Chronic injections of saline produce subsensitivity to nicotine

The routine handling of rats and the injection of saline is a stressor. The authors report that chronic twice daily injections of normal saline (1 ml/kg IP) for 14 days produced subsensitivity to the hypothermic effects of nicotine (1 ml/kg IP). The weekly injection of nicotine (1 mg/kg IP) does not produce this effect. The investigators propose that their findings reflect the effect of chronic stress on a nicotinic mechanism. Lithium, desipramine, fluoxetine, and amitriptyline also alter the thermic response to systemically injected nicotine. A nicotinic mechanism(s) may be involved in the neurobiology of chronic stress, actions of antidepressants, and conceivably the pathophysiology of depression.