Growth Hormone Treatment Promotes Remote Hippocampal Plasticity after Experimental Cortical Stroke

Electroacupuncture modulates abnormal brain connectivity after ischemia reperfusion injury in rats: A graph theory-based approach

BACKGROUND

Electroacupuncture (EA) has been shown to facilitate brain plasticity-related functional recovery following ischemic stroke. The functional magnetic resonance imaging technique can be used to determine the range and mode of brain activation. After stroke, EA has been shown to alter brain connectivity, whereas EA's effect on brain network topology properties remains unclear. An evaluation of EA's effects on global and nodal topological properties in rats with ischemia reperfusion was conducted in this study.

METHODS AND RESULTS

There were three groups of adult male Sprague-Dawley rats: sham-operated group (sham group), middle cerebral artery occlusion/reperfusion (MCAO/R) group, and MCAO/R plus EA (MCAO/R + EA) group. The differences in global and nodal topological properties, including shortest path length, global efficiency, local efficiency, small-worldness index, betweenness centrality (BC), and degree centrality (DC) were estimated. Graphical network analyses revealed that, as compared with the sham group, the MCAO/R group demonstrated a decrease in BC value in the right ventral hippocampus and increased BC in the right substantia nigra, accompanied by increased DC in the left nucleus accumbens shell (AcbSh). The BC was increased in the right hippocampus ventral and decreased in the right substantia nigra after EA intervention, and MCAO/R + EA resulted in a decreased DC in left AcbSh compared to MCAO/R.

CONCLUSION

The results of this study provide a potential basis for EA to promote cognitive and motor function recovery after ischemic stroke.

Leakage beyond the primary lesion: A temporal analysis of cerebrovascular dysregulation at sites of hippocampal secondary neurodegeneration following cortical photothrombotic stroke

We have previously demonstrated that a cortical stroke causes persistent impairment of hippocampal-dependent cognitive tasks concomitant with secondary neurodegenerative processes such as amyloid-β accumulation in the hippocampus, a region remote from the primary infarct. Interestingly, there is emerging evidence suggesting that deposition of amyloid-β around cerebral vessels may lead to cerebrovascular structural changes, neurovascular dysfunction, and disruption of blood-brain barrier integrity. However, there is limited knowledge about the temporal changes of hippocampal cerebrovasculature after cortical stroke. In the current study, we aimed to characterise the spatiotemporal cerebrovascular changes after cortical stroke. This was done using the photothrombotic stroke model targeting the motor and somatosensory cortices of mice. Cerebrovascular morphology as well as the co-localisation of amyloid-β with vasculature and blood-brain barrier integrity were assessed in the cortex and hippocampal regions at 7, 28 and 84 days post-stroke. Our findings showed transient cerebrovascular remodelling in the peri-infarct area up to 28 days post-stroke. Importantly, the cerebrovascular changes were extended beyond the peri-infarct region to the ipsilateral hippocampus and were sustained out to 84 days post-stroke. When investigating vessel diameter, we showed a decrease at 84 days in the peri-infarct and CA1 regions that were exacerbated in vessels with amyloid-β deposition. Lastly, we showed sustained vascular leakage in the peri-infarct and ipsilateral hippocampus, indicative of a compromised blood-brain-barrier. Our findings indicate that hippocampal vasculature may represent an important therapeutic target to mitigate the progression of post-stroke cognitive impairment.

Gonadotropin-releasing hormone and growth hormone act as anti-inflammatory factors improving sensory recovery in female rats with thoracic spinal cord injury

The potential for novel applications of classical hormones, such as gonadotropin-releasing hormone (GnRH) and growth hormone (GH), to counteract neural harm is based on their demonstrated neurotrophic effects in both in vitro and in vivo experimental models and a growing number of clinical trials. This study aimed to investigate the effects of chronic administration of GnRH and/or GH on the expression of several proinflammatory and glial activity markers in damaged neural tissues, as well as on sensory recovery, in animals submitted to thoracic spinal cord injury (SCI). Additionally, the effect of a combined GnRH + GH treatment was examined in comparison with single hormone administration. Spinal cord damage was induced by compression using catheter insufflation at thoracic vertebrae 10 (T10), resulting in significant motor and sensory deficits in the hindlimbs. Following SCI, treatments (GnRH, 60 μg/kg/12 h, IM; GH, 150 μg/kg/24 h, SC; the combination of both; or vehicle) were administered during either 3 or 5 weeks, beginning 24 h after injury onset and ending 24 h before sample collection. Our results indicate that a chronic treatment with GH and/or GnRH significantly reduced the expression of proinflammatory (IL6, IL1B, and iNOS) and glial activity (Iba1, CD86, CD206, vimentin, and GFAP) markers in the spinal cord tissue and improved sensory recovery in the lesioned animals. Furthermore, we found that the caudal section of the spinal cord was particularly responsive to GnRH or GH treatment, as well as to their combination. These findings provide evidence of an anti-inflammatory and glial-modulatory effect of GnRH and GH in an experimental model of SCI and suggest that these hormones can modulate the response of microglia, astrocytes, and infiltrated immune cells in the spinal cord tissue following injury.

