The role of the somatotrophic axis in neuroprotection and neuroregeneration of the addictive brain

Growth Hormone (GH) and Gonadotropin-Releasing Hormone (GnRH) in the Central Nervous System: A Potential Neurological Combinatory Therapy?

This brief review of the neurological effects of growth hormone (GH) and gonadotropin-releasing hormone (GnRH) in the brain, particularly in the cerebral cortex, hypothalamus, hippocampus, cerebellum, spinal cord, neural retina, and brain tumors, summarizes recent information about their therapeutic potential as treatments for different neuropathologies and neurodegenerative processes. The effect of GH and GnRH (by independent administration) has been associated with beneficial impacts in patients with brain trauma and spinal cord injuries. Both GH and GnRH have demonstrated potent neurotrophic, neuroprotective, and neuroregenerative action. Positive behavioral and cognitive effects are also associated with GH and GnRH administration. Increasing evidence suggests the possibility of a multifactorial therapy that includes both GH and GnRH.

Treatment of autistic spectrum disorder with insulin-like growth factors

There are no treatments for the core symptoms of autistic spectrum disorder (ASD), but there is now more knowledge on emerging mechanisms and on mechanism-based therapies. In autism there are altered synapses: genes affected are commonly related to synaptic and immune function. Dysregulation of activity-dependent signaling networks may have a key role the etiology of autism. There is an over-activation of IGF-AKT-mTor in autism spectrum disorders. Morphological and electro-physiological defects of the cerebellum are linked to system-wide ASD-like behavior defects. The molecular basis for a cerebellar contribution has been demonstrated in a mouse model. These have led to a potential mechanism-based use of drug targets and mouse models. Neurotrophic factors are potential candidates for the treatment. Insulin-like growth factor-1 (IGF-1) is altered in autism. It reduces neuro-inflammation: by causing changes of cytokines such as IL-6 and microglial function. IGF-1 reduces the defects in the synapse. It alleviates NMDA-induced neurotoxicity via the IGF-AKT-mTor pathway in microglia. IGF-1 may rescue function in Rett syndrome and ASD caused by changes of the SCHANK3 gene. There are recently pilot studies of the treatment of Rett syndrome and of SCHANK3 gene deficiency syndromes. The FDA has granted Orphan drug designations for Fragile X syndrome, SCHANK3 gene deficiency syndrome and Rett syndrome.

Growth hormone is protective against acute methadone-induced toxicity by modulating the NMDA receptor complex

Human growth hormone (GH) displays promising protective effects in the central nervous system after damage caused by various insults. Current evidence suggests that these effects may involve N-methyl-d-aspartate (NMDA) receptor function, a receptor that also is believed to play a role in opioid-induced neurotoxicity. The aims of the present study were to examine the acute toxic effects of methadone, an opioid receptor agonist and NMDA receptor antagonist, as well as to evaluate the protective properties of recombinant human GH (rhGH) on methadone-induced toxicity. Primary cortical cell cultures from embryonic day 17 rats were grown for 7days in vitro. Cells were treated with methadone for 24h and the 50% lethal dose was calculated and later used for protection studies with rhGH. Cellular toxicity was determined by measuring mitochondrial activity, lactate dehydrogenase release, and caspase activation. Furthermore, the mRNA expression levels of NMDA receptor subunits were investigated following methadone and rhGH treatment using quantitative PCR (qPCR) analysis. A significant protective effect was observed with rhGH treatment on methadone-induced mitochondrial dysfunction and in methadone-induced LDH release. Furthermore, methadone significantly increased caspase-3 and -7 activation but rhGH was unable to inhibit this effect. The mRNA expression of the NMDA receptor subunit GluN1, GluN2a, and GluN2b increased following methadone treatment, as assessed by qPCR, and rhGH treatment effectively normalized this expression to control levels. We have demonstrated that rhGH can rescue cells from methadone-induced toxicity by maintaining mitochondrial function, cellular integrity, and NMDA receptor complex expression.

Neuroprotection by GH against excitotoxic-induced cell death in retinal ganglion cells

