The results demonstrated cell positive biocompatibility with different concentrations of NGLC. The cells underwent a process of adaptation of SN4741 cells to NGLC where their metabolism decreases. This process is related to a decrease of PH3 expression and significant increase SMP30 related to senescence processes. After 7 days, the cells increased the expression of TH and PCNA that is related to processes of DNA replication.On the other hand, cells cultured on top of the film showed axonal-like alignment, edge orientation, and network-like images after 7 days. Neuronal capability was demonstrated to a certain extent through the analysis of significant coexistence between SYP and GIRK2. Furthermore, we found a direct relationship between the thickness of the films and cell maturation. Although these findings share certain similarities to our previous findings with graphene oxide and its derivatives, this particular nanomaterial possesses the advantages of high conductivity and transparency. In conclusion, NGLC could represent a new platform for biomedical applications, such as for use in neural tissue engineering and biocompatible devices.

The effect of rotenone on the dopaminergic cells of the substantia nigra of the midbrain in the adult male albino rats

Background aims. Rotenone is a widely used insecticide has a neurodegenerative effect on the dopaminergic cells of substantia nigra (SN) of midbrain producing Parkinsonism. The aim of this study is to study the effects of rotenone when injected subcutaneously on the dopaminergic cells of the substantia nigra of the midbrain.Methods. The effects of rotenone on the SN of midbrain and the were determinedhistopathologically, immunohistochemically, and by transmission electron microscopy. Results. Subcutaneous rotenone produced Parkinsonism through producing degeneration of the dopaminergic cells of SN of the midbrain. Conclusion. These results indicate that, rotenone has a neurodegenerative effect on the dopaminergic cells of the substantia nigra of the midbrain producing parkinsonism

Activation of Transcription Factor MEF2D by Bis(3)-cognitin Protects Dopaminergic Neurons and Ameliorates Parkinsonian Motor Defects

Parkinson disease (PD) is characterized by the selective demise of dopaminergic (DA) neurons in the substantial nigra pars compacta. Dysregulation of transcriptional factor myocyte enhancer factor 2D (MEF2D) has been implicated in the pathogenic process in in vivo and in vitro models of PD. Here, we identified a small molecule bis(3)-cognitin (B3C) as a potent activator of MEF2D. We showed that B3C attenuated the toxic effects of neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) by activating MEF2D via multiple mechanisms. B3C significantly reduced MPP(+)-induced oxidative stress and potentiated Akt to down-regulate the activity of MEF2 inhibitor glycogen synthase kinase 3β (GSK3β) in a DA neuronal cell line SN4741. Furthermore, B3C effectively rescued MEF2D from MPP(+)-induced decline in both nucleic and mitochondrial compartments. B3C offered SN4741 cells potent protection against MPP(+)-induced apoptosis via MEF2D. Interestingly, B3C also protected SN4741 cells from wild type or mutant A53T α-synuclein-induced cytotoxicity. Using the in vivo PD model of C57BL/6 mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP), we showed that B3C maintained redox homeostasis, promoted Akt function activity, and restored MEF2D level in midbrain neurons. Moreover, B3C greatly prevented the loss of tyrosine hydroxylase signal in substantial nigra pars compacta DA neurons and ameliorated behavioral impairments in mice treated with MPTP. Collectedly, our studies identified B3C as a potent neuroprotective agent whose effectiveness relies on its ability to effectively up-regulate MEF2D in DA neurons against toxic stress in models of PD in vitro and in vivo.

