Effects Of Environmental Factors On The Vocal Characteristics And Related Neurochemicals Of The Brown Voles

Many vertebrates use species-specific vocalizations to communicate information regarding such things as identity (individual or group), their group status or mood (dominance, submissive, fear, or aggression), their next likely behavior (approach, flee, play, groom, or mount), and environmental conditions (presence of predators or location of food) and to facilitate mother-offspring interactions. The transmission of different types of information through vocalizations depends on specific frequency and temporal properties of the acoustic signals (so-called’information-bearing parameters’). Understanding the vocalizations that an animal emits under particular physical, environmental, or social conditions can inform us about these conditions. Moreover, the vocalizations can provide an index of the affective state of the animal. This information is important for understanding the behaviors of animals both in the wild and under laboratory conditions. Stress was once defined as the non-specific result of the body to any demand or challenge to homeostasis, which included two types of stresses:physical stress and social stress. In present study, thermal stimulation, tactile stimulation (experimental touching by the observer) and odor stimulation was belong to physical stress, while early deprivation (ED) was belong to social stress. These stresses, especially early deprivation (ED), influence behavioral and neuroendocrine functions associated with mood disorders. Pups’vocalizations were considered as signals of various stresses that affect normal behavioral routines and biological function. In present study, we explored the effects of physical stress and social stress on vocalizations emitted by pups. Although infant rodents of many species are blind, deaf, poikilothermic and motorically rather incompetent during their first one or two postnatal weeks, they produce a variety of sounds including audible and ultrasonic calls. Oxytocin (OT) system and FOXP2 have been found to associate with the vocalizations of infant rodents, then to affect the parental investment and ontogenetic development. It is still not unclear that whether early deprivation (ED) affects the expression of Oxytocin (OT) and FOXP2, then influences the characteristics of vocalizations. In present study, we established the monogamous mandarin vole (microtus mandarinus) as a model to investigate the following two parts:Part 1:Firstly, we studied whether pups location, namely the distance between pups and their nest in detail, impact the vocalizations characteristics of pups during ontogenetic development. Then we explored the effects of thermal, tactile and olfactory cues on vocalizations characteristics. Part 2: we explored the effects of early deprivation (ED) on the number of vocalizations and the levels of OT, OTR and FOXP2 expression in specific brain region.1. The effects of pups location and various stimulations by thermal, tactile and olfactory cues on vocalizations characteristics:We can easily find that the more distance between pups and their nest, the more number and the longer duration of calls. It was interesting that the peak of vocalizations number emerged at 3 days,9 days and 11 days for pups in the nest, outside the nest and in the new cage respectively. In addition, the pulse duration of vocalization all decreased significantly with age for all pups of these three groups. From spectrogram, we can see that the frequency range of vocalizations remains at 5-70 kHZ during the post-natal period. This study is the first to find that pups vocalizations consist of two parts:ultrasonic and audible vocalizations in mandarin voles, and these two kinds of vocalizations always appear at the same time. In the present study, thermal condition did not only decrease the number, but also shorten the duration of vocalizations, whereas tactile stimuli merely shorten the duration, and olfactory stimuli only decrease the number of vocalizations compared with that of new cage group pups.2. The effects of early deprivation (ED) on the number of vocalizations and related neuroendocrine parameters:In the present research, our data indicated that there were two reasons leading to different levels of the number of vocalizations (1) genetic factor: the pups in the parental care (PC) group emitted high or low number of vocalizations. It means that the pups of mandarin voles may exist distinct individual difference under normal circumstances; (2) social factor:the number of vocalizations from pups in the ED group is significantly less than that of pups in the PC group at postnatal day 11 (P= 0.043). This indicates that early deprivation inhibits the calling of pups at postnatal day 11.OT system:Immunohistochemical results indicated that pups in the PC group expressed higher levels of the OT-IR in the PVN than ED pups (P< 0.001). Our study also found that pups in the PC(H) group (high number group) expressed higher levels of the OT-IR in the PVN(P< 0.001) and SON (P= 0.021)than PC(L) (low number group) pups. Another interesting finding from western blot test is that the levels of OTR between PC and ED group did not exhibit significant difference in the NAcc (P= 0.451) and MeA (P= 0.339), and a similar variation pattern of OTR expression between PC(H) and PC(L) group was observed (NAcc:P= 0.680, MeA:P= 0.373).FOXP2:In the present study, western blot experiment found that pups in the PC group had higher level expression of FOXP2 in the cortex than ED pups (P< 0.001), while pups in the PC group had significant less FOXP2 expression in the striatum than ED pups (P= 0.025). In addition, there were no significant differences on the expression of FOXP2 between PC and ED group in the thalamus (P= 0.800). It is interesting that a similar variation pattern of FOXP2 expression between PC(H) and PC(L) group was observed (cortex:P= 0.02, striatum:P= 0.04, thalamus:P= 0.993).From the above results, the present study concludes that pups’location, namely the distance between pups and their nest in detail, greatly impact the vocalizations characteristics of pups during ontogenetic development. In addition, thermal stimuli, tactile stimuli and olfactory stimuli all affect the acoustic parameters of vocalizations, while the temperature is the major contributors. ED affect the expression of OT and FOXP2 in specific brain region to reduce the number of vocalizations perhaps with lower levels of parental care finally affect the ontogenetic development of pups.