Retinal growth hormone (GH) has been shown to promote cell survival in retinal ganglion cells (RGCs) during developmental waves of apoptosis during chicken embryonic development. The possibility that it might also against excitotoxicity-induced cell death was therefore examined in the present study, which utilized quail-derived QNR/D cells as an in vitro RGC model. QNR/D cell death was induced by glutamate in the presence of BSO (buthionine sulfoxamide) (an enhancer of oxidative stress), but this was significantly reduced (P<0.01) in the presence of exogenous recombinant chicken GH (rcGH). Similarly, QNR/D cells that had been prior transfected with a GH plasmid to overexpress secreted and non-secreted GH. This treatment reduced the number of TUNEL-labeled cells and blocked their release of lactate dehydrogenase (LDH). In a further experiment with dissected neuroretinal explants from ED (embryonic day) 10 embryos, rcGH treatment of the explants also reduced (P<0.01) the number of glutamate-BSO-induced apoptotic cells and blocked the explant release of LDH. This neuroprotective action was likely mediated by increased STAT5 phosphorylation and increased bcl-2 production, as induced by exogenous rcGH treatment and the media from GH-overexpressing QNR/D cells. As rcGH treatment and GH-overexpression cells also increased the content of IGF-1 and IGF-1 mRNA this neuroprotective action of GH is likely to be mediated, at least partially, through an IGF-1 mechanism. This possibility is supported by the fact that the siRNA knockdown of GH or IGF-1 significantly reduced QNR/D cell viability, as did the immunoneutralization of IGF-1. GH is therefore neuroprotective against excitotoxicity-induced RGC cell death by anti-apoptotic actions involving IGF-1 stimulation.

Expression and function of growth hormone in the nervous system: a brief review

There is increasing evidence that growth hormone (GH) expression is not confined exclusively to the pituitary somatotrophs as it is synthesized in many extrapituitary locations. The nervous system is one of those extrapituitary sites. In this brief review we summarize data that substantiate the expression, distribution and characterization of neural GH and detail its roles in neural function, including cellular growth, proliferation, differentiation, neuroprotection and survival, as well as its functional roles in behavior, cognition and neurotransmission. Although systemic GH may exert some of these effects, it is increasingly evident that locally expressed neural GH, acting through intracrine, autocrine or paracrine mechanisms, may also be causally involved as a neurotrophic factor.

Recombinant human growth hormone improves cognitive capacity in a pain patient exposed to chronic opioids

During recent decades, the increasing use of opioids for chronic non-cancer pain has raised concerns regarding tolerance, addiction, and importantly cognitive dysfunction. Current research suggests that the somatotrophic axis could play an important role in cognitive function. Administration of growth hormone (GH) to GH-deficient humans and experimental animals has been shown to result in significant improvements in cognitive capacity. In this report, a patient with cognitive disabilities resulting from chronic treatment with opioids for neuropathic pain received recombinant human growth hormone (rhGH) replacement therapy. A 61-year-old man presented with severe cognitive dysfunction after long-term methadone treatment for intercostal neuralgia and was diagnosed with GH insufficiency by GH releasing hormone-arginine testing. The effect of rhGH replacement therapy on his cognitive capacity and quality of life was investigated. The hippocampal volume was measured using magnetic resonance imaging, and the ratios of the major metabolites were calculated using proton magnetic resonance spectroscopy. Cognitive testing revealed significant improvements in visuospatial cognitive function after rhGH. The hippocampal volume remained unchanged. In the right hippocampus, the N-acetylaspartate/creatine ratio (reflecting nerve cell function) was initially low but increased significantly during rhGH treatment, as did subjective cognitive, physical and emotional functioning. This case report indicates that rhGH replacement therapy could improve cognitive behaviour and well-being, as well as hippocampal metabolism and functioning in opioid-treated patients with chronic pain. The idea that GH could affect brain function and repair disabilities induced by long-term exposure to opioid analgesia is supported.

Cortical ablation induces time-dependent changes in rat pituitary somatotrophs and upregulates growth hormone receptor expression in the injured cortex

The pituitary appears to be vulnerable to brain trauma, and its dysfunction is a common feature after traumatic brain injury. The role of pituitary growth hormone (GH) in brain repair after injury has been envisaged, but more studies must be performed to understand completely the importance of GH in these processes. Because some of the neuroprotective effects of GH are mediated directly through the GH receptor (GHR), we examined GHR expression in the rat cerebral cortex after sensorimotor cortex ablation. RT-PCR, immunohistochemistry, and double immunofluorescence had been performed to analyze the correlation between GHR expression in the injured cortex and activity of GH cells in the pituitary. Our results showed that the volume of GH-immunopositive cells was reduced at days 2 and 7 postsurgery (dps), and volume density of GH cells was significantly decreased at 14 dps, all compared with appropriate sham controls. At 30 dps all investigated parameters had returned to control level. In the injured cortex, GHR expression was transiently upregulated. Increased GHR immunoreactivity was observed in reactive astrocytes at 7 and particularly at 14 dps. In neuronal cells, an increase of GHR immunoreactivity was seen in neuronal cell bodies and well-defined primary dendrites at 14 and especially at 30 dps. The results presented here suggest that, during recovery from brain injury, changes in activity of pituitary GH cells result in upregulation of GHR that may have a role in neuronal arborization and glial proliferation in the injured cortex.

