Long-term soil water limitation and previous tree vigor drive local variability of drought-induced crown dieback in Fagus sylvatica

Ongoing climate warming is increasing evapotranspiration, a process that reduces plant-available water and aggravates the impact of extreme droughts during the growing season. Such an exceptional hot drought occurred in Central Europe in 2018 and caused widespread defoliation in mid-summer in European beech (Fagus sylvatica L.) forests. Here, we recorded crown damage in 2021 in nine mature even-aged beech-dominated stands in northwestern Switzerland along a crown damage severity gradient (low, medium, high) and analyzed tree-ring widths of 21 mature trees per stand. We aimed at identifying predisposing factors responsible for differences in crown damage across and within stands such as tree growth characteristics (average growth rates and year-to-year variability) and site-level variables (mean canopy height, soil properties). We found that stand-level crown damage severity was strongly related to soil water availability, inferred from tree canopy height and plant available soil water storage capacity (AWC). Trees were shorter in drier stands, had higher year-to-year variability in radial growth, and showed higher growth sensitivity to moisture conditions of previous late summer than trees growing on soils with sufficient AWC, indicating that radial growth in these forests is principally limited by soil water availability. Within-stand variation of post-drought crown damage corresponded to growth rate and tree size (diameter at breast height, DBH), i.e., smaller and slower-growing trees that face more competition, were associated with increased crown damage after the 2018 drought. These findings point to tree vigor before the extreme 2018 drought (long-term relative growth rate) as an important driver of damage severity within and across stands. Our results suggest that European beech is less likely to be able to cope with future climate change-induced extreme droughts on shallow soils with limited water retention capacity.

Stress-induced alterations of mesocortical and mesolimbic dopaminergic pathways

Our ability to develop the cognitive strategies required to deal with daily-life stress is regulated by region-specific neuronal networks. Experimental evidence suggests that prolonged stress in mice induces depressive-like behaviors via morphological, functional and molecular changes affecting the mesolimbic and mesocortical dopaminergic pathways. Yet, the molecular interactions underlying these changes are still poorly understood, and whether they affect males and females similarly is unknown. Here, we used chronic social defeat stress (CSDS) to induce depressive-like behaviors in male and female mice. Density of the mesolimbic and mesocortical projections was assessed via immuno-histochemistry combined with Sholl analysis along with the staining of activity-dependent markers pERK and c-fos in the ventral tegmental area (VTA), nucleus accumbens (NAc) and medial prefrontal cortex (mPFC). Our results show that social stress decreases the density of TH⁺ dopaminergic axonal projections in the deep layers of the mPFC in susceptible but not resilient male and female mice. Consistently, our analyses suggest that pERK expression is decreased in the mPFC but increased in the NAc following CSDS in males and females, with no change in c-fos expression in both sexes. Overall, our findings indicate that social defeat stress impacts the mesolimbic and mesocortical pathways by altering the molecular interactions regulating somatic and axonal plasticity in males and females.

Humanizing Oral Health Care through Continuing Education on Social Determinants of Health: Evaluative Case Study of a Canadian Private Dental Clinic

Primary care practitioners are frequently unprepared to take into account the effects of social determinants on underprivileged patients' health and health management. To address this issue among dental professionals, an original onsite continuing education (CE) course on poverty was co-developed by researchers, dental professionals, and community organizations. Integrating patient narratives and a short film, course material aims to elicit critical reflection and provide coaching for practice improvements. A qualitative case study conducted with a large Montreal Canada dental team reveals CE course participants' newfound understandings and increased sensitivity to the causes of poverty and the nature of life on welfare. Participants also describe revised interpretations of certain patient behaviors, subtle changes in communication with patients and improved equity in appointment-giving policy. Unintended outcomes include reinforced judgment and a tendency to moralize certain patient categories. Implications for health professional educators, researchers, and dental regulatory authorities are discussed.

Creatinine and specific gravity normalization in biological monitoring of occupational exposures

