Neuroanatomical distribution of CXCR4 in adult rat brain and its localization in cholinergic and dopaminergic neurons

Accumulating evidence supports a role of chemokines and their receptors in brain function. Up to now scarce evidence has been given of the neuroanatomical distribution of chemokine receptors. Although it is widely accepted that chemokine receptors are present on glial cells, especially in pathological conditions, it remains unclear whether they are constitutively present in normal rat brain and whether neurons have the potential to express such chemokine receptors. CXCR4, a G protein-coupled receptor for the chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) was reported to have possible implications in brain development and AIDS-related dementia. By dual immunohistochemistry on brain sections, we clearly demonstrate that CXCR4 is constitutively expressed in adult rat brain, in glial cells (astrocytes, microglia but not oligodendrocytes) as well as in neurons. Neuronal expression of CXCR4 is mainly found in cerebral cortex, caudate putamen, globus pallidus, substantia innominata, supraoptic and paraventricular hypothalamic nuclei, ventromedial thalamic nucleus and substantia nigra. Using confocal microscopy, a differential distribution of CXCR4 in neuronal perikarya and dendrites can be observed according to the brain structure. Furthermore, this work demonstrates for the first time the coexistence of a chemokine receptor with classical neurotransmitters. A localization of CXCR4 is thus observed in neuronal cell bodies expressing choline acetyltransferase-immunoreactivity in the caudate putamen and substantia innominata, as well as in tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta. In conclusion, the constitutive neuronal CXCR4 expression suggests that SDF-1/CXCL12 could be involved in neuronal communication and possibly linked up with cholinergic and dopaminergic neurotransmission and related disorders.     

Highly regionalized distribution of stromal cell-derived factor-1/CXCL12 in adult rat brain: constitutive expression in cholinergic, dopaminergic and vasopressinergic neurons

The stromal cell-derived factor-1 (SDF-1)/CXCL12 and its receptor CXCR4 are key modulators of immune functions. In the nervous system, SDF-1/CXCL12 is crucial for neuronal guidance in developing brain, intercellular communication and the neuropathogenesis of acquired immunodeficiency syndrome. However, cerebral functions of SDF-1/CXCL12 in adult brain are poorly understood. The understanding of its role in the adult brain needs a detailed neuroanatomical mapping of SDF-1/CXCL12. By dual immunohistochemistry we demonstrate that this chemokine is constitutively expressed not only in astrocytes and microglia but also in neurons, in discrete neuroanatomical regions. Indeed, neuronal expression of SDF-1/CXCL12 is mainly found in cerebral cortex, substantia innominata, globus pallidus, hippocampus, paraventricular and supraoptic hypothalamic nuclei, lateral hypothalamus, substantia nigra and oculomotor nuclei. Moreover, we provide the first evidence that SDF-1/CXCL12 is constitutively expressed in cholinergic neurons in the medial septum and substantia innominata and in dopaminergic neurons in substantia nigra pars compacta and the ventral tegmental area. Interestingly we also show, for the first time, a selective co-localization of SDF-1/CXCL12 with vasopressin-expressing neurons in the supraoptic and paraventricular hypothalamic nuclei. In addition, in the lateral hypothalamic area, SDF-1/CXCL12 was found to be located on melanin concentrating hormone-expressing neurons. Altogether, these original data suggest that SDF-1/CXCL12 could be a modulatory neuropeptide regulating both central cholinergic and dopaminergic systems. In addition, a key role for SDF-1/CXCL12 in neuroendocrine regulation of vasopressin-expressing neurons represents an exciting new field of research.     

