Sex-Specific Regulation of Stress Susceptibility by the Astrocytic Gene Htra1.

Major depressive disorder (MDD) is linked to impaired structural and synaptic plasticity in limbic brain regions. Astrocytes, which regulate synapses and are influenced by chronic stress, likely contribute to these changes. We analyzed astrocyte gene profiles in the nucleus accumbens (NAc) of humans with MDD and mice exposed to chronic stress. Htra1 , which encodes an astrocyte-secreted protease targeting the extracellular matrix (ECM), was significantly downregulated in the NAc of males but upregulated in females in both species. Manipulating Htra1 in mouse NAc astrocytes bidirectionally controlled stress susceptibility in a sex-specific manner. Such Htra1 manipulations also altered neuronal signaling and ECM structural integrity in NAc. These findings highlight astroglia and the brain's ECM as key mediators of sex-specific stress vulnerability, offering new approaches for MDD therapies.

Circuit-wide gene network analysis reveals sex-specific roles for phosphodiesterase 1b in cocaine addiction.

Cocaine use disorder is a significant public health issue without an effective pharmacological treatment. Successful treatments are hindered in part by an incomplete understanding of the molecular mechanisms that underlie long-lasting maladaptive plasticity and addiction-like behaviors. Here, we leverage a large RNA-sequencing dataset to generate gene co-expression networks across 6 interconnected regions of the brain's reward circuitry from mice that underwent saline or cocaine self-administration. We identify phosphodiesterase 1b (Pde1b), a Ca2+/calmodulin-dependent enzyme that increases cAMP and cGMP hydrolysis, as a central hub gene within a nucleus accumbens (NAc) gene module that was bioinformatically associated with addiction-like behavior. Chronic cocaine exposure increases Pde1b expression in NAc D2 medium spiny neurons (MSNs) in male but not female mice. Viral-mediated Pde1b overexpression in NAc reduces cocaine self-administration in female rats, but increases seeking in both sexes. In female mice, overexpressing Pde1b in D1 MSNs attenuates the locomotor response to cocaine, with the opposite effect in D2 MSNs. Overexpressing Pde1b in D1/D2 MSNs had no effect on the locomotor response to cocaine in male mice. At the electrophysiological level, Pde1b overexpression reduces sEPSC frequency in D1 MSNs, while increasing excitability of D2 MSNs. Lastly, Pde1b overexpression significantly reduced the number of differentially expressed genes (DEGs) in NAc following chronic cocaine, with discordant effects on gene transcription between sexes. Together, we identify novel gene modules across the brain's reward circuitry associated with addiction-like behavior and explore the role of Pde1b in regulating the molecular, cellular, and behavioral responses to cocaine.Significance Statement Cocaine use disorder is a major public health challenge without an effective pharmacological treatment. Here, we leverage a combination of genome-wide RNA sequencing, gene co-expression network analysis, and bioinformatic analyses of cocaine self-administration behavior to identify a role for phosphodiesterase 1b (Pde1b) in regulating maladaptive, addiction-like behavior. Our studies reveal cell-type- and sex-specific roles for Pde1b in regulating the molecular, cellular, and behavioral responses to cocaine, yielding insight into the molecular mechanisms by which cocaine induces maladaptive plasticity in the brain's reward circuity to drive addiction-like behavior. These discoveries guide directions for future research investigating the molecular basis of cocaine action and provide a pathway for therapeutic development for cocaine use disorder.

A locus coeruleus to dorsal hippocampus pathway mediates cue-induced reinstatement of opioid self-administration in male and female rats.

Opioid use disorder is a chronic relapsing disorder encompassing misuse, dependence, and addiction to opioid drugs. Long term maintenance of associations between the reinforcing effects of the drug and the cues associated with its intake are a leading cause of relapse. Indeed, exposure to the salient drug-associated cues can lead to drug cravings and drug seeking behavior. The dorsal hippocampus (dHPC) and locus coeruleus (LC) have emerged as important structures for linking the subjective rewarding effects of opioids with environmental cues. However, their role in cue-induced reinstatement of opioid use remains to be further elucidated. In this study, we showed that chemogenetic inhibition of excitatory dHPC neurons during re-exposure to drug-associated cues significantly attenuates cue-induced reinstatement of morphine-seeking behavior. In addition, the same manipulation reduced reinstatement of sucrose-seeking behavior but failed to alter memory recall in the object location task. Finally, intact activity of tyrosine hydroxylase (TH) LC-dHPCTh afferents is necessary to drive cue induced reinstatement of morphine-seeking as inhibition of this pathway blunts cue-induced drug-seeking behavior. Altogether, these studies show an important role of the dHPC and LC-dHPCTh pathway in mediating cue-induced reinstatement of opioid seeking.