Reference values for the biological monitoring of occupational exposures are generally normalized on the basis of creatinine (CR) concentration or specific gravity (SG) to account for fluctuations in urine dilution. For instance, the American Conference of Governmental Industrial Hygienists (ACGIH(®)) uses a reference value of 1g/L for CR. The comparison of urinary concentrations of biomarkers between studies requires the adjustment of results based on a reference CR and/or SG value, although studies have suggested that age, sex, muscle mass, and time of the day can exert non-negligible influences on CR excretion, while SG appears to be less affected. The objective of this study was to propose reference values for urinary CR and SG based on the results of samples sent for analysis by occupational health practitioners to the laboratory of the Occupational Health and Safety Research Institute of Québec (IRSST). We analyzed a database containing 20,395 urinary sample results collected between 1985 and 2010. Linear mixed-effects models with worker as a random effect were used to estimate the influence of sex and collection period on urinary CR and SG. Median CR concentrations were 25-30% higher in men (1.6 g/L or 14.4 mmol/L) than in women (1.2 g/L or 10.2 mmol/L). Four percent of the samples for men and 12% for women were below the acceptable threshold for CR (4.4 mmol/L). For SG, 5% of samples for men and 12% for women were below the threshold of 1.010. The difference in SG levels between sexes was lower than for CR, with a median of 1.024 for men compared to 1.020 for women. Our results suggest that the normalization of reference values based on a standard CR value of 1 g/L as proposed by the ACGIH is a conservative approach. According to the literature, CR excretion is more influenced by physiological parameters than SG. We therefore suggest that correction based on SG should be favored in future studies involving the proposal of reference values for the biological monitoring of occupational exposures.

Epileptiform synchronization and high-frequency oscillations in brain slices comprising piriform and entorhinal cortices

We employed field potential recordings in extended in vitro brain slices form Sprague-Dawley rats containing the piriform and entorhinal cortices (PC and EC, respectively) to identify the characteristics of epileptiform discharges and concomitant high-frequency oscillations (HFOs, ripples: 80-200Hz, fast ripples: 250-500Hz) during bath application of 4-aminopyridine (4AP, 50μM). Ictal-like discharges occurred in PC and EC either synchronously or independently of each other; synchronous ictal discharges always emerged from a synchronous "fast" interictal background whereas asynchronous ictal discharges were preceded by a "slow" interictal event. In addition, asynchronous ictal discharges had longer duration and interval of occurrence than synchronous ictal discharges, and contained a higher proportion of ripples and fast ripples. Cutting the connections between PC and EC made synchronicity disappear and increased ictal discharges duration in the EC but failed in changing HFO occurrence in both areas. Finally, antagonizing ionotropic glutamatergic receptors abolished ictal activity in all experiments, increased the duration and rate of occurrence of interictal discharges occurring in PC-EC interconnected slices while it did not influence the slow asynchronous interictal discharges in both areas. Our results identify some novel in vitro interactions between olfactory (PC) and limbic (EC) structures that presumably contribute to in vivo ictogenesis as well.

Neurosteroids modulate epileptiform activity and associated high-frequency oscillations in the piriform cortex

Allotetrahydrodeoxycorticosterone (THDOC) belongs to a class of pregnane neurosteroidal compounds that enhance brain inhibition by interacting directly with GABAA signaling, mainly through an increase in tonic inhibitory current. Here, we addressed the role of THDOC in the modulation of interictal- and ictal-like activity and associated high-frequency oscillations (HFOs, 80-500 Hz; ripples: 80-200 Hz, fast ripples: 250-500 Hz) recorded in vitro in the rat piriform cortex, a highly excitable brain structure that is implicated in seizure generation and maintenance. We found that THDOC: (i) increased the duration of interictal discharges in the anterior piriform cortex while decreasing ictal discharge duration in both anterior and posterior piriform cortices; (ii) reduced the occurrence of HFOs associated to both interictal and ictal discharges; and (iii) prolonged the duration of 4-aminopyridine-induced, glutamatergic independent synchronous field potentials that are known to mainly result from the activation of GABAA receptors. Our results indicate that THDOC can modulate epileptiform synchronization in the piriform cortex presumably by potentiating GABAA receptor-mediated signaling. This evidence supports the view that neurosteroids regulate neuronal excitability and thus control the occurrence of seizures.

Identification of workers exposed concomitantly to heat stress and chemicals

In the context of climate change, concomitant exposure to heat stress and chemicals takes on great importance. However, little information is available in this regard. The purpose of this research, therefore, was to develop an approach aimed at identifying worker groups that would be potentially most at risk. The approach comprises 5 consecutive steps: - Establishment of a list of occupations for all industry sectors - Determination of heat stress parameters - Identification of occupations at risk of heat stress - Determination of exposure to chemicals - Identification of occupations potentially most at risk. Overall, 1,010 occupations were selected due to their representativeness of employment sectors in Québec. Using a rating matrix, the risk stemming from exposure to heat stress was judged "critical" or "significant" for 257 occupations. Among these, 136 occupations were identified as showing a high potential of simultaneous exposure to heat stress and chemicals. Lastly, a consultation with thirteen experts made it possible to establish a list of 22 priority occupations, that is, 20 occupations in the metal manufacturing sector, as well as roofers and firefighters. These occupations would merit special attention for an investigation and evaluation of the potential effects on workers' health.

