6-OHDA Lesions Research Articles

Dopamine in Auditory Nuclei and Lemniscal Projections is Poised to Influence Acoustic Integration in the Inferior Colliculus.

Dopamine (DA) modulates the activity of nuclei within the ascending and descending auditory pathway. Previous studies have identified neurons and fibers in the inferior colliculus (IC) which are positively labeled for tyrosine hydroxylase (TH), a key enzyme in the synthesis of dopamine. However, the origins of the tyrosine hydroxylase positive projections to the inferior colliculus have not been fully explored. The lateral lemniscus (LL) provides a robust inhibitory projection to the inferior colliculus and plays a role in the temporal processing of sound. In the present study, immunoreactivity for tyrosine hydroxylase was examined in animals with and without 6-hydroxydopamine (6-OHDA) lesions. Lesioning, with 6-OHDA placed in the inferior colliculus, led to a significant reduction in tyrosine hydroxylase immuno-positive labeling in the lateral lemniscus and inferior colliculus. Immunolabeling for dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT), enzymes responsible for the synthesis of norepinephrine (NE) and epinephrine (E), respectively, were evaluated. Very little immunoreactivity for DBH and no immunoreactivity for PNMT was found within the cell bodies of the dorsal, intermediate, or ventral nucleus of the lateral lemniscus. The results indicate that catecholaminergic neurons of the lateral lemniscus are likely dopaminergic and not noradrenergic or adrenergic. Next, high-pressure liquid chromatography (HPLC) analysis was used to confirm that dopamine is present in the inferior colliculus and nuclei that send projections to the inferior colliculus, including the cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus, and auditory cortex (AC). Finally, fluorogold, a retrograde tracer, was injected into the inferior colliculus of adult rats. Each subdivision of the lateral lemniscus contained fluorogold within the somata, with the dorsal nucleus of the lateral lemniscus showing the most robust projections to the inferior colliculus. Fluorogold-tyrosine hydroxylase colocalization within the lateral lemniscus was assessed. The dorsal and intermediate nuclei neurons exhibiting similar degrees of colocalization, while neurons of the ventral nucleus had significantly fewer colocalized fluorogold-tyrosine hydroxylase labeled neurons. These results suggest that several auditory nuclei that project to the inferior colliculus contain dopamine, dopaminergic neurons in the lateral lemniscus project to the inferior colliculus and that dopaminergic neurotransmission is poised to play a pivotal role in the function of the inferior colliculus.

Levodopa affects spike and local field synchronisation in the pedunculopontine nucleus of a rat model of Parkinson's disease.

The pedunculopontine nucleus (PPN) undergoes significant anatomic and electrophysiological alterations in Parkinson’s disease (PD), severely impacting locomotion. However, the effect of 6-hydroxydopamine (6-OHDA) lesion and levodopa (L-DOPA) therapy on the relationships between spike activities and local field potential (LFP) within the PPN is not well-understood. Synchronisation between the spike activity of individual neurones and LFP of neuronal ensembles is a crucial problem in the pathogenesis of PD. In this study, LFP signals and spikes in the PPN of rats in control, lesioned, and L-DOPA groups were recorded synchronously with a multi-unit electrical signal acquisition system and analysed for their coherence value, spike-field coherence, and phase-lock relationship. The spike-LFP relationship in the PPN was markedly increased in specific frequency bands because of the 6-OHDA lesion but differed depending on the animal locomotion state and neuronal type. L-DOPA had a limited therapeutic effect on the 6-OHDA-induced increase in the coherence value. Our study demonstrates that the PPN spike-LFP relationship is involved in the pathogenesis of PD and is critical for the effects of L-DOPA, providing a basis for the clinical treatment of refractory PD symptoms.

