Appetitive cue-evoked ERK signaling in the nucleus accumbens requires NMDA and D1 dopamine receptor activation and regulates CREB phosphorylation.

Conditioned stimuli (CS) can modulate reward-seeking behavior. This modulatory effect can be maladaptive and has been implicated in excessive reward seeking and relapse to drug addiction. We previously demonstrated that exposure to an appetitive CS causes an increase in the activation of extracellular signal-regulated kinase (ERK) and cyclic-AMP response-element binding protein (CREB) in the nucleus accumbens (NAc) of rats, and that CS-evoked ERK activation is critical for CS control over reward seeking. To elucidate the mechanism that mediates CS-driven ERK activation in the NAc, we selectively blocked NMDA glutamate or D1 dopamine receptors in the NAc. To determine whether CS-driven ERK and CREB activation are linked, we selectively blocked ERK signaling in the NAc. We found that both NMDA and D1 receptors are critical for CS-driven ERK signaling in the NAc, and that this recruitment of the ERK cascade is responsible for increased CREB activation in the presence of the CS. Our findings suggest that activation of the NMDAR-D1R/ERK/CREB signal transduction pathway plays a critical role in the control of reward-seeking behavior by reward-predictive cues.

Case-control study of environmental toxins and risk of amyotrophic lateral sclerosis involving the national ALS registry.

Objective: Neurotoxic chemicals are suggested in the etiology of amyotrophic lateral sclerosis (ALS). We examined the association of environmental and occupational risk factors including persistent organochlorine pesticides (OCPs) and ALS risk among cases from the Centers for Disease Control and Prevention National ALS Registry and age, sex, and county-matched controls. Methods: Participants completed a risk factor survey and provided a blood sample for OCP measurement. ALS cases were confirmed through the Registry. Conditional logistic regression assessed associations between ALS and risk factors including OCP levels. Results: 243 matched case-control pairs (61.7% male, mean [SD] age = 62.9 [10.1]) were included. Fifteen of the 29 OCPs examined had sufficient detectable levels for analysis. Modest correlations of self-reported years of exposure to residential pesticide mixtures and OCP serum levels were found (p<.001). Moreover, occupational exposure to lead including soldering and welding with lead/metal dust and use of lead paint/gasoline were significantly related to ALS risk (OR = 1.77, 95% CI: 1.11-2.83). Avocational gardening was a significant risk factor for ALS (OR = 1.57, 95% CI: 1.04-2.37). ALS risk increased for each 10 ng/g of α-Endosulfan (OR = 1.42, 95% CI: 1.14-1.77) and oxychlordane (OR = 1.24, 95% CI: 1.01-1.53). Heptachlor (detectable vs. nondetectable) was also associated with ALS risk (OR = 3.57, 95% CI: 1.50-8.52). Conclusion: This national case-control study revealed both survey and serum levels of OCPs as risk factors for ALS. Despite the United States banning many OCPs in the 1970s and 1980s, their use abroad and long half-lives continue to exert possible neurotoxic health effects.

Defining RNA oligonucleotides that reverse deleterious phase transitions of RNA-binding proteins with prion-like domains.

RNA-binding proteins with prion-like domains, such as FUS and TDP-43, condense into functional liquids, which can transform into pathological fibrils that underpin fatal neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS)/frontotemporal dementia (FTD). Here, we define short RNAs (24-48 nucleotides) that prevent FUS fibrillization by promoting liquid phases, and distinct short RNAs that prevent and, remarkably, reverse FUS condensation and fibrillization. These activities require interactions with multiple RNA-binding domains of FUS and are encoded by RNA sequence, length, and structure. Importantly, we define a short RNA that dissolves aberrant cytoplasmic FUS condensates, restores nuclear FUS, and mitigates FUS proteotoxicity in optogenetic models and human motor neurons. Another short RNA dissolves aberrant cytoplasmic TDP-43 condensates, restores nuclear TDP-43, and mitigates TDP-43 proteotoxicity. Since short RNAs can be effectively delivered to the human brain, these oligonucleotides could have therapeutic utility for ALS/FTD and related disorders.

