Multi-session transcutaneous auricular vagus nerve stimulation for Parkinson's disease: evaluating feasibility, safety, and preliminary efficacy.

Background: In pre-clinical animal models of Parkinson's disease (PD), vagus nerve stimulation (VNS) can rescue motor deficits and protect susceptible neuronal populations. Transcutaneous auricular vagus nerve stimulation (taVNS) has emerged as a non-invasive alternative to traditional invasive cervical VNS. This is the first report summarizing the safety, feasibility, and preliminary efficacy of repeated sessions of taVNS in participants with PD. Objectives: To evaluate the feasibility, safety, and possible efficacy of taVNS for motor and non-motor symptoms in mild to moderate PD. Methods: This is a double-blind, sham controlled RCT (NCT04157621) of taVNS in 30 subjects with mild to moderate PD without cognitive impairment. Participants received 10, 1-h taVNS sessions (25 Hz, 200% of sensory threshold, 500 µs pulse width, 60 s on and 30 s off) over a 2-week period. Primary outcome measures were feasibility and safety of the intervention; secondary outcomes included the MDS-UPDRS, cognitive function and self-reported symptom improvement. Results: taVNS treatment was feasible, however, daily in-office visits were reported as being burdensome for participants. While five participants in the taVNS group and three in the sham group self-reported one or more minor adverse events, no major adverse events occurred. There were no group differences on blood pressure and heart rate throughout the intervention. There were no group differences in MDS-UPDRS scores or self-reported measures. Although global cognitive scores remained stable across groups, there was a reduction in verbal fluency within the taVNS group. Conclusions: taVNS was safe, and well-tolerated in PD participants. Future studies of taVNS for PD should explore at-home stimulation devices and optimize stimulation parameters to reduce variability and maximize engagement of neural targets.

Differential effects of vagus nerve stimulation paradigms guide clinical development for Parkinson's disease.

BACKGROUND: Vagus nerve stimulation (VNS) modifies brain rhythms in the locus coeruleus (LC) via the solitary nucleus. Degeneration of the LC in Parkinson's disease (PD) is an early catalyst of the spreading neurodegenerative process, suggesting that stimulating LC output with VNS has the potential to modify disease progression. We previously showed in a lesion PD model that VNS delivered twice daily reduced neuroinflammation and motor deficits, and attenuated tyrosine hydroxylase (TH)-positive cell loss. OBJECTIVE: The goal of this study was to characterize the differential effects of three clinically-relevant VNS paradigms in a PD lesion model. METHODS: Eleven days after DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, noradrenergic lesion, administered systemically)/6-OHDA (6-hydroxydopamine, dopaminergic lesion, administered intrastriatally) rats were implanted with VNS devices, and received either low-frequency VNS, standard-frequency VNS, or high-frequency microburst VNS. After 10 days of treatment and behavioral assessment, rats were euthanized, right prefrontal cortex (PFC) was dissected for norepinephrine assessment, and the left striatum, bilateral substantia nigra (SN), and LC were sectioned for immunohistochemical detection of catecholamine neurons, α-synuclein, astrocytes, and microglia. RESULTS: At higher VNS frequencies, specifically microburst VNS, greater improvements occurred in motor function, attenuation of TH-positive cell loss in SN and LC, and norepinephrine concentration in the PFC. Additionally, higher VNS frequencies resulted in lower intrasomal α-synuclein accumulation and glial density in the SN. CONCLUSIONS: These data indicate that higher stimulation frequencies provided the greatest attenuation of behavioral and pathological markers in this PD model, indicating therapeutic potential for these VNS paradigms.

Calpain mediated expansion of CD4+ cytotoxic T cells in rodent models of Parkinson's disease.