Neuroprotective effects of Shende’an tablet in the Parkinson’s disease model

BackgroundShende’an tablet (SDA) is a newly capsuled Chinese herbal formula derived from the Chinese traditional medicine Zhengan Xifeng Decoction which is approved for the treatment of neurasthenia and insomnia in China. This study aimed to investigate the neuroprotective effects of SDA against Parkinson’s disease (PD) in vitro and in vivo.MethodsIn the present work, the neuroprotective effects and mechanism of SDA were evaluated in the cellular PD model. Male C57BL/6J mice were subject to a partial MPTP lesion alongside treatment with SDA. Behavioural test and tyrosine-hydroxylase immunohistochemistry were used to evaluate nigrostriatal tract integrity. HPLC analysis and Western blotting were used to assess the effect of SDA on dopamine metabolism and the expression of HO-1, PGC-1α and Nrf2, respectively.ResultsOur results demonstrated that SDA had neuroprotective effect in dopaminergic PC12 cells with 6-OHDA lesion. It had also displayed efficient dopaminergic neuronal protection and motor behavior alleviation properties in MPTP-induced PD mice. In the PC12 cells and MPTP-induced Parkinson’s disease animal models, SDA was highly efficacious in α-synuclein clearance associated with the activation of PGC-1α/Nrf2 signal pathway.ConclusionsSDA demonstrated potential as a future therapeutic modality in PD through protecting dopamine neurons and alleviating the motor symptoms, mediated by the activation of PGC-1α/Nrf2 signal pathway.

Analysis of morphological and neurochemical changes in subthalamic nucleus neurons in response to a unilateral 6-OHDA lesion of the substantia nigra in adult rats.

BackgroundSubthalamic nucleus (STN) neurons undergo changes in their pattern of activity and morphology during the clinical course of Parkinson’s disease (PD). Striatal dopamine depletion and hyperactivity of neurons in the parafascicular nucleus (Pf) of the intralaminar thalamus are predicted to contribute to the STN changes.ObjectiveThis study investigated possible morphological and neurochemical changes in STN neurons in a rat model of unilateral, nigral dopamine neuron loss, in relation to previously documented alterations in Pf neurons.MethodsMale Sprague-Dawley rats received a unilateral injection of 6-hydroxydopamine (6-OHDA) into the substantia nigra pars compacta (SNpc). Rats were randomly divided into two groups (6/group) for study at 1 and 5 months by post-treatment. The extent of SNpc dopamine neuron damage was assessed in an amphetamine-induced rotation test and postmortem assessment of tyrosine hydroxylase mRNA levels using in situ hybridization histochemistry. Neural cross-sectional measurements and assessment of vesicular glutamate transporter-2 (vGlut2) mRNA levels were performed to measure the impact on neurons in the STN.ResultsA unilateral SNpc dopaminergic neuron lesion significantly decreased the cross-sectional area of STN neurons ipsilateral to the lesion, at 1 month (P < 0.05) and 5 months (P < 0.01) post-lesion, while bilateral vGlut2 mRNA levels in STN neurons were unaltered.ConclusionsDecreased size of STN neurons in the presence of sustained vGlut2 mRNA levels following a unilateral SNpc 6-OHDA lesion, indicate altered STN physiology. This study presents further details of changes within the STN, coincident with observed alterations in Pf neurons and behaviour.Data availabilityThe data associated with the findings of this study are available from the corresponding author upon request.

Contributive Role of TNF-α to L-DOPA-Induced Dyskinesia in a Unilateral 6-OHDA Lesion Model of Parkinson's Disease.

Our present objective was to better characterize the mechanisms that regulate striatal neuroinflammation in mice developing L-DOPA-induced dyskinesia (LID). For that, we used 6-hydroxydopamine (6-OHDA)-lesioned mice rendered dyskinetic by repeated intraperitoneal injections of 3,4-dihydroxyphenyl-L-alanine (L-DOPA) and quantified ensuing neuroinflammatory changes in the dopamine-denervated dorsal striatum. LID development was associated with a prominent astrocytic response, and a more moderate microglial cell reaction restricted to this striatal area. The glial response was associated with elevations in two pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-1β. Treatment with the phytocannabinoid cannabidiol and the transient receptor potential vanilloid-1 (TRPV-1) channel antagonist capsazepine diminished LID intensity and decreased TNF-α levels without impacting other inflammation markers. To possibly reproduce the neuroinflammatory component of LID, we exposed astrocyte and microglial cells in culture to candidate molecules that might operate as inflammatory cues during LID development, i.e., L-DOPA, dopamine, or glutamate. Neither L-DOPA nor dopamine produced an inflammatory response in glial cell cultures. However, glutamate enhanced TNF-α secretion and GFAP expression in astrocyte cultures and promoted Iba-1 expression in microglial cultures. Of interest, the antidyskinetic treatment with cannabidiol + capsazepine reduced TNF-α release in glutamate-activated astrocytes. TNF-α, on its own, promoted the synaptic release of glutamate in cortical neuronal cultures, whereas cannabidiol + capsazepine prevented this effect. Therefore, we may assume that the release of TNF-α by glutamate-activated astrocytes may contribute to LID by exacerbating corticostriatal glutamatergic inputs excitability and maintaining astrocytes in an activated state through a self-reinforcing mechanism.