Astrocytic CREB in nucleus accumbens promotes susceptibility to chronic stress.

Background: Increasing evidence implicates astrocytes in stress and depression in both rodent models and human Major Depressive Disorder (MDD). Despite this, little is known about the transcriptional responses to stress of astrocytes within the nucleus accumbens (NAc), a key brain reward region, and their influence on behavioral outcomes. Methods: We used whole cell sorting, RNA-sequencing, and bioinformatic analyses to investigate the NAc astrocyte transcriptome in male mice in response to chronic social defeat stress (CSDS). Immunohistochemistry was used to determine stress-induced changes in astrocytic CREB within the NAc. Finally, astrocytic regulation of depression-like behavior was investigated using viral-mediated manipulation of CREB in combination with CSDS. Results: We found a robust transcriptional response in NAc astrocytes to CSDS in stressed mice, with changes seen in both stress-susceptible and stress-resilient animals. Bioinformatic analysis revealed CREB, a transcription factor widely studied in neurons, as one of the top-predicted upstream regulators of the NAc astrocyte transcriptome, with opposite activation states seen in resilient versus susceptible mice. This bioinformatic result was confirmed at the protein level with immunohistochemistry. Viral overexpression of CREB selectively in NAc astrocytes promoted susceptibility to chronic stress. Conclusions: Together, our data demonstrate that the astrocyte transcriptome responds robustly to CSDS and, for the first time, that transcriptional regulation in astrocytes contributes to depressive-like behaviors. A better understanding of transcriptional regulation in astrocytes may reveal unknown molecular mechanisms underlying neuropsychiatric disorders.

Manipulating ΔFOSB in D1-Type Medium Spiny Neurons of the Nucleus Accumbens Reshapes Whole-Brain Functional Connectivity.

BACKGROUND: The transcription factor ΔFOSB, acting in the nucleus accumbens, has been shown to control transcriptional and behavioral responses to opioids and other drugs of abuse. However, circuit-level consequences of ΔFOSB induction on the rest of the brain, which are required for its regulation of complex behavior, remain unknown. METHODS: We used an epigenetic approach in mice to suppress or activate the endogenous Fosb gene and thereby decrease or increase, respectively, levels of ΔFOSB selectively in D1-type medium spiny neurons of the nucleus accumbens and tested whether these modifications affect the organization of functional connectivity (FC) in the brain. We acquired functional magnetic resonance imaging data at rest and in response to a morphine challenge and analyzed both stationary and dynamic FC patterns. RESULTS: The 2 manipulations modified brainwide communication markedly and differently. ΔFOSB down- and upregulation had overlapping effects on prefrontal- and retrosplenial cortex-centered networks, but also generated specific FC signatures for epithalamus (habenula) and dopaminergic/serotonergic centers, respectively. Analysis of dynamic FC patterns showed that increasing ΔFOSB essentially altered responsivity to morphine and uncovered striking modifications of the roles of the epithalamus and amygdala in brain communication, particularly upon ΔFOSB downregulation. CONCLUSIONS: These novel findings illustrate how it is possible to link activity of a transcription factor within a single cell type of an identified brain region to consequent changes in circuit function brainwide by use of functional magnetic resonance imaging, and they pave the way for fundamental advances in bridging the gap between transcriptional and brain connectivity mechanisms underlying opioid addiction.

Microbial Diversity and Activity of Biofilms from Geothermal Springs in Croatia.