NUP62 localizes to ALS/FTLD pathological assemblies and contributes to TDP-43 insolubility.

A G4C2 hexanucleotide repeat expansion in the C9orf72 gene is the most common genetic cause of ALS and FTLD (C9-ALS/FTLD) with cytoplasmic TDP-43 inclusions observed in regions of neurodegeneration. The accumulation of repetitive RNAs and dipeptide repeat protein (DPR) are two proposed mechanisms of toxicity in C9-ALS/FTLD and linked to impaired nucleocytoplasmic transport. Nucleocytoplasmic transport is regulated by the phenylalanine-glycine nucleoporins (FG nups) that comprise the nuclear pore complex (NPC) permeability barrier. However, the relationship between FG nups and TDP-43 pathology remains elusive. Our studies show that nuclear depletion and cytoplasmic mislocalization of one FG nup, NUP62, is linked to TDP-43 mislocalization in C9-ALS/FTLD iPSC neurons. Poly-glycine arginine (GR) DPR accumulation initiates the formation of cytoplasmic RNA granules that recruit NUP62 and TDP-43. Cytoplasmic NUP62 and TDP-43 interactions promotes their insolubility and NUP62:TDP-43 inclusions are frequently found in C9orf72 ALS/FTLD as well as sporadic ALS/FTLD postmortem CNS tissue. Our findings indicate NUP62 cytoplasmic mislocalization contributes to TDP-43 proteinopathy in ALS/FTLD.

Critical involvement of postsynaptic protein kinase activation in long-term potentiation at hippocampal mossy fiber synapses on CA3 interneurons.

Hippocampal mossy fiber (MF) synapses on area CA3 lacunosum-moleculare (L-M) interneurons are capable of undergoing a Hebbian form of NMDA receptor (NMDAR)-independent long-term potentiation (LTP) induced by the same type of high-frequency stimulation (HFS) that induces LTP at MF synapses on pyramidal cells. LTP of MF input to L-M interneurons occurs only at synapses containing mostly calcium-impermeable (CI)-AMPA receptors (AMPARs). Here, we demonstrate that HFS-induced LTP at these MF-interneuron synapses requires postsynaptic activation of protein kinase A (PKA) and protein kinase C (PKC). Brief extracellular stimulation of PKA with forskolin (FSK) alone or in combination with 1-Methyl-3-isobutylxanthine (IBMX) induced a long-lasting synaptic enhancement at MF synapses predominantly containing CI-AMPARs. However, the FSK/IBMX-induced potentiation in cells loaded with the specific PKA inhibitor peptide PKI(6-22) failed to be maintained. Consistent with these data, delivery of HFS to MFs synapsing onto L-M interneurons loaded with PKI(6-22) induced posttetanic potentiation (PTP) but not LTP. Hippocampal sections stained for the catalytic subunit of PKA revealed abundant immunoreactivity in interneurons located in strata radiatum and L-M of area CA3. We also found that extracellular activation of PKC with phorbol 12,13-diacetate induced a pharmacological potentiation of the isolated CI-AMPAR component of the MF EPSP. However, HFS delivered to MF synapses on cells loaded with the PKC inhibitor chelerythrine exhibited PTP followed by a significant depression. Together, our data indicate that MF LTP in L-M interneurons at synapses containing primarily CI-AMPARs requires some of the same signaling cascades as does LTP of glutamatergic input to CA3 or CA1 pyramidal cells.

Properties and functional implications of I (h) in hippocampal area CA3 interneurons.

The present study examines the biophysical properties and functional implications of I (h) in hippocampal area CA3 interneurons with somata in strata radiatum and lacunosum-moleculare. Characterization studies showed a small maximum h-conductance (2.6 ± 0.3 nS, n = 11), shallow voltage dependence with a hyperpolarized half-maximal activation (V (1/2) = -91 mV), and kinetics characterized by double-exponential functions. The functional consequences of I (h) were examined with regard to temporal summation and impedance measurements. For temporal summation experiments, 5-pulse mossy fiber input trains were activated. Blocking I (h) with 50 µM ZD7288 resulted in an increase in temporal summation, suggesting that I (h) supports sensitivity of response amplitude to relative input timing. Impedance was assessed by applying sinusoidal current commands. From impedance measurements, we found that I (h) did not confer theta-band resonance, but flattened the impedance-frequency relations instead. Double immunolabeling for hyperpolarization-activated cyclic nucleotide-gated proteins and glutamate decarboxylase 67 suggests that all four subunits are present in GABAergic interneurons from the strata considered for electrophysiological studies. Finally, a model of I (h) was employed in computational analyses to confirm and elaborate upon the contributions of I (h) to impedance and temporal summation.