Cytisine is neuroprotective in female but not male 6-hydroxydopamine lesioned parkinsonian mice and acts in combination with 17-β-estradiol to inhibit apoptotic endoplasmic reticulum stress in dopaminergic neurons.

Apoptotic endoplasmic reticulum (ER) stress is a major mechanism for dopaminergic (DA) loss in Parkinson's disease (PD). We assessed if low doses of the partial α4β2 nicotinic acetylcholine receptor agonist, cytisine attenuates apoptotic ER stress and exerts neuroprotection in substantia nigra pars compacta (SNc) DA neurons. Alternate day intraperitoneal injections of 0.2mg/kg cytisine were administered to female and male mice with 6-hydroxydopamine (6-OHDA) lesions in the dorsolateral striatum, which caused unilateral degeneration of SNc DA neurons. Cytisine attenuated 6-OHDA-induced PD-related behaviors in female, but not in male mice. We also found significant reductions in tyrosine hydroxylase (TH) loss within the lesioned SNc of female, but not male mice. In contrast to female mice, DA neurons within the lesioned SNc of male mice showed a cytisine-induced pathological increase in the nuclear translocation of the pro-apoptotic ER stress protein, C/EBP homologous protein (CHOP). To assess the role of estrogen in cytisine neuroprotection in female mice, we exposed primary mouse DA cultures to either 10nM 17-β-estradiol and 200nM cytisine or 10nM 17-β-estradiol alone. 17-β-estradiol reduced expression of CHOP, whereas cytisine exposure reduced 6-OHDA-mediated nuclear translocation of two other ER stress proteins, activating transcription factor 6 and x-box-binding protein 1, but not CHOP. Taken together, these data show that cytisine and 17-β-estradiol work in combination to inhibit all three arms (activating transcription factor 6, x-box-binding protein 1, and CHOP) of apoptotic ER stress signaling in DA neurons, which can explain the neuroprotective effect of low-dose cytisine in female mice.

6-hydroxydopamine and ovariectomy has no effect on heart rate variability parameters of females

OBJECTIVES:In addition to the classic motor symptoms of Parkinson’s disease (PD), patients also present with non-motor symptoms, such as autonomic dysfunction, which is present in almost 90% of patients with PD, affecting the quality of life and mortality. Regarding sex differences in prevalence and presentation, there is increasing concern about how sex affects autonomic dysfunction. However, there are no previous data on autonomic cardiac function in females after 6-hydroxydopamine (6-OHDA) striatal injection.METHODS:Wistar female rats were ovariectomized. After 20 days, the animals received bilateral injections of 6-OHDA (total dose per animal: 48 µg) or a vehicle solution in the striatum. Thirty days after 6-OHDA injection, subcutaneous electrodes were implanted for electrocardiogram (ECG) recording. Ten days after electrode implantation, ECG signals were recorded. Analyses of heart rate variability (HRV) parameters were performed, and the 6-OHDA lesion was confirmed by analyzing the number of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta (SNpc).RESULTS:A high dose of 6-OHDA did not affect HRV of females, independent of ovariectomy. As expected, ovariectomy did not affect HRV or lesions in the SNpc after 6-OHDA injection.CONCLUSIONS:We suggest that females with 6-OHDA present with cardioprotection, independent of ovarian hormones, which could be related to female vagal predominance.

Green coffee extract attenuates Parkinson's-related behaviors in animal models.