Hot spring biofilms are stable, highly complex microbial structures. They form at dynamic redox and light gradients and are composed of microorganisms adapted to the extreme temperatures and fluctuating geochemical conditions of geothermal environments. In Croatia, a large number of poorly investigated geothermal springs host biofilm communities. Here, we investigated the microbial community composition of biofilms collected over several seasons at 12 geothermal springs and wells. We found biofilm microbial communities to be temporally stable and highly dominated by Cyanobacteria in all but one high-temperature sampling site (Bizovac well). Of the physiochemical parameters recorded, temperature had the strongest influence on biofilm microbial community composition. Besides Cyanobacteria, the biofilms were mainly inhabited by Chloroflexota, Gammaproteobacteria, and Bacteroidota. In a series of incubations with Cyanobacteria-dominated biofilms from Tuhelj spring and Chloroflexota- and Pseudomonadota-dominated biofilms from Bizovac well, we stimulated either chemoorganotrophic or chemolithotrophic community members, to determine the fraction of microorganisms dependent on organic carbon (in situ predominantly produced via photosynthesis) versus energy derived from geochemical redox gradients (here simulated by addition of thiosulfate). We found surprisingly similar levels of activity in response to all substrates in these two distinct biofilm communities, and observed microbial community composition and hot spring geochemistry to be poor predictors of microbial activity in the study systems.

Hydrochemical and Seasonally Conditioned Changes of Microbial Communities in the Tufa-Forming Freshwater Network Ecosystem.

Freshwater network ecosystems consist of interconnected lotic and lentic environments within the same catchment area. Using Plitvice Lakes as an example, we studied the changes in environmental conditions and microbial communities (bacteria and fungi) that occur with downstream flow. Water samples from tributaries, interlake streams, connections of the cascading lakes, and the Korana River, the main outflow of the system, were characterized using amplicon sequencing of bacterial 16S rRNA and fungal ITS2 genes. Our results show that different environmental conditions and bacterial and fungal communities prevail among the three stream types within the freshwater network ecosystem during multiple sampling seasons. Microbial community differences were also confirmed along the longitudinal gradient between the most distant sampling sites. The higher impact of "mass effect" was evident during spring and winter, while "species sorting" and "environmental selection" was more pronounced during summer. Prokaryotic community assembly was majorly influenced by deterministic processes, while fungal community assembly was highly dominated by stochastic processes, more precisely by the undominated fraction, which is not dominated by any process. Despite the differences between stream types, the microbial community of Plitvice Lakes is shown to be very stable by the core microbiome that makes up the majority of stream communities. Our results suggest microbial community succession along the river-lake continuum of microbial communities in small freshwater network ecosystems with developed tufa barriers. IMPORTANCE Plitvice Lakes represent a rare freshwater ecosystem consisting of a complex network of lakes and waterfalls connecting them, as well as rivers and streams supplying water to the lake basin. The unique geomorphological, hydrological, biogeochemical, and biological phenomenon of Plitvice Lakes lies in the biodynamic process of forming tufa barriers. In addition to microbial communities, abiotic water factors also have a major influence on the formation of tufa. Therefore, it is important to understand how changes in environmental conditions and microbial community assembly affect the functioning of the ecosystem of a freshwater network with developed tufa barriers.

Data on stable isotopic composition of δ18O and δ15N in nitrate in groundwater, and δ15N in solid matter in the Varazdin area, NW Croatia.

The Varazdin aquifer is the only source of drinking water for inhabitants of the Varazdin County. In the last decades, groundwater contamination with nitrate has become an increasing problem. Therefore, there is a need to define the origin of nitrate as the first step in groundwater remediation. The data in this article consist of δ18O and δ15N values in nitrate in groundwater, and δ15N in solid matter. Groundwater was sampled in the period from April 2018 to December 2019 at 10 different sites by pumping the wells, and directly in the gravel pit in Sijanec. Representative solid samples of plants, soil, manure, and synthetic fertilizers were collected from arable land in two field campaigns (July and October 2019). The presented dataset can be used as a baseline for identification of nitrate sources in groundwater and possible nitrate attenuation processes. The data is related to the research article "Tracking the nitrogen cycle in a vulnerable alluvial system using a multi proxy approach: case study Varazdin alluvial aquifer, Croatia." [1].

Endogenous opioid systems alterations in pain and opioid use disorder.