Parkinson's disease (PD), a debilitating progressive degenerative movement disorder associated with loss of dopaminergic (DA) neurons in the substantia nigra (SN), afflicts approximately one million people in the U.S., including a significant number of Veterans. Disease characteristics include tremor, rigidity, postural instability, bradykinesia, and at a cellular level, glial cell activation and Lewy body inclusions in DA neurons. The most potent medical/surgical treatments do not ultimately prevent disease progression. Therefore, new therapies must be developed to halt progression of the disease. While the mechanisms of the degenerative process in PD remain elusive, chronic inflammation, a common factor in many neurodegenerative diseases, has been implicated with associated accumulation of toxic aggregated α-synuclein in neurons. Calpain, a calcium-activated cysteine neutral protease, plays a pivotal role in SN and spinal cord degeneration in PD via its role in α-synuclein aggregation, activation/migration of microglia and T cells, and upregulation of inflammatory processes. Here we report an increased expression of a subset of CD4+ T cells in rodent models of PD, including MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mice and DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride]/6-hydroxydopamine rats, which produced higher levels of perforin and granzyme B - typically found in cytotoxic T cells. Importantly, the CD4+ cytotoxic subtype was attenuated following calpain inhibition in MPTP mice, suggesting that calpain and this distinct CD4+ T cell subset may have critical roles in the inflammatory process, disease progression, and neurodegeneration in PD.

Inhibitory designer receptors aggravate memory loss in a mouse model of down syndrome.

The pontine nucleus locus coeruleus (LC) is the primary source of noradrenergic (NE) projections to the brain and is important for working memory, attention, and cognitive flexibility. Individuals with Down syndrome (DS) develop Alzheimer's disease (AD) with high penetrance and often exhibit working memory deficits coupled with degeneration of LC-NE neurons early in the progression of AD pathology. Designer receptors exclusively activated by designer drugs (DREADDs) are chemogenetic tools that allow targeted manipulation of discrete neuronal populations in the brain without the confounds of off-target effects. We utilized male Ts65Dn mice (a mouse model for DS), and male normosomic (NS) controls to examine the effects of inhibitory DREADDs delivered via an AAV vector under translational control of the synthetic PRSx8, dopamine ß hydroxylase (DßH) promoter. This chemogenetic tool allowed LC inhibition upon administration of the inert DREADD ligand, clozapine-N-oxide (CNO). DREADD-mediated LC inhibition impaired performance in a novel object recognition task and reversal learning in a spatial task. DREADD-mediated LC inhibition gave rise to an elevation of α-adrenoreceptors both in NS and in Ts65Dn mice. Further, microglial markers showed that the inhibitory DREADD stimulation led to increased microglial activation in the hippocampus in Ts65Dn but not in NS mice. These findings strongly suggest that LC signaling is important for intact memory and learning in Ts65Dn mice and disruption of these neurons leads to increased inflammation and dysregulation of adrenergic receptors.

Effects of vagus nerve stimulation are mediated in part by TrkB in a parkinson's disease model.

Vagus nerve stimulation (VNS) is being explored as a potential therapeutic for Parkinson's disease (PD). VNS is less invasive than other surgical treatments and has beneficial effects on behavior and brain pathology. It has been suggested that VNS exerts these effects by increasing brain-derived neurotrophic factor (BDNF) to enhance pro-survival mechanisms of its receptor, tropomyosin receptor kinase-B (TrkB). We have previously shown that striatal BDNF is increased after VNS in a lesion model of PD. By chronically administering ANA-12, a TrkB-specific antagonist, we aimed to determine TrkB's role in beneficial VNS effects for a PD model. In this study, we administered a noradrenergic neurotoxin, DSP-4, intraperitoneally and one week later administered a bilateral intrastriatal dopaminergic neurotoxin, 6-OHDA. At this time, the left vagus nerve was cuffed for stimulation. Eleven days later, rats received VNS twice per day for ten days, with daily locomotor assessment. Daily ANA-12 injections were given one hour prior to the afternoon stimulation and concurrent locomotor session. Following the final VNS session, rats were euthanized, and left striatum, bilateral substantia nigra and locus coeruleus were sectioned for immunohistochemical detection of neurons, α-synuclein, astrocytes, and microglia. While ANA-12 did not avert behavioral improvements of VNS, and only partially prevented VNS-induced attenuation of neuronal loss in the locus coeruleus, it did stop neuronal and anti-inflammatory effects of VNS in the nigrostriatal system, indicating a role for TrkB in mediating VNS efficacy. However, our data also suggest that BDNF-TrkB is not the sole mechanism of action for VNS in PD.

Diet-induced insulin resistance elevates hippocampal glutamate as well as VGLUT1 and GFAP expression in AßPP/PS1 mice.