Comparison between olanzapine and haloperidol on procedural learning and the relationship with striatal D2 receptor occupancy in schizophrenia

The striatum is known to play a primary role in procedural learning. In this study, the authors simultaneously assessed the effects of two antipsychotic drugs on procedural learning and on striatal dopamine (D2) receptor occupancy. Twenty-seven patients receiving either olanzapine or haloperidol as antipsychotic medication were assessed with the Computed Visual Tracking Task (CVTT) and Single Photon Emission Computed Tomography (SPECT) following the administration of Iodine 123-IBZM (123I-IBZM), a radioligand with a high affinity and specificity for the D2 receptors. The results showed poorer procedural learning in the haloperidol-treated patients than in normal control subjects, while no difference could be found between olanzapine-treated patients and normal control subjects. In the haloperidol but not the olanzapine group, significant correlations were found between procedural learning deficits and striatal D2 receptor occupancy. However, there was no significant difference in D2 receptor occupancy between olanzapine- and haloperidol-treated patients, and this may be related to the high doses of olanzapine and low doses of haloperidol administered. The authors concluded that: 1) striatal D2 receptor blockade may alter procedural learning in humans; and 2) olanzapine may have a protective effect on procedural learning, even at doses that produce striatal D2 receptor occupancy as high as that found with haloperidol. This protective effect of olanzapine may be related to its atypical pharmacological properties.

[Suicide in Abitibi-Temiscamingue region: epidemiological data for the period of 1992-96]

A permanent register of suicide cases has been established and has made it possible to produce a quantitative description of the suicide phenomenon in Abitibi-Témiscamingue for the period 1992-1996. This study reviews 211 suicide cases reported by the Chief Coroner Office of Quebec. A content analysis grid was applied to the coroners' files and has facilitated the study of 87 variables potentially related to suicide. The results show the evolution of suicide rates in this region in relation to those in other parts of Quebec, and the differences among various parts of the region. Several variables are shown to be significantly related to suicide (sex, age, method used, suicide site, etc.). A review of recent literature on suicide throughout the world indicates that patterns of suicide in Abitibi-Témiscamingue follow present trends in North America and Europe, but with aspects particular to the region.

Two types of projection neurons in the internal pallidum of primates: single-axon tracing and three-dimensional reconstruction

The axonal projections of the internal pallidum (GPi) in cynomolgus monkeys (Macaca fascicularis) were studied by labeling small pools of neurons with biotinylated dextran amine. Fifty-two axons were reconstructed entirely from serial sections with a camera lucida. Two types of projection neurons were identified in the GPi on the basis of their target sites. The abundant and centrally located type I neurons gave rise to a long axonal branch that descended directly to the pedunculopontine tegmental nucleus, where it arborized discretely. Other branches ascended to the thalamus and broke into 10-15 thinner collaterals that ran through most of the ventral anterior nucleus, where they terminated as typical plexuses. About half of these axons gave rise to collaterals that arborized in both components of the centre médian/parafascicular thalamic complex. The less numerous and peripherally located type II neurons had an axon that climbed the rostral thalamic pole, coursed along the stria medullaris, and arborized profusely within the lateral habenular nucleus, which stood out as the most densely innervated pallidal target. Some type II axons provided collaterals to the anterior thalamic nuclei. A small proportion of axons of both types had branches that crossed the midline and terminated in contralateral GPi target structures. Three-dimensional reconstruction showed that type I axons arborized principally along the sagittal plane. These data reveal that GPi neurons of type I act through a widely distributed axonal network upon thalamic and brainstem premotor neurons, whereas type II neurons act in a much more focused manner upon lateral habenular neurons.

A re-evaluation of the current model of the basal ganglia

The current model of basal ganglia organization has been developed progressively over the last two decades in the light of key observations made at both experimental and clinical levels. This model has been highly successful in that it has stimulated a large amount of research in the field. However, several experimental and clinical findings that are at odds with the model have accumulated during the last decade. This paper reviews some of our own single-axon tracing studies in primates, which call for a re-evaluation of the current basal ganglia model.

Organization of the basal ganglia: the importance of axonal collateralization

Recent neuroanatomical data obtained with single-axon or single-cell labeling procedures in both rodents and primates have revealed the presence of various types of projection neurons with profusely collateralized axons within each of the major components of the basal ganglia. Such findings call for a reappraisal of current concepts of the anatomical and functional organization of the basal ganglia,which play such a crucial role in the control of motor behavior. The basal ganglia now stand as a widely distributed neuronal network, whose elements are endowed with a highly patterned set of axon collaterals. The elucidation of this finely tuned network is needed to understand the complex spatiotemporal sequence of neural events that ensures the flow of cortical information through the basal ganglia.

