Habenular neuron responses to noxious input are modified by dorsal raphe stimulation

Single-cell experiments were undertaken to characterize the neurons of the rat habenular complex (Hab) which respond to noxious input and the extent to which the noxious responses can be modulated by dorsal raphe stimulation. The reported observations demonstrate that habenular neurons exhibit two response patterns to noxious stimulation termed 'nociceptive-on' and 'nociceptive-off'. In addition, it was demonstrated that dorsal raphe stimulation modulates the noxious input to the 'nociceptive-on' and to the 'nociceptive-off' cells. These findings demonstrated that the habenular complex responds to noxious input and, together with other findings reporting that both direct morphine application into the Hab and electrical stimulation of the Hab produced analgesia, suggest that the habenular complex is integrated into the pain regulatory circuitry.