Anxiety-like behaviors produced by acute fluoxetine administration in male Fischer 344 rats are prevented by prior exercise.
BACKGROUND
Although selective 5-HT reuptake inhibitors (SSRIs) can reduce anxiety after chronic treatment, acute SSRI administration is associated with an increase in anxiety consistent with an acute increase in 5-HT neurotransmission. Exercise is anxiolytic in humans, and wheel running prevents anxiety-like behavioral consequences of uncontrollable stress in rats, but the effects of exercise on acute fluoxetine-induced anxiety-like behaviors are unknown.


OBJECTIVE
The current studies tested the hypothesis that acute administration of the SSRI fluoxetine would produce behaviors in rats resembling those produced by uncontrollable stress and that these behaviors would be blocked by prior wheel running.


RESULTS
Adult, male Fisher 344 rats administered moderate (10 mg/kg) or high (20 mg/kg) doses of fluoxetine demonstrated exaggerated shock-elicited freezing and an interference with shuttle box escape compared to rats given either saline or low-dose fluoxetine (2.5 mg/kg). Fluoxetine-induced behaviors were similar to, but smaller in magnitude than, those produced by uncontrollable stress and were blocked by pretreatment with the 5-HT(2C) receptor antagonist SB 242084 (1 mg/kg). Rats allowed access to running wheels for 6 weeks were protected against the anxiety-like behaviors produced by a single injection of fluoxetine (10 mg/kg).


CONCLUSIONS
Behavioral effects of acute fluoxetine administration resemble those produced by uncontrollable stress. Results are consistent with the idea that exercise can produce resistance against the anxiogenic effects of acute increases in 5-HT and suggest that acute behavioral effects of antidepressants can depend on history of physical activity.
Greenwood
Benjamin N
BN
Department of Integrative Physiology and the Center for Neuroscience, University of Colorado-Boulder, Boulder, CO 80309, USA. Ben.Greenwood@Colorado.edu
Strong
Paul V
PV
Brooks
Leah
L
Fleshner
Monika
M
D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D001007:Anxiety / Q000139:chemically induced* / Q000523:psychology*; D001522:Behavior, Animal / Q000187:drug effects*; D003345:Corticosterone / Q000097:blood; D004305:Dose-Response Relationship, Drug; D016666:Fluvoxamine; D007211:Indoles / Q000494:pharmacology; D008297:Male; D009043:Motor Activity / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000523:psychology*; D051381:Rats; D011916:Rats, Inbred F344; D044405:Receptor, Serotonin, 5-HT2C / Q000187:drug effects; D058826:Serotonin 5-HT2 Receptor Agonists; D017367:Selective Serotonin Reuptake Inhibitors; D013315:Stress, Psychological / Q000523:psychology
D000631:Aminopyridines; D003345:Corticosterone; D016666:Fluvoxamine; D007211:Indoles; D044405:Receptor, Serotonin, 5-HT2C; D058826:Serotonin 5-HT2 Receptor Agonists; D017367:Selective Serotonin Reuptake Inhibitors; C107820:6-chloro-5-methyl-1-((2-(2-methylpyrid-3-yloxy)pyrid-5-yl)carbamoyl)indoline