Oxytocin neurons mediate the effect of social isolation via the VTA circuits
Abstract
Social interaction during adolescence strongly influences brain function and behavior, and the recent pandemic has emphasized the devastating effect of social distancing on mental health. While accumulating evidence has shown the importance of the reward system in encoding specific aspects of social interaction, the consequences of social isolation on the reward system and the development of social skills later in adulthood are still largely unknown. Here, we found that one week of social isolation during adolescence in male mice increased social interaction at the expense of social habituation and social novelty preference. Behavioral changes were accompanied by the acute hyperexcitability of putative dopamine (pDA) neurons in the ventral tegmental area (VTA) and long-lasting expression of GluA2-lacking AMPARs at excitatory inputs onto pDA neurons that project to the prefrontal cortex (PFC). Social isolation-dependent behavioral deficits and changes in neural activity and synaptic plasticity were reversed by chemogenetic inhibition of oxytocin neurons in the paraventricular nucleus (PVN) of the hypothalamus. These results demonstrate that social isolation in male mice has acute and long-lasting effects on social interaction and suggest that homeostatic adaptations mediate these effects within the reward circuit.
Data availability
All data generated or analysed during this study and the statistical results are included in the manuscript and supporting files. Source raw data files have been provided for all the figures and supplement figures: Figures 1 source data, Figures 2 source data, Figures 3 source data, Figures 4 source data, Figures 5 source data, Figures 6 source data, Figure 1-figure supplement 1 source data, Figure 1-figure supplement 2 source data, Figure 1-figure supplement 3 source data, Figure 3-figure supplement 1 source data, Figure 4 -figure supplement 1 source data, Figure 4 -figure supplement 2 source data, Figure 5 -figure supplement 1 source data.
Article and author information
Author details
Funding
Swiss National Science Foundation (31003A_182326)
- Camilla Bellone
ERC consolidator Grant (864552)
- Camilla Bellone
NCCR Synapsy (51NF40-185897)
- Camilla Bellone
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: All the procedures performed at UNIGE complied with the Swiss National Institutional Guidelines on Animal Experimentation and were approved by the Swiss Cantonal Veterinary Office Committees for Animal Experimentation (Licence number GE-168/18).
Copyright
© 2022, Musardo et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Further reading
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At many vertebrate synapses, presynaptic functions are tuned by expression of different Cav2 channels. Most invertebrate genomes contain only one Cav2 gene. The Drosophila Cav2 homolog, cacophony (cac), induces synaptic vesicle release at presynaptic active zones (AZs). We hypothesize that Drosophila cac functional diversity is enhanced by two mutually exclusive exon pairs that are not conserved in vertebrates, one in the voltage sensor and one in the loop binding Caβ and Gβγ subunits. We find that alternative splicing in the voltage sensor affects channel activation voltage. Only the isoform with the higher activation voltage localizes to AZs at the glutamatergic Drosophila larval neuromuscular junction and is imperative for normal synapse function. By contrast, alternative splicing at the other alternative exon pair tunes multiple aspects of presynaptic function. While expression of one exon yields normal transmission, expression of the other reduces channel number in the AZ and thus release probability. This also abolishes presynaptic homeostatic plasticity. Moreover, reduced channel number affects short-term plasticity, which is rescued by increasing the external calcium concentration to match release probability to control. In sum, in Drosophila alternative splicing provides a mechanism to regulate different aspects of presynaptic functions with only one Cav2 gene.
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