Neuroplastic changes in depression: A role for the immune system

• Published in: Psychoneuroendocrinology Vol. 37; no. 9; pp. 1397 - 1416
• Main Authors: Eyre, Harris, Baune, Bernhard T
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.09.2012; Elsevier
• Subjects: Adult and adolescent clinical studies; Animal models; Astrocytes; Behavioral psychophysiology; Biological and medical sciences; Brain - immunology; Brain - metabolism; Brain - physiopathology; c-Jun amino-terminal kinase; Cell survival; Cellular; Circuits; Depression; Depressive Disorder - immunology; Depressive Disorder - metabolism; Depressive Disorder - physiopathology; Endocrinology & Metabolism; Fundamental and applied biological sciences. Psychology; Hormones and behavior; Humans; Humoral; IKK protein; Immune system; Interleukin 6; Interleukin-1 - metabolism; Interleukin-6 - metabolism; Long-term potentiation; Lymphocytes - immunology; Lymphocytes - metabolism; Lymphocytes T; Macrophages; MAP kinase; Medical sciences; Microglia; Monocytes; Mood disorders; Neurogenesis; Neuronal Plasticity - immunology; Neurons - immunology; Neurons - metabolism; Neuroplasticity; Neurotrophins; Plasticity (synaptic); Psychiatry; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Psychopathology. Psychiatry; Recovery; Transcription; Treatment; Tumor necrosis factor; Tumor Necrosis Factor-alpha - metabolism; Neuroplasticity; Cellular; Treatment; Humoral; Depression; Recovery; Immune system; Mood disorder; Brain plasticity
• ISSN: 0306-4530; 1873-3360
• DOI: 10.1016/j.psyneuen.2012.03.019

Summary Accumulating evidence suggests that there is a rich cross-talk between the neuroimmune system and neuroplasticity mechanisms under both physiological conditions and pathophysiological conditions in depression. Anti-neuroplastic changes which occur in depression include a decrease in proliferation of neural stem cells (NSCs), decreased survival of neuroblasts and immature neurons, impaired neurocircuitry (cortical–striatal–limbic circuits), reduced levels of neurotrophins, reduced spine density and dendritic retraction. Since both humoral and cellular immune factors have been implicated in neuroplastic processes, in this review we present a model suggesting that neuroplastic processes in depression are mediated through various neuroimmune mechanisms. The review puts forward a model in that both humoral and cellular neuroimmune factors are involved with impairing neuroplasticity under pathophysiological conditions such as depression. Specifically, neuroimmune factors including interleukin (IL)-1, IL-6, tumour necrosis factor (TNF)-α, CD4+CD25+T regulatory cells (T reg), self-specific CD4+T cells, monocyte-derived macrophages, microglia and astrocytes are shown to be vital to processes of neuroplasticity such as long-term potentiation (LTP), NSC survival, synaptic branching, neurotrophin regulation and neurogenesis. In rodent models of depression, IL-1, IL-6 and TNF are associated with reduced hippocampal neurogenesis; mechanisms which are associated with this include the stress-activated protein kinase (SAPK)/Janus Kinase (JNK) pathway, hypoxia-inducible factors (HIF)-1α, JAK-Signal Transducer and Activator of Transcription (STAT) pathway, mitogen-activated protein kinase (MAPK)/cAMP responsive element binding protein (CREB) pathway, Ras-MAPK, PI-3 kinase, IKK/nuclear factor (NF)-κB and TGFβ activated kinase-1 (TAK-1). Neuroimmunological mechanisms have an active role in the neuroplastic changes associated with depression. Since therapies in depression, including antidepressants (AD), omega-3 polyunsaturated fatty acids (PUFAs) and physical activity exert neuroplasticity-enhancing effects potentially mediated by neuroimmune mechanisms, the immune system might serve as a promising target for interventions in depression.