CXCR4 and CXCL12 Expression is Increased in the Nigro-Striatal System of Parkinson’s Disease

Except for a handful of inherited cases related to known gene defects, Parkinson’s disease (PD) is a sporadic neurodegenerative disease of unknown etiology. There is increasing evidence that inflammation and proliferation of microglia may contribute to the neuronal damage seen in the nigro-striatal dopaminergic system of PD patients. Microglia events that participate in neuronal injury include the release of pro-inflammatory and neurotoxic factors. Characterizing these factors may help to prevent the exacerbation of PD symptoms or to remediate the disease progression. In rodents, the nigro-striatal system exhibits high expression of the chemokine receptor CXCR4. Its natural ligand CXCL12 can promote neuronal apoptosis. Therefore, the present study investigated the expression of CXCR4 and CXCL12 in post-mortem brains of PD and control (non-PD) individuals and in an animal model of PD. In the human substantia nigra (SN), CXCR4 immunoreactivity was high in dopaminergic neurons. Interestingly, the SN of PD subjects exhibited higher expression of CXCR4 expression and CXCL12 than control subjects despite the loss of dopamine (DA) neurons. This effect was accompanied by an increase in activated microglia. However, results from post-mortem brains may not provide indication as to whether CXCL12/CXCR4 can cause the degeneration of DA neurons. To examine the role of these chemokines, we determined the levels of CXCL12 and CXCR4 in the SN of MPTP-treated mice. MPTP produced a time-dependent up-regulation of CXCR4 that preceded the loss of DA neurons. These results suggest that CXCL12/CXCR4 may participate in the etiology of PD and indicate a new possible target molecule for PD.     

止颤汤干预神经干细胞移植帕金森病大鼠脑内多巴胺及其代谢产物的变化*

背景：如何促进脑内多巴胺含量的增加以及减少多巴胺的代谢,是治疗帕金森病的热点所在。 目的：从多巴胺代谢途径角度观察止颤汤对神经干细胞移植帕金森病大鼠的脑黑质中多巴胺及其代谢产物含量的变化。 方法：以大鼠脑立体定位和1-甲基-4-苯基-1,2,3,6-四氢吡啶建立帕金森病大鼠模型。应用高效液相色谱法测定帕金森病大鼠中脑多巴胺及其代谢产物的含量。 结果与结论：止颤汤可以提高神经干细胞移植后帕金森病大鼠中脑多巴胺及其代谢产物双羟苯乙酸的含量,但对代谢产物高香草酸无明显影响。通过促进帕金森病大鼠干细胞移植后神经干细胞的存活,使之定向分化为多巴胺能神经元并分泌多巴胺,同时抑制多巴胺分解达到治疗作用。     

Human immunodeficiency virus type 1 in the central nervous system leads to decreased dopamine in different regions of postmortem human brains

Human immunodeficiency virus type 1 (HIV-1) invades the central nervous system (CNS) shortly after infection and becomes localized in varying concentrations in different brain regions, the most vulnerable is the basal ganglia (BG). It is hypothesized that HIV-1-mediated neuropathogenesis involves degeneration of dopaminergic neurons in the substantia nigra and the loss of dopaminergic terminals in the BG, leading to deficits in the central dopaminergic activity, resulting in progressive impairment of neurocognitive and motor functions. In the era of highly active antiretroviral therapy (HAART), although the incidence of HIV-associated dementia (HAD) has decreased, the neurocognitive and neuropsychological deficits continue to persist after HAART. In this study, We investigated the impact of HIV-1 on dopaminergic activity with respect to concentrations of dopamine (DA) and homovanillic acid (HVA) in different regions of postmortem human brains of HIV-1negative and HIV-1+ individuals and their relationship to neurocognitive impairment. We found that in HIV-1+ as well as HIV-negative cases, dopamine and HVA concentrationsin ranged widely in different brain regions. In HIV-negative brain regions, the highest concentration of DA was found in putamen, caudate, substantia nigra, and the basal ganglia. In HIV-1+ cases, there was a significant decrease in DA levels in caudate nucleus, putamen, globus pallidus, and substantia nigra compared to that in HIV-negative cases. In HIV-1+ cases, a strong correlation was found between DA levels in substantia nigra and other brain regions. Concentration of HVA in HIV-negative cases was also highest in the regions containing high dopamine levels. However, no significant decrease in regional HVA levels was found in HIV-1+ cases. HIV-1 RNA load (nondetectable [ND] to log10 6.9 copies/g tissue) also ranged widely in the same brain regions of HIV-1+ cases. Interestingly, the brain regions having the highest HIV-1 RNA had the maximum decrease in DA levels. Age, gender, ethnicity, and postmortem interval were not correlated with decrease in DA levels. Profile of DA, HVA, and HIV-1 RNA levels in the brain regions of HIV-1+ individuals treated with HAART was similar to those not treated with HAART. A majority of HIV-1+ individuals had variable degrees of neurocognitive impairments, but no specific relationship was found between the regional DA content and severity of neurocognitive deficits. These findings suggest widespread deficits in dopamine in different brain regions of HIV-1-infected cases, and that these deficits may be the results of HIV-1-induced neurodegeneration in the subcortical regions of human brain.     