Decades of research advances have established a central role for endogenous opioid systems in regulating reward processing, mood, motivation, learning and memory, gastrointestinal function, and pain relief. Endogenous opioid systems are present ubiquitously throughout the central and peripheral nervous system. They are composed of four families, namely the µ (MOPR), κ (KOPR), δ (DOPR), and nociceptin/orphanin FQ (NOPR) opioid receptors systems. These receptors signal through the action of their endogenous opioid peptides ß-endorphins, dynorphins, enkephalins, and nociceptins, respectfully, to maintain homeostasis under normal physiological states. Due to their prominent role in pain regulation, exogenous opioids-primarily targeting the MOPR, have been historically used in medicine as analgesics, but their ability to produce euphoric effects also present high risks for abuse. The ability of pain and opioid use to perturb endogenous opioid system function, particularly within the central nervous system, may increase the likelihood of developing opioid use disorder (OUD). Today, the opioid crisis represents a major social, economic, and public health concern. In this review, we summarize the current state of the literature on the function, expression, pharmacology, and regulation of endogenous opioid systems in pain. Additionally, we discuss the adaptations in the endogenous opioid systems upon use of exogenous opioids which contribute to the development of OUD. Finally, we describe the intricate relationship between pain, endogenous opioid systems, and the proclivity for opioid misuse, as well as potential advances in generating safer and more efficient pain therapies.

Microbial community composition and hydrochemistry of underexplored geothermal waters in Croatia.

In Croatia, a variety of geothermal springs with a wide temperature range and varied hydrochemical conditions exist, and they may harbor different niches for the distribution of microbial communities. In this study, 19 different sites, mainly located in central and eastern Croatia, were selected for primary characterization of spring hydrochemistry and microbial community composition. Using 16S rRNA gene amplicon sequencing, it was found that the bacterial communities that dominated most geothermal waters were related to Proteobacteria and Campylobacteria, while most archaeal sequences were related to Crenarchaeota. At the genus level, the prokaryotic community was highly site-specific and was often dominated by a single genus, including sites dominated by Hydrogenophilus, Sulfuricurvum, Sulfurovum, Thiofaba and Nitrospira, while the most abundant archaeal genera were affiliated to the ammonia-oxidizing archaea, Candidatus Nitrosotenuis and Candidatus Nitrososphaera. Whereas the microbial communities were overall highly location-specific, temperature, pH, ammonia, nitrate, total nitrogen, sulfate and hydrogen sulfide, as well as dissolved organic and inorganic carbon, were the abiotic factors that significantly affected microbial community composition. Furthermore, an aquifer-type effect was observed in the community composition, but there was no pronounced seasonal variability for geothermal spring communities (i.e. the community structure was mainly stable during the three seasons sampled). These results surprisingly pointed to stable and geographically unique microbial communities that were adapted to different geothermal water environments throughout Croatia. Knowing which microbial communities are present in these extreme habitats is essential for future research. They will allow us to explore further the microbial metabolisms prevailing at these geothermal sites that have high potential for biotechnological uses, as well as the establishment of the links between microbial community structure and the physicochemical environment of geothermal waters.

Tracking the nitrogen cycle in a vulnerable alluvial system using a multi proxy approach: Case study Varazdin alluvial aquifer, Croatia.

At high concentrations nitrate is considered a serious environmental pollutant which degrades the quality of ground and surface waters. Such high nitrate concentrations (>50 mg NO3/L) have been observed for decades in the alluvial aquifer in the Varazdin region of Croatia. Here we employ a novel cross disciplinary approach (dual isotopes, chemical, bacteria diversity and mixing modelling) to determine sources of nitrate and processes that can influence nitrate concentration within this vulnerable alluvial aquifer. Ten groundwater wells were sampled across the region and in different hydrological conditions for basic chemical, stable isotopes (δ18O-H2O, δ2H-H2O, δ15N-NO3 and δ18O-NO3), and bacterial diversity analyses. In addition, solid samples, i.e. soil samples and fertilizers were collected and analysed for bulk δ15N. The primary nitrate sources were manure, sewage, soil organic N, and ammonia fertilizers, however we observe no clear evidence to indicate that synthetic fertilizers are a major contributor to groundwater nitrate concentrations. Whilst denitrification was observed in the parts of the study area with dissolved oxygen (DO) deficiency, i.e. anoxic conditions, nitrification has been identified as the major process responsible for nitrate behaviour within the aquifer system. Our results will facilitate the creation of a conceptual model of nitrate behaviour in the study area and from this, a numerical groundwater nitrate transport model. These data, understanding of nitrate dynamics and subsequent models will be critical for future sustainable water and agricultural management of the study area.

