Activity-dependent changes of synapse strength have been extensively characterized at chemical synapses, but the relationship between physiological forms of activity and strength at electrical synapses remains poorly characterized and understood. For mammalian electrical synapses comprising hexamers of connexin36, physiological forms of neuronal activity in coupled pairs have thus far only been linked to long-term depression; activity that results in strengthening of electrical synapses has not yet been identified. The thalamic reticular nucleus (TRN), a central brain area primarily interconnected by electrical synapses, regulates cortical input from and attention to the sensory surround. Here, we show in electrically coupled TRN pairs that tonic spiking in one neuron results in long-term potentiation of electrical synapses with a magnitude of plasticity that alters the functionality of the synapse. Potentiation is expressed asymmetrically, indicating that regulation of connectivity depends on the direction of use. Further, potentiation depends on calcium flux, and we thus propose a calcium-based activity rule for bidirectional plasticity of electrical synapse strength. Because electrical synapses dominate intra-TRN connectivity, these synapses and their activity-dependent modifications are key dynamic regulators of thalamic attention circuitry. More broadly, we speculate that bidirectional modifications of electrical synapses may be a widespread and powerful principle for ongoing, dynamic reorganization of neuronal circuitry across the brain.

Examining the evolution of social behavior using a comparative approach across species provides valuable insight into important selection pressures as well as mechanistic commonalities and differences underlying behavior across organisms. However, to utilize comparative strategies, it is necessary to have several species in multiple mammalian families available that exhibit a particular behavioral phenotype of interest. Obtaining a variety of species can be a challenge when searching for species amenable to experimental manipulation in a laboratory setting, especially when the behavioral phenotype of interest is mammalian grouping behavior.Importantly, social behavior is a broad term that encompasses many distinct types of behavior that may not have evolved in a linked manner (Goodson, 2013). For example, a species that is excellent for studying the behavior between bonded mates may not be the

Studies in prairie voles (Microtus ochrogaster) have shown that although formation of the pair bond is accompanied by a suite of behavioral changes, a bond between two voles can dissolve and individuals can form new pair bonds with other conspecifics. However, the neural mechanisms underlying this behavioral flexibility have not been well-studied. Here we examine plasticity of nonapeptide, vasopressin (VP) and oxytocin (OT), neuronal populations in relation to bonding and the dissolution of bonds. Using adult male and female prairie voles, animals were either pair bonded, co-housed with a same-sex sibling, separated from their pair bond partner, or separated from their sibling. We examined neural densities of VP and OT cell groups and observed plasticity in the nonapeptide populations of the paraventricular nucleus of the hypothalamus (PVN). Voles that were pair bonded had fewer PVN OT neurons, suggesting that PVN OT neural densities decrease with pair bonding, but increase and return to a pre-pair bonded baseline after the dissolution of a pair bond. Our findings suggest that the PVN nonapeptide cell groups are particularly plastic in adulthood, providing a mechanism by which voles can exhibit context-appropriate behavior related to bond status.

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