The Relationship Between 5-HT, 5-HT1A Receptor And Social Recognition Of Mandarin Voles Microtus Mandarinus

Social recogniton plays an important role in all mammalian socialbehaviors, including kin recognition, pair bond formation, the care of offspring,inbreeding avoidance, and dominant-subordinate hierarchies. Many experimentalevidences indicate that OT and AVP acting in the brain appear to be critical for socialdiscrimination. More recently, neurochemical and electrophysiological studies suggestthat serotonin is the neurotransmitter involved in the influence of the neurohypophysealhormones and related neuropeptides on brain function, steriod hormones take part in theactivity as well. There is a complex synaptic connection between 5-HT and AVPneurons. Several lines of evidence have emerged to indicate that 5-HT may regulate thesocial recognition of monogamous vole with AVP, androgen. In the present study, we tryto investigate the neurosecretory mechanism of social recognition.Selecting monogamous mandarin voles(Microtus mandarinus) as experimentalanimal, using i.p injection, i.c.v injection, immunohistochemistry and behaviorobservation methods, we investigate the induction of Fos-IRs and AR-IRs expressionby extrinsic 5-HT in male and female brains and the role of 5-HT in partner preferenceand aggressive behavior in male voles.In addition, we detect the distribution of 5-HT1Areceptors in the emotion-related brain regions and the effects of AVP and WAY-100635on the partner preference and aggressive behavior. Our results were the following:1. The data in present experiment showed that i.c.v injection of serotonin significantlyincreased the number of Fos-IRs in the lateral septal nucleus, medial preoptic nucleus,anterior hypothalamic area, zone incerta, piriform cortex, paraventricular hypothalamicnucleus, ventromedial hypothalamic nucleus and supraoptic nucleus of mature malemandarin voles, while the number of Fos-IRs was increased in the medial preopticnucleus, anterior hypothalamic area, bed nucleus of the stria terminalis, paraventricularhypothalamic nucleus and supraoptic nucleus of female mandarin voles. Among thebrain regions detected, the number of Fos-IRs in the MPO, AH, ME, PIR, SCH, PV, SOand VMH have significant differences between male and female animals. These resultssuggested that the serotonin might exert its central action by activating a cellular immediate early gene in specific brain regions. These brain regions were closely relatedwith olfactory memory and mating behavior of rodent. So the relationship betweenserotonin and social recognition may be confirmed, and it may have different ways inthe regulation of social behavior by serotonin between male and female animals.2. After the completion of i.c.v 5-HT injection, male mandarin voles were tested forpartner preference. The results showed that 5-HT could decrease the visiting duration tothe strange opposite sex individuals and no effect on the visiting duration to the mateanimals, while 5-HT could increase the latency of investigating behavior and non-socialbehavior to mate animals. The decrease of visiting duration to the strange individualswith opposite Sex mainly attributed to the reduction of defensive behavior, amicablebehavior and investigating behavior. It is suggest that 5-HT could damage the capacityof male voles recognizing their mates.3. After the completion of i.c.v 5-HT injection, male mandarin voles were tested foraggressive behavior using the resident-intruder paradigm. The .statistics suggest that5-HT could decrease the frequency of aggressive behavior significantly.4. By using antibody of 5-HT1A receptor, specific binding to brain 5-HT1A receptorwas observed in the brains of both male and female monogamous mandarin vole.5-HT1A receptor neurons densities were higher in the emotion-related brain regionssuch as PIR, PV, DMD, PAN, ar, AH, VMH, AMY and hippocampus. The shape of5-HT1AR-IR cells was multiform, which present as oval, subulate or anomalistic. Therewere significantly differences in the number of 5-HT1AR-IR cells in the hippocampusarea which include CA1, CA2, CA3, DG between male and female mandarin voles.These results suggest that 5-HT1A receptor was involved in the social behavior andsocial organization of animals, and may have a different role in social recognitionbetween male and female animals.5. We detected the effects of AVP and WAY-100635 on the partner preference of malemandarin voles. Compared with injection AVP solely, AVP and WAY-100635 treatmentat same time increased the visiting duration and the frequency of amicable behavior tomate and decreased visiting duration to strange heterosexual voles. The brain sections oftreated voles were collected and 5-HT1AR-IR cells in brain were marked after behavior.Compared with injection AVP solely, there were significant decreases in the number of5-HT1AR-IR cells in the LSD, MPO, LD and hippocampus area such as CA2, CA1, DG,PoDG. 6. We detected the effects of AVP and WAY-100635 on the aggressive behavior of malemandarin voles. Compared with injection AVP solely, AVP and WAY-100635 treatmenthad no effects on the frequency and total duration of aggrassive behavior.7. The statistic in'present experiment showed that i.c.v injection of serotoninsignificantly decreased the number of AR-IRs in the anterior hypothalamic area,ventromedial hypothalamic nucleus, bed nucleus of the stria terminalis, paraventricularhypothalamic nucleus and increased the number of AR-IRs in the suprachiasmaticnucleus of mature male mandarin voles, while the number of AR-IRs was increased inthe lateral septal nucleus, medial preoptic nucleus, anterior hypothalamic area, medialamygdaloid nucleus and suprachiasmatic nucleus of female mandarin voles. Among thebrain regions detected, the number of AR-IRs in the LSD, MPO, AH, VMH and SCNhave significant differences between male and female animals. So the relationshipbetween serotonin, androgen and social behavior may be confirmed, and it may havedifferent ways in the regulation of social behavior by serotonin and androgen betweenmale and female animals.All these results suggested that 5-HT, 5-HT1A receptor had profound effects on thesocial behaviors of mandarin voles, and confirmed the relationship between 5-HT, AVP,androgen and mammalian social recognition. This study may play an important part inthe elucidation of neurobiological mechanism of social recognition and the evolution ofmating system.