Single-axon tracing study of neurons of the external segment of the globus pallidus in primate

Axonal projections arising from the external segment of the globus pallidus (GPe) in cynomolgus monkeys (Macaca fascicularis) were mapped after labeling small pools (5-15 cells) of neurons with biotinylated dextran amine. Seventy-six single axons were reconstructed from serial sagittal sections with a camera lucida. The majority of labeled GPe cells displayed long, aspiny, and poorly branched dendrites that arborized mostly along the sagittal plane, whereas others showed dendrites radiating in all directions. Numerous GPe axons emitted short, intranuclear collaterals that arborized close to their parent cell body. Based on their axonal targets, four distinct types of GPe projection neurons have been identified: 1) neurons that project to the internal segment of the globus pallidus (GPi), the subthalamic nucleus (STN), and the substantia nigra, pars reticulata (SNr; 13.2%); 2) neurons that target the GPi and the STN (18.4%); 3) neurons that project to the STN and the SNr (52.6%); and 4) neurons that target the striatum (15.8%). Labeled GPe axons displayed large varicosities that often were closely apposed to the somata and proximal dendrites of STN, GPi, and SNr neurons. At striatal levels, however, GPe axons displayed small axonal varicosities that did not form perineuronal nets. These results suggest that the GPe is an important integrative locus in primate basal ganglia. This nucleus harbors several subtypes of projection neurons that are endowed with a highly patterned set of collaterals. This organization allows single GPe neurons to exert a multifarious effect not only on the STN, which is the claimed GPe target, but also on the two major output structures of the basal ganglia, the SNr and the GPi.

The axonal arborization of single nigrostriatal neurons in rats

Neurons of the substantia nigra pars compacta (SNc) were iontophoretically injected with biotin dextran and their anterogradely labeled axons individually reconstructed from serial sagittal sections. Most nigrostriatal axons travelled directly to the striatum, where they branched abundantly. Other axons arborized profusely in various extrastriatal structures, including the globus pallidus, the entopeduncular and subthalamic nuclei, and branched only sparsely in the striatum. This heterogeneous organization of the nigrostriatal projection allows single SNc neurons to influence differently striatal neurons and to act directly upon extrastriatal components of the basal ganglia via a highly patterned set of collaterals.

The pallidofugal projection system in primates: evidence for neurons branching ipsilaterally and contralaterally to the thalamus and brainstem

This paper summarizes the results of some of our previous neuroanatomical studies on the pallidofugal projections in squirrel monkeys and also reports more recent data obtained with double retrograde and single axon tracing methods. Injections of anterograde tracers in the internal pallidum label axons that reach the ventral tier, centromedian and lateral habenular thalamic nuclei, as well as the pedunculopontine tegmental nucleus. The pallidofugal projections are composed of axons that branch to the ventral tier and pedunculopontine nuclei, and to ventral tier and centromedian nuclei. Double retrograde labeling with fluorescent tracers and single axon tracing confirm this high degree of collateralization. Furthermore, some pallidal labeled axons cross the midline and arborize contralaterally in the major pallidal targets. Double retrograde fluorescent labeling experiments support these findings. Pallidal axons that branch ipsilaterally as well as contralaterally to the thalamus and brainstem could play a crucial role in the functional organization of primate basal ganglia.

Extrastriatal dopaminergic innervation of human basal ganglia

A tyrosine-hydroxylase immunohistochemical analysis of the brains of normal human individuals has revealed nigrostriatal axons providing collaterals that arborize in the pallidum and subthalamic nucleus. These thin and varicose collaterals emerge from thick and smooth axons that course backward along the main output pathways of the basal ganglia, including the ansa lenticularis, the lenticular fasciculus and Wilson's pencils. Many of these fibers run within pallidal medullary laminae before reaching the putamen, whereas others climb along the reticular thalamic nucleus to reach the caudate nucleus. This extrastriatal innervation, which allows nigral dopaminergic neurons to directly affect the pallidum and subthalamic nucleus, may play a crucial role in the functional organization of human basal ganglia, in both health and disease.