Traumatic brain injury: endocrine consequences in children and adults

Traumatic brain injury (TBI) is a common cause of death and disability in young adults with consequences ranging from physical disabilities to long-term cognitive, behavioral, psychological and social defects. Recent data suggest that pituitary hormone deficiency is not infrequent among TBI survivors; the prevalence of reported hypopituitarism following TBI varies widely among published studies. The most common cause of TBI is motor vehicle accidents, including pedestrian-car and bicycle car encounters, falls, child abuse, violence and sports injuries. Prevalence of hypopituitarism, from total to isolated pituitary deficiency, ranges from 5 to 90 %. The time interval between TBI and pituitary function evaluation is one of the major factors responsible for variations in the prevalence of hypopituitarism reported. Endocrine dysfunction after TBI in children and adolescents is common. Adolescence is a time of growth, freedom and adjustment, consequently TBI is also common in this group. Sports-related TBI is an important public health concern, but many cases are unrecognized and unreported. Sports that are associated with an increased risk of TBI include those involving contact and/or collisions such as boxing, football, soccer, ice hockey, rugby, and the martial arts, as well as high velocity sports such as cycling, motor racing, equestrian sports, skiing and roller skating. The aim of this paper is to summarize the best evidence of TBI as a cause of pituitary deficiency in children and adults.

Growth hormone and cognitive function

Emerging data indicate that growth hormone (GH) therapy could have a role in improving cognitive function. GH replacement therapy in experimental animals and human patients counteracts the dysfunction of many behaviours related to the central nervous system (CNS). Various behaviours, such as cognitive behaviours related to learning and memory, are known to be induced by GH; the hormone might interact with specific receptors located in areas of the CNS that are associated with the functional anatomy of these behaviours. GH is believed to affect excitatory circuits involved in synaptic plasticity, which alters cognitive capacity. GH also has a protective effect on the CNS, as indicated by its beneficial effects in patients with spinal cord injury. Data collected from animal models indicates that GH might also stimulate neurogenesis. This Review discusses the mechanisms underlying the interactions between GH and the CNS, and the data emerging from animal and human studies on the relationship between GH and cognitive function. In this article, particular emphasis is given to the role of GH as a treatment for patients with cognitive impairment resulting from deficiency of the hormone.

GH improves spatial memory and reverses certain anabolic androgenic steroid-induced effects in intact rats

GH has previously been shown to promote cognitive functions in GH-deficient rodents. In this study we report the effects of GH on learning and memory in intact rats pretreated with the anabolic androgenic steroid nandrolone. Male Wistar rats received nandrolone decanoate (15 mg/kg) or peanut oil every third day for 3 weeks and were subsequently treated with recombinant human GH (1.0 IU/kg) or saline for 10 consecutive days. During the GH/saline treatment spatial learning and memory were tested in the Morris water maze (MWM). Also, plasma levels of IGF1 were assessed and the gene expression of the GH receptors (Ghr), Igf1 and Igf2, in hippocampus and frontal cortex was analyzed. The results demonstrated a significant positive effect of GH on memory functions and increased gene expression of Igf1 in the hippocampus was found in the animals treated with GH. In addition, GH was demonstrated to increase the body weight gain and was able to attenuate the reduced body weight seen in nandrolone-treated animals. In general, the rats treated with nandrolone alone did not exhibit any pronounced alteration in memory compared with controls in the MWM, and in many cases GH did not induce any alteration. Regarding target zone crossings, considered to be associated with spatial memory, the difference between GH- and steroid-treated animals was significant and administration of GH improved this parameter in the latter group. In conclusion, GH improves spatial memory in intact rats and can reverse certain effects induced by anabolic androgenic steroid.

Recombinant human growth hormone affects the density and functionality of GABAB receptors in the male rat brain

The beneficial effects of growth hormone (GH) on memory and learning have previously been confirmed in both humans and in animal models. An important role of GABAB receptors for multiple forms of learning and memory has also been reported. In this study, we examined the effect of GH on the density and functionality of the metabotropic GABAB receptors in the rat brain. Male Sprague-Dawley rats (n = 24) divided into 3 groups were injected twice daily with recombinant human GH (0.07 or 0.7 IU/kg) for 7 days. The effects of the hormone were determined by quantitative autoradiography and by GABAB stimulated [(35)S]-GTPγS binding using the selective GABAB receptor agonist baclofen. The results demonstrate moderate but significant alterations in both receptor density and functionality in a number of brain regions. For example, a dose-dependent upregulation of GABAB receptors was found in the cingulate cortex, primary motor cortex and caudate putamen, whereas attenuation in the receptor density was encountered in, for example, the medial geniculate nucleus. Although the GH-induced effects on the GABAB receptor in brain areas associated with cognition were fairly pronounced, they were significant and we propose that the physiological responses observed after GH administration at least partly can be mediated through a mechanism involving GABAB receptors.

