MsoTextOrientation not declared

I am creating a powerpoint slide from vb .net.  I have it working where it can add a picture, but I wanted to add a text box.  When I use the following line of code, it says that Name MsoTextOrientation is not declared.  What am I missing?

        oSlide.Shapes.AddTextbox(MsoTextOrientation.msoTextOrientationHorizontal, 2, 2, 2, 2)

Here are my imports at the top:

Imports System.Data
Imports Office = Microsoft.Office.Core
Imports PowerPoint = Microsoft.Office.Interop.PowerPoint
Imports System.Drawing
Imports System.Drawing.Printing

Imports System.ComponentModel
Imports System.ServiceProcess