Effect Of Noise On Emotion,Neural Development And Its Mechanism In Weaned Piglets

Noise is a widespread environmental stress.In modern intensive feeding mode,the noise generated by the dehumidification system,the mechanical fan,the flushing system and the human-animal interaction is harmful to animal welfare.Noise is closely related to negative emotions and the expression of abnormal behaviors by mediating neuroinflammation and inducing apoptosis as well as oxidative damage.As an environmental stressor,noise is difficult to eliminate due to its physical properties,and it also has the potential risk of triggering cell death and dysregulation of neurotransmitter homeostasis on the other hand.In the early stages of life,the low level of neurodevelopment and the high growing capacity make the neural system of newborns plastic,which indicates a strong potential to be shaped by the external environment.Meanwhile,the brain development and immune function are relatively weak,leading to the risk of brain injury from external stimuli.Therefore,early life is the critical period to cope with the environment.After inducing noise stress to weaned piglets,we assessed the neural development of amygdala,hypothalamus and hippocampus to investigate:first,whether the negative effects of noise are reflected in apoptosis,inflammation accumulation and oxidative stress;second,how would these changes affect neural development and how they will interact with neurotransmitter metabolism and behavioral patterns.Piglets have the similar anatomical structures and physiological states to human infants,this study may provide some theoretical support in the field of comparative medicine for auditory stimuli mediating neuroinflammation and emotion.In this study,a total of 72 hybrid piglets(Large White×Duroc×Min pig)were random Ly divided into 3 groups,including noise(recorded mechanical noise,80-85 d B),control(blank,natural background sound,<40 d B),and music(positive control,Mozart K.448,60-70 d B)groups.Three groups were housed in separate equal sized rooms(3×3.8m).Each pen accommodated 6piglets,including 3 males and 3 females with a breeding density of 0.36m~2.The formal trial was conducted after 5 days of adaptation.6 h of auditory exposure were given daily(10:00-16:00)for28 days.During the experiment,a digital sound decibel meter(AS804,Intelligent Sensor Co.,Ltd.,Hong Kong,China)was used to measure the sound loudness.At the end of the experiment,one piglet was randomly selected from each pen and slaughter,and serum,amygdala,hypothalamus,and hippocampal tissues were collected.1.Differences in behavioral expression caused by noise.Piglets’behaviors in the noise,music and control groups were observed to assess state behaviors and event behaviors.Results show that piglets in the noise group were higher arousal and expressed more aggressive behavior,pen interaction and manipulating ears compared to the music group.While piglets in the music group expressed more positive emotion-related behaviors,indicating that the piglets in the noise group were in a high arousal-negative valence state,to be more specific,an emotion of anxiety.2.The physiological manifestations of neurodevelopment after exposed to noise stress.The results showed that in the noise group,the concentration of IL-6、IL-12 and 8-OHd G in the amygdala,hypothalamus and hippocampus were higher than those in the control group(P<0.05),while the concentration of IL-10 were lower(P<0.05),meanwhile,the concentration of serum ACTH and NE was higher than those in the control group(P<0.05),indicating noise caused stress and inflammation in piglets,moreover,the serum CAT and SOD activities were lower than those in the control group(P<0.05),these results are consistent with the relative expression of related genes.We also found that the ultrastructure of the piglets’amygdala in the control and music group exhibited normal morphology and no ultrastructural changes appeared,whereas the ultrastructure of amygdala in the noise group showed that the cytoplasm become darker,and chromatin in the outer nuclear layer gathered with the uneven distribution,the death of cell occurs.Moreover,the amygdala of the control group and the music group displayed normal histology,while hemorrhagic spots with infiltration of inflammation cells can be found in the noise group,and the neuronophagia phenomenon appears as well.3.The molecular mechanism of noise affecting neural development.The effect of noise stress on the relative m RNA level of pro-inflammatory(IL-6,IL-8,IL-12,IL-1β,TNF-α),anti-inflammatory(IL-4,IL-10,TGF),neurotrophic(BDNF),apoptosis(Bax,Caspase3,Caspase9,Bcl2),antioxidant(Nrf2,HO-1,SOD,CAT),DNA damage(P53,STAT3,CHK2,Md M2,CDK2,ATM,ATR),NF-κB(NF-κB,TLR4,MYD88,IκBα)and other related genes were detected.Compared with the control group,the expression of IL-6,IL-8,IL-12,IL-1β,TNF-α,Bax,Caspase3,Caspase9,STAT3,MDM2,CDK2,NF-κB,TLR4,MYD88,and IκBαwere up-regulated,and IL-4,TGF-β,BCl2,Nrf2,HO-1,SOD,CAT,P53,ATM,CHK2,and BDNF were down-regulated.The expression of IL-6,Bax,Caspase3,Caspase9,NF-κB,TLR4 and other genes in the amygdala,hypothalamus,and hippocampus of piglets in the music group were lower than those in the noise group,while IL-4,IL-10,TGF-β,Bcl2,and Nrf2,HO-1,SOD,CAT,STAT3,CHK2,BDNF expression were higher than noise group.The relative protein expression of Bax,Caspase3 and Caspase9 in piglets’amygdala in the noise group were higher than those in the control group,while Bcl2 was significantly lower than that in the control group,suggesting that the apoptotic pathway was activated.The apoptosis pathway was also activated in the hypothalamus and the hippocampus as well.Our results showed that the negative effect caused by noise stress on neural development involves apoptosis,neuroinflammation,oxidative stress,and DNA damage due to the oxidative stress,while music played an opposite role to noise in stimulating the brain.4.The effect of noise stress on the balance of neurotransmitters.Targeted metabolomics was used in this study to detect the concentration of neurotransmitters in amygdala.Results showed that compared to the control group,both noise and music had effects on the regulation of R-noradrenaline,4-Aminobutyric acid,Dopamine,Histamine,L-glutamic acid,L-Glycine,Taurine,L-histidine and other neurotransmitters.Compared with the control group,the concentration of R-noradrenaline,4-Aminobutyric acid,Histamine,L-glutamic acid,L-Glycine,Taurine,L-histidine was up-regulated(P<0.05),while the concentration of dopamine was down-regulated(P<0.05).Meanwhile,after exposing to music,the concentration of R-noradrenaline,dopamine and taurine increased,while the concentration of histamine decreased(P<0.05).The abnormal up-regulation of 4-Aminobutyric acid concentration in the noise group was accompanied by an increase in the aggressive behavior,indicating that neurotransmitter dysregulation is one of the ways that noise induces anxiety and harms neurodevelopment in piglets.Moreover,music may improve the brain function by increasing the concentration of taurine.Results showed that long-term stress induced by noise caused anxiety emotion in piglets,then they expressed more aggressive behaviors and abnormally expressed more neutral behaviors,music can be used as an environmental enrichment,which can efficiently improve piglets’welfare.