A potential target for the treatment of Parkinson's disease: Effect of lateral habenula lesions

ObjectiveParkinson's disease (PD) is a progressive neurodegenerative movement disorder that is caused predominantly by the degeneration of the nigrostriatal dopaminergic pathway. Lateral habenula (LHb) has efferent projections that terminate in the substantia nigra pars compacta (SNpc) and electrical stimulation of the LHb effectively suppresses the activity of dopamine-containing neurons in the SNpc. This study was aimed to investigate whether LHb lesions can ameliorate the syndromes of PD via affecting the activities of SNpc neurons in 6-hydroxydopamine (6-OHDA)-induced PD model rats.MethodsConcentrations of dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum, which is the area projected by the SNpc dopaminergic neurons were assayed by high-performance liquid chromatography (HPLC) coupled with fluorescence detection. The immunohistochemical method was applied to detect the numbers of tyrosine hydroxylase (TH)-positive cells in the substantia nigra.ResultsThe results showed that LHb lesions induced a significant reduction in apomorphine-induced rotational behavior. The DA, DOPAC and HVA levels in the striatum of PD model rats were increased by the LHb lesions.ConclusionTherefore, we speculate that the LHb lesions induced a significant amelioration in motor disorders via increasing the DA levels in the striatum, which may lead to a potential therapeutic strategy for the treatment of PD.     

Release of dopamine evoked by electrical stimulation of the motor and visual areas of the cerebral cortex in both caudate nuclei and in the substantia nigra in the cat

The effects of unilateral focal electrical stimulation of the deep cerebellar nuclei on the activity of the nigrostriatal dopaminergic neurons on both sides of the brain were examined in halothane anaesthetized cats. For this purpose, push-pull cannulae were inserted into both caudate nuclei and both substantia nigrae, and the release of [3H] dopamine ([3H]DA) continuously formed from [3,5-3H]L-tyrosine was estimated in superfusates. The unilateral electrical stimulation of the right cerebellar dentate nucleus induced a long-lasting increase in the release of [3H]DA in the left caudate nucleus and a simultaneous decrease in the release of [3H]transmitter in the right caudate nucleus. These changes were associated with opposite fluctuations in the release of [3H]DA from the corresponding substantia nigrae. Thus, the electrical stimulation of the right dentate nucleus induced a pronounced decrease in the release of the [3H]-amine in the [3H]transmitter in the corresponding substantia nigra, whereas the activity of the contralateral substantia nigra, whereas the release in the ipsilateral substantia nigra was simultaneously increased. In contrast, the unilateral electrical stimulation of the right cerebellar fastigial nucleus resulted only in an increased release of [3H]DA in the ipsilateral (right) caudate nucleus, associated with a decreased release of the [3H]transmitter in the corresponding substantia nigra, whereas the activity of the contralateral (left) dopaminergic system was not significantly affected. These results support a direct functional interaction between the cerebellum and the basal ganglia. They also suggest that the release of DA from dopaminergic axonal terminals is inversely correlated to the extent of the transmitter release from dendrites.     