Epidemiological studies have shown an inverse association between coffee consumption and the development of Parkinson's disease (PD). The effects of the oral treatment with green (non-roasted) coffee extracts (CE, 100 or 400 mg/kg) and caffeine (31.2 mg/kg) were evaluated on catalepsy induced by haloperidol in mice, and unilateral 6-OHDA lesion of medial forebrain bundle (MFB) or striatum in rats. Also, the in vitro antioxidant activity and the monoamine levels in the striatum were investigated. CE presented a mild antioxidant activity in vitro and its administration decreased the catalepsy index. CE at the dose of 400 mg/kg induced ipsilateral rotations 14 days after lesion; however, chronic 30-day CE and caffeine treatments did not interfere with the animals' rotation after apomorphine or methamphetamine challenges in animals with MFB lesion, nor on monoamines levels. Furthermore, CE and caffeine were effective in inhibiting the asymmetry between ipsilateral and contralateral rotations induced by methamphetamine and apomorphine in animals with lesion in the striatum but did not avoid the monoamines depletion. These results indicate that CE components indirectly modulate dopaminergic transmission, suggesting a pro-dopaminergic action of CE, and further investigation must be conducted to elucidate the mechanisms of action and the possible neuroprotective role in PD.

The Effect of Levosimendan on Two Distinct Rodent Models of Parkinson's Disease.

Parkinson's disease (PD) is a common neurodegenerative disorder that is characterized by motor symptoms related to the deficiency in dopamine levels, and cognitive symptoms that are similar in nature to those manifested during Alzheimer's disease. Levosimendan, on the other hand, is a calcium sensitizer and phosphodiesterase inhibitor that was shown to possess neuroprotective, memoryenhancing, and anti-apoptotic properties. In the current study, the possible protective effect of levosimendan was investigated in two animal models of Parkinson's disease. Both intracerebral injection 6-hydroxydopamine (6-OHDA) and the direct injection of lipopolysaccharide (LPS) into the substantia nigra were used as models to induce Parkinson's-like behavior. Levosimendan (12 μg/kg intraperitoneally once weekly) was started 7 days before or 2 days after lesioning of the animals. At day 14 post-lesioning, animals were subjected to apomorphine challenge, which was correlated with dopamine levels in the striatum and tyrosine hydroxylase (TH)-positive nigral cells. Results showed that levosimendan restored the number of rotations in the apomorphine challenge test, the levels of dopamine in the striatum, and the TH-positive nigral cells when administered 7 days before, but not two days after 6-OHDA lesioning. In the LPS model of PD, the number of rotations in the apomorphine challenge test, the levels of dopamine in the striatum, and the TH-positive nigral cells were restored when levosimendan was administered 7 days before as well as two days after lesioning. Levosimendan seems to provide a promising agent with potential clinical value for PD.

The beneficial effect of vanillin on 6-hydroxydopamine rat model of Parkinson's disease.

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is related to neuroinflammation. Vanillin, which possesses both antioxidant, and anti-inflammatory properties, can be a candidate for neuroprotection in PD. This study was aimed to investigate the effects of vanillin on the 6-hydroxydopamine (6-OHDA) rodent model of PD. Male Wistar rats were administrated intraperitoneal (i.p) or oral vanillin at a dose of 20 mg/kg/day for 7 days that was started at three days before or seven days after intracerebral injection of 6-OHDA. The 6-OHDA-induced lesions were assessed behaviorally using the apomorphine rotation test, neurochemically via measuring striatal dopamine concentrations, and through immunohistochemistry. Both oral and IP vanillin at three days before or seven days after 6-OHDA lesioning exhbited significantly lower tight contralateral rotations upon apomorphine challenge, and higher striatal dopamine concentrations. Vanillin seems to offer protective properties against 6-OHDA lesion via preserving striatal dopamine levels.