Dopaminergic cell populations of the rat substantia nigra are differentially affected by essential fatty acid dietary restriction over two generations

Essential fatty acids play a crucial role in the activity of several neurotransmission systems, especially in the monoaminergic systems involved in cognitive and motor aspects of behavior. The present study investigated whether essential fatty acid dietary restriction over two generations could differentially affect dopaminergic cell populations located in the substantia nigra rostro-dorso-medial (SNrm) or caudo-ventro-lateral (SNcv) regions which display distinct neurochemical profile and vulnerability to lesions under selected pathological conditions. Wistar rats were raised from conception on control or experimental diets containing adequate or reduced levels of linoleic and α-linolenic fatty acids, respectively. Stereological methods were used to estimate both the number and soma size of tyrosine hydroxylase (TH)-immunoreactive neurons in the SNrm and SNcv. TH protein levels were assessed with Western blots. Long-term treatment with the experimental diet modified the fatty acid profile of midbrain phospholipids and significantly decreased TH protein levels in the ventral midbrain (3 fold), the number of TH-positive cells in the SNrm (∼20%) and the soma size of these neurons in both SNrm (∼20%) and SNcv (∼10%). The results demonstrate for the first time a differential sensitivity of two substantia nigra dopaminergic cell populations to unbalanced levels of essential fatty acids, indicating a higher vulnerability of SNrm to the harmful effects induced by docosahexaenoic acid brain deficiency.

Cognitive deficits in animal models of basal ganglia disorders

The two most common neurological disorders of the basal ganglia are Parkinson's disease (PD) and Huntington's disease (HD). The most overt symptoms of these diseases are motoric, reflecting the loss of the striatal medium spiny neurons in HD and ascending substantia nigra dopaminergic cells in PD. However, both disease processes induce insidious psychiatric and cognitive syndromes that can manifest well in advance of the onset of motor deficits. These early deficits provide an opportunity for prophylactic therapeutic intervention in order to retard disease progression from the earliest possible point. In order to exploit this opportunity, animal models of HD and PD are being probed for the specific cognitive deficits represented in the disease states. At the neuronal level, these deficits are typically, but not exclusively, mediated by disruption of parallel corticostriatal loops that integrate motor information with sensory and higher order, "executive" cognitive functions. Dysfunction in these systems can be probed with sensitive behavioural tests that selectively probe these cognitive functions in mouse models with focal lesions of striatal or cortical regions, or of specific neurotransmitter systems. Typically these tests were designed and validated in rats. With the advent of genetically modified mouse models of disease, validated tests provide an opportunity to screen mouse models of disease for early onset cognitive deficits. This review seeks to draw together the literature on cognitive deficits in HD and PD, to determine the extent to which these deficits are represented in the current animal models of disease, and to evaluate the viability of selecting cognitive deficits as potential therapeutic targets. This article is part of a Special Issue entitled 'Animal Models'.

An NR2B-Dependent Decrease in the Expression of trkB Receptors Precedes the Disappearance of Dopaminergic Cells in Substantia Nigra in a Rat Model of Presymptomatic Parkinson's Disease

Compensatory changes occurring during presymptomatic stages of Parkinson's disease (PD) would explain that the clinical symptoms of the disease appear late, when the degenerative process is quite advanced. Several data support the proposition that brain-derived neurotrophic factor (BDNF) could play a role in these plastic changes. In the present study, we evaluated the expression of the specific BDNF receptor, trkB, in a rat model of presymptomatic PD generated by intrastriatal injection of the neurotoxin 6-OHDA. Immunohistochemical studies revealed a decrease in trkB expression in SN pars compacta (SNc) seven days after 6-OHDA injection. At this time point, no change in the number of tyrosine hydroxylase (TH) immunoreactive (TH-IR) cells is detected, although a decrease is evident 14 days after neurotoxin injection. The decrease in TH-positive cells and trkB expression in SNc was significantly prevented by systemic administration of Ifenprodil, a specific antagonist of NR2B-containing NMDA receptors. Therefore, an NR2B-NMDA receptor-dependent decrease in trkB expression precedes the disappearance of TH-IR cells in SNc in response to 6-OHDA injection. These results support the idea that a functional coupling between NMDA receptors and BDNF/trkB signalling may be important for the maintenance of the dopaminergic phenotype in SNc during presymptomatic stages of PD.

