Reduced serotonin impairs long-term depression in basolateral amygdala complex and causes anxiety-like behaviors in a mouse model of perimenopause

Perimenopause is characterized by a gradual depletion of ovarian follicles with increased vulnerability to anxiety. However, the underlying mechanisms remain poorly understood. Herein, we show that chronic exposure to 4-vinylcycloxene diepoxide (VCD) in adult female mice (VCD-mice) caused follicles depletion and decline of serum estradiol (E2) and progesterone levels. Serotonin (5-HT) synthesis in dorsal raphe nucleus (DRN) and serotonergic afferents to basolateral amygdala complex (BLA) were reduced in VCD-mice, which were recovered by the supplement E2. VCD-mice appeared anxiety-like behaviors, which was relieved by the treatment with E2 or the co-administration of 5-HT1Ar agonist 8-OH-DPAT and 5-HT2A/Cr agonist DOI. The bath-application of 8-OH-DPAT in the slices obtained from VCD-mice (VCD-slices) corrected the increase in presynaptic glutamate release at external capsule-BLA synaptic transmission. Threshold to induce NMDA receptor (NMDAr)-dependent long-term potentiation (LTP) was declined in VCD-mice with elevation of CaMKII phosphorylation, which was sensitive to 8-OH-DPAT. Notably, the bath-application of 8-OH-DPAT in VCD-slices caused a decrease in the GABAergic feedback inhibition, which was restored by adding DOI. In addition, NMDAr-independent long-term depression (LTD) could not be induced in VCD-mice, which was rescued by the co-application of 8-OH-DPAT with DOI or the GABA_A receptor agonist muscimol. Furthermore, the treatment of VCD-mice with E2 could prevent the facilitation of LTP and recover the LTD induction. Thus, the results indicate that the 5-HT deficiency in the BLA of VCD-mice causes the facilitation of LTP via enhanced glutamate release and impairs the LTD induction through diminished GABAergic inhibition, leading to anxiety-like behaviors.