The symptomologies of Alzheimer's disease (AD) develop over decades suggesting modifiable lifestyle factors may contribute to disease pathogenesis. In humans, hyperinsulinemia associated with type 2 diabetes mellitus increases the risk for developing AD and both diseases share similar age-related etiologies including amyloidogenesis. Since we have demonstrated that soluble Aß42 elicits glutamate release, we wanted to understand how diet-induced insulin resistance alters hippocampal glutamate dynamics, which are important for memory formation and consolidation. Eight to twelve-week-old C57BL/6J and AßPP/PS1 mice were placed on either a low-fat diet or high-fat diet (HFD) for 8 months. A HFD led to significant weight increases as well as impaired insulin sensitivity, glucose tolerance, and learning in both C57BL/6J and AßPP/PS1 mice. AßPP/PS1 low-fat diet mice had elevated hippocampal basal as well as stimulus-evoked glutamate release that was further increased with consumption of a HFD. Immunohistochemistry indicated an increase in vesicular glutamate transporter 1 and glial fibrillary acidic protein density in hippocampal subregions corresponding with this elevated extracellular glutamate. While no differences in hippocampal plaque load were observed, the elevated astrogliotic response surrounding the plaques in AßPP/PS1 HFD mice may have been a compensatory mechanism to control plaque accumulation. These data support that AßPP/PS1 mice have chronically elevated extracellular glutamate that is exacerbated by a HFD and that modifiable lifestyle factors such as obesity-induced insulin resistance can contribute to AD pathogenesis. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* and for *Open Data* because it made the data publicly available. The data can be accessed at https://osf.io/5whvu (figures for data) and https://osf.io/gd5vf (materials and methods). The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14490.

5-HT1F receptor-mediated mitochondrial biogenesis for the treatment of Parkinson's disease.

BACKGROUND AND PURPOSE: Parkinson's disease is characterized by progressive decline in motor function due to degeneration of nigrostriatal dopaminergic neurons, as well as other deficits including cognitive impairment and behavioural abnormalities. Mitochondrial dysfunction, leading to loss of ATP-dependent cellular functions, calcium overload, excitotoxicity and oxidative stress, is implicated in the pathophysiology of Parkinson's disease. Using the 5-HT1F receptor agonist LY344864, a known inducer of mitochondrial biogenesis (MB), we investigated the therapeutic efficacy of stimulating MB on dopaminergic neuron loss in a mouse model of Parkinson's disease. EXPERIMENTAL APPROACH: Male C57BL/6 mice underwent bilateral intrastriatal 6-hydroxydopamine or saline injections and daily treatment with 2 mg·kg-1 LY344864 or vehicle for 14 days beginning 7 days post-lesion. Tyrosine hydroxylase immunoreactivity (TH-ir) and MB were assessed in the brains of all groups following treatment, and locomotor activity was evaluated prior to lesioning, 7 days post-lesion and after treatment. KEY RESULTS: Increased mitochondrial DNA content and nuclear- and mitochondrial-encoded mRNA and protein expression was observed in specific brain regions of LY344864-treated naïve and lesioned mice, indicating augmented MB. LY344864 attenuated TH-ir loss in the striatum and substantia nigra compared to vehicle-treated lesioned animals. LY344864 treatment also increased locomotor activity in 6-hydroxydopamine lesioned mice, while vehicle treatment had no effect. CONCLUSIONS AND IMPLICATIONS: These data revealed that LY344864-induced MB attenuates dopaminergic neuron loss and improves behavioural endpoints in this model. We suggest that stimulating MB may be beneficial for the treatment of Parkinson's disease and that the 5-HT1F receptor may be an effective therapeutic target.

Vagus nerve stimulation improves locomotion and neuronal populations in a model of Parkinson's disease.