Gene Expression Profiling of Embryonic Human Neural Stem Cells and Dopaminergic Neurons from Adult Human Substantia Nigra

Neural stem cells (NSC) with self-renewal and multipotent properties serve as an ideal cell source for transplantation to treat neurodegenerative insults such as Parkinson's disease. We used Agilent's and Illumina Whole Human Genome Oligonucleotide Microarray to compare the genomic profiles of human embryonic NSC at a single time point in culture, and a multicellular tissue from postmortem adult substantia nigra (SN) which are rich in dopaminergic (DA) neurons. We identified 13525 up-regulated genes in both cell types of which 3737 (27.6%) genes were up-regulated in the hENSC, 4116 (30.4%) genes were up-regulated in the human substantia nigra dopaminergic cells, and 5672 (41.93%) were significantly up-regulated in both cell population. Careful analysis of the data that emerged using DAVID has permitted us to distinguish several genes and pathways that are involved in dopaminergic (DA) differentiation, and to identify the crucial signaling pathways that direct the process of differentiation. The set of genes expressed more highly at hENSC is enriched in molecules known or predicted to be involved in the M phase of the mitotic cell cycle. On the other hand, the genes enriched in SN cells include a different set of functional categories, namely synaptic transmission, central nervous system development, structural constituents of the myelin sheath, the internode region of axons, myelination, cell projection, cell somata, ion transport, and the voltage-gated ion channel complex. Our results were also compared with data from various databases, and between different types of arrays, Agilent versus Illumina. This approach has allowed us to confirm the consistency of our obtained results for a large number of genes that delineate the phenotypical differences of embryonic NSCs, and SN cells.

Distribution of Na/K‐ATPase alpha 3 isoform, a sodium‐potassium P‐type pump associated with rapid‐onset of dystonia parkinsonism (RDP) in the adult mouse brain

The Na(+)/K(+)-ATPase1 alpha subunit 3 (ATP1α(3)) is one of many essential components that maintain the sodium and potassium gradients across the plasma membrane in animal cells. Mutations in the ATP1A3 gene cause rapid-onset of dystonia parkinsonism (RDP), a rare movement disorder characterized by sudden onset of dystonic spasms and slowness of movement. To achieve a better understanding of the pathophysiology of the disease, we used immunohistochemical approaches to describe the regional and cellular distribution of ATP1α(3) in the adult mouse brain. Our results show that localization of ATP1α(3) is restricted to neurons, and it is expressed mostly in projections (fibers and punctuates), but cell body expression is also observed. We found high expression of ATP1α(3) in GABAergic neurons in all nuclei of the basal ganglia (striatum, globus pallidus, subthalamic nucleus, and substantia nigra), which is a key circuitry in the fine movement control. Several thalamic nuclei structures harboring connections to and from the cortex expressed high levels of the ATP1α(3) isoform. Other structures with high expression of ATP1α(3) included cerebellum, red nucleus, and several areas of the pons (reticulotegmental nucleus of pons). We also found high expression of ATP1α(3) in projections and cell bodies in hippocampus; most of these ATP1α(3)-positive cell bodies showed colocalization to GABAergic neurons. ATP1α(3) expression was not significant in the dopaminergic cells of substantia nigra. In conclusion, and based on our data, ATP1α(3) is widely expressed in neuronal populations but mainly in GABAergic neurons in areas and nuclei related to movement control, in agreement with RDP symptoms.

6-Hydroxydopamine induced apoptosis of dopaminergic cells in the rat substantia nigra.

The pathologic hallmark of Parkinson's disease is the dopaminergic cell death in the substantia nigra (SN). The cause of the cell death is, however, unknown. Even the question on whether the cells die by apoptosis or necrosis has not been answered with certainty. In 6-Hydroxydopamine induced Parkinsonian rats, the present study observed apoptotic nuclei from 1 day to 14 days after lesioning, using the TdT(terminal deoxynucleotidyl transferase)-mediated dUTP-biotin nick-end labeling method. Tyrosine hydroxylase immunohistochemistry and haematoxylin staining further revealed that these apoptotic cells are dopaminergic cells in the substantia nigra. The results suggest that dopaminergic cells in SN undergo apoptosis in the rat model of Parkinson's disease.

