Você pode registrar a chamada do JS via code behind conforme exemplo:
//Sem UpdatePanel
this.Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "Ancora", "ancora('topo');", true);
//Com UpdatePanel
ToolkitScriptManager.RegisterClientScriptBlock(this, this.GetType(), "Ancora", "ancora('topo');", true);
Diego Cotini do Couto - MCTS .NET Framework 3.5, ASP.NET Applications