Apparatus (10) is provided for treating an intervertebral disc (20) of a subject. The apparatus (10) includes a first electrode (30), configured to be inserted into a nucleus pulposus (40) of the disc (20), and a second electrode (32), configured to be placed outside of the nucleus pulposus (40), in a vicinity of the nucleus pulposus (40). A control unit (34) is configured to drive a current between the first and second electrodes (30, 32), and to configure the current to electroosmotically drive fluid between inside and outside the nucleus pulposus (40). Other embodiments are also described.
