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.

Calcitriol promotes augmented dopamine release in the lesioned striatum of 6-hydroxydopamine treated rats.

Current therapies for Parkinson's disease (PD) offer symptomatic relief but do not provide a cure or slow the disease process. Treatments that could halt progression of the disease or help restore function to damaged neurons would be of substantial benefit. Calcitriol, the active metabolite of vitamin D, has been shown to have significant effects on the brain. These effects include upregulating trophic factor levels, and reducing the severity of some central nervous system lesions. While previous studies have shown that calcitriol can be neuroprotective in 6-hydroxydopamine (6-OHDA) rodent models of PD, the present experiments were designed to examine the ability of calcitriol to promote restoration of extracellular dopamine (DA) levels and tissue content of DA in animals previously lesioned with 6-OHDA. Male Fischer-344 rats were given a single injection of 12 µg 6-OHDA into the right striatum. Four weeks later the animals were administered vehicle or calcitriol (0.3 or 1.0 µg/kg, s.c.) once a day for eight consecutive days. Three weeks after the calcitriol treatments in vivo microdialysis experiments were conducted to measure potassium and amphetamine evoked overflow of DA from both the left and right striata. In control animals treated with 6-OHDA and vehicle there were significant reductions in both potassium and amphetamine evoked overflow of DA on the lesioned side of the brain compared to the contralateral side. In animals treated with 6-OHDA followed by calcitriol there was significantly greater potassium and amphetamine evoked overflow of DA from the lesioned striatum compared to that from the control animals. The calcitriol treatments also led to increases in postmortem tissue levels of DA in the striatum and substantia nigra. These results suggest that calcitriol may help promote recovery of dopaminergic functioning in injured nigrostriatal neurons.

Calcitriol protects against reductions in striatal serotonin in rats treated with neurotoxic doses of methamphetamine.

The present experiments were designed to examine the ability of calcitriol to protect against methamphetamine (METH)-induced reductions in striatal serotonin (5-HT) release and content. Male Fischer-344 rats were administered vehicle or calcitriol (0.3, 1.0, or 3.0 µg/kg, s.c.) once a day for 8 consecutive days. After the seventh day of treatment the animals were given METH (5 mg/kg, s.c.) or saline 4 times in 1 day at 2 h intervals. Seven days after the METH or saline treatments in vivo microdialysis experiments were conducted to measure potassium and d-amphetamine evoked overflow of 5-HT from the striatum. In animals treated with vehicle and METH there were significant reductions in both potassium and d-amphetamine evoked overflow of 5-HT. The 1.0 and 3.0 µg/kg/day doses of calcitriol provided significant protection against the 5-HT depleting effects of METH. A similar pattern of neuroprotection was found for post-mortem tissue levels of 5-HT. The calcitriol treatments did not prevent hyperthermia during the multiple injections of METH, indicating that the protective effects of calcitriol are not due to prevention of METH-induced increases in body temperature. These results suggest that calcitriol can provide significant protection against the 5-HT depleting effects of neurotoxic doses of METH.

Trichloroethylene induces dopaminergic neurodegeneration in Fisher 344 rats.

Trichloroethylene, a chlorinated solvent widely used as a degreasing agent, is a common environmental contaminant. Emerging evidence suggests that chronic exposure to trichloroethylene may contribute to the development of Parkinson's disease. The purpose of this study was to determine if selective loss of nigrostriatal dopaminergic neurons could be reproduced by systemic exposure of adult Fisher 344 rats to trichloroethylene. In our experiments, oral administration of trichloroethylene induced a significant loss of dopaminergic neurons in the substantia nigra pars compacta in a dose-dependent manner, whereas the number of both cholinergic and GABAergic neurons were not decreased in the striatum. There was a robust decline in striatal levels of 3, 4-dihydroxyphenylacetic acid without a significant depletion of striatal dopamine. Rats treated with trichloroethylene showed defects in rotarod behavior test. We also found a significantly reduced mitochondrial complex I activity with elevated oxidative stress markers and activated microglia in the nigral area. In addition, we observed intracellular alpha-synuclein accumulation in the dorsal motor nucleus of the vagus nerve, with some in nigral neurons, but little in neurons of cerebral cortex. Overall, our animal model exhibits some important features of Parkinsonism, and further supports that trichloroethylene may be an environmental risk factors for Parkinson's disease.

