Influence of naloxone on antidepressant drug effects in the forced swimming test in mice.

The influence of naloxone on the effects of several antidepressant drugs, atropine and caffeine was studied in the forced swimming test in mice. Naloxone itself has no effect in this test, but significantly reduces that of two tricyclic antidepressants, clomipramine (20 and 30 mg/kg) and desipramine (20 and 30 mg/kg). Except for clorgyline at the high dose of 60 mg/kg, no significant reduction of activity by naloxone was observed with other antidepressants (pargyline, nomifensine and mianserin), nor with caffeine and atropine. These results are discussed in terms of the pharmacological characteristics of each drug and of the test used. No straightforward interaction between cholinergic or monoaminergic and endorphinic systems is evident. Possible action at opiate receptor sites is discussed.