Dynamic regulation of excitatory and inhibitory synaptic transmission by growth hormone in the developing mouse brain

Normal sensory and cognitive function of the brain relies on its intricate and complex neural network. Synaptogenesis and synaptic plasticity are critical to neural circuit formation and maintenance, which are regulated by coordinated intracellular and extracellular signaling. Growth hormone (GH) is the most abundant anterior pituitary hormone. Its deficiencies could alter brain development and impair learning and memory, while GH replacement therapy in human patients and animal models has been shown to ameliorate cognitive deficits caused by GH deficiency. However, the underlying mechanism remains largely unknown. In this study, we investigated the neuromodulatory function of GH in young (pre-weaning) mice at two developmental time points and in two different brain regions. Neonatal mice were subcutaneously injected with recombinant human growth hormone (rhGH) on postnatal day (P) 14 or 21. Excitatory and inhibitory synaptic transmission was measured using whole-cell recordings in acute cortical slices 2 h after the injection. We showed that injection of rhGH (2 mg/kg) in P14 mice significantly increased the frequency of mEPSCs, but not that of mIPSCs, in both hippocampal CA1 pyramidal neurons and L2/3 pyramidal neurons of the barrel field of the primary somatosensory cortex (S1BF). Injection of rhGH (2 mg/kg) in P21 mice significantly increased the frequency of mEPSCs and mIPSCs in both brain regions. Perfusion of rhGH (1 μM) onto acute brain slices in P14 mice had similar effects. Consistent with the electrophysiological results, the dendritic spine density of CA1 pyramidal neurons and S1BF L2/3 pyramidal neurons increased following in vivo injection of rhGH. Furthermore, NMDA receptors and postsynaptic calcium-dependent signaling contributed to rhGH-dependent regulation of both excitatory and inhibitory synaptic transmission. Together, these results demonstrate that regulation of excitatory and inhibitory synaptic transmission by rhGH occurs in a developmentally dynamic manner, and have important implication for identifying GH treatment strategies without disturbing excitation/inhibition balance.

Research progress on the role of hormones in ischemic stroke

Ischemic stroke is a major cause of death and disability around the world. However, ischemic stroke treatment is currently limited, with a narrow therapeutic window and unsatisfactory post-treatment outcomes. Therefore, it is critical to investigate the pathophysiological mechanisms following ischemic stroke brain injury. Changes in the immunometabolism and endocrine system after ischemic stroke are important in understanding the pathophysiological mechanisms of cerebral ischemic injury. Hormones are biologically active substances produced by endocrine glands or endocrine cells that play an important role in the organism's growth, development, metabolism, reproduction, and aging. Hormone research in ischemic stroke has made very promising progress. Hormone levels fluctuate during an ischemic stroke. Hormones regulate neuronal plasticity, promote neurotrophic factor formation, reduce cell death, apoptosis, inflammation, excitotoxicity, oxidative and nitrative stress, and brain edema in ischemic stroke. In recent years, many studies have been done on the role of thyroid hormone, growth hormone, testosterone, prolactin, oxytocin, glucocorticoid, parathyroid hormone, and dopamine in ischemic stroke, but comprehensive reviews are scarce. This review focuses on the role of hormones in the pathophysiology of ischemic stroke and discusses the mechanisms involved, intending to provide a reference value for ischemic stroke treatment and prevention.

