Individual differences in the boldness of female zebrafish are associated with alterations in serotonin function.

One of the most prevalent axes of behavioral variation in both humans and animals is risk taking, where individuals that are more willing to take risk are characterized as bold while those that are more reserved as shy. Brain monoamines (i.e., serotonin, dopamine, and norepinephrine) have been found to play a role in a variety of behaviors related to risk taking. Genetic variation related to monoamine function have also been linked to personality in both humans and animals. Using zebrafish, we investigated the relationship between monoamine function and boldness behavior during exploration of a novel tank. We found a sex-specific correlation between serotonin metabolism (5-HIAA:5-HT ratio) and boldness that was limited to female animals; there were no relationships between boldness and dopamine or norepinephrine. To probe differences in serotonergic function, we administered a serotonin reuptake inhibitor, escitalopram, to bold and shy fish, and assessed their exploratory behavior. We found that escitalopram had opposing effects on thigmotaxis in female animals with bold fish spending more time near the center of the tank and shy fish spent more time near the periphery. Taken together, our findings suggest that variation in serotonergic function makes sex-specific contributions to individual differences in risk taking behavior.

Abuse-like toluene exposure during early adolescence alters subsequent ethanol and cocaine behavioral effects and brain monoamines in male mice.

Currently, there is a gap in understanding the neurobiological impact early adolescent toluene exposure has on subsequent actions of other drugs. Adolescent (PND 28-32) male Swiss-Webster mice (N = 210) were exposed to 0, 2000, or 4000 ppm of toluene vapor for 30 min/day for 5 days. Immediately following the last toluene exposure (PND 32; n = 15) or after a short delay (PND 35; n = 15), a subset of subjects' brains was collected for monoamine analysis. Remaining mice were assigned to one of two abstinence periods: a short 4-day (PND 36) or long 12-day (PND 44) delay after toluene exposure. Mice were then subjected to a cumulative dose response assessment of either cocaine (0, 2.5, 5, 10, 20 mg/kg; n = 60), ethanol (0, 0.5, 1, 2, 4 g/kg; n = 60), or saline (5 control injections; n = 60). Toluene concentration-dependently increased locomotor activity during exposure. When later challenged, mice exposed previously to toluene were significantly less active after cocaine (10 and 20 mg/kg) compared to air-exposed controls. Animals were also less active at the highest dose of alcohol (4 g/kg) following prior exposure to 4000 ppm when compared to air-exposed controls. Analysis of monoamines and their metabolites using High Pressure Liquid Chromatography (HPLC) within the medial prefrontal cortex (mPFC), nucleus accumbens (NAc), dorsal striatum (dSTR), and ventral tegmental area (VTA) revealed subtle effects on monoamine or metabolite levels following cumulative dosing that varied by drug (cocaine and ethanol) and abstinence duration. Our results suggest that early adolescent toluene exposure produces behavioral desensitization to subsequent cocaine-induced locomotor activity with subtle enhancement of ethanol's depressive effects and less clear impacts on levels of monoamines.

Approaches and considerations of studying neuronal ensembles: a brief review.

First theorized by Hebb, neuronal ensembles have provided a framework for understanding how the mammalian brain operates, especially regarding learning and memory. Neuronal ensembles are discrete, sparsely distributed groups of neurons that become activated in response to a specific stimulus and are thought to provide an internal representation of the world. Beyond the study of region-wide or projection-wide activation, the study of ensembles offers increased specificity and resolution to identify and target specific memories or associations. Neuroscientists interested in the neurobiology of learning, memory, and motivated behavior have used electrophysiological-, calcium-, and protein-based proxies of neuronal activity in preclinical models to better understand the neurobiology of learned and motivated behaviors. Although these three approaches may be used to pursue the same general goal of studying neuronal ensembles, technical differences lead to inconsistencies in the output and interpretation of data. This mini-review highlights some of the methodologies used in electrophysiological-, calcium-, and protein-based studies of neuronal ensembles and discusses their strengths and weaknesses.

