Effects of Adolescent Labored Breathing on Anxiety-like Behaviors and Neuroendocrine Function in Adult Mice

Open Access
Author:
Chen, Mary
Area of Honors:
Biobehavioral Health
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Sonia Angele Cavigelli, Thesis Supervisor
  • David John Vandenbergh, Honors Advisor
Keywords:
  • asthma
  • anxiety
  • depression
  • SERT
  • CORT
  • adolescence
  • mice
  • periadolescence
  • internalizing behavior
  • Penh
  • enhanced pause
Abstract:
BACKGROUND: In humans, individuals who develop asthma in adolescence have been found to have a doubled risk for developing internalizing disorders such as adult anxiety and depression. The goal of this study is help elucidate the physiological and behavioral mechanisms underlying this co-morbidity and potential bidirectional relationship using a rodent model of asthma. Specifically, this study focuses on experimentally determining how induced severe and frequent labored breathing in periadolescent mice affects adult anxiety-like behaviors and both glucocorticoid and serotonin regulation. The goals of the study are clinically relevant in evaluating possible interventions for minimizing the risk of anxiety in asthmatic adolescents. METHODS: To induce labored breathing, aerosolized methacholine was administered to mice. Mice were divided into one of five treatment groups: (1) non-handled control (n=9), (2) vehicle control (n=10), (3) low methacholine exposure (n=12), (4) medium methacholine exposure (n=12), and (5) high methacholine exposure (n=13). To measure baseline anxiety-related temperament, neonatal isolation-induced ultrasonic vocalizations (USV) were used to characterize high- and low- aversive affective (i.e. anxiety-prone) pups prior to methacholine treatment. On PND 22-57, experimental groups (N = 3-5) were treated with the bronchoconstrictor methacholine while procedural controls received PBS saline using similar methods and non-handle controls received no treatment. Labored breathing was measured as enhanced pause (Penh) via whole-body plethysmography. In adulthood, anxiety and depression-like behaviors (PND 60, 63) relative to baseline individual differences in anxiety were measured by standard tests such as exploratory activity in the elevated plus maze (EPM) and anhedonic measures in the sucrose preference test (SPT). To measure glucocorticoid regulation, fecal samples were collected (i.e. for analysis of fecal corticosterone metabolites) for a two-day period (PND 58-59). To measure serotonin regulation, brainstem sections were preserved for analysis of serotonin transporter gene expression (Sert), and serum samples were collected at necropsy (PND 80) and analyzed for corticosterone levels. RESULTS: Mice with greater labored breathing (Penh) during adolescence were found to have elevated adult anxiety-like behavior (EPM) compared to controls, regardless of basal affective behavior (USV). Increased labored breathing was found to have a significant linear relationship with adult anxiety behavior, explaining 19.0% of the variance in anxiety-related behavior after accounting for cohort effects. Penh and EPM were not significantly associated with Sert gene expression, CORT levels, or sucrose preference. Interestingly, body weight had a significant effect on Penh values, presumably because labored breathing was more difficult to detect in small (i.e. <15 g) periadolescent mice. CONCLUSION: Labored breathing had a significant linear relationship with anxiety-related behavior in adulthood. Going forward, the findings from this study may help researchers develop more accurate mouse models for studying the relationship between adolescent asthma and adult anxiety.