Depressed patients … The finding of a negative correlation between AATSH and post-APO ACTH and Cortisol values in patients without a history of suicidal behavior is rather paradoxical. Owing to the regulations between HPT and DA systems, one could have expected a positive correlation and not a negative

one (ie, an increase in TRH secretion should have led to a decrease in D2 function). Whether hypofunctionality of D2 receptors exists on both hypothalamic and pituitary levels, the absence of GH, ACTH, and Cortisol response to APO in depression would suggest, an upregulation of other DA receptor subtypes (such as D1) in the hypothalamus. Indeed, Inhibitors,research,lifescience,medical GH, ACTH, and Cortisol response to Inhibitors,research,lifescience,medical APO reflects primarily stimulation of the hypothalamic releasing inhibitors hormones (GHreleasing hormone and CRH, respectively) rather than a direct, effect on the

pituitary Moreover, Cortisol response to APO, which is correlated to ACTH (p=0.74; n=98; P<0.00001), can be considered as an index of central DA function connected with the regulation of the HPA axis. Thus, the negative correlation between ΔΔSH and post-APO ACTH and Cortisol Inhibitors,research,lifescience,medical values in patients without a history of suicidal behavior suggests that the efficacy of compensatory mechanisms requires a new functional balance between HPT and DA systems. In the depressed group with a history of suicidal behavior, the absence of a functional link between HPT and DA activity in the hypothalamus may play a role in the pathophysiology of suicidal behavior. However, one may note that half of the patients of this Inhibitors,research,lifescience,medical group showed HPT and DA functional adjustment (Figure 4; ie, those exhibiting blunted ΔΔTSH values), suggesting that this requirement

is not sufficient Inhibitors,research,lifescience,medical in the efficacy of compensatory mechanisms. In other words, other processes – so far unknown – are also involved in the efficacy of compensatory mechanisms. Conclusions Taken together our findings in depressed inpatients suggest, that: HPA axis hyperactivity is not responsible for the reduced 5-HT activity found in patients with a history of suicidal behavior. HPT dysregulation may be regarded as a compensatory mechanism for diminished central 5-HT Farnesyltransferase activity. Cooccurrence of HPT axis and tuberoinfundibular DA dysregulation is compatible with a decreased TRH and D2 receptor function (possibly secondary to increased TRH tone). The absence of a functional link between HPT and DA activity in the hypothalamus may be implicated in the pathogenesis of suicidal behavior. A better knowledge of processes involved in the efficacy of compensatory mechanisms could lead to new therapeutic strategies in patients with recurrent major depressive disorder, especially those with a history of suicidal behavior.