Have no fear, erythropoietin is here: erythropoietin protects fear conditioning performances after functional inactivation of the amygdala

Erythropoietin prevents the effect of chronic restraint stress on the number of hippocampal CA3c dendritic terminals-relation to expression of genes involved in synaptic plasticity, angiogenesis, inflammation, and oxidative stress in male rats

Stress-induced allostatic load affects a variety of biological processes including synaptic plasticity, angiogenesis, oxidative stress, and inflammation in the brain, especially in the hippocampus. Erythropoietin (EPO) is a pleiotropic cytokine that has shown promising neuroprotective effects. Recombinant human EPO is currently highlighted as a new candidate treatment for cognitive impairment in neuropsychiatric disorders. Because EPO enhances synaptic plasticity, attenuates oxidative stress, and inhibits generation of proinflammatory cytokines, EPO may be able to modulate the effects of stress-induced allostatic load at the molecular level. The aim of this study was therefore to investigate how EPO and repeated restraint stress, separately and combined, influence (i) behavior in the novelty-suppressed feeding test of depression/anxiety-related behavior; (ii) mRNA levels of genes encoding proteins involved in synaptic plasticity, angiogenesis, oxidative stress, and inflammation; and (iii) remodeling of the dendritic structure of the CA3c area of the hippocampus in male rats. As expected, chronic restraint stress lowered the number of CA3c apical dendritic terminals, and EPO treatment reversed this effect. Interestingly, these effects seemed to be mechanistically distinct, as stress and EPO had differential effects on gene expression. While chronic restraint stress lowered the expression of spinophilin, tumor necrosis factor α, and heat shock protein 72, EPO increased expression of hypoxia-inducible factor-2α and lowered the expression of vascular endothelial growth factor in hippocampus. These findings indicate that the effects of treatment with EPO follow different molecular pathways and do not directly counteract the effects of stress in the hippocampus.

Erythropoietin Pathway: A Potential Target for the Treatment of Depression

During the past decade, accumulating evidence from both clinical and experimental studies has indicated that erythropoietin may have antidepressant effects. In addition to the kidney and liver, many organs have been identified as secretory tissues for erythropoietin, including the brain. Its receptor is expressed in cerebral and spinal cord neurons, the hypothalamus, hippocampus, neocortex, dorsal root ganglia, nerve axons, and Schwann cells. These findings may highlight new functions for erythropoietin, which was originally considered to play a crucial role in the progress of erythroid differentiation. Erythropoietin and its receptor signaling through JAK2 activate multiple downstream signaling pathways including STAT5, PI3K/Akt, NF-κB, and MAPK. These factors may play an important role in inflammation and neuroprogression in the nervous system. This is particularly true for the hippocampus, which is possibly related to learning, memory, neurocognitive deficits and mood alterations. Thus, the influence of erythropoietin on the downstream pathways known to be involved in the treatment of depression makes the erythropoietin-related pathway an attractive target for the development of new therapeutic approaches. Focusing on erythropoietin may help us understand the pathogenic mechanisms of depression and the molecular basis of its treatment.

Erythropoietin: a candidate treatment for mood symptoms and memory dysfunction in depression

OBJECTIVE

Current pharmacological treatments for depression have a significant treatment-onset-response delay, an insufficient efficacy for many patients and fail to reverse cognitive dysfunction. Erythropoietin (EPO) has neuroprotective and neurotrophic actions and improves cognitive function in animal models of acute and chronic neurodegenerative conditions and in patients with cognitive decline.

METHODS

We systematically reviewed the published findings from animal and human studies exploring the potential of EPO to treat depression-related cognitive dysfunction and depression.

RESULTS

We identified five animal studies (two in male rats, two in male mice and one in male rats and mice) and seven human proof-of-concept studies (five in healthy volunteers and two in depressed patients) that investigated the above. All of the reviewed animal studies but one and all human studies demonstrated beneficial effects of EPO on hippocampus-dependent memory and antidepressant-like effects. These effects appear to be mediated through direct neurobiological actions of EPO rather than upregulation of red cell mass.

