Insulin induces tyrosine phosphorylation of the insulin receptor and SHC, and SHC/GRB2 association in cerebellum but not in forebrain cortex of rats

A growth-related branch of the insulin-signaling pathway was studied in the forebrain cortex and cerebellum of Wistar rats. Anesthetized rats received a bolus injection of saline or insulin through the cava vein after which fragments of cerebellum and forebrain cortex were excised and immediately homogenized. Insulin receptor and p46(SHCA) phosphorylation, and p46(SHCA)/GRB2 association were detected by immunoprecipitation and blotting with specific antibodies. Insulin stimulated the rapid phosphorylation of its receptor in cerebellum, followed by p46(SHCA) phosphorylation and GRB2 recruitment. The optimal insulin dose for the induction of p46(SHCA)/GRB2 binding was 60 mu g, and time-course experiments showed that maximum phosphorylation/binding occurred 2-3 min after stimulation. Although insulin receptors and SHC were present in forebrain cortex, there was no increase in their phosphorylation, nor was there any recruitment of GRB2 following stimulation with insulin. Thus, although elements involved in the early intracellular response to insulin are present in the central nervous system, differences in their activation/regulation may account for the functional roles of insulin in these tissues. (C) 1999 Published by Elsevier Science B.V. All rights reserved.