Effects of chronic activity wheel running or antidepressant pharmacotherapy on appetitive behavior and gene expression in rat locus coeruleus after olfactory ulbectomy
O'Neal, Heather Abney Merriott
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Evidence suggests that exercise can be effective for the prevention and treatment of depression. A meta-analysis was conducted to quantify effects from studies examining the effect of an exercise intervention on depression scores. The overall effect was moderate, d = -0.57 (95% CI, -0.79 to -0.34), suggesting that exercise groups exhibit a 1/2 SD reduction in depression relative to comparison groups. |However, biological mechanisms to explain such effects have not been established. Common antidepressant medications target the noradrenergic system, and exercise influences noradrenergic transmission. Thus, adaptations in central noradrenergic function represent a plausible mechanism to explain antidepressant effects of exercise. The first study examined the effect of 6 weeks of treadmill training on gene expression for preprogalanin (GAL) and tyrosine hydroxylase (TH) within the locus coeruleus using in situ hybridization. Levels of GAL messenger RNA (mRNA) were higher in treadmill-trained compared to sedentary animals, but there was no effect on TH mRNA. These results support a potential role of GAL in modulating noradrenergic activity after chronic exercise. |The second study examined the effect of chronic activity wheel running andimipramine administration on appetitive behavior and gene expression in the locus coeruleus using the olfactory bulbectomy model of depression. Male rats were randomly assigned to the following conditions: (1) bilateral olfactory bulbectomy or sham surgery, (2) activity wheel running or sedentary home cage, and (3) daily imipramine or saline injections. After 21 days, animals underwent behavioral testing for sucrose preference and copulatory activity. Levels of TH, GAL, and prepro-neuropeptide Y (NPY) mRNA were measured using in situ hybridization. Bulbectomized animals exhibited reductions in sucrose intake and decrements in copulatory performance compared to sham animals. Imipramine administration was also associated with decreased copulatory rates and ejaculation frequency. However, activity wheel running after bulbectomy improved copulation rates, reduced ejaculation latency, and increased ejaculation frequency. Level of GAL mRNA was increased after imipramine treatment whereas activity wheel running after bulbectomy increased gene expression for NPY. No differences were found in TH mRNA. Adaptations in noradrenergic function after 3 weeks of imipramine treatment and activity wheel running do not appear to occur via similar mechanisms of gene expression within the locus coeruleus.