BACKGROUND: Parkinson's disease (PD) is a progressive, neurodegenerative disorder with no disease-modifying therapies, and symptomatic treatments are often limited by debilitating side effects. In PD, locus coeruleus noradrenergic (LC-NE) neurons degenerate prior to substantia nigra dopaminergic (SN-DA) neurons. Vagus nerve stimulation (VNS) activates LC neurons, and decreases pro-inflammatory markers, allowing improvement of LC targets, making it a potential PD therapeutic. OBJECTIVE: To assess therapeutic potential of VNS in a PD model. METHODS: To mimic the progression of PD degeneration, rats received a systemic injection of noradrenergic neurotoxin DSP-4, followed one week later by bilateral intrastriatal injection of dopaminergic neurotoxin 6-hydroxydopamine. At this time, a subset of rats also had vagus cuffs implanted. After eleven days, rats received a precise VNS regimen twice a day for ten days, and locomotion was measured during each afternoon session. Immediately following final stimulation, rats were euthanized, and left dorsal striatum, bilateral SN and LC were sectioned for immunohistochemical detection of monoaminergic neurons (tyrosine hydroxylase, TH), α-synuclein, astrocytes (GFAP) and microglia (Iba-1). RESULTS: VNS significantly increased locomotion of lesioned rats. VNS also resulted in increased expression of TH in striatum, SN, and LC; decreased SN α-synuclein expression; and decreased expression of glial markers in the SN and LC of lesioned rats. Additionally, saline-treated rats after VNS, had higher LC TH and lower SN Iba-1. CONCLUSIONS: Our findings of increased locomotion, beneficial effects on LC-NE and SN-DA neurons, decreased α-synuclein density in SN TH-positive neurons, and neuroinflammation suggest VNS has potential as a novel PD therapeutic.

Accumbens nNOS Interneurons Regulate Cocaine Relapse.

Relapse to drug use can be initiated by drug-associated cues. The intensity of cue-induced relapse is correlated with the induction of transient synaptic potentiation (t-SP) at glutamatergic synapses on medium spiny neurons (MSNs) in the nucleus accumbens core (NAcore) and requires spillover of glutamate from prefrontal cortical afferents. We used a rodent self-administration/reinstatement model of relapse to show that cue-induced t-SP and reinstated cocaine seeking result from glutamate spillover, initiating a metabotropic glutamate receptor 5 (mGluR5)-dependent increase in nitric oxide (NO) production. Pharmacological stimulation of mGluR5 in NAcore recapitulated cue-induced reinstatement in the absence of drug-associated cues. Using NO-sensitive electrodes, mGluR5 activation by glutamate was shown to stimulate NO production that depended on activation of neuronal nitric oxide synthase (nNOS). nNOS is expressed in ∼1% of NAcore neurons. Using a transgene strategy to express and stimulate designer receptors that mimicked mGluR5 signaling through Gq in nNOS interneurons, we recapitulated cue-induced reinstatement in the absence of cues. Conversely, using a transgenic caspase strategy, the intensity of cue-induced reinstatement was correlated with the extent of selective elimination of nNOS interneurons. The induction of t-SP during cued reinstatement depends on activating matrix metalloproteinases (MMPs) and selective chemogenetic stimulation of nNOS interneurons recapitulated MMP activation and t-SP induction (increase in AMPA currents in MSNs). These data demonstrate critical involvement of a sparse population of nNOS-expressing interneurons in cue-induced cocaine seeking, revealing a bottleneck in brain processing of drug-associated cues where therapeutic interventions could be effective in treating drug addiction. SIGNIFICANCE STATEMENT: Relapse to cocaine use in a rat model is associated with transient increases in synaptic strength at prefrontal cortex synapses in the nucleus accumbens. We demonstrate the sequence of events that mediates synaptic potentiation and reinstated cocaine seeking induced by cocaine-conditioned cues. Activation of prefrontal inputs to the accumbens by cues initiates spillover of synaptic glutamate, which stimulates metabotropic glutamate receptor 5 (mGluR5) on a small population of interneurons (∼1%) expressing neuronal nitric oxide synthase. Stimulating these glutamate receptors increases nitric oxide (NO) production, which stimulates matrix metalloprotease-2 (MMP-2) and MMP-9 activity in the extracellular space. Manipulating the interaction between mGluR5, NO production, or MMP-2 and MMP-9 pharmacologically or genetically is sufficient to recapitulate transient synaptic potentiation and reinstate cocaine seeking.

Neuronal exosomes reveal Alzheimer's disease biomarkers in Down syndrome.

