Proteomic investigation of the prefrontal cortex in the rat clomipramine model of depression

Abstract

Neonatal rodents chronically treated with the tricyclic antidepressant clomipramine show depression-like behavior, which persists throughout adulthood. Therefore, this animal model is suitable to investigate the pathomechanism of depression, which is still largely unknown at the molecular level beyond monoaminergic dysfunctions. Here, we describe protein level changes in the prefrontal cortex of neonatally clomipramine-treated adult rats correlating with behavioral abnormalities. Clomipramine was administered to rat pups twice daily between postnatal days 8-21, while controls received saline injections. Behavioral tests were performed on 3months old rats. The proteomic study was conducted using two-dimensional differential gel electrophoresis. We have identified 32 proteins by mass spectrometry analysis of the significantly altered protein spots. The changed proteins are related to several biological functions, such as inflammation, transcription, cell metabolism and cytoskeleton organization. Among the altered proteins, the level of macrophage migration inhibitory factor showed the largest alteration, which was confirmed with Western blot. Macrophage migration inhibitory factor showed widespread distribution and was predominantly expressed in astrocytes in the forebrain of rats which were described using immunohistochemistry. We conclude that neonatal clomipramine exposure induces sustained modification in the proteome, which may form the molecular basis of the observed depression-like behavior in adult rats.

Biological significance: It is known that some of the psychiatric disorders, such as autism, depression or schizophrenia may be at least in part, developmental disorders. We hypothesized that clomipramine treatment in early stage of brain development, which is known to induce depression-like behavior in adult rats, results in pathological distortion in neuronal and glial network development, which can be reflected by the cellular proteome in adulthood. Thus, we performed an unbiased proteomics experiment in adult rats, which were neonatally administered with clomipramine to reveal protein level changes three months after treatment. Many of the identified changed proteins are previously associated with depressive symptoms, e.g., the macrophage migration inhibitory factor (MIF), the level of which showed the largest alteration among the identified proteins. Based on our data, we suggest that neonatal clomipramine treatment is a reliable model to study the developmental effect of psychoactive drugs applied in the sensitive early phase of brain development. Furthermore, our findings support the idea that the alteration of early development of the brain induced by antidepressant treatment could result in sustained pathological changes in the cellular phenotype in the prefrontal cortex leading to depression-like behavioral symptoms.

Keywords: Clomipramine treatment; Depression-like behavior; Macrophage migration inhibitory factor (MIF); Prefrontal cortex (PFC); Two-dimensional differential gel electrophoresis (2D-DIGE).