Participação do núcleo central da amígdala na aquisição de memórias de medo em camundongos fêmeas C57BL/6

Abstract

Cued fear memory, whose main neural substrate is the amygdala, is hampered by the chronic deprivation of ovarian hormones in mice. Here, we verified the role of the central nucleus of the amygdala (CeA) and the influence of estrogens during the acquisition of cued fear memories in female mice C57BL/6. Classical conditioning paradigm consisted of pairing a tone (CS) to a footshock (US). Freezing behavior was evaluated 24 hours later in test session, during the CS presentation, as a measure of cued fear memory. Our results demonstrated that CeA inhibition (muscimol 30ng/side) during training session is detrimental to the acquisition of fear memory in normocycling females. In ovariectomized females (OVX 12 weeks), in which conditioning is impaired, the disinhibition of this structure pre-training (bicuculline 100ng/side) restored fear memory, suggesting an increase in CeA tonic inhibition of OVX mice. This hypothesis was supported by a greater immunoreactivity to GAD65/67 enzymes, which are part of GABA synthesis machinery, in response to OVX (12 weeks). Estrogen effects on the CeA was also evaluated in a physiological scenario by employing estrogen receptors (ER) antagonists injected intraCeA prior to training session in normocycling females. We identified that the ERα antagonism (TPBM 50ng/side) impaired the acquisition of conditioned responses. There was no effect when ERβ (PHTPP 0.2ng/side) and GPER (G15 7.4ng/side) were blocked in CeA. Therefore, we demonstrated that CeA is essential for acquiring cued fear memories in normocyling female mice and appears to be inhibited in OVX females (12 weeks). Among the hormones affected by ovariectomy, estrogens were necessary for the acquisition of fear memory through the activation of ERα in CeA. Estrogen deficiency may be related to the impairments observed in OVX females. Thus, the present study explored the particularities of the female’s fear circuit, helping to clarify how sex hormones interact with the emergence of acquired defensive behaviors.