Amitriptyline produces dose-dependent supersensitivity of a central cholinergic mechanism

The discontinuation of tricyclic antidepressants (TCAs) can produce symptoms suggesting cholinergic overdrive. The authors previously proposed that these withdrawal states are the consequence of TCA affected cholinergic system supersensitivity. Evidence that chronic treatment with amitriptyline produces dose-dependent supersensitization of a central cholinergic mechanism is now presented. Core temperature is subject to a hypothalamic muscarinic mechanism. The thermic response of adult male rats to oxotremorine was telemetrically measured after 7 days of treatment with saline or amitriptyline 3, 10, and 20 mg/kg given intraperitoneally twice daily. Treatment with the TCA produced dose-dependent enhancement of oxotremorine-induced hypothermia. The data support the hypothesis that at least some TCA withdrawal phenomena involves supersensitization of muscarinic systems.