Probiotics Treatment Improves Hippocampal Dependent Cognition in a Rodent Model of Parkinson’s Disease

Parkinson’s disease (PD) is a neurological disorder with motor dysfunction and a number of psychiatric symptoms. Symptoms such as anxiety and cognitive deficits emerge prior to motor symptoms and persist over time. There are limited treatments targeting PD psychiatric symptoms. Emerging studies reveal that the gut microbe is altered in PD patients. Here we assessed the effect of a probiotic treatment in a rat model of PD. We used the neurotoxin (6-hydroxydopamine, 6-OHDA) in a preclinical PD model to examine the impact of a probiotic treatment (Lacticaseibacillus rhamnosus HA-114) on anxiety and memory. Rats underwent either sham surgery or received 6-OHDA bilaterally into the striatum. Three weeks post-surgery, rats were divided into three experimental groups: a sham group that received probiotics, a 6-OHDA group that received probiotics, and the third group of 6-OHDA received the placebo formula. All rats had access to either placebo or probiotics formula for 6 weeks. All groups were assessed for anxiety-like behaviour using the elevated plus maze. Cognition was assessed for both non-hippocampal and hippocampal dependent tasks using the novel object recognition and novel place recognition. We report that the 6-OHDA lesion induced anxiety-like behaviour and deficits in hippocampal dependent cognition. Interestingly, the probiotics treatment had no impact on anxiety-like behaviour but selectively improved hippocampal dependent cognition deficits. Together, the results presented here highlight the utility of animal models in examining the neuropsychiatric symptoms of PD and the potential of probiotics as adjunctive treatment for non-motor symptoms of PD.

Deferred Administration of Afobazole Induces Sigma1R-Dependent Restoration of Striatal Dopamine Content in a Mouse Model of Parkinson's Disease.

Previously, we demonstrated that the immediate administration of multitarget anxiolytic afobazole slows down the progression of neuronal damage in a 6-hydroxidodamine (6-OHDA) model of Parkinson’s disease due to the activation of chaperone Sigma1R. The aim of the present study is to evaluate the therapeutic potential of deferred afobazole administration in this model. Male ICR mice received a unilateral 6-OHDA lesion of the striatum. Fourteen days after the surgery, mice were treated with afobazole, selective Sigma1R agonist PRE-084, selective Sigma1R antagonist BD-1047, and a combination of BD-1047 with afobazole or PRE-084 for another 14 days. The deferred administration of afobazole restored the intrastriatal dopamine content in the 6-OHDA-lesioned striatum and facilitated motor behavior in rotarod tests. The action of afobazole accorded with the effect of Sigma1R selective agonist PRE-084 and was blocked by Sigma1R selective antagonist BD-1047. The present study illustrates the Sigma1R-dependent effects of afobazole in a 6-OHDA model of Parkinson’s disease and reveals the therapeutic potential of Sigma1R agonists in treatment of the condition.

Systematic Evaluation of DBS Parameters in the Hemi-Parkinsonian Rat Model.

Electrical stimulation of the subthalamic nucleus (STN) is clinically employed to ameliorate several symptoms of manifest Parkinson’s Disease (PD). Stimulation parameters utilized by chronically implanted pulse generators comprise biphasic rectangular short (60–100 μs) pulses with a repetition frequency between 130 and 180 Hz. A better insight into the effect of electrical stimulation parameters could potentially reveal new possibilities for the improvement of deep brain stimulation (DBS) as a treatment. To this end, we employed single-sided 6-hydroxidopamine (6-OHDA) lesioning of the medial forebrain bundle (MFB) in rats to systematically investigate alternative stimulation parameters. These hemi-parkinsonian (hemi-PD) rats underwent individualized, ipsilateral electrical stimulation to the STN of the lesioned hemisphere, while the transiently induced contralateral rotational behavior was quantified to assess the effect of DBS parameter variations. The number of induced rotations during 30 s of stimulation was strongly correlated with the amplitude of the stimulation pulses. Despite a general linear relation between DBS frequency and rotational characteristics, a plateau effect was observed in the rotation count throughout the clinically used frequency range. Alternative waveforms to the conventional biphasic rectangular (Rect) pulse shapes [Triangular (Tri), Sinusoidal (Sine), and Sawtooth (Lin.Dec.)] required higher charges per phase to display similar behavior in rats as compared to the conventional pulse shape. The Euclidean Distance (ED) was used to quantify similarities between different angular trajectories. Overall, our study confirmed that the effect of different amplitude and frequency parameters of STN-DBS in the hemi-PD rat model was similar to those in human PD patients. This shows that induced contralateral rotation is a valuable readout in testing stimulation parameters. Our study supports the call for more pre-clinical studies using this measurement to assess the effect of other DBS parameters such as pulse-width and interphase intervals.

