Apparatus for use in a gastrointestinal tract of a subject, the apparatus including a straightening rod (8), and a flexible tubular anchor (1) having a distal end (2) and an open proximal end (4), and sized to fit in the gastrointestinal tract. The anchor (1) comprises a material that has an elastic memory which biases the anchor (1) towards assuming a pre-selected bent configuration. The anchor (1) is shaped so as to define a central core (7) extending from the open proximal end (4) toward the distal end (2). The anchor (1) is configured to be straightened from the pre-selected bent configuration by insertion of the straightening rod (8) in the central core (7). The apparatus further includes a device (70) coupled to the anchor, selected from the list consisting of: a therapeutic device, and a transmitting device. Other embodiments are also described.