Axonal arborization of corticostriatal and corticothalamic fibers arising from prelimbic cortex in the rat

This study aimed at elucidating the branching pattern of striatal and thalamic projections arising from prelimbic (Cg3) cortex in the rat. Small pools (5-15 cells) of neurons were microiontophoretically injected with biotin-dextran or biocytin and their labeled axons were individually reconstructed from serial horizontal sections immunostained for calbindin-D28k to delineate striatal patch/matrix compartments. Reconstruction of > 40 axons shows that all Cg3 corticofugal fibers, including corticothalamic axons from layer VI, course through the patch network in the rostromedial sector of the striatum. Corticostriatal projections arise from two types of layer V cells: (i) long-range corticofugal neurons, whose main axons reach the brainstem and/or spinal cord, and (ii) neurons arborizing into both striatum and claustrum, either ipsi-, contra- or bilaterally. The axons of these two types of neurons arborize profusely in striatal patches and only sparsely in the matrix. Layer VI neurons do not arborize in the striatum but target principally the thalamus. The same corticothalamic axon can innervate the anterior, rostral intralaminar and mediodorsal thalamic nuclei. These findings support the concept that no corticofugal fiber system exists that is solely devoted to the striatum. They also shed new light on how neural information from prelimbic cortex is conveyed to various subcortical limbic structures in the rat.

Axonal arborizations of corticostriatal and corticothalamic fibers arising from the second somatosensory area in the rat

Corticostriatal and corticothalamic projections arising from the second somatosensory area in the rat were studied after labeling small pools of neurons in laminae V and VI with biocytin. Tracing the axon of single neurons revealed the following principles of organization: (i) all corticostriatal and corticothalamic projections arising from layer V cells are collaterals of long-range corticofugal axons that also project below the thalamic level; (ii) all layer V cells that project to the thalamus also project to the striatum; (iii) all layer VI corticothalamic cells project exclusively to the thalamus; (iv) cells of the upper part of lamina VI send collaterals to the thalamic reticular nucleus and arborize in the ventrobasal complex forming rod-like terminal fields; and (v) cells of the lower part of lamina VI also send collaterals to the thalamic reticular nucleus, give off few branches in the ventrobasal complex and terminate principally in the caudal part of the posterior thalamic group. On the basis of these findings, and in the light of previous anatomical studies, it is proposed that the above mentioned organizing principles represent general rules that also apply to corticostriatal and corticothalamic pathways arising from other areas of the neocortex.

Positron emission tomography study of letter and object processing: empirical findings and methodological considerations

The study of functional-anatomical correlations of higher-order cognitive processing has benefited from recent advances in brain imaging techniques such as positron emission tomography (PET) measurements of regional cerebral blood flow (CBF). Comparisons of CBF changes by paired image subtraction provide the opportunity to isolate cerebral areas participating in the realization of the processes that differentiate two tasks. However, the subtraction method is based on assumptions that are not entirely compatible with cerebral cognitive processing, and the derived pattern of activation specifically associated with the processes that differentiate two tasks is relative to the activation associated with the subtracted task and may therefore vary as a function of the processes actually performed in this subtracted task. To examine the implications of this procedure, a PET study with the 15O water bolus technique was carried out on normal adults. Subjects performed three tasks that made nonoverlapping cognitive processing demands: a semantic categorization of visual objects, a spatial discrimination of visually presented letters, and a phonological decision on visually presented single letters. Each task produced distinct patterns of activation consistent with evidence from neurological patients, specifically in the left occipital cortex in the semantic categorization of objects, in the parietal cortex of both hemispheres in the letter-spatial task, and in the left frontal and superior temporal cortex in the letter-sound task. However, the comparisons between the two letter tasks did not result in the expected CBF changes even though these two tasks make distinct processing requirements and are dissociable by brain injury. In addition, the phonological task resulted in activation of areas of the frontal cortex that earlier PET studies had identified as participating in semantic operations, whereas letters have no semantic property. These results suggest that the interpretation of patterns of activation is confronted with difficulties due to the automatic, and uncontrolled, processing of verbal stimuli that raises the threshold for significant CBF changes between two conditions that use the same stimuli but different task demands.

Organization of the 5S rRNA genes in the soybean Glycine max (L.) Merrill and conservation of the 5S rDNA repeat structure in higher plants

The 5S rRNA gene of the soybean Glycine max (L.) Merr. has been cloned on a 556-bp fragment of DNA and sequenced. This fragment contains two copies of the soybean 5S rDNA sequence, one intact and one truncated, separated by noncoding DNA. We have used this clone to investigate the organization of the 5S genes within the soybean genome and the extent of their methylation. Our results demonstrate that soybean 5S genes are clustered, organized into tandem repeats of 330 bp, and extensively methylated. Hybridization of the 5S sequence to Southern transfers of soybean DNA digested with BamHI reveals a striking ladderlike pattern. Hybridization of the soybean 5S sequence to a wide variety of plant DNAs results in similar patterns, suggesting that the 5S rDNA sequence, gene organization, and methylation pattern are conserved in many higher plants.