Peripheral benzodiazepine receptor/18kDa translocator protein positron emission tomography imaging in a rat model of acute brain injury.

The activation of microglia in various brain pathologies is accompanied by an increase in the expression of peripheral benzodiazepine receptor/18kDa translocator protein (PBR/TSPO). However, whether activated microglia have a neuroprotective or neurotoxic effect on neurons in the brain is yet to be determined. In this study, we investigated the ability of the novel PBR/TSPO ligand FEPPA to detect activated microglia in an animal model of primary neurotoxic microglia activation. [18F] FEPPA positron emission tomography (PET) imaging was performed before and after intraperitoneal administration of lipopolysaccharide (LPS) (LPS group) or saline (control group) in a unilateral 6-hydroxydopamine (6-OHDA) lesion rat model of Parkinson's disease. Images were compared between these groups. After imaging, the brains were collected, and the activated microglia at the disease sites were analyzed by the expression of inflammatory cytokines and immunohistochemistry staining. These results were then comparatively examined with those obtained by PET imaging. In the unilateral 6-OHDA lesion rat model, the PBR/TSPO PET signal was significantly increased in the LPS group compared with the saline group. As the increased signal was observed 4h after the injection, we considered it an acute response to brain injury. In the post-imaging pathological examination, activated microglia were found to be abundant at the site where strong signals were detected, and the expression of the inflammatory cytokines TNF-α and IL-1β was increased. Intraperitoneal LPS administration further increased the expression of inflammatory cytokines, and the PBR/TSPO PET signal increased concurrently. The increase in inflammatory cytokine expression correlated with enhanced signal intensity. PET signal enhancement by PBR/TSPO at the site of brain injury correlated with the activation of microglia and production of inflammatory cytokines. Furthermore, because FEPPA enables the detection of neurotoxic microglia on PET images, we successfully constructed a novel PET detection system that can monitor neurodegenerative diseases.

Erythropoietin modulates striatal antioxidant signalling to reduce neurodegeneration in a toxicant model of Parkinson's disease

The current study sought to characterize the pro-survival effects of erythropoietin (EPO) in a toxicant model of Parkinson's disease (PD). EPO treatment induced time-dependent elevations of antioxidant glutathione peroxidase (GPx) and anti-apoptotic factors (pAkt and pBad/Bad) within the striatum and substantia nigra pars compacta (SNc). Intriguingly, our results indicated a region- and lesion size- dependence of pro-survival effects of EPO. Indeed, intra-striatal (but not intra-nigral) infusion of EPO was effective at preventing dopaminergic terminal degeneration and sSNc neuronal loss induced by two different doses of 6-OHDA. These neuroprotective consequences were paralleled by a diminution of microglial morphological changes, along with enhanced motor functioning seen through a reduction in apomorphine-induced rotational behaviour. Finally, in the context of the 6-OHDA lesion, EPO again induced anti-apoptotic (Bcl-2) and antioxidant (GPx) factors within the striatum. Taken together, these results raise the possibility of EPO's potential use as an adjuvant therapy in the treatment of PD, or at least, suggest possible brain-region specific targets for the protective effects of EPO.

Serotonin2B receptor blockade in the rat dorsal raphe nucleus suppresses cocaine-induced hyperlocomotion through an opposite control of mesocortical and mesoaccumbens dopamine pathways