Neurturin effects on nigrostriatal dopamine release and content: comparison with GDNF.

Neurturin (NTN) is a member of the glial cell line-derived neurotrophic factor (GDNF) family; and, while GDNF has been shown to increase dopamine (DA) release in normal animals, the ability of NTN to alter DA release has not been previously reported. The purpose of the present study was to determine if NTN could alter striatal DA release, and to compare the effects of NTN to GDNF. Male Fischer-344 rats were given a single injection of vehicle or 5 microg NTN or GDNF into the right substantia nigra. Three weeks later microdialysis experiments were conducted to assess striatal DA release. Basal extracellular levels of striatal DA were not affected by either NTN or GDNF. However, both NTN and GDNF led to increases in amphetamine-evoked overflow of DA from the ipsilateral striatum, and there was a trend for potassium-evoked overflow to be augmented. Postmortem tissue levels of DA were decreased by approximately 20% in the striatum, and increased by approximately 100% in the substantia nigra, on the ipsilateral side of the brain compared to the contralateral side following both NTN and GDNF injection. Thus, NTN, like GDNF, can augment striatal DA release, and the magnitude of the NTN effects are similar to those of GDNF.

Strain difference in the up-regulation of FGF-2 protein following a neurotoxic lesion of the nigrostriatal pathway.

Lesions of the nigrostriatal pathway are known to induce a compensatory up-regulation of various neurotrophic factors. In this study we examined protein content of basic fibroblast growth factor (FGF-2) in tissue samples taken from the ventral midbrain and striatum at two different time points following a neurotoxic lesion of the nigrostriatal pathway in two different rat strains, the outbred Sprague-Dawley (SD) and inbred F344 9 Brown Norway F1 hybrid (F344BNF1). Despite both rat strains having comparable lesions of the nigrostriatal pathway, we observed a difference in the temporal up-regulation of FGF-2 in ventral midbrain samples taken from the side ipsilateral to the lesion. Basic FGF was significantly upregulated in ventral midbrain in SD rats 1 week post-lesion while we did not observe an up-regulation of FGF-2 in the lesioned ventral midbrain of F344BNF1 at this same time point. However, both strains showed a significant up-regulation of FGF-2 in the lesioned ventral midbrain 3 weeks post-lesion. Sprague-Dawley rats also appeared to be more sensitive to the lesion in terms of up-regulating FGF-2 expression. The differences reported here suggest currently unknown genetic differences between these two strains may be important factors for regulating the compensatory release of neurotrophic factors, such as FGF-2, in response to a neurotoxic lesion of the nigrostriatal pathway.

Intrastriatal lipopolysaccharide injection induces parkinsonism in C57/B6 mice.

A role for inflammation has been hypothesized in the etiology and progression of Parkinson's disease (PD). In this study, we generated, characterized, and validated the first progressive PD-related mouse model (C57/B6) with intrastriatal injection of lipopolysaccharide (LPS). We showed progressive and specific dopaminergic neurodegeneration in the substantia nigra, which is accompanied by striatal dopamine depletion and progressive behavioral impairment, which was alleviated by the use of the PD drug L-Dopa. We focused on the role of nitric oxide (NO) in inflammation-promoted cell death and suggest that the expression of the inducible NO synthase plays a role in the progressive loss of dopaminergic neurons but not the initial loss induced by LPS. With this model, future research can be performed in gene knockout mice to study other potential mechanisms of inflammation-induced neurodegeneration. In addition, this model can be used to screen therapeutics for PD at a more clinically relevant time (i.e., after LPS injection but before manifestation of PD-related behavioral impairment), because most PD drugs are screened in animal models in which inhibitors are given predisease induction. Thus, this novel PD-related model should be further characterized and strongly considered as a tool for future drug studies.

Trichloroethylene: Parkinsonism and complex 1 mitochondrial neurotoxicity.

