Autoradiographic and immunohistochemical localization of insulin-like growth factor-I receptor binding sites in brain of the brown trout, Salmo trutta

Insulin-like growth factor signalling and its significance as a biomarker in fish and shellfish research

The insulin-like growth factor signalling system comprises insulin-like growth factors, insulin-like growth factor receptors and insulin-like growth factor-binding proteins. Along with the growth hormones, insulin-like growth factor signalling is very pivotal in the growth and development of all vertebrates. In fishes, insulin-like growth factors play an important role in osmoregulation, besides the neuroendocrine regulation of growth. Insulin-like growth factor concentration in plasma can assess the growth in fishes and shellfishes and therefore widely applied in nutritional research as an indicator to evaluate the performance of selected nutrients. The present review summarizes the role of insulin-like growth factor signalling in fishes and shellfishes, its significance in aquaculture and in evaluating growth, reproduction and development, and discusses the utility of this system as biomarkers for early indication of growth in aquaculture.

Gender differences and lateralization in the distribution pattern of insulin-like growth factor-1 receptor in developing rat hippocampus: an immunohistochemical study

Numerous investigators have provided data supporting essential roles for insulin-like growth factor-I (IGF-I) in development of the brain. The aim of this study was to immunohistochemically determine the distinct regional distribution pattern of IGF-1 receptor (IGF-IR) expression in various portions of newborn rat hippocampus on postnatal days 0 (P0), 7 (P7), and 14 (P14), with comparison between male/female and right/left hippocampi. We found an overall significant increase in distribution of IGF-IR-positive (IGF-IR+) cells in CA1 from P0 until P14. Although, no marked changes in distribution of IGF-IR+ cells in areas CA2 and CA3 were observed; IGF-IR+ cells in DG decreased until P14. The smallest number of immunoreactive cells was present in CA2 and the highest number in DG at P0. Moreover, in CA1, CA3, and DG, the number of IGF-IR+ cells was markedly higher in both sides of the hippocampus in females. Our data also showed a higher mean number of IGF-IR+ cells in the left hippocampus of female at P7. By contrast, male pups showed a significantly higher number of IGF-IR+ cells in the DG of the right hippocampus. At P14, the mean number of immunoreactive cells in CA1, CA3, and DG areas found to be significantly increased in left side of hippocampus of males, compared to females. These results indicate the existence of a differential distribution pattern of IGF-IR between left-right and male-female hippocampi. Together with other mechanisms, these differences may underlie sexual dimorphism and left-right asymmetry in the hippocampus.

Stroke neuroprotection: oestrogen and insulin-like growth factor-1 interactions and the role of microglia

Oestrogen has been shown to be neuroprotective for stroke and other neural injury models. Oestrogen promotes a neuroprotective phenotype through myriad actions, including stimulating neurogenesis, promoting neuronal differentiation and survival, suppressing neuroinflammation and maintaining the integrity of the blood-brain barrier. At the molecular level, oestrogen directly modulates genes that are beneficial for repair and regeneration via the canonical oestrogen receptor. Increasingly, evidence indicates that oestrogen acts in concert with growth factors to initiate neuroprotection. Oestrogen and insulin-like growth factor (IGF)-1 act cooperatively to influence cell survival, and combined steroid hormone/growth factor interaction has been well documented in the context of neurones and astrocytes. Here, we summarise the evidence that oestrogen-mediated neuroprotection is critically dependent on IGF-1 signalling, and specifically focus on microglia as the source of IGF-1 and the locus of oestrogen-IGF-1 interactions in stroke neuroprotection.

Feedback regulation of growth hormone synthesis and secretion in fish and the emerging concept of intrapituitary feedback loop

Growth hormone (GH) is known to play a key role in the regulation of body growth and metabolism. Similar to mammals, GH secretion in fish is under the control of hypothalamic factors. Besides, signals generated within the pituitary and/or from peripheral tissues/organs can also exert a feedback control on GH release by effects acting on both the hypothalamus and/or anterior pituitary. Among these feedback signals, the functional role of IGF is well conserved from fish to mammals. In contrast, the effects of steroids and thyroid hormones are more variable and appear to be species-specific. Recently, a novel intrapituitary feedback loop regulating GH release and GH gene expression has been identified in fish. This feedback loop has three functional components: (i) LH induction of GH release from somatotrophs, (ii) amplification of GH secretion by GH autoregulation in somatotrophs, and (iii) GH feedback inhibition of LH release from neighboring gonadotrophs. In this article, the mechanisms for feedback control of GH synthesis and secretion are reviewed and functional implications of this local feedback loop are discussed. This intrapituitary feedback loop may represent a new facet of pituitary research with potential applications in aquaculture and clinical studies.

Organ-specific expression of IGF-I during early development of bony fish as revealed in the tilapia, Oreochromis niloticus, by in situ hybridization and immunohistochemistry: indication for the particular importance of local IGF-I

The cellular sites of insulin-like growth factor I (IGF-I) synthesis in the early developing tilapia (0-140 days post fertilization, DPF) were investigated. IGF-I mRNA and peptide appeared in liver as early as 4 DPF and in gastro-intestinal epithelial cells between 5-9 DPF. In exocrine pancreas, the expression of IGF-I started at 4 DPF and continued until 90 DPF. IGF-I production was detected in islets at 6 DPF in non-insulin cells and occurred throughout life. In renal tubules and ducts, IGF-I production started at 8 DPF. IGF-I production in chondrocytes had its onset at 4 DPF, was more pronounced in growing regions and was also found in adults. IGF-I mRNA and peptide appeared in the cytoplasm of skeletal muscle cells at 4 DPF. In gill chloride cells, IGF-I production started at 6 DPF. At 13 DPF, IGF-I was detected in cardiac myocytes. IGF-I-producing epidermal cells appeared at 5 DPF. In brain and ganglia, IGF-I was expressed in virtually all neurones from 6 to 29 DPF, their number decreasing with age. Neurosecretory IGF-I-immunoreactive axons were first seen in the neurohypophysis around 17 DPF. Endocrine cells of the adenohypophysis exhibited IGF-I mRNA at 28 DPF and IGF-I immunoreactivity at 40 DPF. Thus, IGF-I appeared early (4-5 DPF), first in liver, the main source of endocrine IGF-I, and then in organs involved in growth or metabolism. The expression of IGF-I was more pronounced during development than in juvenile and adult life. Local IGF-I therefore seems to have a high functional impact in early growth, metabolism and organogenesis.