Modification of nociceptively identified neurons in thalamic parafascicularis by chemical stimulation of dorsal raphe with glutamate, morphine, serotonin and focal dorsal raphe electrical stimulation.

The properties of local application of glutamate, morphine and serotonin in the dorsal raphe (DR) area and the effects of DR electrical stimulation on the spontaneous activity and on the nociceptive responses of 135 parafascicularis (PF) neurons were studied. It was observed that local glutamate application within the DR exerts an effect upon the "nociceptive-on" PF neuronal activity similar to that induced by focal electrical stimulation of the DR in intact animals and in animals after dorsal spinal cord section. In addition, local application of morphine and serotonin in the DR area elicits different effects on the spontaneous activity versus the nociceptive responses of PF neurons. These observations suggest that opioids and serotonin at least in part participate in modulation of pathways from DR to PF. This observation is consistent with the hypothesis that the DR ascending path modulates nociceptive input to the PF (at least in part) via activations of both opioid and serotonergic receptors.