Microbial marker for seawater intrusion in a coastal Mediterranean shallow Lake, Lake Vrana, Croatia.

Climate change-induced rising sea levels and prolonged dry periods impose a global threat to the freshwater scarcity on the coastline: salinization. Lake Vrana is the largest surface freshwater resource in mid-Dalmatia, while the local springs are heavily used in agriculture. The karstified carbonate ridge that separates this shallow lake from the Adriatic Sea enables seawater intrusion if the lakes' precipitation-evaporation balance is disturbed. In this study, the impact of anthropogenic activities and drought exuberated salinization on microbial communities was tracked in Lake Vrana and its inlets, using 16S rRNA gene sequencing. The lack of precipitation and high water temperatures in summer months introduced an imbalance in the water regime of the lake, allowing for seawater intrusion, mainly via the karst conduit Jugovir. The determined microbial community spatial differences in the lake itself and the main drainage canals were driven by salinity, drought, and nutrient loading. Particle-associated and free-living microorganisms both strongly responded to the ecosystem perturbations, and their co-occurrence was driven by the salinization event. Notably, a bloom of halotolerant taxa, predominant the sulfur-oxidizing genus Sulfurovum, emerged with increased salinity and sulfate concentrations, having the potential to be used as an indicator for salinization of shallow coastal lakes. Following summer salinization, lake water column homogenization took from a couple of weeks up to a few months, while the entire system displayed increased salinity despite increased precipitation. This study represents a valuable contribution to understanding the impact of the Freshwater Salinization Syndrome on Mediterranean lakes' microbial communities and the ecosystem resilience.

Pain induces adaptations in ventral tegmental area dopamine neurons to drive anhedonia-like behavior.

The persistence of negative affect in pain leads to co-morbid symptoms such as anhedonia and depression-major health issues in the United States. The neuronal circuitry and contribution of specific cellular populations underlying these behavioral adaptations remains unknown. A common characteristic of negative affect is a decrease in motivation to initiate and complete goal-directed behavior, known as anhedonia. We report that in rodents, inflammatory pain decreased the activity of ventral tegmental area (VTA) dopamine (DA) neurons, which are critical mediators of motivational states. Pain increased rostromedial tegmental nucleus inhibitory tone onto VTA DA neurons, making them less excitable. Furthermore, the decreased activity of DA neurons was associated with reduced motivation for natural rewards, consistent with anhedonia-like behavior. Selective activation of VTA DA neurons was sufficient to restore baseline motivation and hedonic responses to natural rewards. These findings reveal pain-induced adaptations within VTA DA neurons that underlie anhedonia-like behavior.

Pain, negative affective states and opioid-based analgesics: Safer pain therapies to dampen addiction.

Across centuries and civilizations opioids have been used to relieve pain. In our modern societies, opioid-based analgesics remain one of the most efficient treatments for acute pain. However, the long-term use of opioids can lead to the development of analgesic tolerance, opioid-induced hyperalgesia, opioid use disorders, and overdose, which can ultimately produce respiratory depressant effects with fatal consequences. In addition to the nociceptive sensory component of pain, negative affective states arising from persistent pain represent a risk factor for developing an opioid use disorder. Several studies have indicated that the increase in prescribed opioid analgesics since the 1990s represents the root of our current opioid epidemic. In this review, we will present our current knowledge on the endogenous opioid system within the pain neuroaxis and the plastic changes occurring in this system that may underlie the occurrence of pain-induced negative affect leading to misuse and abuse of opioid medications. Dissecting the allostatic neuronal changes occurring during pain is the most promising avenue to uncover novel targets for the development of safer pain medications. We will discuss this along with current and potential approaches to treat pain-induced negative affective states that lead to drug misuse. Moreover, this chapter will provide a discussion on potential avenues to reduce the abuse potential of new analgesic drugs and highlight a basis for future research and drug development based on recent advances in this field.

Data on stable isotopic composition of δ18O and δ2H in precipitation in the Varazdin area, NW Croatia.

