Long-lasting BDNF signaling alterations in the amygdala of adolescent female rats exposed to the activity-based anorexia model

Abstract

Introduction: Anorexia nervosa (AN) is a severe psychiatric disorder characterized by a pathological fear of gaining weight, excessive physical exercise, and emotional instability. Since the amygdala is a key region for emotion processing and BDNF has been shown to play a critical role in this process, we hypothesized that alteration in the amygdalar BDNF system might underline vulnerability traits typical of AN patients.Methods: To this end, adolescent female rats have been exposed to the Activity-Based Anorexia (ABA) protocol, characterized by the combination of caloric restriction and intense physical exercise.Results: The induction of the anorexic phenotype caused hyperactivity and body weight loss in ABA animals. These changes were paralleled by amygdalar hyperactivation, as measured by the up-regulation of cfos mRNA levels. In the acute phase of the pathology, we observed reduced Bdnf exon IX, exon IV, and exon VI gene expression, while mBDNF protein levels were enhanced, an increase that was, instead, uncoupled from its downstream signaling as the phosphorylation of TrkB, Akt, and S6 in ABA rats were reduced. Despite the body weight recovery observed 7 days later, the BDNF-mediated signaling was still downregulated at this time point.Discussion: Our findings indicate that the BDNF system is downregulated in the amygdala of adolescent female rats under these experimental conditions, which mimic the anorexic phenotype in humans, pointing to such dysregulation as a potential contributor to the altered emotional processing observed in AN patients. In addition, since the modulation of BDNF levels is observed in other psychiatric conditions, the persistent AN-induced changes of the BDNF system in the amygdala might contribute to explaining the onset of comorbid psychiatric disorders that persist in patients even beyond recovery from AN.

Anorexia-Induced Hypoleptinemia Drives Adaptations in the JAK2/STAT3 Pathway in the Ventral and Dorsal Hippocampus of Female Rats

“…As previously published, the combination of food restriction and running activity causes the development of the AN phenotype in the ABA animals by reaching the maximum-allowed weight loss combined with the hyperactive behavior at PND42, representative of the acute phase [ 39 ]. In particular, at this time point, ABA rats showed reduced bodyweight versus CTRL (−65%, p < 0.001) and EXE (−54%, p < 0.001) rats; interestingly, even though they ate the same amount of food (FR: 9 g; ABA: 8 g), ABA rats displayed reduced bodyweight even compared to FR rats (−22%, p < 0.01).…”

“…Data were collected in individual animals (independent determinations) and are presented as means ± standard errors. Behavioral changes were analyzed by a two-way ANOVA with repeated measures followed by Bonferroni’s multiple comparisons test; for further details, please refer to [ 39 ]. Molecular changes were analyzed by a two-way ANOVA, testing physical activity (sedentary vs. exercise) and food availability (food ad libitum vs. food restriction) as independent variables at the two different time points analyzed, PND42 or PND49.…”

“…A representative timeline of the experiment is shown in Figure 1A. vHip and dHip were immediately dissected from the whole brain according to the plates 47-90 (from −1.72 mm to −6.84 mm from Bregma) of the Paxinos and Watson Rat Brain Atlas [45], frozen on dry ice and stored at −80 • C, and plasma were collected in a previous study [39]. Bodyweight, food intake and wheel-running activity were evaluated per each animal daily at 9.30 a.m., and these behavioral measurements were already reported in our previous study [39].…”

“…The DNA methyl transferase Dnmt1 , through DNA methylation, inhibits the binding of transcription factors or indirectly blocks the chromatin remodeling functions by repressing the hippocampal transcription of genes involved in LTP and memory consolidation [ 37 , 38 ]. In this manuscript, we employed animals from a previously published study [ 39 ] for two primary reasons. Firstly, we aimed to comply with the new regulations regarding the use of animals for scientific research, which seek to minimize their number, where possible.…”

“…In particular, in the acute phase of the pathology, we observed that ABA rats reduced bodyweight significantly more than only food-restricted rats, despite eating the same amount of food. Concurrently, unlike EXE animals that maintained a stable activity on the wheel, ABA rats constantly increased running activity over days [ 39 ]. The generation of this food restriction-induced hyperactivity represents a hallmark of the maladaptive behavior characteristic of AN [ 40 ].…”