Serotonin2B receptor (5-HT2BR) antagonists inhibit cocaine-induced hyperlocomotion independently of changes of accumbal dopamine (DA) release. Given the tight relationship between accumbal DA activity and locomotion, and the inhibitory role of medial prefrontal cortex (mPFC) DA on subcortical DA neurotransmission and DA-dependent behaviors, it has been suggested that the suppressive effect of 5-HT2BR antagonists on cocaine-induced hyperlocomotion may result from an activation of mPFC DA outflow which would subsequently inhibit accumbal DA neurotransmission. Here, we tested this hypothesis by means of the two selective 5-HT2BR antagonists, RS 127445 and LY 266097, using a combination of neurochemical, behavioral and cellular approaches in male rats.The intraperitoneal (i.p.) administration of RS 127445 (0.16 mg/kg) or LY 266097 (0.63 mg/kg) potentiated cocaine (10 mg/kg, i.p.)-induced mPFC DA outflow. The suppressant effect of RS 127445 on cocaine-induced hyperlocomotion was no longer observed in rats with local 6-OHDA lesions in the mPFC. Also, RS 127445 blocked cocaine-induced changes of accumbal glycogen synthase kinase (GSK) 3β phosphorylation, a postsynaptic cellular marker of DA neurotransmission. Finally, in keeping with the location of 5-HT2BRs on GABAergic interneurons in the dorsal raphe nucleus (DRN), the intra-DRN perfusion of the GABAAR antagonist bicuculline (100 μM) prevented the effect of the systemic or local (1 μM, intra-DRN) administration of RS 127445 on cocaine-induced mPFC DA outflow. Likewise, intra-DRN bicuculline injection (0.1 μg/0.2 μl) prevented the effect of the systemic RS 127445 administration on cocaine-induced hyperlocomotion and GSK3β phosphorylation.These results show that DRN 5-HT2BR blockade suppresses cocaine-induced hyperlocomotion by potentiation of cocaine-induced DA outflow in the mPFC and the subsequent inhibition of accumbal DA neurotransmission.

Biological Sex and Sex Hormone Impacts on Deficits in Episodic-Like Memory in a Rat Model of Early, Pre-motor Stages of Parkinson's Disease.

Episodic memory deficits are among the earliest appearing and most commonly occurring examples of cognitive impairment in Parkinson's disease (PD). These enduring features can also predict a clinical course of rapid motor decline, significant cognitive deterioration, and the development of PD-related dementia. The lack of effective means to treat these deficits underscores the need to better understand their neurobiological bases. The prominent sex differences that characterize episodic memory in health, aging and in schizophrenia and Alzheimer's disease suggest that neuroendocrine factors may also influence episodic memory dysfunction in PD. However, while sex differences have been well-documented for many facets of PD, sex differences in, and sex hormone influences on associated episodic memory impairments have been less extensively studied and have never been examined in preclinical PD models. Accordingly, we paired bilateral neostriatal 6-hydroxydopamine (6-OHDA) lesions with behavioral testing using the What-Where-When Episodic-Like Memory (ELM) Task in adult rats to first determine whether episodic-like memory is impaired in this model. We further compared outcomes in gonadally intact female and male subjects, and in male rats that had undergone gonadectomy—with and without hormone replacement, to determine whether biological sex and/or sex hormones influenced the expression of dopamine lesioned-induced memory deficits. These studies showed that 6-OHDA lesions profoundly impaired recall for all memory domains in male and female rats. They also showed that in males, circulating gonadal hormones powerfully modulated the negative impacts of 6-OHDA lesions on What, Where, and When discriminations in domain-specific ways. Specifically, the absence of androgens was shown to fully attenuate 6-OHDA lesion-induced deficits in ELM for “Where” and to partially protect against lesion-induced deficits in ELM for “What.” In sum, these findings show that 6-OHDA lesions in rats recapitulate the vulnerability of episodic memory seen in early PD. Together with similar evidence recently obtained for spatial working memory, the present findings also showed that diminished androgen levels provide powerful, highly selective protections against the harmful effects that 6-OHDA lesions have on memory functions in male rats.

Ventral striatum regulates behavioral response to ethanol and MDMA combination.

Our previous studies consistently showed that MDMA-induced locomotor hyperactivity is dramatically increased by coadministration of ethanol (EtOH) in rats, indicating possible potentiation of MDMA abuse liability. Thus, we aimed to identify the brain region(s) and neuropharmacological substrates involved in the pharmacodynamics of this potentiation. We first showed that potentiation of locomotor activity by the combination of ip administration of EtOH (1.5 g/kg) and MDMA (6.6 mg/kg) is delay sensitive and maximal when both drugs are injected simultaneously. Then, we used the 2-deoxyglucose quantitative autoradiography technique to assess the impact of EtOH, MDMA, or their combination on local cerebral metabolic rates for glucose (CMRglcs). We showed a specific metabolic activation in the ventral striatum (VS) under MDMA + EtOH versus MDMA or EtOH alone. We next tested if reversible (tetrodotoxin, TTX) or permanent (6-hydrodoxyopamine, 6-OHDA) lesion of the VS could affect locomotor response to MDMA and MDMA + EtOH. Finally, we blocked dopamine D1 or glutamate NMDA receptors in the VS and measured the effects of MDMA and MDMA + EtOH on locomotor activity. We showed that bilateral reversible inactivation (TTX) or permanent lesion (6-OHDA) of the VS prevented the potentiation by EtOH of MDMA-induced locomotor hyperactivity. Likewise, blockade of D1 or NMDA receptors in the VS also reduced the potentiation of MDMA locomotor activity by EtOH. These data indicate that dopamine D1 and glutamate NMDA receptor-driven mechanisms in the VS play a key role in the pharmacodynamics of EtOH-induced potentiation of the locomotor effects of MDMA.