Norepinephrine depletion in the brain sex-dependently modulates aspects of spatial learning and memory in female and male rats.

RATIONALE: The contribution of norepinephrine on the different phases of spatial memory processing remains incompletely understood. To address this gap, this study depleted norepinephrine in the brain and then conducted a spatial learning task with multiple phases. METHODS: Male and female Wistar rats were administered 50 mg/kg/i.p. of DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine) to deplete norepinephrine. After 10 days, rats were trained on a 20-hole Barnes maze spatial navigation task for 5 days. On the fifth day, animals were euthanized and HPLC was used to confirm depletion of norepinephrine in select brain regions. In Experiment 2, rats underwent a similar Barnes maze procedure that continued beyond day 5 to investigate memory retrieval and updating via a single probe trial and two reversal learning periods. RESULTS: Rats did not differ in Barnes maze acquisition between DSP-4 and saline-injected rats; however, initial acquisition differed between the sexes. HPLC analysis confirmed selective depletion of norepinephrine in dorsal hippocampus and cingulate cortex without impact to other monoamines. When retrieval was tested through a probe trial, DSP-4-improved memory retrieval in males but impaired it in females. Cognitive flexibility was transiently impacted by DSP-4 in males only. CONCLUSIONS: Despite significantly reducing levels of norepinephrine, DSP-4 had only a modest impact on spatial learning and behavioral flexibility. Memory retrieval and early reversal learning were most affected and in a sex-specific manner. These data suggest that norepinephrine has sex-specific neuromodulatory effects on memory retrieval with a lesser effect on cognitive flexibility and no impact on acquisition of learned behavior.

A novel preclinical model of environment-like combined benzene, toluene, ethylbenzene, and xylenes (BTEX) exposure: Behavioral and neurochemical findings.

Environmental exposure to toxicants is a major health issue and a leading risk factor for premature mortality worldwide, including environmental exposures to volatile organic compounds (VOCs), specifically Benzene, Toluene, Ethylbenzene, and Xylene (BTEX). While exposure to these compounds individually has shown behavioral and neurochemical effects, this investigation examined the impact of exposure to combined BTEX using a preclinical model. Male Swiss Webster mice were exposed to BTEX vapors designed to approximate environmental levels in urban communities. Animals were exposed to one of four treatment conditions: a 0-ppm (air control), two BTEX groups representing levels of environmental-like exposure, and a fourth group modeling occupational-like exposure. These exposures were conducted in 1.5-h sessions, 2 sessions/day, 5 days/week, for 3 weeks. Effects on coordination (i.e., rotarod and inverted screen test), learning and memory (i.e., Y-maze), and locomotor behavior (i.e., movement during exposure) were assessed during and after exposure. Monoamine levels in the medial prefrontal cortex and nucleus accumbens were assessed immediately following exposure. Effects of BTEX exposure were found on the variance of locomotor activity but not in other behavioral or neurochemical assessments. These results indicate that the combination of inhaled BTEX at environmentally representative concentrations has demonstrable, albeit subtle, effects on behavior.

Acute exposure to abuse-like concentrations of toluene induces inflammation in mouse lungs and brain.

Toluene is an aromatic hydrocarbon commonly abused by young adolescents for its central nervous system depressant effects. Although toluene's pharmacological effects at high concentrations are relatively well-known, few studies have assessed toluene's effects on lung and brain tissues. The present study characterized the pathological effects of acute inhaled toluene exposure in the lungs and brains of male Swiss-Webster mice (N = 68). Using a static vapor exposure chamber, mice (PND 28) received a single 30-min toluene administration (0, 1000, 2000, or 4000 ppm). Lung and brain tissues were extracted 24-h post-exposure. Histology results revealed significant changes in the morphology of lung tissue (e.g., irregular cellular architecture) with the 2000- and 4000-ppm exposures expressing greater signs of pathology than control 0-ppm exposure. Markers of immune system activity (F4/80 and Ly-6G) and cellular proliferation (Ki-67) in the lung revealed no significant differences. Additionally, brain tissues were analyzed for changes of astrogliosis (glial fibrillary acidic protein [GFAP]) and oxidative stress (glutathione peroxidase [GPx]). GFAP showed increased astrogliosis in the striatum with 2000-ppm toluene showing significantly higher expression than control (p < 0.05) and a marginal effect in the hippocampus. No other markers showed significant changes. The increased signs of inflammation and cellular damage suggest that exposure to a single high concentration of toluene, typical of abuse, is capable of producing pathology in both lung and brain tissue.

