Unilateral hemispherectomy at adulthood asymmetrically affects immobile behavior of male Swiss mice

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.

Are cerebral and behavioural lateralization related to anxiety-like traits in the animal model zebrafish (Danio rerio)?

Brain lateralization refers to hemispheric asymmetries in functions and/or neuroanatomical structures. Functional specialization in non-human animals has been mainly inferred through observation of lateralized motor responses and sensory perception. Only in a few cases has the influence of brain asymmetries on behaviour been described. Zebrafish has rapidly become a valuable model to investigate this issue as it displays epithalamic asymmetries that have been correlated to some lateralized behaviours. Here we investigated the relation between neuroanatomical or behavioural lateralization and anxiety using a light-dark preference test in adult zebrafish. In Experiment 1, we observed how scototaxis response varied as a function of behavioural lateralization measured in the detour task as turning preference in front of a dummy predator. In Experiment 2, foxD3:GFP transgenic adult zebrafish with left or right parapineal position, were tested in the same light-dark test as fish in Experiment 1. No correlation was found between the behaviour observed in the detour test and in the scototaxis test nor between the left- and right-parapineal fish and the scototaxis response. The consistency of results obtained in both experiments indicates that neither behavioural nor neuroanatomical asymmetries are related to anxiety-related behaviours measured in the light-dark test.

Mood-related behavioral and neurochemical alterations in mice exposed to low chlorpyrifos levels during the brain growth spurt

Organophosphates are among the most used pesticides. Particularly, chlorpyrifos (CPF) is responsible for a number of deleterious effects on brain development, which may program behavioral changes later in life. Here, we investigated whether a regimen of early low level CPF exposure that did not result in a significant inhibition of acetylcholinesterase (AChE) had deleterious effects on mood-related behaviors, as well as on cholinergic and serotonergic biomarkers in the mice brain. From the 3^rd to 9^th postnatal day (PN), male and female Swiss mice were subcutaneously injected with CPF. Mice were submitted to a battery of behavioral tests from PN60 to PN63: open field, elevated plus maze and forced swimming tests. The cholinergic and serotonergic biomarkers were assessed at PN10 and PN63. Our data indicated that early CPF exposure increased anxiety-like behavior in females and altered decision-making behavior in both sexes. Most biochemical alterations were sex-dependent and restricted to females. At PN10, CPF female mice showed increased serotonin and choline transporter binding in cerebral cortex. Distinctively, in adult females, the effects indicated a hypoactive state: CPF exposure reduced 5-HT_1a receptor binding in cerebral cortex, as well as serotonin transporter binding and choline acetyltransferase activity in brainstem. Our results indicate that CPF exposure during the brain growth spurt deregulates serotonergic and cholinergic biomarkers. The effects are consistent with impaired synaptic function, may be related to long-term mood disorders and point out to higher female susceptibility.

Methamidophos exposure during the early postnatal period of mice: immediate and late-emergent effects on the cholinergic and serotonergic systems and behavior

Organophosphates (OPs) are among the most used pesticides. Although some OPs have had their use progressively more restricted, other OPs are being used without sufficient investigation of their effects. Here, we investigated the immediate neurochemical and delayed neurochemical and behavioral actions of the OP methamidophos to verify whether there are concerns regarding exposure during early postnatal development. From the third to the nineth postnatal day (PN), Swiss mice were sc injected with methamidophos (1mg/kg). At PN10, we assessed cholinergic and serotonergic biomarkers in the cerebral cortex and brainstem. From PN60 to PN63, mice were submitted to a battery of behavioral tests and subsequently to biochemical analyses. At PN10, the effects were restricted to females and to the cholinergic system: Methamidophos promoted increased choline transporter binding in the brainstem. At PN63, in the brainstem, there was a decrease in choline transporter, a female-only decrease in 5HT1A and a male-only increase in 5HT2 receptor binding. In the cortex, choline acetyltransferase activity was decreased and 5HT2 receptor binding was increased both in males and females. Methamidophos elicited behavioral alterations, suggestive of increased depressive-like behavior and impaired decision making. There were no significant alterations on anxiety-related measures and on memory/learning. Methamidophos elicited cholinergic and serotonergic alterations that depended on brain region, sex, and age of the animals. These outcomes, together with the behavioral effects, indicate that this OP is deleterious to the developing brain and that alterations are indeed identified long after the end of exposure.

Unilateral hemispherectomy at adulthood asymmetrically affects motor performance of male Swiss mice

Evidence exists indicating that cerebral lateralization is a fundamental feature of all vertebrates. In humans, a series of studies demonstrated that the left hemisphere plays a major role in controlling movement. No such asymmetries have been identified in rodents, in spite of the fact that these animals have been frequently used in studies assessing motor behavior. In this regard, here, we used unilateral hemispherectomy to study the relative importance of each hemisphere in controlling movement. Adult Swiss mice were submitted to right unilateral hemispherectomy (RH), left unilateral hemispherectomy (LH) or sham surgery. Fifteen days after surgery, motor performance was assessed in the accelerating rotarod test and in the foot-fault test (in which performance depends on skilled limb use) and in the elevated body swing test (in which performance depends on trunk movements). The surgical removal of the right hemisphere caused a more pronounced impairment in performance than the removal of the left hemisphere both in the rotarod and in the foot-fault tests. In the rotarod, the RH group presented smaller latencies to fall than both LH and sham groups. In the foot-fault test, while both the sham and the LH groups showed no differences between left and right hind limbs, the RH group showed significantly worse performance with the left hind limb than with the right one. The elevated body swing test revealed a similar impairment in the two hemispherectomized groups. Our data suggest a major role of the right hemisphere in controlling skilled limb movements in mice.