Neuroprotection and Neuronal Differentiation Studies Using Substantia Nigra Dopaminergic Cells Derived from Transgenic Mouse Embryos

The major pathological lesion of Parkinson's disease (PD) is the selective cell death of dopaminergic (DA) neurons in substantia nigra (SN). Although the initial cause and subsequent molecular signaling mechanisms leading to DA cell death underlying the PD process remain elusive, brain-derived neurotrophic factor (BDNF) is thought to exert neuroprotective as well as neurotrophic roles for the survival and differentiation of DA neurons in SN. Addressing molecular mechanisms of BDNF action in both primary embryonic mesencephalic cultures and in vivo animal models has been technically difficult because DA neurons in SN are relatively rare and present with many heterogeneous cell populations in midbrain. We have developed and characterized a DA neuronal cell line of embryonic SN origin that is more accessible to molecular analysis and can be used as an in vitro model system for studying SN DA neurons. A clonal SN DA neuronal progenitor cell line SN4741, arrested at an early DA developmental stage, was established from transgenic mouse embryos containing the targeted expression of the thermolabile SV40Tag in SN DA neurons. The phenotypic and morphological differentiation of the SN4741 cells could be manipulated by environmental cues in vitro. Exogenous BDNF treatment produced significant neuroprotection against 1-methyl-4-phenylpyridinium, glutamate, and nitric oxide-induced neurotoxicity in the SN4741 cells. Simultaneous phosphorylation of receptor tyrosine kinase B accompanied the neuroprotection. This SN DA neuronal cell line provides a unique model system to circumvent the limitations associated with primary mesencephalic cultures for the elucidation of molecular mechanisms of BDNF action on DA neurons of the SN.

Expression of acetylcholinesterase messenger RNA in human brain: An in situ hybridization study

The distribution of messenger RNA coding for acetylcholinesterase was studied in human post mortem brain and rhesus monkey by in situ hybridization histochemistry and compared to the distribution of acetylcholinesterase activity. Acetylcholinesterase messenger RNA had—similar to acetylcholinesterase enzymatic activity—a widespread distribution in human brain. Acetylcholinesterase messenger RNA positive cells corresponded to perikarya rich in acetylcholinesterase activity in most but not all regions. Examples for mismatches included the inferior olive and human cerebellar cortex. The presence of hybridization signals in cerebral cortex and an enrichment in layer III and V of most isocortical areas confirmed that perikaryal acetylcholinesterase in cerebral cortex is of postsynaptic origin and not derived from cholinergic projections. In striatum the expression of high levels of acetylcholinesterase messenger RNA was restricted to a small population of large striatal neurons. In addition, low levels of expression were found in most medium sized striatal neurons. Cholinergic neurons tended to express high levels of acetylcholinesterase messenger RNA whereas in cholinoceptive neurons the levels were moderate to low. However, some noncholinergic neurons like dopaminergic cells in substantia nigra, noradrenergic cells in locus coeruleus, serotoninergic cells in raphédorsalis, GABAergic cells in thalamic reticular nucleus, granular cells in cerebellar cortex and pontine relay neurons expressed levels comparable to cholinergic neurons in basal forebrain. It is suggested that neurons expressing high levels of acetylcholinesterase messenger RNA may synthesize acetylcholinesterase for axonal transport whereas neurons with an expression of acetylcholinesterase confined to somatodendritic regions tend to contain lower levels of acetylcholinesterase messenger RNA.

