The hippocampal network plays critical roles in certain types of learning and memory. Synaptic plasticity provides the basis for most models of learning and memory in neural circuits. There are multiple forms of plasticity in the hippocampal circuitry, including synapse-specific Hebbian forms of plasticity, e.g. long-term potentiation (LTP) and depression (LTD), homeostatic plasticity, such as synaptic scaling. Homeostatic plasticity is a global process that regulates overall levels of neuronal and network activity while synapses are modified independently in Hebbian plasticity. Studies on Hebbian and homeostatic plasticity give us a hint that there is a spatial gap. Accordingly, it is important to address whether and how another mechanism exists to maintain an appropriate level of total excitation, as well as allow it to be distributed in different ways across the synapses of a network by Hebbian processes. Some findings also indicate that LTP and LTD are activated at the same time in the same synaptic pathway. Thus, we propose combinatorial plasticity, in combination of LTP and LTD, to protect from lasting effects of noise and endow the system with flexibility and stability. In general, combinatorial plasticity is endowed with homeostatic property via Hebbian processes, and may be required to bridge the spatial gap of synaptic scaling and Hebbian forms of plasticity. In the present study, we find that the distribution of mEPSC amplitudes fit to double-peak Gauss distribution, using blind whole-cell recordings from CA1 pyramidal neurons in acute hippocampal slice. The cumulative fraction of mEPSCrecordings indicates a significant shift in amplitude to the right after TBS induction. Intracellular application of Pep-A2, which specifically interfered with LTP rather than LTD, had no effect on the distribution of mEPSC amplitudes. Meanwhile, TBS induction didn’t alter the distribution of mEPSC amplitudes with intracellular application of Pep-A2. These results may provide a foundation for combinatorial plasticity and further studies on the memory process. Reports on social isolation provided evidence for an enhanced anxiety-like phenotype and depressive-like symptoms, whereas sexual experience could induce significant changes in affective state, decreasing anxiety-like and depressive-like responses. However, it is almost unknown about the behavioral and emotional alterations in male rats treated with isolation after sexual experience. In the present study, we explored anxiety-like and depressive-like parameters as well as USVs emissions in male rats with a period of isolation (control, 1 day, 2 days and 7 days) following 1 week social (male-male paired housing) or sexual (male-female paired housing) interaction. We observed that the pattern of behavioral alterations changed across isolation time in sexually inexperienced rats, while rats with sexual experience exhibited comparable levels of emotionality at each isolation time. These results suggest that prior sexual interaction would counterbalance altered emotional response to environmental stressful stimuli, such as social isolation.
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