Of mice and men: modelling post-stroke depression experimentally

Postischemic Anhedonia Associated with Neurodegenerative Changes in the Hippocampal Dentate Gyrus of Rats

Poststroke depression is one of the major symptoms observed in the chronic stage of brain stroke such as cerebral ischemia. Its pathophysiological mechanisms, however, are not well understood. Using the transient right middle cerebral artery occlusion- (MCAO-, 90 min) operated rats as an ischemia model in this study, we first observed that aggravation of anhedonia spontaneously occurred especially after 20 weeks of MCAO, and it was prevented by chronic antidepressants treatment (imipramine or fluvoxamine). The anhedonia specifically associated with loss of the granular neurons in the ipsilateral side of hippocampal dentate gyrus and was also prevented by an antidepressant imipramine. Immunohistochemical analysis showed increased apoptosis inside the granular cell layer prior to and associated with the neuronal loss, and imipramine seemed to recover the survival signal rather than suppressing the death signal to prevent neurons from apoptosis. Proliferation and development of the neural stem cells were increased transiently in the subgranular zone of both ipsi- and contralateral hippocampus within one week after MCAO and then decreased and almost ceased after 6 weeks of MCAO, while chronic imipramine treatment prevented them partially. Overall, our study suggests new insights for the mechanistic correlation between poststroke depression and the delayed neurodegenerative changes in the hippocampal dentate gyrus with effective use of antidepressants on them.

Anti-depressant effects of phosphodiesterase 3 inhibitor cilostazol in chronic mild stress-treated mice after ischemic stroke

RATIONALE

Phosphodiesterase 3 (PDE3) inhibitor cilostazol ameliorates negative effects of cerebral hypoperfusion against cerebral ischemic injury through the phosphodiesterase 3-cyclic adenosine monophosphate (cAMP) signaling cascade.

OBJECTIVES

We investigated the question of whether cilostazol would have an anti-depressant effect on chronic mild stress (CMS)-treated mice after ischemic stroke.

METHODS

An animal model of post-stroke depression was developed by additional CMS procedures in middle cerebral artery occlusion (MCAO). We performed behavioral, histological, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), immunohistochemical, Western blot and enzyme linked immunosorbent assays (ELISA).

RESULTS

In the open field, sucrose preference, forced swim and Morris water maze test, treatment with cilostazol resulted in reduction of all depressive behaviors examined, particularly in the Morris water maze test. Treatment with cilostazol reduced prominent atrophic changes in the ipsilateral striatum and hippocampus of CMS-treated ischemic mice through inhibition of neuronal cell death and microglial activation. In addition, treatment of the CMS-treated ischemic mice with cilostazol resulted in significantly increased phosphorylation of cAMP response element-binding protein (CREB) and expression of mature brain-derived neurotrophic factor (BDNF) with its receptor tropomyosin receptor kinase B (TrkB) in the ipsilateral striatum and hippocampus. Phosphorylation of CREB was also demonstrated in the dopaminergic neurons of the midbrain. Treatment with cilostazol also resulted in an increased number of newly formed cells and enhanced differentiation into neurons in the ipsilateral striatum and hippocampus.

CONCLUSIONS

Our results suggest that phosphodiesterase 3 inhibitor cilostazol may have anti-depressant effects on post-stroke depression through inhibition of neurodegeneration in the primary lesion and secondary extrafocal sites and promotion of neurogenesis. These beneficial effects on post-stroke depression may be involved in activation of CREB/BDNF signaling.

