Abstract
Endocrine state is an important determinant of learning and memory in animals. In Drosophila, rejection of male courtship overtures by mated females leads to an aversive response manifested as courtship memory. Here we report that ecdysis triggering hormone (ETH) is an obligatory enabler of long-term courtship memory (LTM). ETH deficiency suppresses LTM, whereas augmented ETH release reduces the minimum training period required for LTM induction. ETH receptor knockdown either in the mushroom body (MB) γ lobe or in octopaminergic dorsal-anterior-lateral (DAL) neurons impairs memory performance, indicating its direct action in these brain areas. Consistent with these findings, brain exposure to ETH mobilizes calcium in MB γ lobe neuropils and DAL neurons. ETH receptor (ETHR) knockdown in the corpus allatum (CA) to create juvenile hormone (JH) deficiency also suppresses LTM, as does knockdown of the JH receptor Met in the MB γ lobe, indicating a convergence of ETH and JH signaling in this region of the brain. Our findings identify endocrine-enabled neural circuit components in the brain that are critical for persistent behavioral changes resulting from aversive social experience.
Highlights
Social experiences profoundly influence internal states and subsequent behavioral patterns in a broad range of animal species, including the fruit fly, Drosophila melanogaster (Chabaud et al, 2009; Shohat-Ophir et al, 2012)
We showed that genetic disruption of the ecdysis triggering hormone (ETH)-juvenile hormone (JH) hormonal cascade impairs courtship short-term memory (STM), whereby normal males suppress courtship overtures by ∼30% toward an immobilized virgin female for up to 2 h following a 1-h training interval with a mated female (Lee et al, 2017)
Since we have demonstrated that the ETH-JH signaling cascade is required for courtship long-term courtship memory (LTM) and that augmented Inka cell activity during the training session improves LTM performance (Figure 1), we asked whether augmented corpus allatum (CA) activity through expression of Drosophila TrpA1 (dTrpA1) would enhance courtship LTM via increased JH levels
Summary
Social experiences profoundly influence internal states and subsequent behavioral patterns in a broad range of animal species, including the fruit fly, Drosophila melanogaster (Chabaud et al, 2009; Shohat-Ophir et al, 2012). Endocrine Cascades for Courtship LTM distinct neural pathways involved in memory recall depend on the reproductive state (mated vs virgin) of target females during the post-training test session (Ejima et al, 2007; Keleman et al, 2012). This type of associative memory may be influenced by additional internal components, among which could be endocrine state. While the steroid ecdysone promotes both short- and long-term courtship memories through distinct neural pathways (Ishimoto et al, 2009, 2013), how hormonal influences regulate learning and memory processes under courtship conditioning is still poorly understood
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