Hippocampal gene expression patterns in oxytocin male knockout mice are related to impaired social interaction

Social interaction between animals is crucial for the survival and life in groups. It is well demonstrated that oxytocin (OT) and vasopressin (AVP) play critical roles in the regulation of social behaviors in mammals, however, other neurotransmitters and hormones are involved in the brain circuitry related to these behaviors. The present study aimed to investigate the gene expression of neurotransmitter receptors in the brain of OT knockout (OTKO) male mice. In this study, we evaluated the expression levels of the OT receptor (Oxtr), AVP receptors 1a and 1b (Avpr1a; Avpr1b), dopamine receptor 2 (Drd2), and the estrogen receptors alpha and beta (Esr1; Esr2) genes in the hippocampus (HPC), olfactory bulb (OB), hypothalamus (HPT) and prefrontal cortex (PFC). AVP gene (Avp) expression was analyzed in the HPT. Gene expression results were discussed regarding to social interaction and sexual behavior findings. Additionally, we analyzed the influence of OT absence on the Avp mRNA expression levels in the HPT. RNA extraction and cDNAs synthesis followed by quantitative polymerase chain reaction were performed for gene expression determination. Results were calculated with the 2^-ΔΔCt method. Our main finding was that HPC is more susceptible to gene expression changes due to the lack of OT. OTKOs exhibited decreased expression of Drd2 and Avpr1b, but increased expression of Oxtr in the HPC. In the PFC, Esr2 was increased. In the HPT, there was a reduced Avp expression in the OTKO group. No differences were detected in the OB and HPT. Despite these changes in gene expression, sexual behavior was not affected. However, OTKO showed higher social investigation and lower aggressive performance than wild-type mice. Our data highlight the importance of OT for proper gene expression of neurotransmitter receptors related to the regulation of social interaction in male mice.