Age-dependent alterations of corticostriatal activity in the YAC128 mouse model of Huntington disease.

Huntington disease is a genetic neurodegenerative disorder that produces motor, neuropsychiatric, and cognitive deficits and is caused by an abnormal expansion of the CAG tract in the huntingtin (htt) gene. In humans, mutated htt induces a preferential loss of medium spiny neurons in the striatum and, to a lesser extent, a loss of cortical neurons as the disease progresses. The mechanisms causing these degenerative changes remain unclear, but they may involve synaptic dysregulation. We examined the activity of the corticostriatal pathway using a combination of electrophysiological and optical imaging approaches in brain slices and acutely dissociated neurons from the YAC128 mouse model of Huntington disease. The results demonstrated biphasic age-dependent changes in corticostriatal function. At 1 month, before the behavioral phenotype develops, synaptic currents and glutamate release were increased. At 7 and 12 months, after the development of the behavioral phenotype, evoked synaptic currents were reduced. Glutamate release was decreased by 7 months and was markedly reduced by 12 months. These age-dependent alterations in corticostriatal activity were paralleled by a decrease in dopamine D(2) receptor modulation of the presynaptic terminal. Together, these findings point to dynamic alterations at the corticostriatal pathway and emphasize that therapies directed toward preventing or alleviating symptoms need to be specifically designed depending on the stage of disease progression.

Acute inhibition of the CNS-specific kinase TTBK1 significantly lowers tau phosphorylation at several disease relevant sites.

Hyperphosphorylated tau protein is a pathological hallmark of numerous neurodegenerative diseases and the level of tau pathology is correlated with the degree of cognitive impairment. Tau hyper-phosphorylation is thought to be an early initiating event in the cascade leading to tau toxicity and neuronal death. Inhibition of tau phosphorylation therefore represents an attractive therapeutic strategy. However, the widespread expression of most kinases and promiscuity of their substrates, along with poor selectivity of most kinase inhibitors, have resulted in systemic toxicities that have limited the advancement of tau kinase inhibitors into the clinic. We therefore focused on the CNS-specific tau kinase, TTBK1, and investigated whether selective inhibition of this kinase could represent a viable approach to targeting tau phosphorylation in disease. In the current study, we demonstrate that TTBK1 regulates tau phosphorylation using overexpression or knockdown of this kinase in heterologous cells and primary neurons. Importantly, we find that TTBK1-specific phosphorylation of tau leads to a loss of normal protein function including a decrease in tau-tubulin binding and deficits in tubulin polymerization. We then describe the use of a novel, selective small molecule antagonist, BIIB-TTBK1i, to study the acute effects of TTBK1 inhibition on tau phosphorylation in vivo. We demonstrate substantial lowering of tau phosphorylation at multiple sites implicated in disease, suggesting that TTBK1 inhibitors may represent an exciting new approach in the search for neurodegenerative disease therapies.

Exposure to environmental tobacco smoke during pregnancy in rats yields less effect on indices of brain cell number and size than does postnatal exposure.

While there is evidence that human perinatal exposure to environmental tobacco smoke (ETS) can result in an increased risk of respiratory disorders and sudden infant death syndrome, evidence linking ETS exposure to neurodevelopmental handicaps is suggestive but less compelling. We previously noted that postnatal ETS exposure, rather than prenatal exposure, resulted in reduced concentration of hindbrain DNA and increased protein/DNA ratio when rat brain tissue was studied at 9 weeks postnatal age. We have now evaluated the effects of ETS exposure during pregnancy on brain development by assaying brain tissue at term. ETS exposure had no detectable effects on regional brain concentrations of DNA, protein and cholesterol or on protein/DNA and cholesterol/DNA ratios. While ETS exposure during pregnancy also had no detectable effects on the weights of the individual fetuses or on the weights of various organs, certain regions of the fetal skeleton demonstrated accelerated ossification. The findings of this study are contrasted to the developmental effects of both nicotine and ETS in Rhesus macaques. Additional studies designed specifically to assess the risk of prenatal ETS exposure on brain development in non-human primates and other precocial species are warranted.

Dopamine modulates release from corticostriatal terminals.

Normal striatal function is dependent on the availability of synaptic dopamine to modulate neurotransmission. Within the striatum, excitatory inputs from cortical glutamatergic neurons and modulatory inputs from midbrain dopamine neurons converge onto dendritic spines of medium spiny neurons. In addition to dopamine receptors on medium spiny neurons, D2 receptors are also present on corticostriatal terminals, where they act to dampen striatal excitation. To determine the effect of dopamine depletion on corticostriatal activity, we used the styryl dye FM1-43 in combination with multiphoton confocal microscopy in slice preparations from dopamine-deficient (DD) and reserpine-treated mice. The activity-dependent release of FM1-43 out of corticostriatal terminals allows a measure of kinetics quantified by the halftime decay of fluorescence intensity. In DD, reserpine-treated, and control mice, exposure to the D2-like receptor agonist quinpirole revealed modulation of corticostriatal kinetics with depression of FM1-43 destaining. In DD and reserpine-treated mice, quinpirole decreased destaining to a greater extent, and at a lower dose, consistent with hypersensitive corticostriatal D2 receptors. Compared with controls, slices from DD mice did not react to amphetamine or to cocaine with dopamine-releasing striatal stimulation unless the animals were pretreated with l-3,4-dihydroxyphenylalanine (l-dopa). Electron microscopy and immunogold labeling for glutamate terminals within the striatum demonstrated that the observed differences in kinetics of corticostriatal terminals in DD mice were not attributable to aberrant cytoarchitecture or glutamate density. Microdialysis revealed that basal extracellular striatal glutamate was normal in DD mice. These data indicate that dopamine deficiency results in morphologically normal corticostriatal terminals with hypersensitive D2 receptors.