Involvement of prolactin, vasopressin and opioids in post-ictal antinociception induced by electroshock in rats

The local and endogenous nicotinic neuronal transmissions of dopaminergic neurons in the substantia nigra were confirmed electrophysiologically using a slice-patch technique. After identifying dopaminergic neurons based on their electrophysiological characteristics, miniature postsynaptic inward currents were recorded in the presence of atropine (a muscarinic acetylcholine receptor antagonist), bicuculline (a GABA receptor antagonist) and L-glutamic acid diethyl ester (GDEE) (a non-selective glutamate receptor antagonist). Under conditions that eliminated muscarinic, GABAergic and glutamatergic synaptic transmissions, we found miniature currents that were inhibited by the specific neuronal nicotinic receptor antagonists, dihydro-beta-erythroidine (DHbetaE) and/or methyllycaconitine (MLA) (selective alpha4beta2 and/or alpha7 nicotinic acetylcholine receptor antagonists, respectively). Under the same extracellular conditions, local stimulations in the vicinity of a target neuron evoked excitatory postsynaptic inward currents (EPSCs). These EPSCs were elicited in an extracellular Ca(2+) dependent manner and were also blocked by DHbetaE and/or MLA. These results suggest that dopaminergic neurons in the substantia nigra receive excitatory cholinergic inputs that are mediated via at least two types of postsynaptic nicotinic receptors, namely alpha7 and alpha4beta2 subtypes.     

GDNF improves dopamine function in the substantia nigra but not the putamen of unilateral MPTP-lesioned rhesus monkeys

Microdialysis measurements of dopamine (DA) and DA metabolites were carried out in the putamen and substantia nigra of unilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned rhesus monkeys that received intraventricular injections of vehicle or glial-derived neurotrophic factor (GDNF, 300 μg) 3 weeks prior to the microdialysis studies. Following behavioral measures in the MPTP-lesioned monkeys, they were anesthetized with isoflurane and placed in a stereotaxic apparatus. Magnetic resonance imaging (MRI)-guided sterile stereotaxic procedures were used for implantations of the microdialysis probes. Basal extracellular levels of DA and the DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were found to be decreased by >95% in the right putamen of the MPTP-lesioned monkeys as compared to normal animals. In contrast, basal DA levels were not significantly decreased, and DOPAC and HVA levels were decreased by only 65% and 30%, respectively, in the MPTP-lesioned substantia nigra. Significant reductions in -amphetamine-evoked DA release were also observed in the MPTP-lesioned substantia nigra and putamen of the monkeys as compared to normal animals. A single intraventricular administration of GDNF into one group of MPTP-lesioned monkeys elicited improvements in the parkinsonian symptoms in these animals at 2–3 weeks post-administration. In addition, -amphetamine-evoked overflow of DA was significantly increased in the substantia nigra but not the putamen of MPTP-lesioned monkeys that had received GDNF. Moreover, post-mortem brain tissue studies showed increases in whole tissue levels of DA and DA metabolite levels primarily within the substantia nigra in MPTP-lesioned monkeys that had received GDNF. Taken together, these data support that single ventricular infusions of GDNF produce improvements in motoric behavior in MPTP-lesioned monkeys that correlate with increases in DA neuronal function that are localized to the substantia nigra and not the putamen.     

The dorsal and medial raphe projections to the substantia nigra in the rat: Electrophysiological, biochemical and behavioural observations

Electrophysiological experiments have been performed in urethane anaesthetized rats to investigate the projections from the dorsal (DRN) and medial raphe nuclei (MRN) to the substantia nigra. The biochemical and behavioural effects following discrete electrolytic lesions in the dorsal and medial raphe have also been investigated.Stimulation of the DRN produced predominantly inhibition of spontaneous activity of single neurones in the substantia nigra though some neurones were also excited. Bilateral stimulation of the substantia nigra produced antidromic spikes in DRN and MRN neurones.Lesions of the DRN and MRN produced a significant reduction in substantia nigra 5-HT concentration. Additionally, DRN lesions reduced striatal 5-HT, while MRN lesions reduced hippocampal 5-HT. Both lesions increased substantia nigra HVA concentration but did not affect DA concentration. Neither DRN nor MRN lesions affected striatal HVA, although DA levels were significantly elevated after 14 days.Animals with DRN lesions explored more than controls or MRN-lesioned animals. However, this behaviour was transient and was not observed after 14 days. On the other hand, MRN-lesioned animals were significantly hyperactive.These observations suggest that the substantia nigra receives a direct monosynaptic inhibitory input from the DRN and MRN and that these pathways use 5-HT as a neurotransmitter serving to tonically inhibit dopaminergic neurones. While 5-HT and dopamine appear to be involved in the control of motor behaviour, the precise relationship between these serotoninergic and dopaminergic systems in this respect is unclear.     

