Locomotor response to acute nicotine in adolescent mice is altered by maternal undernutrition during lactation

Maternal protein restriction during the lactation period disrupts the ontogenetic development of behavioral traits in male Wistar rat offspring

Neonatal undernutrition in rats results in short- and long-term behavioral and hormonal alterations in the offspring. It is not clear, however, whether these effects are present since the original insult or if they develop at some specific age later in life. Here, we assessed the ontogenetic profile of behavioral parameters associated with anxiety, exploration and memory/learning of Wistar rat offspring that were subjected to protein malnutrition during lactation. Dams and respective litters were separated into two groups: (1) protein-restricted (PR), which received a hypoproteic chow (8% protein) from birth to weaning [postnatal day (PN) 21]; (2) control (C), which received normoproteic chow. Offspring's behaviors, corticosterone, catecholamines, T3 and T4 levels were assessed at PN21 (weaning), PN45 (adolescence), PN90 (young adulthood) or PN180 (adulthood). PR offspring showed an age-independent reduction in the levels of anxiety-like behaviors in the Elevated Plus Maze and better memory performance in the Radial Arm Water Maze. PR offspring showed peak exploratory activity in the Open Field earlier in life, at PN45, than C, which showed theirs at PN90. Corticosterone was reduced in PR offspring, particularly at young adulthood, while catecholamines were increased at weaning and adulthood. The current study shows that considerable age-dependent variations in the expression of the observed behaviors and hormonal levels exist from weaning to adulthood in rats, and that protein restriction during lactation has complex variable-dependent effects on the ontogenesis of the assessed parameters.

Under or Absent Reporting of Light Stimuli in Testing of Anxiety-Like Behaviors in Rodents: The Need for Standardization

Behavioral neuroscience tests such as the Light/Dark Test, the Open Field Test, the Elevated Plus Maze Test, and the Three Chamber Social Interaction Test have become both essential and widely used behavioral tests for transgenic and pre-clinical models for drug screening and testing. However, as fast as the field has evolved and the contemporaneous involvement of technology, little assessment of the literature has been done to ensure that these behavioral neuroscience tests that are crucial to pre-clinical testing have well-controlled ethological motivation by the use of lighting (i.e., Lux). In the present review paper, N = 420 manuscripts were examined from 2015 to 2019 as a sample set (i.e., n = ~20–22 publications per year) and it was found that only a meager n = 50 publications (i.e., 11.9% of the publications sampled) met the criteria for proper anxiogenic and anxiolytic Lux reported. These findings illustrate a serious concern that behavioral neuroscience papers are not being vetted properly at the journal review level and are being released into the literature and public domain making it difficult to assess the quality of the science being reported. This creates a real need for standardizing the use of Lux in all publications on behavioral neuroscience techniques within the field to ensure that contributions are meaningful, avoid unnecessary duplication, and ultimately would serve to create a more efficient process within the pre-clinical screening/testing for drugs that serve as anxiolytic compounds that would prove more useful than what prior decades of work have produced. It is suggested that improving the standardization of the use and reporting of Lux in behavioral neuroscience tests and the standardization of peer-review processes overseeing the proper documentation of these methodological approaches in manuscripts could serve to advance pre-clinical testing for effective anxiolytic drugs. This report serves to highlight this concern and proposes strategies to proactively remedy them as the field moves forward for decades to come.

Caloric restriction or cafeteria diet from birth to adulthood increases the sensitivity to ephedrine in anxiety and locomotion in Wistar rats

INTRODUCTION

Obesity and undernutrition, consequences of malnutrition, have been linked to the development of mental illnesses. Both states have been linked to increased sensitivity to some drugs, but there are few data for this association considering drugs with noradrenergic-dopaminergic action.

OBJECTIVE

To evaluate the nutritional status of animals treated with either a caloric restriction (CR) or cafeteria (CAF) diet from birth and their behavior after ephedrine application.

METHODS

During the lactation period, 12 litters of Wistar rats (dam + 8 pups) were fed one of three diets: control (n = 4), CR (n = 4), and CAF (n = 4). After weaning, the males were placed in individual boxes and received the same diet as their respective dams. Nutritional assessments were performed after weaning and in adulthood. In adulthood, males received either saline or ephedrine (20 mg/kg) and underwent behavioral tests including the elevated plus-maze, open-field, and food intake tests.

RESULTS

The CR group exhibited higher serum high-density lipoprotein (HDL) levels and lower food and caloric intake, weight gain, and fat mass than the control group. The CAF group exhibited lower food intake and higher fat caloric intake, fat mass, and serum low-density lipoprotein (LDL), triglyceride, total cholesterol, and hepatic lipid levels than the control group. These results indicated that the CR and CAF groups had developed undernutrition and obesity, respectively. In the elevated plus-maze and open-field tests, the CR and CAF groups showed lower anxiety-like behaviors than the control group after ephedrine application. This result indicates that the animal's nutritional status (undernutrition or obesity) can enhance ephedrine sensitivity.

CONCLUSION

The CR group exhibited undernutrition, whereas the CAF group exhibited obesity. Ephedrine altered anxiety and locomotion in animals that received the CR and CAF diets in manner different than that observed in animals receiving the standard diet.

