Effects of repeated noxious thermal stimuli on the responses of neurons in the lateral cervical nucleus of cats: evidence for an input from A-nociceptors to the spinocervicothalamic pathway.

Recent findings indicate that the lateral cervical nucleus (LCN) in cats is capable of transmitting to the ventrobasal thalamus information that may contribute to nociception. In the present study, we examined the effects of repeated noxious thermal stimulation on the responses of LCN neurons in unanesthetized cats that were decerebrated and partially spinalized. Seventeen LCN neurons were recorded that responded to noxious mechanical stimuli. The most responsive area of the receptive field of each neuron was exposed to repeated and sustained thermal stimuli of up to 55 degrees C. Such stimulation decreased the thermal thresholds of all 17 LCN neurons and increased the frequencies of their responses to identical thermal stimuli. The characteristics of this sensitization suggest that the spinocervicothalamic pathway receives a prominent input from A-nociceptors.