Chronicl-DOPA-pretreatment of rats: an electrophysiological and biochemical study in the basal ganglia

Treatment of rats withl-DOPA (251.25 mg as the methyl ester HCl/kg) plus benserazide (B, 50 mg/kg) (l-DOPA+B), twice daily (i.p.) for 5 days or 12 days resulted in the dopamine (DA) neurons ofthe substantia nigra pars compacta becoming subsensitive to the rate-depressing effects ofd-amphetamine (i.v.) 16 to 24 h after the last chronic drug dose. In contrast, pretreated rats were significantly less sensitive than control rats to the rate depressant effects of apomorphine (i.v.) after 12, but not 5 days ofl-DOPA+B-pretreatment. After 5, but not 12 days ofl-DOPA+B-pretreatment, a significant increase in the number of spontaneously active DA neurons was noted in the substantia nigra pars compacta. Caudate tyrosine hydroxylase was examined and a significant increase in apparent V_max was noted after 5 days ofl-DOPA+B, with no apparent change being noted in K_m for cofactor. At this time, no change was noted in caudate DA or HVA concentrations. Several distinct processes may be occuring in response to thel-DOPA+B-pretreatment: (1) the DA autoreceptors located on cell bodies in the substantia nigra have become subsensitive after 12 days ofl-DOPA+B-pretreatment; (2) the subsensitivity tod-amphetamine seen after both chronic schedules is probably unrelated to the subsensitive DA autoreceptors and may depend upon homeostatic alterations in neurotransmitter systems other than those utilising DA; (3) the activation of tyrosine hydroxylase may be a reflection of the increase in the number of spontaneously active units.     

Vesicular glutamate transporter 3 (VGLUT3) identifies spatially segregated excitatory terminals in the rat substantia nigra

The excitability of dopaminergic (DA) neurons in the substantia nigra is controlled by the convergent activity of multiple glutamatergic afferents. Here, we show that vesicular glutamate transporter 3 (VGLUT3)-immunoreactive (ir) terminals segregate to the perisomatic region of DA neurons in the substantia nigra pars compacta, and VGLUT3 decorates a synapse population distinct from those marked by vesicular glutamate transporters 1 and 2. VGLUT3-ir nerve endings form asymmetric terminals on DA neurons. Retrograde tracing suggests the superior colliculus as an origin of excitatory VGLUT3-ir afferents. Collectively, our data indicate that VGLUT3 identifies a novel excitatory terminal subset that contributes to the tuning of DA cell excitability in the substantia nigra.     

Activation of the Subthalamic Nucleus and Pedunculopontine Tegmentum: Does it Affect Dopamine Levels in the Substantia Nigra,Nucleus Accumbens and Striatum?

