Brain monoaminergic, neuroendocrine, and immune responses to an immune challenge in relation to brain and behavioral lateralization.

Host responses to immune challenges involve central neurotransmission, the hypothalamo-pituitary adrenal axis, and the immune system. In the present work, we investigated the possibility of an asymmetry in the modification of brain monoamine metabolism induced by a systemic injection of lipopolysaccharide (LPS) in adult female mice. We also studied the possible influence of behavioral lateralization, as assessed by a paw preference test, on the reactivity of the nervous, neuroendocrine, and immune systems to a LPS challenge. The results showed that LPS administration induced an enhanced brain activity as demonstrated by an increase in noradrenergic, serotoninergic, and dopaminergic metabolism. Increased serotonin metabolism, observed in the hypothalamus and hippocampus, only occurred on the left side. Furthermore, the increase in serotonin turnover in the medial hypothalamus, the elevation of plasma adrenocorticotropin levels, and the decrease in T lymphocyte proliferation were observed in right-handed and ambidextrous mice but not in left-handed animals. Taken together, the results demonstrate that an immune challenge could induce neurochemical, neuroendocrine, and immune responses similar to those of stress, suggesting that LPS may be a stress inducer. Interestingly, these responses that may be asymmetrically expressed appear to depend on behavioral lateralization.

Distribution of brain monoamines in left- and right-handed mice injected with bacillus Calmette-Guerin.

Concentrations of brain monoamines from various cerebral structures were determined in right and left sides of the brain from female mice selected for paw preference and injected or not with BCG 8 weeks before. BCG-induced changes in brain monoamine distribution in prefrontal cortex, medial hypothalamus and brain stem were only observed in right-handers. In the posterior hypothalamus, even though there was no BCG effect, norepinephrine asymmetry observed in right-handed controls was suppressed after BCG-injection. Moreover, BCG-induced brain monoamine changes in right-handers mainly involved the right hemisphere except the NE decrease in brain stem which was left-sided. This work demonstrates that the injection of BCG leads to long lasting asymmetrical changes in brain monoamine distribution that furthermore depend on behavioral lateralization of mice.