Protein phosphatases 1 and 2A are both required for long-term depression and associated dephosphorylation of cAMP response element binding protein in hippocampal area CA1 in vivo.

Evidence shows that the serine/threonine protein phosphatase 1 (PP1) plays a critical role in synaptic plasticity and memory. Little is known about the contribution of the serine/threonine phosphatase 1 (PP2A) to synaptic plasticity. Both protein phosphatases can target the transcription factor cAMP response element binding protein (CREB), whose phosphorylation at Ser133, we previously found, was downregulated during long-term depression (LTD) of glutamatergic transmission in area CA1 of the adult hippocampus in vivo. Other work from our group showed that the activity of PP2A, as well as that of PP1, is increased after LTD induction in area CA1 in vivo. We therefore investigated here whether both protein phosphatases are necessary for LTD in area CA1, and whether they both are involved in the LTD-associated modification of CREB. We found that inhibition of either PP1 or PP2A interferes with the establishment of LTD. Furthermore, inhibition of either enzyme alone abrogated the LTD-associated dephosphorylation of CREB. Interestingly, inhibition of PP1 disrupted CREB dephosphosphorylation rapidly after LTD-inducing stimulation, whereas inhibition of PP2A did not blunt the CREB modification until a later time point. Thus, both PP1 and PP2A regulate CREB during LTD in area CA1, although possibly through different signaling pathways. Our results demonstrate that PP2A, similar to PP1, plays an essential role in the molecular events that underlie LTD at glutamatergic synapses in hippocampal area CA1 in vivo. We propose that one of the mechanisms through which these protein phosphatases may contribute to the prolonged maintenance of LTD is through the regulation of CREB.

Cue-elicited reward-seeking requires extracellular signal-regulated kinase activation in the nucleus accumbens.

The motivation to seek out rewards can come under the control of stimuli associated with reward delivery. The ability of cues to motivate reward-seeking behavior depends on the nucleus accumbens (NAcc). The molecular mechanisms in the NAcc that underlie the ability of a cue to motivate reward-seeking are not well understood. We examined whether extracellular signal-regulated kinase (ERK), an important intracellular signaling pathway in learning and memory, has a role in these motivational processes. We first examined p42 ERK (ERK2) activation in the NAcc after rats were trained to associate an auditory stimulus with food delivery and found that, as a consequence of training, presentation of the auditory cue itself was sufficient to increase ERK2 activation in the NAcc. To examine whether inhibition of ERK in the NAcc prevents cue-induced reward-seeking, we infused an inhibitor of ERK, U0126, into the NAcc before assessing rats' instrumental responding in the presence versus absence of the conditioned cue. We found that, whereas vehicle-infused rats showed increased instrumental responding during cue presentation, rats infused with U0126 showed a profound impairment in cue-induced instrumental responding. In contrast, intra-NAcc U0126 infusion had no effect on rats' food-reinforced instrumental responding or their ability to execute conditioned approach behavior. Our results demonstrate learning-related changes in ERK signaling in the NAcc, and that disruption of ERK activation in this structure interferes with the incentive-motivational effects of conditioned stimuli. The molecular mechanisms described here may have implications for cue-elicited drug craving after repeated exposure to drugs of abuse.

Appetitive Pavlovian conditioned stimuli increase CREB phosphorylation in the nucleus accumbens.