GIT2 acts as a potential keystone protein in functional hypothalamic networks associated with age-related phenotypic changes in rats

The aging process affects every tissue in the body and represents one of the most complicated and highly integrated inevitable physiological entities. The maintenance of good health during the aging process likely relies upon the coherent regulation of hormonal and neuronal communication between the central nervous system and the periphery. Evidence has demonstrated that the optimal regulation of energy usage in both these systems facilitates healthy aging. However, the proteomic effects of aging in regions of the brain vital for integrating energy balance and neuronal activity are not well understood. The hypothalamus is one of the main structures in the body responsible for sustaining an efficient interaction between energy balance and neurological activity. Therefore, a greater understanding of the effects of aging in the hypothalamus may reveal important aspects of overall organismal aging and may potentially reveal the most crucial protein factors supporting this vital signaling integration. In this study, we examined alterations in protein expression in the hypothalami of young, middle-aged, and old rats. Using novel combinatorial bioinformatics analyses, we were able to gain a better understanding of the proteomic and phenotypic changes that occur during the aging process and have potentially identified the G protein-coupled receptor/cytoskeletal-associated protein GIT2 as a vital integrator and modulator of the normal aging process.

Growth hormone promotes the survival of retinal cells in vivo

Growth hormone (GH) is synthesized and present in the developing chick retina, where it may have local actions in retinal cell differentiation similar to those of conventional growth factors. We have previously shown that retinal GH has neuroprotective effects in retinal ganglion cells. In this paper, we extend our earlier functional studies by examining the in vivo effects of a GH siRNA (NR-cGH-1) after microinjection into the eye cup of the developing chick embryo in ovo. We show that intra-vitreous cGH siRNA lowers both GH mRNA and insulin-like growth factor-1 (IGF-1) mRNA levels in the retina in vivo, and concomitantly elevates the numbers of apoptotic cells in the retina. These effects are apparent 6h after treatment, and persist for at least 24h. The apoptotic cells induced by GH withdrawal were primarily located close to the optic fissure of the developing eye, and were distributed in clusters, suggesting that there are sub-populations of retinal cells that are particularly susceptible to apoptotic stimuli. These results support our view that a GH/IGF-1 axis in retinal cells regulates retinal cell survival in vivo.

Visualizing hormone actions in the brain

Profound and multifaceted effects of hormones on the development, maturation and function of the CNS are well documented. Recent developments in magnetic resonance imagining (MRI) and positron emission tomography (PET) permit detailed in vivo studies of cerebral structure and function in humans. Techniques to measure subtle differences in cerebral structure, regional brain activation, changes in blood flow and other physiological biomarkers allow us to translate experimental evidence of hormone effects obtained from animal models to humans. Here we review the imaging techniques available to support studies of hormone effects on the CNS, emphasizing the recent developments of MRI. In summarizing the major current studies we discuss the potential of these techniques for an emerging new field in endocrinology.

Growth hormone improves hippocampal adult cell survival and counteracts the inhibitory effect of prolonged sleep deprivation on cell proliferation

Sleep deprivation (SD) produces numerous deleterious changes in brain cells, including apoptosis. It has been demonstrated that growth hormone (GH) stimulates cell growth and counteracts apoptosis, although this anti-apoptotic effect has not been tested against SD. To determine the protective effect of GH administration on cell proliferation and survival in the dentate gyrus (DG) of the hippocampus after sleep deprivation; we injected Wistar adult rats with a low dose of recombinant human GH (rhGH 5 ng/kg) per seven days and then we gently sleep deprived the animals for 48 consecutive hours. 5-Bromodeoxiuridine (BrdU) was administered to assess cell proliferation after the GH treatment and NeuN was used as marker of cell fate. Our results indicate that GH produced a three fold increase in the number of BrdU positive cells within the DG [Control = 1044 ± 106.38 cells, rhGH = 2952 ± 99.84 cells, P<0.01]. In contrast, 48 h of SD significantly reduced cell proliferation but this effect was antagonized by the GH administration [SD = 540 ± 18.3 cells, rhGH + SD = 1116 ± 84.48 cells, P<0.004]. Paradoxically, SD and GH administration increased cell survival separately but no significantly compared with control animals. However, cell survival was increased in animals treated with rhGH+SD compared to rats injected with saline solution [P<0.04]. Within the survival cells, the percentage of neurons was higher in SD animals [95%] compared with saline group, while this percentage (NeuN positive cells) was increased in animals treated with rhGH+SD [120%] compared with rhGH [25%] alone. Our findings indicate that GH strongly promotes cell proliferation in the adult brain and also protects the hippocampal neuronal precursors against the deleterious effect of prolonged sleep loss.