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1. 1. The effects of several antidepressants and 5-hydroxytryptamine on dissociation of 3 H-imipramine from solubilized binding sites were investigated. 2. 2. Binding sites were solubilized from rat brain membranes and gelfiltrated on a column of Sephacryl S-300. 3. 3. Most of the agents used allowed biphasic dissociation with 1mM of displacing agent and without using dilution-induced dissociation. This biphasic dissociation without nonspecific effects of membranes may be due to the existence of low-affinity binding sites. 4. 4. Dissociation of up to 40 min followed first-order kinetics. The dissociation half-life of 3 H-imipramine with the various displacing agents was calculated at from 15.0 to 25.0 min, and the differences among the agents were not so significant as the attenuation or the acceleration of the dissociation was indicated. The lower concentration of the displacing agents may obscure the modulation of the dissociation.

1. No significant difference in the density (Bmax) of platelet 3H imipramine recognition sites were found between the group of 20 unmedicated depressed patients and 10 healthy volunteers. The mean KD value was significantly higher in the population of depressives than in controls. 2. Non-responders (after 2 weeks of treatment with antidepressants) had significantly lower initial Bmax values than responders or control subjects. Density of platelet 3H imipramine site may thus be a predictor of early response to antidepressant therapy. 3. No significant sex differences were found in KD or Bmax values in the depressed group or in control subjects. There was, however, a seasonal variation in Bmax but not in KD values of platelet 3H imipramine binding.