Neuroprotective and Regenerative Effects of Growth Hormone (GH) in the Embryonic Chicken Cerebral Pallium Exposed to Hypoxic-Ischemic (HI) Injury

Prenatal hypoxic−ischemic (HI) injury inflicts severe damage on the developing brain provoked by a pathophysiological response that leads to neural structural lesions, synaptic loss, and neuronal death, which may result in a high risk of permanent neurological deficits or even newborn decease. It is known that growth hormone (GH) can act as a neurotrophic factor inducing neuroprotection, neurite growth, and synaptogenesis after HI injury. In this study we used the chicken embryo to develop both in vitro and in vivo models of prenatal HI injury in the cerebral pallium, which is the equivalent of brain cortex in mammals, to examine whether GH exerts neuroprotective and regenerative effects in this tissue and the putative mechanisms involved in these actions. For the in vitro experiments, pallial cell cultures obtained from chick embryos were incubated under HI conditions (<5% O2, 1 g/L glucose) for 24 h and treated with 10 nM GH, and then collected for analysis. For the in vivo experiments, chicken embryos (ED14) were injected in ovo with GH (2.25 µg), exposed to hypoxia (12% O2) for 6 h, and later the pallial tissue was obtained to perform the studies. Results show that GH exerted a clear anti-apoptotic effect and promoted cell survival and proliferation in HI-injured pallial neurons, in both in vitro and in vivo models. Neuroprotective actions of GH were associated with the activation of ERK1/2 and Bcl-2 signaling pathways. Remarkably, GH protected mature neurons that were particularly harmed by HI injury, but was also capable of stimulating neural precursors. In addition, GH stimulated restorative processes such as the number and length of neurite outgrowth and branching in HI-injured pallial neurons, and these effects were blocked by a specific GH antibody, thus indicating a direct action of GH. Furthermore, it was found that the local expression of several synaptogenic markers (NRXN1, NRXN3, GAP-43, and NLG1) and neurotrophic factors (GH, BDNF, NT-3, IGF-1, and BMP4) were increased after GH treatment during HI damage. Together, these results provide novel evidence supporting that GH exerts protective and restorative effects in brain pallium during prenatal HI injury, and these actions could be the result of a joint effect between GH and endogenous neurotrophic factors. Also, they encourage further research on the potential role of GH as a therapeutic complement in HI encephalopathy treatments.

Growth Hormone Increases BDNF and mTOR Expression in Specific Brain Regions after Photothrombotic Stroke in Mice

Aims

We have shown that growth hormone (GH) treatment poststroke increases neuroplasticity in peri-infarct areas and the hippocampus, improving motor and cognitive outcomes. We aimed to explore the mechanisms of GH treatment by investigating how GH modulates pathways known to induce neuroplasticity, focusing on association between brain-derived neurotrophic factor (BDNF) and mammalian target of rapamycin (mTOR) in the peri-infarct area, hippocampus, and thalamus.

Methods

Recombinant human growth hormone (r-hGH) or saline was delivered (0.25 μl/hr, 0.04 mg/day) to mice for 28 days, commencing 48 hours after photothrombotic stroke. Protein levels of pro-BDNF, total-mTOR, phosphorylated-mTOR, total-p70S6K, and phosporylated-p70S6K within the peri-infarct area, hippocampus, and thalamus were evaluated by western blotting at 30 days poststroke.

Results

r-hGH treatment significantly increased pro-BDNF in peri-infarct area, hippocampus, and thalamus (p < 0.01). r-hGH treatment significantly increased expression levels of total-mTOR in the peri-infarct area and thalamus (p < 0.05). r-hGH treatment significantly increased expression of total-p70S6K in the hippocampus (p < 0.05).

Conclusion

r-hGH increases pro-BDNF within the peri-infarct area and regions that are known to experience secondary neurodegeneration after stroke. Upregulation of total-mTOR protein expression in the peri-infarct and thalamus suggests that this might be a pathway that is involved in the neurorestorative effects previously reported in these animals and warrants further investigation. These findings suggest region-specific mechanisms of action of GH treatment and provide further understanding for how GH treatment promotes neurorestorative effects after stroke.

