Date Published: April 22, 2019
Publisher: Public Library of Science
Author(s): François Trudeau, Kim Gilbert, Annie Tremblay, Thomas A. Tompkins, Roger Godbout, Guy Rousseau, Ferenc Gallyas.
Caspase-3 activation in the limbic system and depressive-like symptoms are observed after an acute myocardial infarction (MI) and studies suggest that inflammation may play a significant role. Combined treatment with the probiotic strains Bifidobacterium longum and Lactobacillus helveticus in rats has been shown to attenuate caspase-3 activation and depressive-like behaviour together with a reduction in pro-inflammatory cytokines. The present study was designed to determine the respective contribution of these two strains on caspase-3 activity in the limbic system and on depressive-like behaviour. Sprague-Dawley rats were assigned to one of four groups: Vehicle, L. helveticus R0052, B. longum R0175 and L. salivarius HA-118, administered orally for 14 days (109CFU daily) before inducing MI by occlusion of the left anterior descending artery for 40 min followed by 14 days of reperfusion. Animals were then tested for socialisation, passive avoidance and forced swim test to assess depressive-like behaviour. At day 18 the animals were sacrificed; infarct size was estimated, plasma C-reactive protein concentration and brain caspase-3 activity were measured. Results indicated that infarct size did not vary across the different treatments. Rats treated with B. longum spent more time socializing, learned more rapidly the passive avoidance test and spent less time immobile in the forced swim test compared to the vehicle groups. Caspase-3 activity and plasma C-reactive protein concentrations were reduced in the lateral and medial amygdala as well as in the dentate gyrus of B. longum-supplemented animals. The only significant effect in the two groups receiving Lactobacilli compared to vehicle was that rats receiving L. salivarius learned more rapidly in the step-down passive avoidance test.
Myocardial infarction (MI) is an inflammatory disease that has several impacts on the health of surviving patients . One of the consequences that is regularly observed following myocardial infarction is the development of depression  which increases the mortality rate of these patients over the months that follow . Although the mechanism linking the cardiac tissue and the brain has not been fully elucidated, inflammation is certainly a key component in this relationship . In experimental studies, interventions mitigating the inflammatory process following myocardial infarction have been shown to attenuate depressive-like behaviour. Pentoxifylline , omega-3 fatty acids and resolvin D1 (RvD1)  are among the experimental interventions that have been shown to reduce post-MI depressive-like behaviour as well as having an effect on inflammation.
This study was aimed at assessing the effects of three individual bacterial strains on the behaviour and biochemical changes in the brain after myocardial infarction. In this context, B. longum mitigated the depressive-like symptoms assessed by three different behaviour tests and reduced caspase-3 activity in the limbic system. Administration of the two Lactobacillus strains did not affect these parameters compared to controls, except for L. salivarius in the passive avoidance step-down test. These effects were independent of the infarct size since no difference was detected between the groups.