INTRODUCTION: Individuals with Down syndrome (DS) exhibit Alzheimer's disease (AD) neuropathology and dementia early in life. Blood biomarkers of AD neuropathology would be valuable, as non-AD intellectual disabilities of DS and AD dementia overlap clinically. We hypothesized that elevations of amyloid ß (Aß) peptides and phosphorylated-tau in neuronal exosomes may document preclinical AD. METHODS: AD neuropathogenic proteins Aß1-42, P-T181-tau, and P-S396-tau were quantified by enzyme-linked immunosorbent assays in extracts of neuronal exosomes purified from blood of individuals with DS and age-matched controls. RESULTS: Neuronal exosome levels of Aß1-42, P-T181-tau, and P-S396-tau were significantly elevated in individuals with DS compared with age-matched controls at all ages beginning in childhood. No significant gender differences were observed. DISCUSSION: These early increases in Aß1-42, P-T181-tau, and P-S396-tau in individuals with DS may provide a basis for early intervention as targeted treatments become available.

Enhanced Cognition and Hypoglutamatergic Signaling in a Growth Hormone Receptor Knockout Mouse Model of Successful Aging.

Growth hormone receptor knockout (GHR-KO) mice are long lived with improved health span, making this an excellent model system for understanding biochemical mechanisms important to cognitive reserve. The purpose of the present study was to elucidate differences in cognition and glutamatergic dynamics between aged (20- to 24-month-old) GHR-KO and littermate controls. Glutamate plays a critical role in hippocampal learning and memory and is implicated in several neurodegenerative disorders, including Alzheimer's disease. Spatial learning and memory were assessed using the Morris water maze (MWM), whereas independent dentate gyrus (DG), CA3, and CA1 basal glutamate, release, and uptake measurements were conducted in isoflurane anesthetized mice utilizing an enzyme-based microelectrode array (MEA) coupled with constant potential amperometry. These MEAs have high temporal and low spatial resolution while causing minimal damage to the surrounding parenchyma. Littermate controls performed worse on the memory portion of the MWM behavioral task and had elevated DG, CA3, and CA1 basal glutamate and stimulus-evoked release compared with age-matched GHR-KO mice. CA3 basal glutamate negatively correlated with MWM performance. These results support glutamatergic regulation in learning and memory and may have implications for therapeutic targets to delay the onset of, or reduce cognitive decline, in Alzheimer's disease.

Altered glutamate release in the dorsal striatum of the MitoPark mouse model of Parkinson's disease.

Mitochondrial dysfunction has been implicated in the degeneration of dopamine (DA) neurons in Parkinson's disease (PD). In addition, animal models of PD utilizing neurotoxins, such as 6-hydroxydopamine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, have shown that these toxins disrupt mitochondrial respiration by targeting complex I of the electron transport chain, thereby impairing DA neurons in these models. A MitoPark mouse model was created to mimic the mitochondrial dysfunction observed in the DA system of PD patients. These mice display the same phenotypic characteristics as PD, including accelerated decline in motor function and DAergic systems with age. Previously, these mice have responded to L-Dopa treatment and develop L-Dopa induced dyskinesia (LID) as they age. A potential mechanism involved in the formation of LID is greater glutamate release into the dorsal striatum as a result of altered basal ganglia neurocircuitry due to reduced nigrostriatal DA neurotransmission. Therefore, the focus of this study was to assess various indicators of glutamate neurotransmission in the dorsal striatum of MitoPark mice at an age in which nigrostriatal DA has degenerated. At 28 weeks of age, MitoPark mice had, upon KCl stimulation, greater glutamate release in the dorsal striatum compared to control mice. In addition, uptake kinetics were slower in MitoPark mice. These findings were coupled with reduced expression of the glutamate re-uptake transporter, GLT-1, thus providing an environment suitable for glutamate excitotoxic events, leading to altered physiological function in these mice.

Memory and hippocampal architecture following short-term midazolam in western diet-treated rats.