CONCLUSIONS

The reviewed studies demonstrate beneficial effects of EPO on hippocampus-dependent memory function and on depression-relevant behavior, thus highlighting EPO as a candidate agent for future management of cognitive dysfunction and mood symptoms in depression. Larger-scale clinical trials of EPO as a treatment for mood and neurocognitive symptoms in patients with mood disorder are therefore warranted.

Erythropoietin induction by electroconvulsive seizure, gene regulation, and antidepressant-like behavioral effects

BACKGROUND

The neuroprotective and trophic actions of erythropoietin (EPO) have been tested in several animal models of insult, injury, and neurodegeneration. Recent studies in human volunteers demonstrated that EPO improves cognition and also elicits antidepressant effects. It is believed that the behavioral effects are mediated by EPO's trophic effect on neuronal systems. We therefore tested whether EPO is able to alter behavior and brain gene expression in rats.

METHODS

The expression of EPO and EPO receptor (EPOR) in multiple brain regions was examined by quantitative polymerase chain reaction, in situ hybridization, and immunohistochemistry. The regulation of EPO and the transcription factor hypoxia-induced factor-alpha (HIF1alpha) after electroconvulsive seizure (ECS) was investigated. Behavioral effects of EPO were tested in the rodent forced swimming and novelty-induced hypophagia (NIH) models. EPO gene profiles were obtained by microarray analysis of the hippocampus after intracerebroventricular infusion.

RESULTS

EPO and EPOR were widely expressed in the brain albeit at low levels. Highest level of EPO and EPOR were in the choroid plexus and striatum, respectively. Peripheral administration of EPO was sufficient to produce a robust antidepressant-like effect in the forced swim and NIH tests. Gene expression profiles revealed that EPO induces the expression of neurotrophic genes such as brain-derived neurotrophic factor, VGF (nonacronymic), and neuritin.

CONCLUSIONS

EPO is induced by ECS and independently exhibits antidepressant-like efficacy in the forced swim and NIH tests. EPO regulates the expression of genes implicated in antidepressant action and appears to be a candidate molecule for further testing in neuropsychiatry.

Behavioral effects of corpus callosum transection and environmental enrichment in adult rats

A common assumption about the corpus callosum transection (CCX) is that it only affects behaviors heavily relying on interhemispheric communication. However, cerebral laterality is ubiquitous across motor and perceptual, cognitive and emotional domains, and the corpus callosum is important for its establishment. Several recent studies showed that the partial denervation of the sensorimotor isocortex through CCX derepressed neural growth processes that were sensitive to motor demand (experience-dependent neural plasticity). We investigated whether the facilitatory effects of CCX on cortical neural plasticity, shaped by differential housing, extended beyond the motor domain. Adult rats were housed in enriched (EE), standard (SE) or impoverished environments (IE) for 10 weeks, that is, 2 weeks before they underwent CCX or sham surgery, and, then, 8 weeks throughout the experiments. After they recovered from surgery, the behavioral performance of rats was tested using open-field, spontaneous alternation in the T-maze, paw preference, Morris water maze, and tone fear conditioning. The results indicated that the effects of CCX and housing on open-field behavior were independent, with CCX increasing the time spent in the center of the field at the beginning of the observation (i.e., emotionality), and EE and IE increasing rearing (emotionality) and reducing teeth-chattering (habituation), respectively. CCX reduced the frequency of spontaneous alternation, denoting spatial working memory deficits, while housing did not influence this performance. Neither CCX, nor housing significantly affected paw preference lateralization, although CCX was associated with a leftward bias in paw preference. In the Morris water maze, housing had effects on spatial acquisition, while CCX reduced activity, without interfering with spatial memory. CCX did not influence tone fear conditioning, but context fear conditioning seemed to benefit from EE. We conclude that CCX in adult rats has subtle, but specific behavioral effects pertaining to emotionality, spatial working memory, and, possibly, aversively motivated exploration, and these effects are either independent or only peripherally interact with the effects of housing.