The dataset in this article consists of one year of monthly observations of water stable isotopes in precipitation (July 2019 - May 2020). The samples were collected by rain gauge installed in the Hrascica village in the Varazdin area, NW Croatia. The data presented in the article are raw isotope data of precipitation supplemented by calculated d-excess values, and local meteoric water lines (LMWL). The measured data is an extension to previous two year investigations (June 2017 - June 2019), which was published in the research article "Application of Stable Water Isotopes to Improve Conceptual Model of Alluvial Aquifer in the Varazdin Area" [1]. Local meteoric water lines (LMWL) are calculated for the entire period for which isotope analyses exist (June 2017 - May 2020). Presented data can be used as a background for investigation of precipitation, groundwater and surface water origin and their interrelationships.

Microinjection of urotensin II into the pedunculopontine tegmentum leads to an increase in the consumption of sweet tastants.

The pedunculopontine tegmentum (PPTg) plays a role in processing multiple sensory inputs and innervates brain regions associated with reward-related behaviors. The urotensin II receptor, activated by the urotensin II peptide (UII), is selectively expressed by the cholinergic neurons of the PPTg. Although the exact function of cholinergic neurons of the PPTg is unknown, they are thought to contribute to the perception of reward magnitude or salience detection. We hypothesized that the activation of PPTg cholinergic neurons would alter sensory processing across multiple modalities (ex. taste and hearing). Here we had three aims: first, determine if cholinergic activation is involved in consumption behavior of palatable solutions (sucrose). Second, if so, distinguish the impact of the caloric value by using saccharin, a zero calorie sweetener. Lastly, we tested the UII-mediated effects on perception of acoustic stimuli by measuring acoustic startle reflex (ASR). Male Sprague-Dawley rats were bilaterally cannulated into the PPTg, then placed under food restriction lasting the entire consumption experiment (water ad lib.). Treatment consisted of a microinjection of either 1 µL of aCSF or 1 µL of 10 µM UII into the PPTg, and the rats were immediately given access to either sucrose or saccharin. For the remaining five days, rats were allowed one hour access per day to the same sweet solution without any further treatments. During the saccharin experiment rats were tested in a contact lickometer which recorded each individual lick to give insight into the microstructure of the consumption behavior. ASR testing consisted of a baseline (no treatment), treatment day, and two additional days (no treatment). Immediately following the microinjection of UII, consumption of both saccharin and sucrose increased compared to controls. This significant increase persisted for days after the single administration of UII, but there was no generalized arousal or increase in water consumption between testing sessions. The effects on ASR were not significant. Activating cholinergic PPTg neurons may lead to a miscalculation of the salience of external stimuli, implicating the importance of cholinergic input in modulating a variety of behaviors. The long-lasting effects seen after UII treatment support further research into the role of sensory processing on reward related-behaviors at the level of the PPTg cholinergic neurons.

Pain-Induced Negative Affect Is Mediated via Recruitment of The Nucleus Accumbens Kappa Opioid System.

Negative affective states affect quality of life for patients suffering from pain. These maladaptive emotional states can lead to involuntary opioid overdose and many neuropsychiatric comorbidities. Uncovering the mechanisms responsible for pain-induced negative affect is critical in addressing these comorbid outcomes. The nucleus accumbens (NAc) shell, which integrates the aversive and rewarding valence of stimuli, exhibits plastic adaptations in the presence of pain. In discrete regions of the NAc, activation of the kappa opioid receptor (KOR) decreases the reinforcing properties of rewards and induces aversive behaviors. Using complementary techniques, we report that in vivo recruitment of NAc shell dynorphin neurons, acting through KOR, is necessary and sufficient to drive pain-induced negative affect. Taken together, our results provide evidence that pain-induced adaptations in the kappa opioid system within the NAc shell represent a functional target for therapeutic intervention that could circumvent pain-induced affective disorders. VIDEO ABSTRACT.

Experimental Determination of Zinc Isotope Fractionation in Complexes with the Phytosiderophore 2'-Deoxymugeneic Acid (DMA) and Its Structural Analogues, and Implications for Plant Uptake Mechanisms.