Parkinson's disease is a neurodegenerative disorder, of which the most prominent morphological feature is the progressive loss of dopaminergic nigrostriatal neurons. Increased glutamatergic transmission in the basal ganglia has been implicated in the pathophysiology of Parkinson's disease (PD). This study investigated whether death of substantia nigra (SN) dopaminergic neurons could be caused by the hyperactivity of afferent pathways resulting in the release of a toxic dose of excitatory amino acids in the SN. Twice-daily unilateral stimulation of the subthalamic nucleus (STN) for 21 days, using two different pulse frequencies and current strengths, significantly increased amphetamine-induced rotation, whereas sham stimulated rats showed significantly reduced rotation. Striatal and SN dopamine (DA) levels were unaffected when compared to naı̈ve and sham stimulated rats. However, levels of the DA metabolite, homovanillic acid (HVA), were significantly higher in the ipsilateral anterior striata of rats that had been stimulated at high frequency (100 Hz) and low current (100 μA) as compared to sham treated animals. Stimulation of the pedunculopontine tegmentum (PPT), using a single kainic acid injection, did not affect DA concentration in the ipsilateral striatum and nucleus accumbens when compared to sham-treated rats. DA levels in the contralateral striatum and nucleus accumbens of lesioned rats were significantly higher than ipsilateral levels. DOPAC/DA ratios were lower in the contralateral striatum and nucleus accumbens, suggesting decreased DA turnover. Glutamic acid decarboxylase activity was significantly higher in the ipsilateral than the contralateral SN. The physical manifestations of PD require a large reduction in caudate and putamen DA levels and no such depletion was measured in this study. These results, therefore, do not support the hypothesis that Parkinson's disease may result from an overstimulation of substantia nigral DAneurons by glutamate afferents originating from the STN or PPT.     

经侧脑室注射脂多糖诱导大鼠黑质部位小胶质细胞激活及多巴胺能神经元损伤的研究

目的观察经脑室注射脂多糖(LPS)后大鼠的黑质部小胶质细胞激活及多巴胺(DA)能神经元的变化,探讨脑内炎性反应在黑质DA能神经元慢性变性过程中的作用。方法健康雄性SD大鼠30只,随机分为生理盐水(NS)对照组和LPS组,分别向大鼠右侧脑室注射20μL NS或50μg LPS,40周后用免疫组织化学方法检测大鼠黑质小胶质细胞是否激活、激活的程度(OX-42及OX-6抗体水平),以及酪氨酸羟化酶(TH)阳性神经元的形态和数量。以Fluoro-Jade B(FJB)染色法检测黑质部位神经元变性情况。结果 (1)NS对照组大鼠黑质部位OX-42阳性小胶质细胞呈静息状态,染色浅。LPS组大鼠黑质部OX-42阳性小胶质细胞呈部分激活状态,染色深。两组大鼠黑质部位均未发现OX-6阳性小胶质细胞。(2)NS对照组大鼠黑质部位有大量深染的TH阳性神经元。LPS组大鼠黑质部位TH阳性染色神经元数目(99.11±20.31)比NS对照组(189.52±12.12)减少47.7%(P<0.01)。(3)两组大鼠黑质部位均未见FJB阳性染色神经元。结论经侧脑室单次注射LPS可能造成大鼠黑质部位小胶质细胞长期慢性激活及DA能神经元慢性迟发性功能性损伤。     

Immunohistochemical localization of voltage-gated calcium channels in substantia nigra dopamine neurons

The rhythmic firing of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc) is thought to be mediated by nifedipine-sensitive Ca(2+) channels, although an involvement of omega-conotoxin-sensitive Ca(2+) channels is also suggested. In an attempt to localize such Ca(2+) channels at both the regional and cellular levels, their expression and distribution patterns were immunohistochemically investigated in the rat SNc. The three distinct subtypes of voltage-gated Ca(2+) channels were tested: the class B N-type alpha 1 subunit (CNB1), the class C L-type alpha 1 subunit (CNC1) and the class D L-type alpha 1 subunit (CND1). A large number of SNc neurons showed intense immunoreactivity against CND1 and they were distributed throughout the entire extent. By contrast, many fewer neurons displayed less intense CNC1 immunoreactivity and many of them were located in the lateral aspect of the SNc. No immunoreactivity against CNB1 was detected in the SNc. Moreover, double immunofluorescence analysis in combination with tyrosine hydroxylase staining revealed that virtually all DA neurons were CND1-immunoreactive whereas many DA neurons especially in the medial SNc exhibited only faint or no immunoreactivity against CNC1. Both CNC1 and CND1 were expressed in cell bodies and proximal dendrites of SNc DA neurons, whilst their distal dendrites that penetrated into the substantia nigra pars reticulata expressed CND1 alone. Thus, the ubiquitously and intensely expressed class D alpha 1 subunit of L-type Ca(2+) channels that is sensitive to both nifedipine and omega-conotoxin may be responsible for the pacemaker activity of SNc DA neurons.     