Effects of inhaled combined Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX): Toward an environmental exposure model.

Combined environmental exposures to the volatile organic compounds (VOCs) Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) pose clear risks to public health. Research into these risks is under-studied even as BTEX levels in the atmosphere are predicted to rise. This review focuses on the available literature using single- and combined-BTEX component inhaled solvent exposures in animal models, necessarily also drawing on findings from models of inhalant abuse and occupational exposures. Health effects of these exposures are discussed for multiple organ systems, but with particular attention on neurobehavioral outcomes such as locomotor activity, impulsivity, learning, and psychopharmacological responses. It is clear that animal models have significant differences in the concentrations, durations and patterns of exposure. Experimental evidence of the deleterious health and neurobehavioral consequences of exposures to the individual components of BTEX were found, but these effects were typically assessed using concentrations and exposure patterns not characteristic of environmental exposure. Future studies with animal models designed appropriately to explore combined BTEX will be necessary and advantageous to discovering health outcomes and more subtle neurobehavioral impacts of long-term environmental exposures.

Abstinence following toluene exposure increases anxiety-like behavior in mice.

The intentional misuse of volatile solvents like toluene is a persistent public health concern. Limited clinical data suggest that chronic inhalant abusers may experience signs of withdrawal, including anxiety. Behavioral withdrawal from toluene has not been examined in a preclinical model. In the current study, young adult male Swiss Webster mice were exposed to either 5000-ppm toluene vapor or air (0ppm) for 30min or 24h. Mice were tested in a battery of four behavioral tasks reflective of anxiety either immediately (0h), 24h, or 72h after the toluene exposure. Mice exposed briefly (30min) to toluene showed decreases in anxiety-like behaviors, whereas mice abstinent from toluene for 24h after a prolonged (24-h) exposure, displayed increases in anxiety-like behaviors. These increases in anxiety-like behavior were not observed 72h post toluene. However, a brief re-exposure to toluene (30min at 5000ppm) immediately before testing 24h after the prolonged exposure ameliorated behavioral differences on the plus maze task. These results of 1) decreased anxiety-like behavior immediately following acute toluene, and 2) the contrasting increase in anxiety-like behavior during abstinence from a prolonged toluene exposure, and 3) the amelioration of increases in an anxiety-like behavior following toluene re-exposure, are consistent with an interpretation of withdrawal from the single 24-hr toluene exposure. These findings support clinical reports of increased anxiety during abstinence following periods of toluene use/abuse. The results also imply that experiencing anxiety during withdrawal from toluene may contribute to the persistent use of inhalants and may be relevant to clinical treatment of inhalant abuse/addiction.

Hyperspectral cathodoluminescence examination of defects in a carbonado diamond.

Hyperspectral cathodoluminescence mapping is used to examine a carbonado diamond. The hyperspectral dataset is examined using a data clustering algorithm to interpret the range of spectral shapes present within the dataset, which are related to defects within the structure of the diamond. The cathodoluminescence response from this particular carbonado diamond can be attributed to a small number of defect types: N-V0, N2V, N3V, a 3.188 eV line, which is attributed to radiation damage, and two broad luminescence bands. Both the N2V and 3.188 eV defects require high-temperature annealing, which has implications for interpreting the thermal history of the diamond. In addition, bright halos observed within the diamond cathodoluminescence, from alpha decay radiation damage, can be attributed to the decay of 238U.