Black soldier fly (Diptera: Stratiomyidae) colonization of pig carrion in south Georgia.

The black soldier fly, Hermetia illucens (L.), is thought to colonize corpses 20-30 days postmortem. However, recent observations indicate this might not be true for all cases. Therefore, we conducted a study examining colonization by the black soldier fly and other Diptera on pig carrion in a plowed field in southern Georgia from 20 September through 21 February. Our data indicate black soldier flies could colonize a corpse within the first week after death. Knowing this information could prevent a serious mistake in estimating the time at which a corpse is colonized by this species. This study also represents the first record of Chrysomya rufifacies in Georgia.

Rearing methods for the black soldier fly (Diptera: Stratiomyidae).

The black soldier fly, Heretia illucens (L.), is a nonpest tropical and warm-temperate region insect that is useful for managing large concentrations of animal manure and other biosolids. Manure management relying on wild fly oviposition has been successful in several studies. However, confidence in this robust natural system was low and biological studies were hampered by the lack of a dependable source of eggs and larvae. Larvae had been reared easily by earlier investigators, but achieving mating had been problematic. We achieved mating reliably in a 2 by 2 by 4-m screen cage in a 7 by 9 by 5-m greenhouse where sunlight and adequate space for aerial mating were available. Mating occurred during the shortest days of winter if the sun was not obscured by clouds. Adults were provided with water, but no food was required. Techniques for egg collection and larval rearing are given. Larvae were fed a moist mixture of wheat bran, corn meal, and alfalfa meal. This culture has been maintained for 3 yr. Maintainance of a black soldier fly laboratory colony will allow for development of manure management systems in fully enclosed animal housing and in colder regions.

Susceptibility of black soldier fly (Diptera: Stratiomyidae) larvae and adults to four insecticides.

Dosage-mortality regressions were determined for black soldier fly, Hermetia illucens (L.), larvae fed cyromazine or pyriproxifen treated media. Cyromazine LC50 for larvae dying before becoming prepupae ranged from 0.25 to 0.28 ppm with dosage-mortality regression slopes between 5.79 and 12.04. Cyromazine LC50s for larvae dying before emergence ranged from 0.13 to 0.19 ppm with dosage-mortality regression slopes between 3.94 and 7.69. Pyriproxifen dosage-mortality regressions were not generated for larvae failing to become prepupae since <32% mortality was recorded at the highest concentration of 1,857 ppm. LC50s for larvae failing to become adults ranged from 0.10 to 0.12 ppm with dosage mortality-regression slopes between 1.67 and 2.32. Lambda-cyhalothrin and permethrin dosage-mortality regressions were determined for wild adult black soldier flies and house flies, Musca domestica L., and for susceptible house flies. Our results indicate that the wild house fly, unlike the black soldier fly, population was highly resistant to each of these pyrethroids. Regression slopes for black soldier flies exposed to lambda-cyhalothrin were twice as steep as those determined for the wild house fly strain. Accordingly, LC50s for the black soldier fly and susceptible house fly were 10- to 30-fold lower than those determined for wild house flies. The differential sensitivity between wild black soldier flies and house flies might be due to behavioral differences. Adult house flies usually remain in animal facilities with the possibility of every adult receiving pesticide exposure, while black soldier fly adults are typically present only during emergence and oviposition thereby limiting their exposure.

Increased O-GlcNAcylation reduces pathological tau without affecting its normal phosphorylation in a mouse model of tauopathy.

Neurofibrillary tangles (NFT), mainly consisting of fibrillar aggregates of hyperphosphorylated tau, are a defining pathological feature of Alzheimer's Disease and other tauopathies. Progressive accumulation of tau into NFT is considered to be a toxic cellular event causing neurodegeneration. Tau is subject to O-linked N-acetylglucosamine (O-GlcNAc) modification and O-GlcNAcylation of tau has been suggested to regulate tau phosphorylation. We tested if an increase in tau O-GlcNAcylation affected tau phosphorylation and aggregation in the rTg4510 tau transgenic mouse model. Acute treatment of rTg4510 mice with an O-GlcNAcase inhibitor transiently reduced tau phosphorylation at epitopes implicated in tau pathology. More importantly, long-term inhibitor treatment strongly increased tau O-GlcNAcylation, reduced the number of dystrophic neurons, and protected against the formation of pathological tau species without altering the phosphorylation of non-pathological tau. This indicates that O-GlcNAcylation prevents the aggregation of tau in a manner that does not affect its normal phosphorylation state. Collectively, our results support O-GlcNAcase inhibition as a potential therapeutic strategy for the treatment of Alzheimer's Disease and other tauopathies.

Repeated exposure to methamphetamine causes long-lasting presynaptic corticostriatal depression that is renormalized with drug readministration.

Addiction-associated behaviors such as drug craving and relapse are hypothesized to result from synaptic changes that persist long after withdrawal and are renormalized by drug reinstatement, although such chronic synaptic effects have not been identified. We report that exposure to the dopamine releaser methamphetamine for 10 days elicits a long-lasting (>4 month) depression at corticostriatal terminals that is reversed by methamphetamine readministration. Both methamphetamine-induced chronic presynaptic depression and the drug's selective renormalization in drug-experienced animals are independent of corresponding long-term changes in synaptic dopamine release but are due to alterations in D1 dopamine and cholinergic receptor systems. These mechanisms might provide a synaptic basis that underlies addiction and habit learning and their long-term maintenance.