Increased drought frequency and severity are a pervasive global threat, yet the capacity of mesic temperate forests to maintain resilience in response to drought remains poorly understood. We deployed a throughfall removal experiment to simulate a once in a century drought in New Hampshire, USA, which coupled with the region-wide 2016 drought, intensified moisture stress beyond that experienced in the lifetimes of our study trees. To assess the sensitivity and threshold dynamics of two dominant northeastern tree genera (Quercus and Pinus), we monitored sap flux density (Js), leaf water potential and gas exchange, growth and intrinsic water-use efficiency (iWUE) for one pretreatment year (2015) and two treatment years (2016-17).
View Article and Find Full Text PDFStable carbon isotope ratios (δ13C) in tree rings have been widely used to study changes in intrinsic water-use efficiency (iWUE), sometimes with limited consideration of how C-isotope discrimination is affected by tree height and canopy position. Our goals were to quantify the relationships between tree size or tree microenvironment and wood δ13C for eight functionally diverse temperate tree species in northern New England and to better understand the physical and physiological mechanisms underlying these differences. We collected short increment cores in closed-canopy stands and analyzed δ13C in the most recent 5 years of growth.
View Article and Find Full Text PDFMidbrain dopaminergic neurons are essential for appropriate voluntary movement, as epitomized by the cardinal motor impairments arising in Parkinson's disease. Understanding the basis of such motor control requires understanding how the firing of different types of dopaminergic neuron relates to movement and how this activity is deciphered in target structures such as the striatum. By recording and labeling individual neurons in behaving mice, we show that the representation of brief spontaneous movements in the firing of identified midbrain dopaminergic neurons is cell-type selective.
View Article and Find Full Text PDFNitrogen (N) deposition and changing climate patterns in the northeastern USA can influence forest productivity through effects on plant nutrient relations and water use. This study evaluates the combined effects of N fertilization, climate and rising atmospheric CO2on tree growth and ecophysiology in a temperate deciduous forest. Tree ring widths and stable carbon (δ(13)C) and oxygen (δ(18)O) isotopes were used to assess tree growth (basal area increment, BAI) and intrinsic water use efficiency (iWUE) ofQuercus velutinaLamb.
View Article and Find Full Text PDFDopamine function is disturbed in Parkinson's disease (PD), but whether and how release of dopamine from surviving neurons is altered has long been debated. Nicotinic acetylcholine receptors (nAChRs) on dopamine axons powerfully govern dopamine release and could be critical contributing factors. We revisited whether fundamental properties of dopamine transmission are changed in a parkinsonian brain and tested the potentially profound masking effects of nAChRs.
View Article and Find Full Text PDFParkinson's disease (PD) is a neurodegenerative disorder classically characterized by the death of dopamine (DA) neurons in the substantia nigra pars compacta and by intracellular Lewy bodies composed largely of α-synuclein. Approximately 5-10% of PD patients have a familial form of Parkinsonism, including mutations in α-synuclein. To better understand the cell-type specific role of α-synuclein on DA neurotransmission, and the effects of the disease-associated A30P mutation, we generated and studied a novel transgenic model of PD.
View Article and Find Full Text PDFACS Chem Neurosci
May 2013
The neuromodulators dopamine (DA) and serotonin (5-hydroxytryptamine; 5-HT) are similar in a number of ways. Both monoamines can act by volume transmission at metabotropic receptors to modulate synaptic transmission in brain circuits. Presynaptic regulation of 5-HT and DA is governed by parallel processes, and behaviorally, both exert control over emotional processing.
View Article and Find Full Text PDFStriatal dopamine plays key roles in our normal and pathological goal-directed actions. To understand dopamine function, much attention has focused on how midbrain dopamine neurons modulate their firing patterns. However, we identify a presynaptic mechanism that triggers dopamine release directly, bypassing activity in dopamine neurons.
View Article and Find Full Text PDFAims: Clinical markers of cardiac autonomic function, such as heart rate and response to exercise, are important predictors of cardiovascular risk. Tetrahydrobiopterin (BH4) is a required cofactor for enzymes with roles in cardiac autonomic function, including tyrosine hydroxylase and nitric oxide synthase. Synthesis of BH4 is regulated by GTP cyclohydrolase I (GTPCH), encoded by GCH1.
View Article and Find Full Text PDFGenetic variation in 5-HT transporter (5-HTT) expression is a key risk factor for psychiatric disorder and has been linked to changes in the expression of certain 5-HT receptor subtypes. This study investigated the effect of variation in 5-HTT expression on 5-HT₄ receptor levels in both 5-HTT knockout (KO) and overexpressing (OE) mice using autoradiography with the selective 5-HT₄ receptor radioligand, [³H]SB207145. Compared to wild-type (5-HTT⁺/⁺) controls, homozygous 5-HTT KO mice (5-HTT⁻/⁻) had reduced 5-HT₄ receptor binding site density in all brain regions examined (35-65% of 5-HTT⁺/⁺).
View Article and Find Full Text PDFHuman gene association studies have produced conflicting findings regarding the relationship between the 5-HT transporter (5-HTT) and anxiety. In the present study genetically modified mice were utilised to examine the effects of changes in 5-HTT expression on anxiety. In addition, the influence of 5-HTT expression on two innate "species-typical" behaviours (burrowing and marble burying) and body weight was explored.
View Article and Find Full Text PDFMuch evidence suggests that variation in expression of the 5-hydroxytryptamine (5-HT) transporter (5-HTT) is linked to risk of psychiatric illness, but the neurobiological basis of this association is uncertain. In this study, we investigated the impact of variation in 5-HTT expression on subsecond fluctuations in extracellular 5-HT concentrations ([5-HT](o) ). Stimulus-evoked [5-HT](o) was detected using fast-scan cyclic voltammetry at carbon-fibre microelectrodes in the substantia nigra in brain slices from 5-HTT knockout (KO) and 5-HTT over-expressing (OE) mice.
View Article and Find Full Text PDFBoth the anterior cingulate cortex (ACC) and mesolimbic dopamine, particularly in the nucleus accumbens (NAc), have been implicated in allowing an animal to overcome effort constraints to obtain greater benefits. However, their exact contribution to such decisions has, to date, never been directly compared. To investigate this issue we tested rats on an operant effort-related cost-benefit decision-making task where animals selected between two response alternatives, one of which involved investing effort by lever pressing on a high fixed-ratio (FR) schedule to gain high reward [four food pellets (HR)], whereas the other led to a small amount of food on an FR schedule entailing less energetic cost [two food pellets, low reward (LR)].
View Article and Find Full Text PDFA commonly occurring polymorphic variant of the human 5-hydroxytryptamine (5-HT) transporter (5-HTT) gene that increases 5-HTT expression has been associated with reduced anxiety levels in human volunteer and patient populations. However, it is not known whether this linkage between genotype and anxiety relates to variation in 5-HTT expression and consequent changes in 5-HT transmission. Here we test this hypothesis by measuring the neurochemical and behavioral characteristics of a mouse genetically engineered to overexpress the 5-HTT.
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