Hippocampal growth hormone modulates relational memory and the dendritic spine density in CA1

Growth Hormone Alters Remapping in the Hippocampal Area CA1 in a Novel Environment

Growth hormone (GH) is a neuromodulator that binds to receptors in the hippocampus and alters synaptic plasticity. A decline in GH levels is associated with normal aging, stress, and disease, and the mechanisms proposed involve the hippocampal circuit plasticity. To see how GH affects the hippocampal neural code, we recorded single neurons in the CA1 region of male Long-Evans rats with locally altered GH levels. Rats received injections of adeno-associated viruses into the hippocampus to make the cells overexpress either GH or an antagonizing mutated GH (aGH). Place cells were recorded in both familiar and novel environments to allow the assessment of pattern separation in the neural representations termed remapping. All the animals showed intact and stable place fields in the familiar environment. In the novel environment, aGH transfection increased the average firing rate, peak rate, and information density of the CA1 place fields. The tendency of global remapping increased in the GH animals compared with the controls, and only place cells of control animals showed significant rate remapping. Our results suggest that GH increases hippocampal sensitivity to novel information. Our findings show that GH is a significant neuromodulator in the hippocampus affecting how place cells represent the environment. These results could help us to understand the mechanisms behind memory impairments in GH deficiency as well as in normal aging.

Assessment of Executive Function Skills in Children with Isolated Growth Hormone Deficiency: A Cross-sectional Study

Objective

The aim of this study was to evaluate executive function (EF), such as inhibition and working memory, in children with isolated growth hormone deficiency (IGHD) using performance-based tests and parent-report scales.

Methods

A total of seventy children between the ages of 7 and 12 years were included in the study. Half (n=35) had children with IGHD and half were healthy controls. To evaluate the EF performances of the participants, the Visual Aural Digit Span Test-B Form (VADS-B) and Stroop task were applied. EF was also evaluated using the Behavior Rating Inventory of Executive Function (BRIEF).

Results

Children with IGHD scored lower on the VADS-B form for short-term memory (p<0.05) compared to healthy controls. In addition, the completion time for the Stroop-color/word test was significantly longer in children with IGHD (p<0.05). For children with IGHD, their parents reported higher scores on all sub-scales of the BRIEF scale, with statistically significant differences for all sub-scales with the exception of “organization of materials” (p<0.05).

Conclusion

In this study, children with IGHD had poorer EF skills compared to unaffected peers. EF skills may influence academic success by affecting children’s language skills, mathematical comprehension, cognitive flexibility, and hypothetical thinking. We believe that psychiatric evaluation of children with IGHD before and during treatment may positively contribute to both their academic performance and social relationships.

The effects of peripheral hormone responses to exercise on adult hippocampal neurogenesis

Over the last decade, a considerable amount of new data have revealed the beneficial effects of exercise on hippocampal neurogenesis and the maintenance or improvement of cognitive function. Investigations with animal models, as well as human studies, have yielded novel understanding of the mechanisms through which endocrine signaling can stimulate neurogenesis, as well as the effects of exercise on acute and/or chronic levels of these circulating hormones. Considering the effects of aging on the decline of specific endocrine factors that affect brain health, insights in this area of research are particularly important. In this review, we discuss how different forms of exercise influence the peripheral production of specific endocrine factors, with particular emphasis on brain-derived neurotrophic factor, growth hormone, insulin-like growth factor-1, ghrelin, estrogen, testosterone, irisin, vascular endothelial growth factor, erythropoietin, and cortisol. We also describe mechanisms through which these endocrine responses to exercise induce cellular changes that increase hippocampal neurogenesis and improve cognitive function.

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.

The role of growth hormone in hippocampal function

Growth hormone is a multifunctional molecule with broad cellular targets. This pituitary hormone is currently used as a therapeutic agent against several brain injuries due to its neurotrophic activity. The hippocampus is one of the brain regions where the growth hormone plays a role in normal and pathologic conditions. This brain structure is associated with several cognitive functions such as learning, memory, and mood, which are frequently affected by brain traumatism. The present chapter describes the experimental and clinical evidence that supports a central role of growth hormone in the hippocampus functionality.

An exercise "sweet spot" reverses cognitive deficits of aging by growth-hormone-induced neurogenesis

Hippocampal function is critical for spatial and contextual learning, and its decline with age contributes to cognitive impairment. Exercise can improve hippocampal function, however, the amount of exercise and mechanisms mediating improvement remain largely unknown. Here, we show exercise reverses learning deficits in aged (24 months) female mice but only when it occurs for a specific duration, with longer or shorter periods proving ineffective. A spike in the levels of growth hormone (GH) and a corresponding increase in neurogenesis during this sweet spot mediate this effect because blocking GH receptor with a competitive antagonist or depleting newborn neurons abrogates the exercise-induced cognitive improvement. Moreover, raising GH levels with GH-releasing hormone agonist improved cognition in nonrunners. We show that GH stimulates neural precursors directly, indicating the link between raised GH and neurogenesis is the basis for the substantially improved learning in aged animals.