Regulation of System Xc-by the Neuropeptide PACAP: Implications for Glutamate Transmission in Drug Addiction

Drug addiction is a chronic brain disorder characterized by heightened relapse susceptibility. Drug-induced aberrant glutamate signaling in corticostriatal circuitry contributes to behaviors in virtually every preclinical model of drug seeking and correlates with drug craving in human. Here, we propose that glutamate signaling is a product of integrated activity between neurons and astrocytes, such that disruptions within astrocytes can stem from abnormal neuronal signaling (e.g., altered corticostriatal firing) and be the source of additional disruptions in other neuronal circuits. The astrocytic mechanism studied in these experiments is system xc- (Sxc) since drug-induced changes to this non-vesicular glutamate release mechanism contribute to heightened relapse vulnerability in preclinical models of addiction. My first objective was to determine whether neurons or neuronal factors regulate Sxc activity in astrocytes (Chapter II and III) since this would illustrate the degree to which glutamate signaling involves integrated activity of multiple cell types. We found that neurons release a soluble factor that potently increases Sxc activity. Moreover, we discovered that the neuropeptide PACAP (pituitary adenylate cyclase-activating peptide) likely contributes to this effect since it upregulates Sxc activity in astrocytes (Chapters II and III). Next, we focused on the importance of PACAP regulation of Sxc to synaptic transmission in the nucleus accumbens (NAc), since this structure is highly implicated in drug addiction (Chapter IV). PACAP depressed synaptic transmission in NAc neurons projecting to the substantia nigra, an important efferent that encodes motivated behaviors. Interestingly, PACAP-induced control over synaptic transmission required enhanced Sxc activity. Given this, we then determined the behavioral impact of increasing PACAP signaling in the NAc on drug-seeking behavior (Chapter IV). Specifically, we found that microinfusion of PACAP into the NAc attenuated cocaine-primed reinstatement of drug seeking. Lastly, we determined that PACAP is expressed in corticostriatal projections to the NAc, and that endogenous PACAP is an unrecognized factor influencing relapse vulnerability (Chapter IV). Collectively, this dissertation reveals that a novel form of neuron-astrocyte communication, namely PACAP regulation of Sxc, is a critical link integrating the glutamate network that mediates motivated behavior

Pituitary Adenylate Cyclase-Activating Polypeptide Orchestrates Neuronal Regulation Of The Astrocytic Glutamate-Releasing Mechanism System x\u3csub\u3ec\u3c/sub\u3e\u3csup\u3e−\u3c/sup\u3e

Glutamate signaling is achieved by an elaborate network involving neurons and astrocytes. Hence, it is critical to better understand how neurons and astrocytes interact to coordinate the cellular regulation of glutamate signaling. In these studies, we used rat cortical cell cultures to examine whether neurons or releasable neuronal factors were capable of regulating system xc-(Sxc), a glutamate-releasing mechanism that is expressed primarily by astrocytes and has been shown to regulate synaptic transmission. We found that astrocytes cultured with neurons or exposed to neuronal-conditioned media displayed significantly higher levels of Sxc activity. Next, we demonstrated that the pituitary adenylate cyclase-activating polypeptide (PACAP) may be a neuronal factor capable of regulating astrocytes. In support, we found that PACAP expression was restricted to neurons, and that PACAP receptors were expressed in astro-cytes. Interestingly, blockade of PACAP receptors in cultures comprised of astrocytes and neurons significantly decreased Sxc activity to the level observed in purified astrocytes, whereas application of PACAP to purified astrocytes increased Sxc activity to the level observed in cultures comprised of neurons and astrocytes. Collectively, these data reveal that neurons coordinate the actions of glutamate-related mechanisms expressed by astrocytes, such as Sxc, a process that likely involves PACAP

PACAP and Cocaine Reinstatement: A Neuropeptide Expressed by Corticostriatal Neurons that Regulates Nucleus Accumbens Astrocytes

Drug addiction involves heightened relapse vulnerability arising from persistent drug-induced neuro-adaptations, including a) hypofrontality which is thought to reflect reduced firing of cortical afferents to the nucleus accumbens (NAcc) and b) altered glutamate homeostasis in NAcc that likely involves reduced glutamate release and uptake by astrocytes. An important question is whether these forms of pathological plasticity are functionally linked such that reduced corticostriatal firing may result in aberrant regulation of astrocytes in the NAcc. To begin to evaluate this possibility, we first determined whether neurons regulate system xc- (Sxc) activity, a mechanism of non-vesicular glutamate release by astrocytes. We found that the rate of Sxc activity in astrocyte cultures was significantly increased in cells exposed to neuronal conditioned media achieved using neuronal inserts. These experiments demonstrate that releasable neuronal factors significantly upregulate Sxc activity. We hypothesize that the pituitary adenylyl cyclase activating peptide (PACAP) may be the neuronal factor regulating glutamate release by astrocytes involving Sxc. First we determined that PACAP mimics a neuronal insert in that it significantly upregulates Sxc activity in astrocytes. Next, we verified the expression of PACAP in neurons from the prefrontal cortex (PFC) projecting to NAcc. Together, these data support the hypothesis that reduced corticostriatal firing may result in decreased PACAP release in NAcc which could potentially blunt Sxc activity in NAcc astrocytes. To determine whether this would impact relapse vulnerability, we microinjected PACAP into the NAcc and found that this significantly reduced cocaine-primed reinstatement, suggesting that increased PACAP signaling, consistent with other approaches capable of increasing Sxc activity, may blunt relapse vulnerability. In order to determine whether reduced PACAP signaling is sufficient to increase relapse vulnerability, we microinjected the PAC1R inhibitor PACAP6-38 into the NAcc. Preliminary data indicate that this is sufficient to produce an increase in cocaine reinstatement. Collectively, these studies demonstrate that neuropeptide PACAP is a powerful regulator of cocaine-related behaviors, likely through the modulation of glutamate homeostasis as maintained by astrocytes. As a result, an unrecognized consequence of hypofrontality may be impairing neuron-astrocyte interactions in a manner that determines the magnitude of relapse vulnerability