The serotonergic system in the neurobiology of depression: Relevance for novel antidepressants

The monoamine hypothesis of depression posits that an imbalance in monoaminergic neurotransmission is causally related to the clinical features of depression. Antidepressants influencing serotonin mainly aim at raising serotonin concentrations, thereby increasing serotonergic transmission at the level of the synapse, for example by inhibiting the serotonin transporter. However, the serotonin system is multifaceted. Different serotonin receptor subtypes turn the serotonergic system into a complex neurochemical arrangement that influences diverse neurotransmitters in various brain regions. Classical antidepressants as well as other psychopharmacological agents have various crucial effects on serotonin receptors. We aim at providing a clinically useful characterization of serotonin receptor subtypes in the treatment of depression. Clarifying the mode of action and the interplay of serotonin receptors with pharmacological agents should help antidepressant mechanisms and typical side effects to be better understood. Against this background, we feature the novel antidepressants vortioxetine, vilazodone and milnacipran/levomilnacipran with regard to their serotonin receptor targets such as the 5-HT1A, 5-HT3 and 5-HT7 which may account for their specific effects on certain symptoms of depression (e.g. cognition and anxiety) as well as a characteristic side-effect profile.

MRI heralds secondary nigral lesion after brain ischemia in mice: a secondary time window for neuroprotection

Cerebral ischemia in the territory of the middle cerebral artery (MCA) can induce delayed neuronal cell death in the ipsilateral substantia nigra (SN) remote from the primary ischemic lesion. This exofocal postischemic neuronal degeneration (EPND) may worsen stroke outcomes. However, the mechanisms leading to EPND are poorly understood. Here, we studied the time course of EPND via sequential magnetic resonance imaging (MRI) and immunohistochemistry for up to 28 days after 30 minutes' occlusion of the MCA (MCAo) and reperfusion in the mouse. Furthermore, the effects of delayed treatment with FK506 and MK-801 on the development of EPND were investigated. Secondary neuronal degeneration in the SN occurred within the first week after MCAo and was characterized by a marked neuronal cell loss on histology. Sequential neuroimaging examinations revealed transient MRI changes, which were detectable as early as day 4 after MCAo and thus heralding histologic evidence of EPND. Treatment with MK-801, an established anti-excitotoxic agent, conferred protection against EPND even when initiated days after the initial ischemic event, which was not evident with FK506. Our findings define a secondary time window for delayed neuroprotection after stroke, which may provide a promising target for the development of novel therapies.

Striatal Infarction Elicits Secondary Extrafocal MRI Changes in Ipsilateral Substantia Nigra

Focal ischemia may induce pathological alterations in brain areas distant from the primary lesion. In animal models, exofocal neuron death in the ipsilateral midbrain has been described after occlusion of the middle cerebral artery (MCA). Using sequential magnetic resonance imaging (T2- and diffusion-weighted) at 3 Tesla, we investigated acute ischemic stroke patients on days 1, 2, 6, 8, and 10 after stroke onset. Sixteen consecutive patients who had suffered a stroke involving the caudate nucleus and/or putamen of either hemisphere were recruited into the study. Four additional patients with strokes sparing the caudate nucleus and putamen but encompassing at least one-third of the MCA territory served as controls. Ischemic lesions involving striatal structures resulted in hyperintense lesions in ipsilateral midbrain that emerged between days 6 and 10 after stroke and were not present on the initial scans. In contrast, none of the control stroke patients developed secondary midbrain lesions. Hyperintense lesions in the pyramidal tract or the brain stem caused by degeneration of the corticospinal tract could be clearly distinguished from these secondary midbrain gray matter lesions and were detectable from day 2 after ischemia. Co-registration of high-resolution images with a digitized anatomic atlas revealed localization of secondary lesions primarily in the substantia nigra pars compacta. Apparent diffusion coefficient (ADC) values in the secondary lesions showed a delayed sharp decline through day 10. Normalization of ADC values was observed at late measurements. Taken together, our study demonstrates that striatal infarction elicits delayed degenerative changes in ipsilateral substantia nigra pars compacta.

Found in translation? Commentary on a BJP themed issue about animal models in neuropsychiatry research

This themed issue of Br J Pharmacol is dedicated to the utility and needs of animal models in psychiatry research. The following articles document strengths and weaknesses, indicate areas where better models are sorely needed and provide examples where pharmacological studies may result in mechanistic breakthrough and aid in drug development. In addition, complicating factors both in disease and treatment strategies are canvassed, such as sex differences, genetic and environmental influences. While not exhaustive, the intention was to use a number of exemplars to stimulate discussion around how animal models can aid in improving our understanding and treatment of many devastating conditions.