THE EFFECT OF CHEMORECEPTOR STIMULATION ON THE CENTRIPETAL TRANSFER OF SOMATOSENSORY INFORMATION IN THE URETHANE-ANESTHETIZED RAT

In urethane-anaesthetized rats, stimulation of carotid body chemorecep tors desynchronizes the cortical electroencephalogram and increases th e sensitivity of thalamic and cortical somatosensory neurones to perip heral sensory nerve stimulation. Peripheral chemoreceptors were stimul ated by injecting a bolus (30 ml) or infusing 100 ml of 0.18 M NaCl so lution equilibrated with 100% CO2 into an internal carotid artery, the cortical electroencepharogram and ventilation were monitored routinel y. This stimulus induced hyperventilation and desynchronization of the cortical electroencephalogram. Anaesthetized rats also showed spontan eous periodic increases in ventilation rate accompanied by changes of the cortical electroencephalogram from high-voltage low frequency to l ow-voltage high frequency which seemed to be identical with those evok ed by stimulating chemoreceptors. The activity of identified somatosen sory neurons in the thalamic ventrobasal complex, layer IV of the soma tosensory cortex, or the cuneate nucleus was recorded extracellularly during and following chemoreceptor activation. Neurones in the ventrob asal thalamus and somatosensory cortex showed a decrease in latency an d an increase in probability of discharge to supramaximal electrical s timulation of the forepaw which was more pronounced following infusion stimulation of the carotid body than following bolus stimulation. In contrast, neurons within the cuneate nucleus showed a slight increase in latency to onset and a decrease in the probability of firing follow ing the same stimulus. The results indicate that stimulation of the ca rotid body chemoreceptors leads to an enhancement of the response of s omatosensory neurons to their normal physiological input. (C) 1998 IBR O. Published by Elsevier Science Ltd.