Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Revue d'histoire du Bas-Saint-Laurent, vol. 13 (2)

Éditorial -- Tourisme et Loisirs dans le Bas-Saint-Laurent : 1960-1986 -- Le tourisme dans le Bas-Saint-Laurent Le circuit de 1930 -- Le B.A.E.Q., l'Entente Canada-Québec et le tourisme dans l'est -- Nouvelles brève

Striatal circuits and habit formation: Assessing dopamine dynamics in the mouse striatum during reward learning tasks

As organisms learn through trial and error, dopamine is released in the striatum to support reward learning. Presently, dopamine’s role in reward learning is suggested to be more heterogenic than what has been previously thought. However, few studies have been able to measure dopamine levels in the striatum with high spatiotemporal precision and a clear description of phasic dopamine dynamics during reward learning is lacking. Our project capitalized on cutting-edge fibre-photometry and biosensor technologies to measure dopamine in the mouse striatum during an innovative touchscreen-based reward learning paradigm. We observed sharp increases in dopamine in the dorsolateral striatum, dorsomedial striatum and nucleus accumbens following correct choice and reward collection. However, in all three regions, sharp decreases in dopamine signalling were seen when an incorrect choice was made. Taken together, these findings will advance fundamental cognitive theories and draw together important connections between dopamine activity and behaviour

Revue d'histoire du Bas-Saint-Laurent, vol. 13 (1)

Éditorial: Et de 13 ... -- La Romancière Frances Brooke et l'ermite de l'Île Saint-Barnabé -- Un roman de «par chez-nous»: Napoléon Tremblay d'Augus Graham -- Elise Belzile: une femme de lettre chez les agriculteurs -- Chroniques littéraires -- Une poète pour la Méti

A role for nature-based citizen science in promoting individual and collective climate change action? A systematic review of learning outcomes

As a model of communication and engagement, citizen science has the potential to promote individual and collective climate change action. This article systematically reviewed literature that jointly addressed climate change and nature-based citizen science and identified 23 reported learning outcomes. Overall, evidence related to learning outcomes was limited across reviewed studies, but documentation of outcomes that are directly relevant to collective climate action was particularly scarce. Findings suggest more research examining citizen science from a collective climate action perspective is needed. To support future research efforts, results link the 23 revealed learning outcomes to two potential evaluation frameworks

Age-dependent and region-specific alteration of parvalbumin neurons, perineuronal nets and microglia in the mouse prefrontal cortex and hippocampus following obesogenic diet consumption

Emergent evidence demonstrates that excessive consumption of high fat and high sugar (HFHS) diets has negative consequences on hippocampal and prefrontal cortex (PFC) function. Moreover, the delayed maturation of the PFC including the late development of parvalbumin-expressing (PV) interneurons and perineuronal nets (PNNs) may promote vulnerability to HFHS diet-induced nutritional stress. However, the young brain may have some resistance to diet-induced neuroinflammation. Thus, we examined the impact of a HFHS diet commencing either in adolescence or adulthood in male mice. PV interneurons, PNNs and microglia were assessed using immunohistochemistry. We observed greater numbers of PV neurons and PNNs in the hippocampus and the prelimbic and infralimbic PFC in adult mice in comparison to our younger cohort. Mice that consumed HFHS diet as adults had reduced numbers of hippocampal PV neurons and PNNs, which correlated with adiposity. However, we saw no effects of diet on PV and PNNs in the PFC. HFHS diet increased microgliosis in the adult cohort, and morphological changes to microglia were observed in the PFC and hippocampus of the adolescent cohort, with a shift to activated microglia phenotypes. Taken together, these findings demonstrate different regional and age-specific effects of obesogenic diets on PV neurons, PNNs and microglia

Tau hyperphosphorylation induced by the anesthetic agent ketamine/xylazine involved the calmodulin‐dependent protein kinase II

International audienceTau hyperphosphorylation is a major neuropathological hallmark of many neurodegenerative disorders such as Alzheimer's disease. Several anesthetics have been shown previously to induced marked tau hyperphosphorylation. Although the ketamine/xylazine mixture is one of the most commonly used anesthetic agents in animal research and veterinary practice, the effect of this anesthetic agent on tau phosphorylation still remains to be determined. Here, we found that ketamine-/xylazine-induced a rapid and robust hyperphosphorylation of tau in a dose-dependent manner under normothermic and hypothermic conditions in mice. When used together, ketamine and xylazine exerted a synergistic action on tau phosphorylation most strongly not only on epitopes S396 and S262, but also on other residues (T181, and S202/T205). We observed that activation of the calmodulin-dependent protein kinase II (CaMKII) is the major upstream molecular event leading to tau hyperphosphorylation following ketamine/xylazine anesthesia in mice. Moreover, we observed that intracerebroventricular injection of the selective CaMKII inhibitor KN93 attenuated tau hyperphosphorylation. Since ketamine/xylazine also had a marked impact on other key molecular signaling pathways involving the MAP/microtubule affinity-regulating kinase (MARK), extracellular signal-regulated kinase (ERK), and glycogen synthase kinase-3 (GSK3), our study calls for high caution and careful monitoring when using this anesthetic agent in laboratory animal settings across all fields of biological sciences in order to avoid artifactual results