The transcription factor cAMP response element-binding protein (CREB) in the nucleus accumbens (NAc) has been shown to regulate an animal's behavioral responsiveness to emotionally salient stimuli, and an increase in CREB phosphorylation in the NAc has been observed during exposure to rewarding stimuli, such as drugs of abuse. Here we show that CREB phosphorylation increases in the NAc also during exposure to cues that an animal has associated with delivery of natural rewards. Adult male Sprague-Dawley rats (rattus norvegicus) were trained to associate an auditory stimulus with delivery of food pellets, and CREB phosphorylation was examined in the striatum following training. We found that repeated tone-food pairings resulted in an increase in CREB phosphorylation in the NAc but not in the adjacent dorsal striatum or in the NAc 3h after the final training session. We further found that the cue itself, as opposed to the food pellets, the training context, or tone-food pairings, was sufficient to increase CREB phosphorylation in the NAc. These results suggest that the processing of primary rewarding stimuli and of environmental cues that predict them triggers similar accumbal signaling mechanisms.

RNA Binding Antagonizes Neurotoxic Phase Transitions of TDP-43.

TDP-43 proteinopathy is a pathological hallmark of amyotrophic lateral sclerosis and frontotemporal dementia where cytoplasmic TDP-43 inclusions are observed within degenerating regions of patient postmortem tissue. The mechanism by which TDP-43 aggregates has remained elusive due to technological limitations, which prevent the analysis of specific TDP-43 interactions in live cells. We present an optogenetic approach to reliably induce TDP-43 proteinopathy under spatiotemporal control. We show that the formation of pathologically relevant inclusions is driven by aberrant interactions between low-complexity domains of TDP-43 that are antagonized by RNA binding. Although stress granules are hypothesized to be a conduit for seeding TDP-43 proteinopathy, we demonstrate pathological inclusions outside these RNA-rich structures. Furthermore, we show that aberrant phase transitions of cytoplasmic TDP-43 are neurotoxic and that treatment with oligonucleotides composed of TDP-43 target sequences prevent inclusions and rescue neurotoxicity. Collectively, these studies provide insight into the mechanisms that underlie TDP-43 proteinopathy and present a potential avenue for therapeutic intervention.

Axotomy-induced neurotrophic withdrawal causes the loss of phenotypic differentiation and downregulation of NGF signalling, but not death of septal cholinergic neurons.

BACKGROUND: Septal cholinergic neurons account for most of the cholinergic innervations of the hippocampus, playing a key role in the regulation of hippocampal synaptic activity. Disruption of the septo-hippocampal pathway by an experimental transection of the fimbria-fornix drastically reduces the target-derived trophic support received by cholinergic septal neurons, mainly nerve growth factor (NGF) from the hippocampus. Axotomy of cholinergic neurons induces a reduction in the number of neurons positive for cholinergic markers in the medial septum. In several studies, the reduction of cholinergic markers has been interpreted as analogous to the neurodegeneration of cholinergic cells, ruling out the possibility that neurons lose their cholinergic phenotype without dying. Understanding the mechanism of cholinergic neurodegeneration after axotomy is relevant, since this paradigm has been extensively explored as an animal model of the cholinergic impairment observed in neuropathologies such as Alzheimer's disease.The principal aim of this study was to evaluate, using modern quantitative confocal microscopy, neurodegenerative changes in septal cholinergic neurons after axotomy and to assess their response to delayed infusion of NGF in rats. RESULTS: We found that there is a slow reduction of cholinergic cells labeled by ChAT and p75 after axotomy. However, this phenomenon is not accompanied by neurodegenerative changes or by a decrease in total neuronal number in the medial septum. Although the remaining axotomized-neurons appear healthy, they are unable to respond to delayed NGF infusion. CONCLUSIONS: Our results demonstrate that at 3 weeks, axotomized cholinergic neurons lose their cholinergic phenotype without dying and down-regulate their NGF-receptors, precluding the possibility of a response to NGF. Therefore, the physiological role of NGF in the adult septal cholinergic system is to support phenotypic differentiation and not survival of neurons. This evidence raises questions about the relationship between transcriptional regulation of the cholinergic phenotype by retrograde-derived trophic signaling and the transcriptional changes experienced when retrograde transport is impaired due to neuropathological conditions.