The impact of short-term benzodiazepine exposure on cognition in middle-aged or older patients is a highly debated topic among anesthesiologists, critical care physicians and public media. "Western diet" (WD) consumption is linked to impaired cognition as well. The combination of benzodiazepines with substantial exposure to WD might set the stage for increased hippocampal vulnerability for benzodiazepines leading to exaggerated cognitive impairment in the postoperative period. In this study, Fischer 344 rats were fed either WD or standard rodent diet from 5 to 10.5 months of age. Rats were exposed to midazolam or placebo two days prior to an MRI scan using Diffusional Kurtosis Imaging (DKI) to assess brain microstructural integrity, followed by behavioral testing using a water radial arm maze. Hippocampal tissue was collected to assess alterations in protein biochemistry in brain regions associated with learning and memory. Our results showed that rats exposed to the combination of midazolam and WD had significantly delayed time of learning and exhibited spatial memory impairment. Further, we observed an overall increase of kurtosis metrics in the hippocampus and increased expression of the mitochondrial protein VDAC2 in midazolam-treated rats. Our data suggest that both the short-acting benzodiazepine midazolam and WD contribute to negatively affect the brain in middle-aged rats. This study is the first application of DKI on the effects of midazolam and WD exposure, and the findings demonstrate that diffusion metrics are sensitive indicators of changes in the complexity of neurite architecture.

Cocaine Self-Administration and Extinction Leads to Reduced Glial Fibrillary Acidic Protein Expression and Morphometric Features of Astrocytes in the Nucleus Accumbens Core.

BACKGROUND: As a more detailed picture of nervous system function emerges, diversity of astrocyte function becomes more widely appreciated. While it has been shown that cocaine experience impairs astroglial glutamate uptake and release in the nucleus accumbens (NAc), few studies have explored effects of self-administration on the structure and physiology of astrocytes. We investigated the effects of extinction from daily cocaine self-administration on astrocyte characteristics including glial fibrillary acidic protein (GFAP) expression, surface area, volume, and colocalization with a synaptic marker. METHODS: Cocaine or saline self-administration and extinction were paired with GFAP Westerns, immunohistochemistry, and fluorescent imaging of NAc core astrocytes (30 saline-administering and 36 cocaine-administering male Sprague Dawley rats were employed). Imaging was performed using a membrane-tagged lymphocyte protein tyrosine kinase-green fluorescent protein (Lck-GFP) driven by the GFAP promoter, coupled with synapsin I immunohistochemistry. RESULTS: GFAP expression was significantly reduced in the NAc core following cocaine self-administration and extinction. Similarly, we observed an overall smaller surface area and volume of astrocytes, as well as reduced colocalization with synapsin I, in cocaine-administering animals. Cocaine-mediated reductions in synaptic contact were reversed by the ß-lactam antibiotic ceftriaxone. CONCLUSIONS: Multiple lines of investigation indicate that NAc core astrocytes exist in a hyporeactive state following cocaine self-administration and extinction. Decreased association with synaptic elements may be particularly meaningful, as cessation of chronic cocaine use is associated with changes in synaptic strength and resistance to the induction of synaptic plasticity. We hypothesize that the reduced synaptic colocalization of astrocytes represents an important maladaptive cellular response to cocaine and the mechanisms underlying relapse vulnerability.

Cognitive Impairment, Neuroimaging, and Alzheimer Neuropathology in Mouse Models of Down Syndrome.

Down syndrome (DS) is the most common non-lethal genetic condition that affects approximately 1 in 700 births in the United States of America. DS is characterized by complete or segmental chromosome 21 trisomy, which leads to variable intellectual disabilities, progressive memory loss, and accelerated neurodegeneration with age. During the last three decades, people with DS have experienced a doubling of life expectancy due to progress in treatment of medical comorbidities, which has allowed this population to reach the age when they develop early onset Alzheimer's disease (AD). Individuals with DS develop cognitive and pathological hallmarks of AD in their fourth or fifth decade, and are currently lacking successful prevention or treatment options for dementia. The profound memory deficits associated with DS-related AD (DS-AD) have been associated with degeneration of several neuronal populations, but mechanisms of neurodegeneration are largely unexplored. The most successful animal model for DS is the Ts65Dn mouse, but several new models have also been developed. In the current review, we discuss recent findings and potential treatment options for the management of memory loss and AD neuropathology in DS mouse models. We also review agerelated neuropathology, and recent findings from neuroimaging studies. The validation of appropriate DS mouse models that mimic neurodegeneration and memory loss in humans with DS can be valuable in the study of novel preventative and treatment interventions, and may be helpful in pinpointing gene-gene interactions as well as specific gene segments involved in neurodegeneration.