OBJECTIVE: To analyze a cluster of 30 industrial coworkers with Parkinson's disease and parkinsonism subjected to long-term (8-33 years) chronic exposure to trichloroethylene. METHODS: Neurological evaluations were conducted on the 30 coworkers, including a general physical and neurological examination and the Unified Parkinson's Disease Rating Scale. In addition, fine motor speed was quantified and an occupational history survey was administered. Next, animal studies were conducted to determine whether trichloroethylene exposure is neurotoxic to the nigrostriatal dopamine system that degenerates in Parkinson's disease. The experiments specifically analyzed complex 1 mitochondrial neurotoxicity because this is a mechanism of action of other known environmental dopaminergic neurotoxins. RESULTS: The three workers with workstations adjacent to the trichloroethylene source and subjected to chronic inhalation and dermal exposure from handling trichloroethylene-soaked metal parts had Parkinson's disease. Coworkers more distant from the trichloroethylene source, receiving chronic respiratory exposure, displayed many features of parkinsonism, including significant motor slowing. Neurotoxic actions of trichloroethylene were demonstrated in accompanying animal studies showing that oral administration of trichloroethylene for 6 weeks instigated selective complex 1 mitochondrial impairment in the midbrain with concomitant striatonigral fiber degeneration and loss of dopamine neurons. INTERPRETATION: Trichloroethylene, used extensively in industry and the military and a common environmental contaminant, joins other mitochondrial neurotoxins, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and some pesticides, as a risk factor for parkinsonism.

PINK1 deficiency is associated with increased deficits of adult hippocampal neurogenesis and lowers the threshold for stress-induced depression in mice.

Parkinson's disease (PD) is characterized by motor impairments and several non-motor features, including frequent depression and anxiety. Stress-induced deficits of adult hippocampal neurogenesis (AHN) have been linked with abnormal affective behavior in animals. It has been speculated that AHN defects may contribute to affective symptoms in PD, but this hypothesis remains insufficiently tested in animal models. Mice that lack the PD-linked kinase PINK1 show impaired differentiation of adult-born neurons in the hippocampus. Here, we examined the relationship between AHN deficits and affective behavior in PINK1-/- mice under basal (no stress) conditions and after exposure to chronic stress. PINK1 loss and corticosterone negatively and jointly affected AHN, leading to lower numbers of neural stem cells and newborn neurons in the dentate gyrus of corticosterone-treated PINK1-/- mice. Despite increased basal AHN deficits, PINK1-deficient mice showed normal affective behavior. However, lack of PINK1 sensitized mice to corticosterone-induced behavioral despair in the tail suspension test at a dose where wildtype mice were unaffected. Moreover, after two weeks of chronic restraint stress male PINK1-/- mice displayed increased immobility in the forced swim test, and protein expression of the glucocorticoid receptor in the hippocampus was reduced. Thus, while impaired AHN as such is insufficient to cause affective dysfunction in this PD model, PINK1 deficiency may lower the threshold for chronic stress-induced depression in PD. Finally, PINK1-deficient mice displayed reduced basal voluntary wheel running but normal rotarod performance, a finding whose mechanisms remain to be determined.

GDNF reduces oxidative stress in a 6-hydroxydopamine model of Parkinson's disease.

Many current theories of Parkinson's disease (PD) suggest that oxidative stress is involved in the neurodegenerative process. Potential neuroprotective agents could protect neurons through inherent antioxidant properties or through the upregulation of the brain's antioxidant defenses. Glial cell line-derived neurotrophic factor (GDNF) has been shown to protect and restore dopamine neurons in experimental models of PD and to improve motor function in human patients. This study was designed to investigate GDNF's effect on oxidative stress in a model of PD. GDNF or vehicle was injected into the right striatum of male Fischer-344 rats. Three days later 6-OHDA or saline was injected into the same striatum. The striatum and substantia nigra from both sides of the brain were removed 24h after 6-OHDA or saline injection and analyzed for the oxidative stress markers protein carbonyls and 4-hydroxynonenal. Both markers were significantly reduced in GDNF+6-OHDA treated animals compared to vehicle+6-OHDA treated animals. In addition, in animals allowed to recover for 3.5-4 weeks after the 6-OHDA administration, the GDNF led to significant protection against loss of striatal and nigral tissue levels of dopamine. These results suggest that the protective effects of GDNF against 6-OHDA involve a reduction in oxidative stress.

Fenbendazole treatment may influence lipopolysaccharide effects in rat brain.

In evaluating discrepant results between experiments in our laboratory, we collected data that challenge the notion that anthelminthic drugs like FBZ do not alter inflammatory responses. We found that FBZ significantly modulates inflammation in F344 rats intrastriatally injected with LPS. FBZ treatment of LPS-injected rats significantly increased weight loss, microglial activation, and dopamine loss; in addition, FBZ attenuated the LPS-induced loss of astrocytes. Therefore, FBZ treatment altered the effects of LPS injection. Caution should be used in interpreting data collected from rats treated with LPS and FBZ.