Behavioral Assessment of Acute Inhibition of System x\u3csub\u3ec\u3c/sub\u3e\u3csup\u3e -\u3c/sup\u3e in rats

Rationale Gaps in our understanding of glutamatergic signaling may be key obstacles in accurately modeling complex CNS diseases. System xc - is an example of a poorly understood component of glutamate homeostasis that has the potential to contribute to CNS diseases. Objectives This study aims to determine whether system xc - contributes to behaviors used to model features of CNS disease states. Methods In situ hybridization was used to map mRNA expression of xCT throughout the brain. Microdialysis in the prefrontal cortex was used to sample extracellular glutamate levels; HPLC was used to measure extracellular glutamate and tissue glutathione concentrations. Acute administration of sulfasalazine (8–16 mg/kg, IP) was used to decrease system xc - activity. Behavior was measured using attentional set shifting, elevated plus maze, open-field maze, Porsolt swim test, and social interaction paradigm. Results The expression of xCT mRNA was detected throughout the brain, with high expression in several structures including the basolateral amygdala and prefrontal cortex. Doses of sulfasalazine that produced a reduction in extracellular glutamate levels were identified and subsequently used in the behavioral experiments. Sulfasalazine impaired performance in attentional set shifting and reduced the amount of time spent in an open arm of an elevated plus maze and the center of an open-field maze without altering behavior in a Porsolt swim test, total distance moved in an open-field maze, or social interaction. Conclusions The widespread distribution of system xc - and involvement in a growing list of behaviors suggests that this form of nonvesicular glutamate release is a key component of excitatory signaling

Reduction in Phencyclidine Induced Sensorimotor Gating Deficits in the Rat Following Increased System Xc − Activity in the Medial Prefrontal Cortex

Rationale: Aspects of schizophrenia, including deficits in sensorimotor gating, have been linked to glutamate dysfunction and/or oxidative stress in the prefrontal cortex. System xc −, a cystine–glutamate antiporter, is a poorly understood mechanism that contributes to both cellular antioxidant capacity and glutamate homeostasis. Objectives: Our goal was to determine whether increased system xc − activity within the prefrontal cortex would normalize a rodent measure of sensorimotor gating. Methods: In situ hybridization was used to map messenger RNA (mRNA) expression of xCT, the active subunit of system xc −, in the prefrontal cortex. Prepulse inhibition was used to measure sensorimotor gating; deficits in prepulse inhibition were produced using phencyclidine (0.3–3 mg/kg, sc). N-Acetylcysteine (10–100 μM) and the system xc − inhibitor (S)-4-carboxyphenylglycine (CPG, 0.5 μM) were used to increase and decrease system xc − activity, respectively. The uptake of 14C-cystine into tissue punches obtained from the prefrontal cortex was used to assay system xc − activity. Results: The expression of xCT mRNA in the prefrontal cortex was most prominent in a lateral band spanning primarily the prelimbic cortex. Although phencyclidine did not alter the uptake of 14C-cystine in prefrontal cortical tissue punches, intraprefrontal cortical infusion of N-acetylcysteine (10–100 μM) significantly reduced phencyclidine- (1.5 mg/kg, sc) induced deficits in prepulse inhibition. N-Acetylcysteine was without effect when coinfused with CPG (0.5 μM), indicating an involvement of system xc −. Conclusions: These results indicate that phencyclidine disrupts sensorimotor gating through system xc − independent mechanisms, but that increasing cystine–glutamate exchange in the prefrontal cortex is sufficient to reduce behavioral deficits produced by phencyclidine

The Zakharov system and its soliton solutions

This book focuses on the theory of the Zakharov system in the context of plasma physics. It has been over 40 years since the system was first derived by V. E. Zakharov – and in the course of those decades, many innovative achievements with major impacts on other research fields have been made. The book represents a first attempt to highlight the mathematical theories that are most important to researchers, including the existence and unique problems, blow-up, low regularity, large time behavior and the singular limit. Rather than attempting to examine every aspect of the Zakharov system in detail, it provides an effective road map to help readers access the frontier of studies on this system.

A Case Study of Damage Energy Analysis and an Early Warning by Microseismic Monitoring for Large Area Roof Caving in Shallow Depth Seams

Shallow depth coal seams are widely spread in Shendong mining area, which is located in the Northwestern region of China. When working face is advanced out of concentrated coal pillar in upper room and pillar goaf, strong strata behaviors often cause support crushing accidents, and potentially induce large area residual pillars instability and even wind blast disaster. In order to predict the precise time when the accident happens, guaranteeing life-safety of miner, microseismic monitoring system was for the first time applied in shallow coal seam. Based on damage mechanics correlation theory, the damage energy model is established to describe relationship between damage level and cumulative energy of microseismic events. According to microseismic monitoring data of two support crushing accidents, the damage energy model is verified and an effective early warning method of these accidents is proposed. The field application showed that the early warning method had avoided miners suffering from all support crushing accidents in Shigetai coal mine

Radiation-Induced Degradation Analysis and Reliability Modeling of COTS ADCs for Space-Borne Miniature Fiber-Optic Gyroscopes

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