Using Frame inside XBAP for navigation purposes

I have got a Page inside which I have a toolbar that contains ComboBox and buttons as its first row. In the second row I have a Frame for hosting pages. The reason why I host the pages in the frame is because I don't want my toolbar would change for different pages. 

But when I change the source of the Frame or I navigate the Frame to the desire Page, the whole page changes (ie my toolbar vanishes). How can I force the Internet explorer to navigate the pages inside the Frame rather than in itself? 

          private void UserInformationUri_Click(object sender, RoutedEventArgs e)
          {
              frame.NavigationService.Navigate(new Uri("Pages/UserInformation.xaml", UriKind.Relative));
              //frame.Source = new Uri("Pages/UserInformation.xaml",UriKind.Relative);
          }