Reduced ability of calcitriol to promote augmented dopamine release in the lesioned striatum of aged rats.

Parkinson's disease (PD) is a progressive and debilitating neurodegenerative disorder that affects over one million people in the United States. Previous studies, carried out in young adult rats, have shown that calcitriol, the active metabolite of vitamin D, can be neuroprotective in 6-hydroxydopamine (6-OHDA) models of PD. However, as PD usually affects older individuals, the ability of calcitriol to promote dopaminergic recovery was examined in lesioned young adult (4 month old), middle-aged (14 month old) and aged (22 month old) rats. Animals were given a single injection of 12 µg 6-OHDA into the right striatum. Four weeks later they were administered vehicle or calcitriol (1.0 µg/kg, s.c.) once a day for eight consecutive days. In vivo microdialysis experiments were carried out three weeks after the calcitriol or vehicle treatments to measure potassium and amphetamine evoked overflow of DA from both the left and right striata. In control animals treated with 6-OHDA and vehicle there were significant reductions in evoked overflow of DA on the lesioned side of the brain compared to the contralateral side. The calcitriol treatments significantly increased evoked overflow of DA from the lesioned striatum in both the young adult and middle-aged rats. However, the calcitriol treatments did not significantly augment DA overflow in the aged rats. Postmortem tissue levels of striatal DA were also increased in the young and middle-aged animals, but not in the aged animals. In the substantia nigra, the calcitriol treatments led to increased levels of DA in all three age groups. Thus, the effects of calcitriol were similar in the young adult and middle-aged animals, but in the aged animals the effects of calcitriol were diminished. These results suggest that calcitriol may help promote recovery of dopaminergic functioning in injured nigrostriatal neurons; however, the effectiveness of calcitriol may be reduced in aging.

Pioglitazone Attenuates Neuroinflammation and Promotes Dopaminergic Neuronal Survival in the Nigrostriatal System of Rats after Diffuse Brain Injury.

Increasing evidence suggests that traumatic brain injury (TBI) may raise the risk of developing late-onset Parkinson's disease (PD). Recently, the peroxisome proliferation-activated receptor gamma (PPARγ) agonist pioglitazone has been demonstrated to be neuroprotective in animal models of neurodegeneration. The present study investigates the vulnerability of the nigrostriatal system after TBI, and intervention with pioglitazone treatment. Adult male Sprague-Dawley rats were subjected to sham or moderate midline fluid percussion brain injury (mFPI), followed by an intraperitoneal injection of 10 mg/kg pioglitazone or vehicle beginning 30 min after the injury and subsequently every 24 h for 5 days. Following injury, pro-inflammatory cytokines and chemokine were acutely increased in the striatum and substantia nigra within 6 h. Dopaminergic axonal damage and microglial activation were revealed using immunohistochemistry in the medial forebrain bundle at 1 day post-injury. Microglial activation identified by Iba1 and OX-6 immunostaining was persistently increased in the substantia nigra pars compacta 7 to 28 days post-injury. Further, brain injury induced significant dopaminergic neuronal loss, which was quantified by tyrosine hydroxylase immunostaining and retrograde fluorescent tracer fluorogold labeling in the nigra at 28 days. Loss of neurons was accompanied by increased extracellular dopamine (DA) turnover in the striatum, indicating enhanced dopaminergic activity in functional compensation after nigrostriatal damage. Strikingly, pioglitazone treatment greatly attenuated microglial activation and improved dopaminergic neuronal survival in the nigrostriatal system, which may promote locomotor recovery. These results suggest that interventions that attenuate secondary inflammation could be a feasible therapeutic treatment to improve outcome after TBI.

Calcitriol protects against the dopamine- and serotonin-depleting effects of neurotoxic doses of methamphetamine.

