Effect of streptozocin-induced diabetes on insulin-receptor tyrosine kinase activity in obese Zucker rats

We examined insulin binding, insulin-stimulated autophosphorylation, and phosphorylation of poly(Glu.Na,Tyr)4:1 by liver and skeletal muscle insulin receptor from lean, obese, and obese streptozocin-induced diabetic Zucker rats. Induction of diabetes with streptozocin (30 mg/kg) lowered the lasting insulin level from 11.4 to 3.8 ng/ml, which was not significantly greater than the lean control level. Autophosphorylation and tyrosine kinase activity of liver insulin receptors were increased 70-100% in the obese control group (relative to lean rats), but diabetes reversed this hyperresponsiveness to insulin. In muscle, obesity was associated with a 40-50% decrease in autophosphorylation and tyrosine kinase activity, which was also reversed in the diabetic state. Autophosphorylation and tyrosine kinase activity were significantly correlated in liver and muscle and were also correlated with fasting insulin levels. These data suggest that insulin-receptor tyrosine kinase activity is regulated differently in liver and muscle and that the abnormalities in kinase activity associated with the obese Zucker rat are at least partly secondary to hyperinsulinemia.     

Transgenerational modification of dopaminergic dysfunctions induced by maternal immune activation

Prenatal exposure to infectious and/or inflammatory insults is increasingly recognized to contribute to the etiology of psychiatric disorders with neurodevelopmental components. Recent research using animal models suggests that maternal immune activation (MIA) can induce transgenerational effects on brain and behavior, possibly through epigenetic mechanisms. Using a mouse model of MIA that is based on gestational treatment with the viral mimeticpoly(I:C) (= polyriboinosinic-polyribocytidilic acid), the present study explored whether the transgenerational effects of MIA are extendable to dopaminergic dysfunctions. We show that the direct descendants born to poly(I:C)-treated mothers display signs of hyperdopaminergia, as manifested by a potentiated sensitivity to the locomotor-stimulating effects of amphetamine (Amph) and increased expression of tyrosine hydroxylase (Th) in the adult ventral midbrain. In stark contrast, second- and third-generation offspring of MIA-exposed ancestors displayed blunted locomotor responses to Amph and reduced expression of Th. Furthermore, we found increased DNA methylation at the promoter region of the dopamine-specifying factor, nuclear receptor-related 1 protein (Nurr1), in the sperm of first-generation MIA offspring and in the ventral midbrain of second-generation offspring of MIA-exposed ancestors. The latter effect was further accompanied by reduced mRNA levels of Nurr1 in this brain region. Together, our results suggest that MIA has the potential to modify dopaminergic functions across multiple generations with opposite effects in the direct descendants and their progeny. The presence of altered DNA methylation in the sperm of MIA-exposed offspring highlights the possibility that epigenetic processes in the male germline play a role in the transgenerational effects of MIA.Subject terms: Neuroimmunology, Developmental disorders     

Characterization of [Phe(13), Tyr(19)]-MCH analog binding activity to the MCH receptor

Melanin concentrating hormone (MCH), a hypothalamic neuropeptide, is an important regulator of energy homeostasis in mammals. Characterization of an MCH specific receptor has been hampered by the lack of a suitable radioligand. The [Phe(13), Tyr(19)]-MCH analog has been shown by different investigators to bind specifically to cell lines of epithelial or pigment cell origin. Recently, using functional assays, the MCH receptor has been characterized as a seven transmembrane G-coupled protein initially identified as SLC-1. In the present study, we used tyrosine iodinated [Phe(13), Tyr(19)]-MCH analog, which stimulates food intake in a manner similar to that of MCH, as well as native MCH to conduct binding studies. Specific binding could not be demonstrated in intact cells of several cell lines, including A431 and B16. Specific binding associated with membranes localized to the microsomal, not the plasma membrane, fraction. Message for SLC-1 was absent in these cell lines, as assessed by Northern blot analysis. We conclude that cells previously reported to express the MCH receptor do not express SLC-1 and that both iodinated MCH and the [Phe(13), Tyr(19)]-MCH have a large component of non-specific binding. These ligands may be useful for binding studies in transfected cells with high levels of SLC-1 expression. However they do not appear to be suitable for screening for the MCH receptor as most cells demonstrate significant low affinity non-specific binding.