Activation and Blockade of Serotonin-4 Receptors in the Lateral Habenula Produce Antidepressant Effects in the Hemiparkinsonian Rat

Background: The 5-hydroxytryptamine (5-HT) neurotransmitter system and lateral habenula (LHb) are involved in the regulation of depression, while the mechanisms remain to be clarified. Objectives: The effects and possible mecha-nism underlying activation or blockade of 5-HT₄ receptors (5-HT₄Rs) in the LHb in depression were investigated by behavioral and neurochemical methods based on a Parkinson’s disease (PD) rat model. Method: 6-Hydroxydopamine (6-OHDA) was injected unilaterally into the substantia nigra pars compacta to establish the PD rat model. The depressive-like behaviors were measured by the forced swimming test (FST) and sucrose preference test (SPT). The concentrations of dopamine (DA), noradrenaline (NA) and 5-HT in the related brain regions were measured by a neurochemical method. Results: The 6-OHDA lesions increased the immobility time in the FST and decreased the sucrose consumption in the SPT, suggesting the induction of depressive-like behaviors. Intra-LHb injection of BIMU-8 (5-HT₄R agonist) or GR113808 (5-HT₄R antagonist) produced antidepressant effects in the lesioned rats. Intra-LHb injection of BIMU-8 significantly increased the DA levels in the medial prefrontal cortex (mPFC) and ventral hippocampus (vHip), increased the 5-HT level in the mPFC and decreased the NA level in the vHip only in the lesioned rats, while intra-LHb injection of GR113808 changed DA, NA and 5-HT levels in the mPFC, LHb and vHip in both sham and the lesioned rats. Conclusions: All these results suggest that activation or blockade of the LHb 5-HT₄Rs produce antidepressant effects in the 6-OHDA-lesioned rats, which are related to the changes of monoamines in the limbic and limbic-related regions.

Investigation of nerve pathways mediating colorectal dysfunction in Parkinson's disease model produced by lesion of nigrostriatal dopaminergic neurons.

Gastrointestinal (GI) dysfunction, including constipation, is a common non-motor symptom of Parkinson's disease (PD). The toxin 6-hydroxydopamine (6OHDA) produces the symptoms of PD, surprisingly including constipation, after it is injected into the medial forebrain bundle (MFB). However, the mechanisms involved in PD-associated constipation caused by central application of 6OHDA remain unknown. We investigated effects of 6OHDA lesioning of the MFB on motor performance and GI function. Male Sprague Dawley rats were unilaterally injected with 6OHDA in the MFB. Colorectal propulsion was assessed by bead expulsion after 4weeks and by recording colorectal contractions and propulsion after 5weeks. Enteric nervous system (ENS) neuropathy was examined by immunohistochemistry. When compared to shams, 6OHDA-lesioned rats had significantly increased times of bead expulsion from the colorectum, indicative of colon dysmotility. Administration of the colokinetic, capromorelin, that stimulates defecation centers in the spinal cord, increased the number of contractions and colorectal propulsion in both groups compared to baseline; however, the effectiveness of capromorelin in 6OHDA-lesioned rats was significantly reduced in comparison with shams, indicating that 6OHDA animals have reduced responsiveness of the spinal defecation centers. Enteric neuropathy was observed in the distal colon, revealing that lesion of the MFB has downstream effects at the cellular level, remote from the site of 6OHDA administration. We conclude that there are trans-synaptic effects of the proximal, forebrain, lesion of pathways from the brain that send signals down the spinal cord, at the levels of the defecation centers and the ENS.