Fibroblast growth factors enhance dopamine fiber formation from nigral grafts

Members of the fibroblast growth factor (FGF) family have earlier been shown to exert potent trophic effects on cells of both the central and peripheral nervous system. The presence of FGF-1 and -2 (FGF-1, acidic FGF; FGF-2, basic FGF) has recently been demonstrated in the dopaminergic cells of substantia nigra in rat and FGF-2 has been shown to be able to increase survival and promote neurite outgrowth of cultured mesencephalic neurons. In the present study, we have investigated possible trophic effects of FGF-1 and FGF-2 on developing rat ventral mesencephalon of different fetal stages by utilizing the in vivo method of intraocular transplantation to sympathetically denervated hosts. Survival and growth of developing grafts after growth factor treatment was followed in oculo. The Falck-Hillarp technique was used for evaluation of catecholaminergic fiber outgrowth into the host iris in whole-mount preparations. FGF-2 significantly increased the volume of the mesencephalic grafts when compared to grafts treated with the vehicle alone. The mean volume of FGF-1-treated grafts was larger than that of control grafts, but this difference was not statistically significant. FGF-1 significantly increased the area of outgrowth of dopaminergic fibers into the host iris without a corresponding increase in the number of dopaminergic neurons, as evaluated by TH immunohistochemistry. FGF-2 had no effect on dopaminergic fiber outgrowth on grafted E14 ventral mesencephalon but it did have a significant effect on fiber outgrowth from E15 and E16 grafts. Moreover, the FGF-2 treated E16 grafts contained a larger number of dopaminergic neurons as compared to controls. These findings suggest that both FGF-1 and FGF-2 may exert trophic effects on dopaminergic neurons of the ventral mesencephalon in vivo. The two FGF's enhance the outgrowth of histochemically verified catecholamine-containing nerve fibers from grafted substantia nigra neurons with factor specific patterns.

Role of the subthalamic nucleus in the regulation of nigral dopamine neuron activity.

The influence of subthalamic nucleus (STN) afferents on dopaminergic (DA) neurons of the rat substantia nigra (SN) was investigated. Hemisections of the brain placed between the STN and the SN or located anterior to the STN caused an increase in the firing rate of DA cells without producing significant changes in their firing pattern. In contrast, electrolytic and ibotenic acid lesions of the STN resulted in 93% and 49% reductions, respectively, in the level of burst firing without affecting the firing rate of DA cells recorded in the lateral SN. Furthermore, procedures which interrupted the STN input to the SN produced rapid pacemaker-like firing in 18% of the lateral SN DA neurons recorded. Activation of the STN using single pulses of electrical stimulation caused: 1) a 20-50 msec inhibition of DA cell firing followed by an excitation, which in 35% of DA cells was accompanied by spikes occurring in a burst-like pattern, and 2) a short-latency inhibition lasting 5-25 msec in 75% of non-DA SN zona reticulata (ZR) neurons. On the other hand, stimulation of the STN for 1 minute at 20 Hz resulted in an initial decrease in DA cell burst firing followed by elevated firing rates and increased burst firing by 30-60 minutes after the stimulation. Pharmacological activation of the STN by infusion of bicuculline caused a rapid inhibition of DA cells followed by a two-fold increase in burst firing 6-14 minutes later, whereas SN ZR cells responded with an elevation in firing rate which dissipated in 6-14 minutes. Muscimol-induced STN inhibition produced complimentary biphasic changes in SN neuron firing: 1) an initial increase followed by a decrease in burst firing and firing rate of DA neurons and 2) a rapid inhibition followed by an excitation of ZR cells over a similar time course. Thus, the STN appears to exert a dual action on SN DA cells: 1) initial inhibition possibly mediated through STN excitation of the inhibitory SN ZR projections to DA cells, and 2) a facilitation of burst firing which may be a direct effect of excitatory STN afferents.

Does cholecystokinin colocalize with dopamine in the human substantia nigra?

In situ hybridization was used to examine the distribution of neurons containing cholecystokinin (CCK) mRNA in human, monkey and rat brain. In rat and monkey brain CCK mRNA was visualized in the substantia nigra pars compacta and in the ventral tegmental area. The dopaminergic cell bodies in the human substantia nigra did not however show detectable amounts CCK mRNA. Low levels of CCK mRNA were observed in the nucleus paranigralis, the human equivalent of the rodent ventral tegmental area. High levels of CCK mRNA were seen in other regions of the same brains including the cortex and the hippocampus. Thus, the adult human substantia nigra dopaminergic cells, in contrast to primate and rodent substantia nigra, do not express CCK. These results question the hypothesis of an involvement of CCK in the regulation of dopaminergic neurons and help to explain the absence of decreased CCK levels in the caudate and putamen of Parkinson's disease victims.