Forced swimming stress increases natatory activity of lead-exposed mice

Recent evidence points to the relationship between lead toxicity and the function of the hypothalamic-pituitary-adrenal axis, which suggests that lead exposure could influence how an individual cope with stress. Here we test this hypothesis by investigating the behavioral effects of lead exposure in mice during the forced swimming test (FST), a parading in which animals are exposed to a stressful situation and environment. Swiss mice received either 180 ppm or 540 ppm of lead acetate (Pb) in their ad-lib water supply for 60-90 days, starting at postnatal day 30. Control (Ctrl) mice drank tap water. At the end of the exposure period, mice were submitted to a 5-min session of FST or to an open-field session of the same duration. Data from naïve animals showed that corticosterone levels were higher for animals tested in the FST compared to animals tested in the open-field. Blood-lead levels (BLL) in Pb-exposed mice ranged from 14.3 to 106.9 µg/dL. No differences were observed in spontaneous locomotion between Ctrl and Pb-exposed groups in the open-field. However, in the FST, Pb-treated mice displayed higher swimming activity than Ctrl ones and this effect was observed even for animals with BLL higher than 20 µg/dL. Furthermore, significant differences in brain glutathione levels, used as an indicator of led toxicity, were only observed for BLL higher than 40 µg/dL. Overall, these findings suggest that swimming activity in the FST is a good indicator of lead toxicity and confirm our prediction that lead toxicity influences behavioral responses associated to stress.

Sex- and age-dependent differences in nicotine susceptibility evoked by developmental exposure to tobacco smoke and/or ethanol in mice

Either tobacco smoking or alcohol consumption during pregnancy sex-selectively increases susceptibility to drugs of abuse later in life. Considering that pregnant smoking women are frequently intermittent consumers of alcoholic beverages, here, we investigated whether a short-term ethanol exposure restricted to the brain growth spurt period when combined with chronic developmental exposure to tobacco smoke aggravates susceptibility to nicotine in adolescent and adult mice. Swiss male and female mice were exposed to tobacco smoke (SMK; research cigarettes 3R4F, whole-body exposure, 8 h/daily) or ambient air during the gestational period and until the tenth postnatal day (PN). Ethanol (ETOH, 2 g/Kg, 25%, i.p.) or saline was injected in the pups every other day from PN2 to PN10. There were no significant differences in cotinine (nicotine metabolite) and ethanol serum levels among SMK, ETOH and SMK + ETOH groups. During adolescence (PN30) and adulthood (PN90), nicotine (NIC, 0.5 mg/Kg) susceptibility was evaluated in the conditioned place preference and open field tests. NIC impact was more evident in females: SMK, ETOH and SMK + ETOH adolescent females were equally more susceptible to nicotine-induced place preference than control animals. At adulthood, SMK and SMK + ETOH adult females exhibited a nicotine-evoked hyperlocomotor profile in the open field, with a stronger effect in the SMK + ETOH group. Our results indicate that ethanol exposure during the brain growth spurt, when combined to developmental exposure to tobacco smoke, increases nicotine susceptibility with stronger effects in adult females. This result represents a worsened outcome from the early developmental dual exposure and may predispose nicotine use/abuse later in life.

Energy drink enhances the behavioral effects of alcohol in adolescent mice

Mixing alcohol with energy drinks has become increasingly popular among teenagers and young adults due to the prevailing view that the stimulant properties of energy drinks decrease the depressant effects of alcohol. Surprisingly, in spite of energy drinks being heavily marketed to and consumed by adolescents, there is scarcely available preclinical data on the neurobehavioral effects of energy drinks mixed with alcohol during adolescence. Thus, here we examine the effects of the combined exposure to alcohol and energy drink on adolescent mice using a variety of behavioral tasks to assess locomotor activity, righting reflex and motor coordination. At postnatal day 40, male and female Swiss mice were assigned to the following experimental groups: alcohol diluted in energy drink (Ed+Etoh), alcohol diluted in water (Etoh) or controls (Ctrl: energy drink or water). Alcohol and energy drink (Red Bull) concentrations were 4g/kg and 8ml/kg, respectively, and all solutions were administered via oral gavage. When compared to Etoh mice, Ed+Etoh animals displayed greater locomotor activity and increased anxiety-like behaviors in the open-field, lost their righting reflexes sooner and displayed poorer motor coordination in the rotarod. Collectively, our findings indicate that alcohol-induced deficits in adolescent mice are worsened by energy drink and go against the view that the stimulant properties of energy drinks can antagonize the adverse effects of alcohol.

Cardiovascular effects of linalyl acetate in acute nicotine exposure

Backgroud

Smoking is a risk factor for cardiovascular diseases as well as pulmonary dysfunction. In particular, adolescent smoking has been reported to have a higher latent risk for cardiovascular disease. Despite the risk to and vulnerability of adolescents to smoking, the mechanisms underlying the effects of acute nicotine exposure on adolescents remain unknown. This study therefore evaluated the mechanism underlying the effects of linalyl acetate on cardiovascular changes in adolescent rats with acute nicotine exposure.

Methods

Parameters analyzed included heart rate (HR), systolic blood pressure, lactate dehydrogenase (LDH) activity, vascular contractility, and nitric oxide levels.

Results

Compared with nicotine alone, those treated with nicotine plus 10 mg/kg (p = 0.036) and 100 mg/kg (p = 0.023) linalyl acetate showed significant reductions in HR. Moreover, the addition of 1 mg/kg (p = 0.011), 10 mg/kg (p = 0.010), and 100 mg/kg (p = 0.011) linalyl acetate to nicotine resulted in significantly lower LDH activity. Nicotine also showed a slight relaxation effect, followed by a sustained recontraction phase, whereas nicotine plus linalyl acetate or nifedipine showed a constant relaxation effect on contraction of mouse aorta (p < 0.001). Furthermore, nicotine-induced increases in nitrite levels were decreased by treatment with linalyl acetate (p < 0.001).

Conclusions

Taken together, our findings suggest that linalyl acetate treatment resulted in recovery of cell damage and cardiovascular changes caused by acute nicotine-induced cardiovascular disruption. Our evaluation of the influence of acute nicotine provides potential insights into the effects of environmental tobacco smoke and suggests linalyl acetate as an available mitigating agent.