Resistance of hypothalamic dopaminergic neurons to neonatal 6-hydroxydopamine toxicity

We studied the effects of neonatal intracisternal administration of the 6-hydroxydopamine (6-OHDA) following desipramine pretreatment on dopaminergic (DA) neurons in the rat hypothalamus and substantia nigra by immunocytochemistry with an antiserum against tyrosine hydroxylase (TH). Neonatal intracisternal 6-OHDA injection induced almost complete loss of the TH-immunoreactivity in the substantia nigra and the caudate-putamen when examined at final (adult) stage. However, in this stage, no difference of TH-immunoreactivity was observed in hypothalamic DA neurons in the arcuate nucleus (A 12), peri ventricular area (A14), zona incerta (A 13), and posterior hypothalamic area (All). In the initial (neonatal) stage after the 6-OHDA injection, nigral DA neurons started to degenerate in 12 h and were almost completely destructed in 96 h, but hypothalamic DA neurons did not show any degenerative change at any time examined. The route of the injection (cistern, third ventricle or lateral ventricle) of the toxin did not influence the distribution of damage. These data show that 6-OHDA is not equally toxic to all brain DA neurons in neonates, and that all hypothalamic DA neuronal groups resist the toxicity of 6-OHDA, despite their anatomical and functional differences.     

Effects of homocysteine on the dopaminergic system and behavior in rodents

Long-term treatment of levodopa for Parkinson's disease (PD) patients is known to elevate homocysteine level in their plasma. The present study was designed to examine the possible neurotoxic effects of the increased homocysteine level on the dopaminergic system. Homocysteine was administered into Sprague-Dawley male rats intracerebroventricularly or C57BL/6 mice intraperitoneally. Following homocysteine injection the locomotor activities, the levels of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and immunohistochemistry of dopaminergic neurons were examined. The results obtained indicate that homocysteine administration (1 or 2 micromol, i.c.v.) into the rat brains for 5 days significantly decreased the locomotor activities and dopamine as well as its metabolites, DOPAC and HVA, in the rat striatal regions. Two different doses of homocysteine (50 and 100mg/100g, i.p. daily) were administered into mice for 36 days to evaluate the effect of systemic treatment of homocysteine on the dopaminergic neurons of the brain. The intraperitoneal injections of two doses of homocysteine significantly increased homocysteine levels in the striatal regions of mouse brains by 21.5 and 39.2%, while reducing dopamine turnover rates in the striatal regions by decreasing (DOPAC+HVA)/DA, 23.7 and 51.6%, respectively. Accordingly, homocysteine decreased locomotor activities significantly by decreasing movement time by 29 and 38%, total distance by 32 and 42%, and numbers of movement by 28 and 41%, respectively. Moreover, homocysteine decreased tyrosine hydroxylase immunoreactivity in substantia nigra of mouse brain. The data obtained indicate that the potential of homocysteine to be toxic to the dopaminergic system. Consequently, long-term levodopa therapy for PD may accelerate the progression of PD, at least in part by elevated homocysteine.     

The chemokine CXCL10 modulates excitatory activity and intracellular calcium signaling in cultured hippocampal neurons

In this study, we provide evidence for direct modulatory effects of the chemokine, CXCL10, on the physiology of hippocampal neurons maintained in primary culture. CXCL10 elicited a rise in intracellular Ca2+ and enhanced both spontaneous and evoked electrical activity of hippocampal neurons. CXCL10-induced elevations in intracellular Ca2+ were associated with an increase in neuronal firing and an alteration in the relationship between the evoked Ca2+ signal and neuronal activity. The effects of CXCL10 were not accompanied by a shift in resting membrane potential (RMP) or input resistance. Expression of the CXCR3 chemokine receptor supports a direct effect of CXCL10 on hippocampal neurons.