Growth Hormone (GH) Enhances Endogenous Mechanisms of Neuroprotection and Neuroplasticity after Oxygen and Glucose Deprivation Injury (OGD) and Reoxygenation (OGD/R) in Chicken Hippocampal Cell Cultures

As a classical growth promoter and metabolic regulator, growth hormone (GH) is involved in development of the central nervous system (CNS). This hormone might also act as a neurotrophin, since GH is able to induce neuroprotection, neurite growth, and synaptogenesis during the repair process that occurs in response to neural injury. After an ischemic insult, the neural tissue activates endogenous neuroprotective mechanisms regulated by local neurotrophins that promote tissue recovery. In this work, we investigated the neuroprotective effects of GH in cultured hippocampal neurons exposed to hypoxia-ischemia injury and further reoxygenation. Hippocampal cell cultures obtained from chick embryos were incubated under oxygen-glucose deprivation (OGD, <5% O₂, 1 g/L glucose) conditions for 24 h and simultaneously treated with GH. Then, cells were either collected for analysis or submitted to reoxygenation and normal glucose incubation conditions (OGD/R) for another 24 h, in the presence of GH. Results showed that OGD injury significantly reduced cell survival, the number of cells, dendritic length, and number of neurites, whereas OGD/R stage restored most of those adverse effects. Also, OGD/R increased the mRNA expression of several synaptogenic markers (i.e., NRXN1, NRXN3, NLG1, and GAP43), as well as the growth hormone receptor (GHR). The expression of BDNF, IGF-1, and BMP4 mRNAs was augmented in response to OGD injury, and exposure to OGD/R returned it to normoxic control levels, while the expression of NT-3 increased in both conditions. The addition of GH (10 nM) to hippocampal cultures during OGD reduced apoptosis and induced a significant increase in cell survival, number of cells, and doublecortin immunoreactivity (DCX-IR), above that observed in the OGD/R stage. GH treatment also protected dendrites and neurites during OGD, inducing plastic changes reflected in an increase and complexity of their outgrowths during OGD/R. Furthermore, GH increased the expression of NRXN1, NRXN3, NLG1, and GAP43 after OGD injury. GH also increased the BDNF expression after OGD, but reduced it after OGD/R. Conversely, BMP4 was upregulated by GH after OGD/R. Overall, these results indicate that GH protective actions in the neural tissue may be explained by a synergic combination between its own effect and that of other local neurotrophins regulated by autocrine/paracrine mechanisms, which together accelerate the recovery of tissue damaged by hypoxia-ischemia.

More than motor impairment: A spatiotemporal analysis of cognitive impairment and associated neuropathological changes following cortical photothrombotic stroke

There is emerging evidence suggesting that a cortical stroke can cause delayed and remote hippocampal dysregulation, leading to cognitive impairment. In this study, we aimed to investigate motor and cognitive outcomes after experimental stroke, and their association with secondary neurodegenerative processes. Specifically, we used a photothrombotic stroke model targeting the motor and somatosensory cortices of mice. Motor function was assessed using the cylinder and grid walk tasks. Changes in cognition were assessed using a mouse touchscreen platform. Neuronal loss, gliosis and amyloid-β accumulation were investigated in the peri-infarct and ipsilateral hippocampal regions at 7, 28 and 84 days post-stroke. Our findings showed persistent impairment in cognitive function post-stroke, whilst there was a modest spontaneous motor recovery over the investigated period of 84 days. In the peri-infarct region, we detected a reduction in neuronal loss and decreased neuroinflammation over time post-stroke, which potentially explains the spontaneous motor recovery. Conversely, we observed persistent neuronal loss together with concomitant increased neuroinflammation and amyloid-β accumulation in the hippocampus, which likely accounts for the persistent cognitive dysfunction. Our findings indicate that cortical stroke induces secondary neurodegenerative processes in the hippocampus, a region remote from the primary infarct, potentially contributing to the progression of post-stroke cognitive impairment.

Corticosterone Administration Alters White Matter Tract Structure and Reduces Gliosis in the Sub-Acute Phase of Experimental Stroke

White matter tract (WMT) degeneration has been reported to occur following a stroke, and it is associated with post-stroke functional disturbances. White matter pathology has been suggested to be an independent predictor of post-stroke recovery. However, the factors that influence WMT remodeling are poorly understood. Cortisol is a steroid hormone released in response to prolonged stress, and elevated levels of cortisol have been reported to interfere with brain recovery. The objective of this study was to investigate the influence of corticosterone (CORT; the rodent equivalent of cortisol) on WMT structure post-stroke. Photothrombotic stroke (or sham surgery) was induced in 8-week-old male C57BL/6 mice. At 72 h, mice were exposed to standard drinking water ± CORT (100 µg/mL). After two weeks of CORT administration, mice were euthanised and brain tissue collected for histological and biochemical analysis of WMT (particularly the corpus callosum and corticospinal tract). CORT administration was associated with increased tissue loss within the ipsilateral hemisphere, and modest and inconsistent WMT reorganization. Further, a structural and molecular analysis of the WMT components suggested that CORT exerted effects over axons and glial cells. Our findings highlight that CORT at stress-like levels can moderately influence the reorganization and microstructure of WMT post-stroke.