Repeated methamphetamine (METH) administration to animals can result in long-lasting decreases in brain dopamine (DA) and serotonin (5-HT) content. Calcitriol, the active metabolite of vitamin D, has potent effects on brain cells, both in vitro and in vivo, including the ability to upregulate trophic factors and protect against various lesions. The present experiments were designed to examine the ability of calcitriol to protect against METH-induced reductions in striatal and nucleus accumbens levels of DA and 5-HT. Male Fischer-344 rats were administered vehicle or calcitriol (1 microg/kg, s.c.) once a day for eight consecutive days. After the seventh day of treatment the animals were given METH (5 mg/kg, s.c.) or saline four times in 1 day at 2-h intervals. Seven days later the striata and accumbens were harvested from the animals for high-performance liquid chromatography (HPLC) analysis of monoamines and metabolites. In animals treated with vehicle and METH, there were significant reductions in DA, 5-HT, and their metabolites in both the striatum and accumbens. In animals treated with calcitriol and METH, the magnitude of the METH-induced reductions in DA, 5-HT, and metabolites was substantially and significantly attenuated. The calcitriol treatments did not reduce the hyperthermia associated with multiple injections of METH, indicating that the neuroprotective effects of calcitriol are not due to the prevention of increases in body temperature. These results suggest that calcitriol can provide significant protection against the DA- and 5-HT-depleting effects of neurotoxic doses of METH.

Human immunodeficiency virus-1 protein tat and methamphetamine interactions.

The human immunodeficiency virus-1 (HIV-1) affects the central nervous system (CNS) in approximately 30% of infected individuals and basal ganglia structures seem to be most affected. The HIV-1-transactivating protein, Tat, has been suggested to be pathogenically relevant in HIV-1-induced neuronal injury. The abuse of methamphetamine (METH), which is great among this patient population, also affects the basal ganglia, causing degeneration of dopaminergic terminals. In previous studies, we demonstrated that coexposure to these two toxins caused a synergistic loss of striatal dopamine and binding to the dopamine transporter (DAT), suggesting a loss of dopamine terminals. Because the loss of dopamine and DAT, however, do not necessarily reflect dopamine terminal degeneration, we have used silver staining and TH immunohistochemistry to further examine this issue. We have also examined the glial reaction using GFAP as a marker of astrocyte activation and OX-42 as a marker of activated microglia. Lastly, we have begun to explore the mechanism of synergy by investigating the role that the cytokine TNF-alpha might play in Tat + METH synergy. Our data indicate that the synergistic loss of dopamine is likely the result of dopamine terminal degeneration. This injury is not a direct result of the number of activated glia but does involve TNF-alpha.

Protection by GDNF and other trophic factors against the dopamine-depleting effects of neurotoxic doses of methamphetamine.

Repeated methamphetamine (METH) administration to animals can result in long-lasting decreases in striatal dopamine (DA) content. It has previously been shown that glial cell line-derived neurotrophic factor (GDNF) can reduce the DA-depleting effects of neurotoxic doses of METH. However, there are several other trophic factors that are protective against dopaminergic toxins. Thus, the present experiments further investigated the protective effect of GDNF as well as the protective effects of several other trophic factors. Male Fischer-344 rats were given an intracerebral injection of trophic factor (2-10 microg) 1 day before METH (5 mg/kg, s.c., 4 injections at 2-h intervals). Seven days later DA levels in the striatum were measured using high-performance liquid chromatography (HPLC). Initial experiments indicated that only intrastriatal GDNF, and not intranigral GDNF, was protective. Thereafter, all other trophic factors were administered into the striatum. Members of the GDNF family (GDNF, neurturin, and artemin) all provided significant protection against the DA-depleting effects of METH, with GDNF providing the greatest protection. Brain-derived neurotrophic factor, neurotrophin-3, acidic fibroblast growth factor, basic fibroblast growth factor, ciliary neurotrophic factor, transforming growth factor-alpha (TGF-alpha), heregulin beta1 (HRG-beta1), and amphiregulin (AR) provided no significant protection at the doses examined. These results suggest that the GDNF family of trophic factors can provide significant protection against the DA-depleting effects of neurotoxic doses of METH.

Glial cell line-derived neurotrophic factor increases stimulus-evoked dopamine release and motor speed in aged rhesus monkeys.