BDNF levels are increased by aminoindan and rasagiline in a double lesion model of Parkinson׳s disease.

The anti-Parkinsonian drug rasagiline is a selective, irreversible inhibitor of monoamine oxidase and is used in the treatment of Parkinson׳s disease (PD). Its postulated neuroprotective effects may be attributed to MAO inhibition, or to its propargylamine moiety. The major metabolite of rasagiline, aminoindan, has shown promising neuroprotective properties in vitro but there is a paucity of studies investigating in vivo effects of this compound. Therefore, we examined neuroprotective effects of rasagiline and its metabolite aminoindan in a double lesion model of PD. Male Fisher 344 rats received i.p. injections of the noradrenergic neurotoxin DSP-4 and intra-striatal stereotaxic microinjections of the dopamine neurotoxin 6-OHDA. Saline, rasagiline or aminoindan (3mg/kg/day s.c.) were delivered via Alzet minipumps for 4 weeks. Rats were then tested for spontaneous locomotion and a novel object recognition task. Following behavioral testing, brain tissue was processed for ELISA measurements of growth factors and immunohistochemistry. Double-lesioned rats treated with rasagiline or aminoindan had reduced behavioral deficits, both in motor and cognitive tasks compared to saline-treated double-lesioned rats. BDNF levels were significantly increased in the hippocampus and striatum of the rasagiline- and aminoindan-lesioned groups compared to the saline-treated lesioned group. Double-lesioned rats treated with rasagiline or aminoindan exhibited a sparing in the mitochondrial marker Hsp60, suggesting mitochondrial involvement in neuroprotection. Tyrosine hydroxylase (TH) immunohistochemistry revealed a sparing of TH-immunoreactive terminals in double-lesioned rats treated with rasagiline or aminoindan in the striatum, hippocampus, and substantia nigra. These data provide evidence of neuroprotection by aminoindan and rasagiline via their ability to enhance BDNF levels.

Gq-DREADD Selectively Initiates Glial Glutamate Release and Inhibits Cue-induced Cocaine Seeking.

BACKGROUND: Glial cells of the central nervous system directly influence neuronal activity by releasing neuroactive small molecules, including glutamate. Long-lasting cocaine-induced reductions in extracellular glutamate in the nucleus accumbens core (NAcore) affect synaptic plasticity responsible for relapse vulnerability. METHODS: We transduced NAcore astrocytes with an adeno-associated virus vector expressing hM3D designer receptor exclusively activated by a designer drug (DREADD) under control of the glial fibrillary acidic protein promoter in 62 male Sprague Dawley rats, 4 dominant-negative soluble N-ethylmaleimide-sensitive factor attachment protein receptor mice, and 4 wild-type littermates. Using glutamate biosensors, we measured NAcore glutamate levels following intracranial or systemic administration of clozapine N-oxide (CNO) and tested the ability of systemic CNO to inhibit reinstated cocaine or sucrose seeking following self-administration and extinction training. RESULTS: Administration of CNO in glial fibrillary acidic protein-hM3D-DREADD transfected animals increased NAcore extracellular glutamate levels in vivo. The glial origin of released glutamate was validated by an absence of CNO-mediated release in mice expressing a dominant-negative soluble N-ethylmaleimide-sensitive factor attachment protein receptor variant in glia. Also, CNO-mediated release was relatively insensitive to N-type calcium channel blockade. Systemic administration of CNO inhibited cue-induced reinstatement of cocaine seeking in rats extinguished from cocaine but not sucrose self-administration. The capacity to inhibit reinstated cocaine seeking was prevented by systemic administration of the group II metabotropic glutamate receptor antagonist LY341495. CONCLUSIONS: DREADD-mediated glutamate gliotransmission inhibited cue-induced reinstatement of cocaine seeking by stimulating release-regulating group II metabotropic glutamate receptor autoreceptors to inhibit cue-induced synaptic glutamate spillover.

Effects of aging on glutamate neurotransmission in the substantia nigra of Gdnf heterozygous mice.