Cell Proliferation in the Piriform Cortex of Rats with Motor Cortex Ablation Treated with Growth Hormone and Rehabilitation

Traumatic brain injury represents one of the main health problems in developed countries. Growth hormone (GH) and rehabilitation have been claimed to significantly contribute to the recovery of lost motor function after acquired brain injury, but the mechanisms by which this occurs are not well understood. In this work, we have investigated cell proliferation in the piriform cortex (PC) of adult rats with ablation of the frontal motor cortex treated with GH and rehabilitation, in order to evaluate if this region of the brain, related to the sense of smell, could be involved in benefits of GH treatment. Male rats were either ablated the frontal motor cortex in the dominant hemisphere or sham-operated and treated with GH or vehicle at 35 days post-injury (dpi) for five days. At 36 dpi, all rats received daily injections of bromodeoxyuridine (BrdU) for four days. We assessed motor function through the paw-reaching-for-food task. GH treatment and rehabilitation at 35 dpi significantly improved the motor deficit caused by the injury and promoted an increase of cell proliferation in the PC ipsilateral to the injury, which could be involved in the improvement observed. Cortical ablation promoted a greater number of BrdU+ cells in the piriform cortex that was maintained long-term, which could be involved in the compensatory mechanisms of the brain after injury.

Exploring How Low Oxygen Post Conditioning Improves Stroke-Induced Cognitive Impairment: A Consideration of Amyloid-Beta Loading and Other Mechanisms

Cognitive impairment is a common and disruptive outcome for stroke survivors, which is recognized to be notoriously difficult to treat. Previously, we have shown that low oxygen post-conditioning (LOPC) improves motor function and limits secondary neuronal loss in the thalamus after experimental stroke. There is also emerging evidence that LOPC may improve cognitive function post-stroke. In the current study we aimed to explore how exposure to LOPC may improve cognition post-stroke. Experimental stroke was induced using photothrombotic occlusion in adult, male C57BL/6 mice. At 72 h post-stroke animals were randomly assigned to either normal atmospheric air or to one of two low oxygen (11% O2) exposure groups (either 8 or 24 h/day for 14 days). Cognition was assessed during the treatment phase using a touchscreen based paired-associate learning assessment. At the end of treatment (17 days post-stroke) mice were euthanized and tissue was collected for subsequent histology and biochemical analysis. LOPC (both 8 and 24 h) enhanced learning and memory in the 2nd week post-stroke when compared with stroke animals exposed to atmospheric air. Additionally we observed LOPC was associated with lower levels of neuronal loss, the restoration of several vascular deficits, as well as a reduction in the severity of the amyloid-beta (Aβ) burden. These findings provide further insight into the pro-cognitive benefits of LOPC.

Similar cognitive deficits in mice and humans in the chronic phase post-stroke identified using the touchscreen-based paired-associate learning task

For many chronic stroke survivors, persisting cognitive dysfunction leads to significantly reduced quality of life. Translation of promising therapeutic strategies aimed at improving cognitive function is hampered by existing, disparate cognitive assessments in animals and humans. In this study, we assessed post-stroke cognitive function using a comparable touchscreen-based paired-associate learning task in a cross-sectional population of chronic stroke survivors (≥ 5 months post-stroke, n = 70), age-matched controls (n = 70), and in mice generated from a C57BL/6 mouse photothrombotic stroke model (at six months post-stroke). Cognitive performance of stroke survivors was analysed using linear regression adjusting for age, gender, diabetes, systolic blood pressure and waist circumference. Stroke survivors made significantly fewer correct choices across all tasks compared with controls. Similar cognitive impairment was observed in the mice post-stroke with fewer correct choices compared to shams. These results highlight the feasibility and potential value of analogous modelling of clinically meaningful cognitive impairments in chronic stroke survivors and in mice in chronic phase after stroke. Implementation of validated, parallel cross-species test platforms for cognitive assessment offer the potential of delivering a more useful framework for evaluating therapies aimed at improving long-term cognitive function post-stroke.