Changes in the functional dynamics of dopamine release and regulation in the basal ganglia have been posited to contribute to age-related slowing of motor functions. Here, we report the effects of glial cell line-derived neurotrophic factor (GDNF) on the stimulus-evoked release of dopamine and motor speed in aged monkeys (21-27 years of age; n = 10). Although no changes were observed in the vehicle controls (n = 5), chronic infusions of 7.5 microg of GDNF per day for 2 months into the right lateral ventricle initially increased hand movement speed up to 40% on an automated hand-reach task. These effects were maintained for at least 2 months after replacing GDNF with vehicle, and increased up to another 10% after the reinstatement of GDNF treatment for 1 month. In addition, upper-limb motor performance times of the aged GDNF-treated animals (n = 5) recorded at the end of the study were similar to those of five young adult monkeys (8-12 years of age). The stimulus-evoked release of dopamine was significantly increased, up to 130% in the right caudate nucleus and putamen and up to 116% in both the right and left substantia nigra of the aged GDNF recipients compared with vehicle controls. Also, basal extracellular levels of dopamine were bilaterally increased, up to 163% in the substantia nigra of the aged GDNF-treated animals. The data suggest that the effects of GDNF on the release of dopamine in the basal ganglia may be responsible for the improvements in motor functions and support the hypothesis that functional changes in dopamine release may contribute to motor dysfunctions characterizing senescence.

Reductions in spontaneous locomotor activity in aged male, but not female, rats in a model of early Parkinson's disease.

The excessive loss of dopamine (DA) neurons that occurs with Parkinson's disease is usually confined to older individuals. While 6-hydroxydopamine (6-OHDA) is often used in animal models of DA neuron degeneration, there have been relatively few studies that have examined the effects of 6-OHDA in older animals. In the present study, we compared the effects of a bilateral, partial lesion with 6-OHDA in young (4 months), middle-aged (14 months), and aged (24 months) Fischer-344 rats of both sexes. Animals were given a single injection of vehicle or 100 mug 6-OHDA into the right lateral ventricle. Four weeks later, spontaneous locomotor activity was monitored. Microdialysis experiments were carried out 1 to 3 days later. The 6-OHDA treatments had no effect on horizontal activity or total distance traveled in young adults. However, with aged rats, there was a decrease in both measures in the vehicle-treated control rats compared to young adult controls, and a further decrease in the lesioned aged male rats. The 6-OHDA treatments led to significant decreases in both potassium- and amphetamine-evoked overflow of DA from the striatum in all groups. Thus, partial bilateral lesions of the nigrostriatal DA system led to decreases in evoked release of DA in the striatum of male and female rats of all three ages, but to changes in spontaneous activity only in the aged males. These results indicate that there are both age and sex differences in the brain's response to 6-OHDA, and imply that compensatory or neuroprotective mechanisms in the young brain and aged female brain are more efficient than in the aged male brain.

Methodology and effects of repeated intranasal delivery of DNSP-11 in a rat model of Parkinson's disease.

BACKGROUND: To circumvent the challenges associated with delivering large compounds directly to the brain for the treatment of Parkinson's disease (PD), non-invasive procedures utilizing smaller molecules with protective and/or restorative actions on dopaminergic neurons are needed. NEW METHOD: We developed a methodology for evaluating the effects of a synthetic neuroactive peptide, DNSP-11, on the nigrostriatal system using repeated intranasal delivery in both normal and a unilateral 6-hydroxydopamine (6-OHDA) lesion rat model of PD. RESULTS: Normal rats repeatedly administered varying doses of DNSP-11 intranasally for 3 weeks exhibited a significant increase in dopamine (DA) turnover in both the striatum and substantia nigra (SN) at 300µg, suggestive of a stimulative effect of the dopaminergic system. Additionally, a protective effect was observed following repeated intranasal administration in 6-OHDA lesioned rats, as suggested by: a significant decrease in d-amphetamine-induced rotation at 2 weeks; a decrease in DA turnover in the lesioned striatum; and an increased sparing of tyrosine hydroxylase (TH) positive (+) neurons in a specific sub-region of the lesioned substantia nigra pars compacta (SNpc). Finally, tracer studies showed (125)I-DNSP-11 distributed diffusely throughout the brain, including the striatum and SN, as quickly as 30min after a single intranasal dose. COMPARISON WITH EXISTING METHODS: The results of bilateral intranasal administration of DNSP-11 are compared to our unilateral single infusion studies to the brain in rats. CONCLUSIONS: These studies support that DNSP-11 can be delivered intranasally and maintain its neuroactive properties in both normal rats and in a unilateral 6-OHDA rat model of PD.