Glial cell line-derived neurotrophic factor (GDNF) helps protect dopaminergic neurons in the nigrostriatal tract. Although the cause of nigrostriatal degeneration is unknown, one theory is that excess glutamate from the subthalamic nucleus results in excitotoxic events in the substantia nigra (SN). Because dopaminergic degeneration is accompanied by a reduction in GDNF, we examined glutamate neurotransmission in the SN using a Gdnf heterozygous mouse model (Gdnf(+/-)) at 8 and 12 months of age. At 8 months, Gdnf(+/-) mice have greater glutamate release and higher basal glutamate levels, which precede the SN dopaminergic degeneration observed at 12 months of age. However, at 12 months, Gdnf(+/-) mice have lower basal levels of glutamate and less glutamate release than wild-type mice. Also at 8 months, Gdnf(+/-) mice have lower levels of glutamate transporter-1 and greater glial fibrillary acidic protein levels in the SN compared with wild-type mice, differences that increase with age. These data suggest that reduced levels of GDNF induce excess glutamate release and dysregulation of glutamate transporter-1, causing excitotoxicity in the SN that precedes dopaminergic degeneration.

Designer receptors enhance memory in a mouse model of Down syndrome.

Designer receptors exclusively activated by designer drugs (DREADDs) are novel and powerful tools to investigate discrete neuronal populations in the brain. We have used DREADDs to stimulate degenerating neurons in a Down syndrome (DS) model, Ts65Dn mice. Individuals with DS develop Alzheimer's disease (AD) neuropathology and have elevated risk for dementia starting in their 30s and 40s. Individuals with DS often exhibit working memory deficits coupled with degeneration of the locus coeruleus (LC) norepinephrine (NE) neurons. It is thought that LC degeneration precedes other AD-related neuronal loss, and LC noradrenergic integrity is important for executive function, working memory, and attention. Previous studies have shown that LC-enhancing drugs can slow the progression of AD pathology, including amyloid aggregation, oxidative stress, and inflammation. We have shown that LC degeneration in Ts65Dn mice leads to exaggerated memory loss and neuronal degeneration. We used a DREADD, hM3Dq, administered via adeno-associated virus into the LC under a synthetic promoter, PRSx8, to selectively stimulate LC neurons by exogenous administration of the inert DREADD ligand clozapine-N-oxide. DREADD stimulation of LC-NE enhanced performance in a novel object recognition task and reduced hyperactivity in Ts65Dn mice, without significant behavioral effects in controls. To confirm that the noradrenergic transmitter system was responsible for the enhanced memory function, the NE prodrug l-threo-dihydroxyphenylserine was administered in Ts65Dn and normosomic littermate control mice, and produced similar behavioral results. Thus, NE stimulation may prevent memory loss in Ts65Dn mice, and may hold promise for treatment in individuals with DS and dementia.

Pilot Study and Review: Physiological Differences in BDNF, a Potential Biomarker in Males and Females with Autistic Disorder.

AIMS: There is a need for more biologic research in autistic disorder (AD) to determine if biomarkers exist that would be useful for correlating to symptom severity and/or clinical improvement during treatment. Given the fact that AD is 4 times more common in males than females, gender differences in physiological biomarkers may be present. One potential biomarker that has begun to be studied is brain-derived neurotropic factor (BDNF), a peptide involved in the regulation of neuronal cell survival, differentiation, and plasticity, and possessing an ability to influence neurotransmitter systems by modulating gene expression. This pilot study examined whether serum BDNF differed according to gender in children with AD and whether differences were associated with a behavioral phenotype or severity of illness. STUDY DESIGN: Data for this investigation were collected during the participants' baseline visit of an intervention study. Participants were males (n=29) and females (n=7), aged 5 to 12 years diagnosed with AD. Baseline serum BDNF concentration was determined for comparison to clinical ratings using an autism severity measure and the Pervasive Developmental Disorder-Behavior Inventory (PDD-BI). RESULTS: BDNF serum concentrations were higher in females (p<0.049). The baseline BDNF value corresponded significantly to hyperactivity in females (p<0.0002) but not in males. BDNF did not correlate with severity of disease in either gender. CONCLUSION: Although this is a small study, a better understanding of the central role of BDNF may provide insight into the pathophysiology of the disease and elucidate why gender differences exist in prevalence and behavioral phenotype of AD.