The stable isotope signatures of zinc and other metals are increasingly used to study plant and soil processes. Complexation with phytosiderophores is a key reaction and understanding the controls of isotope fractionation is central to such studies. Here, we investigated isotope fractionation during complexation of Zn2+ with the phytosiderophore 2'-deoxymugeneic acid (DMA), and with three commercially available structural analogues of DMA: EDTA, TmDTA, and CyDTA. We used ion exchange chromatography to separate free and complexed zinc, and identified appropriate cation exchange resins for the individual systems. These were Chelex-100 for EDTA and CyDTA, Amberlite CG50 for TmDTA and Amberlite IR120 for DMA. With all the ligands we found preferential partitioning of isotopically heavy zinc in the complexed form, and the extent of fractionation was independent of the Zn:ligand ratio used, indicating isotopic equilibrium and that the results were not significantly affected by artifacts during separation. The fractionations (in ‰) were +0.33 ± 0.07 (1σ, n = 3), + 0.45 ± 0.02 (1σ, n = 2), + 0.62 ± 0.05 (1σ, n = 3) and +0.30 ± 0.07 (1σ, n = 4) for EDTA, TmDTA, CyDTA, and DMA, respectively. Despite the similarity in Zn-coordinating donor groups, the fractionation factors are significantly different and extent of fractionation seems proportional to the complexation stability constant. The extent of fractionation with DMA agreed with observed fractionations in zinc uptake by paddy rice in field experiments, supporting the possible involvement of DMA in zinc uptake by rice.

Assessment of sensorimotor gating following selective lesions of cholinergic pedunculopontine neurons.

Sensorimotor gating is the state-dependent transfer of sensory information into a motor system. When this occurs at an early stage of the processing stream it enables stimuli to be filtered out or partially ignored, thereby reducing the demands placed on advanced systems. Prepulse inhibition (PPI) of the acoustic startle reflex (ASR) is the standard measure of sensorimotor gating. A brainstem-midbrain circuitry is widely viewed as mediating both PPI and ASR. In this circuitry, the pedunculopontine tegmental nucleus (PPTg) integrates sensory input and cortico-basal ganglia output and, via presumed cholinergic signaling, inhibits ASR-generating neurons within the reticular formation. Non-selective damage to all neuronal types within PPTg reduces PPI. We assessed whether this effect originates in the loss of cholinergic signaling by examining ASR and PPI in rats bearing non-selective (excitotoxic) or selective cholinergic (Dtx-UII) lesions of PPTg. Excitotoxic lesions had no effect on ASR but reduced PPI at all prepulse levels tested. In contrast, selective depletion of cholinergic neurons reduced ASR to the extent that PPI was not measurable with standard (10-20 s) inter-trial intervals. Subsequent testing revealed appreciable ASRs could be generated when the inter-trial interval was increased (180 s). Under these conditions, PPI was assessed and no deficits were found after lesions of cholinergic PPTg neurons. These results show that cholinergic output from PPTg is essential for rapidly regenerating the ASR, but has no influence on PPI. Results are discussed in terms of sensorimotor integration circuitry and psychiatric disorders that feature disrupted ASR and PPI.

Deficits in motor performance after pedunculopontine lesions in rats--impairment depends on demands of task.

Anatomically and functionally located between basal ganglia and brainstem circuitry, the pedunculopontine tegmental nucleus (PPTg) is in a pivotal position to contribute to motor behavior. Studies in primates have reported akinesia and postural instability following destruction of the PPTg. In humans, the PPTg partially degenerates in Parkinson's disease and stimulation of this region is under investigation as a possible therapeutic. Studies in rats report no crude motor impairment following PPTg lesion, although a detailed assessment of the role of the PPTg in rat motor function has not been reported. Our studies applied motor tests generally used in rodent models of Parkinson's disease to rats bearing either excitotoxic damage to all neuronal populations within PPTg, or selective destruction of the cholinergic subpopulation created with the toxin Dtx-UII. Neither lesion type altered baseline locomotion. On the rotarod, excitotoxic lesions produced a persistent impairment on the accelerating, but not fixed speed, conditions. In the vermicelli handling task (a quantitative measure of fine motor control and effective behavioral sequencing) excitotoxic lesions produced no single impairment, but globally increased the number of normal and abnormal behaviors. In contrast, depletion of cholinergic PPTg neurons produced impairment on the accelerating rotarod but no changes in vermicelli handling. Together, these results show that while PPTg lesions produce no impairment in the execution of individual motor actions, impairments emerge when the demands of the task increase. Results are discussed in terms of PPTg acting as part of a rapid action selection system, which integrates sensory information into motor output.