Search for biological correlates of depression and mechanisms of action of antidepressant treatment modalities. Do neuropeptides play a role?

Dysregulation of the monoaminergic systems is likely a sufficient but not a necessary cause of depression. A wealth of data indicates that neuropeptides, e.g., NPY, CRH, somatostatin, tachykinins and CGRP play a role in affective disorders and alcohol use/abuse. This paper focuses on NPY in etiology and pathophysiology of depression. Decreased peptide and mRNA NPY were found in hippocampus of both the genetic, e.g., the FSL strain, and environmental rat models of depression, e.g., chronic mild stress and early life maternal separation paradigms. Rat models of alcoholism also show altered NPY. Furthermore, NPY is also reduced in CSF of depressed patients. Antidepressive treatments tested so far (lithium, topiramate, SSRIs, ECT and ECS, wheel running) increase NPY selectively in rat hippocampus and in human CSF. Moreover, NPY given icv to rat has antidepressive effects which are antagonized by NPY-Y1 blockers. The data support our hypothesis that the NPY system dysregulation constitutes one of the biological underpinnings of depression and that one common mechanism of action of antidepressive treatment modalities may be effects on NPY and its receptors. In a novel paradigm, early life maternal separation was superimposed on "depressed" FSL and control rats and behavioral and brain neurochemistry changes observed in adulthood. The consequences were more deleterious in genetically vulnerable FSL. Early antidepressive treatment modulated the adult sequelae. Consequently, if these data are confirmed, the ethical and medical question that will be asked is whether it is permissible and advisable to consider prophylactically treating persons at risk.

Effects of maternal separation on neuropeptide Y and calcitonin gene-related peptide in "depressed" Flinders Sensitive Line rats: a study of gene-environment interactions.

Interactions between genetic vulnerability to stress/depression and early life experience may play a crucial role in the pathogenesis of mood disorders. Here we explore this hypothesis by superimposing early life trauma in the form of maternal deprivation for 180 min per day from postnatal day 2 to 14 onto a genetic model of depression/susceptibility to depression, Flinders Sensitive Line (FSL) and their controls, Flinders Resistant Line (FRL) rats. We investigate effects on neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) like immunoreactivity (LI) in 10 brain regions as these neuropeptides are affected by antidepressants and are altered in cerebrospinal fluid of depressed patients. NPY-LI was reduced while CGRP-LI was elevated in hippocampus and frontal cortex of "genetically depressed" FSL rats. The two peptides displayed a significant negative correlation in these regions that was strongest in the FSL strain. Maternal deprivation exacerbated the strain difference in hippocampal CGRP-LI, while it was without effect on NPY-LI. FSL rats had higher tissue concentration of both neuropeptides in periaqueductal grey and higher NPY-LI in caudate/putamen. Maternal deprivation selectively raised CGRP-LI in amygdala of the FRL control stain. Thus, in two brain regions implicated in the neurobiology of depression, hippocampus and frontal cortex, changes in CGRP-LI and NPY-LI were in opposite direction, and CGRP-LI appears to be more responsive to adverse experience. Our findings thus support the hypothesis that genetic disposition and developmental stress may contribute to the susceptibility to depression by exerting selective neuropeptide- and brain region-specific effects on adult neurobiology.