Transgenesis and neuroendocrine physiology: a transgenic rat model expressing growth hormone in vasopressin neurones

Abstract

Human growth hormone (hGH) and bovine neurophysin (bNP) DNA reporter fragments were inserted into the rat vasopressin (VP) and oxytocin (OT) genes in a 44 kb cosmid construct used to generate two lines of transgenic rats, termed JP17 and JP59. Both lines showed specific hGH expression in magnocellular VP cells in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). hGH was also expressed in parvocellular neurones in suprachiasmatic nuclei (SCN), medial amygdala and habenular nuclei in JP17 rats; the rat OT-bNP (rOT-bNP) transgene was not expressed in either line. Immunohistochemistry and radioimmunoassay showed hGH protein in the hypothalamus from where it was transported in varicose fibres via the median eminence to the posterior pituitary gland. Immunogold electron microscopy showed hGH co-stored with VP-NP in the same granules. The VP-hGH transgene did not affect water balance, VP storage or release in vivo. Drinking 2 % saline for 72 h increased hypothalamic transgene hGH mRNA expression, and depleted posterior pituitary hGH and VP stores in parallel. In anaesthetised, water-loaded JP17 rats, hGH was released with VP in response to an acute hypovolumic stimulus (sodium nitrosopentacyano, 400 microg I.V.). JP17 rats had a reduced growth rate, lower anterior pituitary rGH contents, and a reduced amplitude of endogenous pulsatile rGH secretion assessed by automated blood microsampling in conscious rats, consistent with a short-loop feedback of the VP-hGH on the endogenous GH axis. This transgenic rat model enables us to study physiological regulation of hypothalamic transgene protein production, transport and secretion, as well as its effects on other neuroendocrine systems in vivo.

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

“…Activation of GHR by GH overexpression in the mouse hypothalamus has a powerful orexigenic effect [ 74 ]. Furthermore, a transgenic model of GH overexpression in GHRH- and vasopressin neurons in the hypothalamus expressed a dwarf rat phenotype, showing that local production is able to decrease the positive effects of the releasing factors in the pituitary gland [ 97 , 98 ].…”

The contribution of animal models to the study of obesity

“…Studies of genetically-modified animal models have not only informed our understanding of the regulation of food intake and energy balance, but have also played a key role in advancing our understanding of the links between obesity and disorders such as diabetes and the metabolic syndrome. For example, the late-onset obesity rat (termed LOB) was discovered as a result of transgenic manipulations originally created to investigate the growth hormone expression in the vasopressin system (Wells et al 2003). When compared with most classic spontaneous mutations, several differences were found in this transgenic model.…”

Hepatic and Adipose Tissue Depot‐Specific Changes in Lipid Metabolism in Late‐Onset Obese (LOB) Rats

“…The LOB rat (Late-onset OBesity) model, first described by Bains et al [10], develops a male-specific, lateonset, central obesity despite a normal intake of low fat diet. These rats were originally generated to study the regulation of the vasopressin/oxytocin (VP/OT) locus targeting human GH to the posterior pituitary [11]. However, as previously reported [1] one of the lines differed from the other lines since it slowly developed an obesity phenotype with unusual characteristics.…”