Endogenous analgesic systems are known to be activated by peripheral noxious stimulation as well as arterial carbon dioxide elevation. In the present study, neuronal activities in the rostral ventrolateral medulla were identified and classified
in
according to their rhythmic activities and their responses to noxious peripheral nerve stimulations before and after elevating the arterial carbon dioxide partial pressure were investigated.
Using extracellular recording technic, a total of 53 spontaneously active neurons were recorded from the rostral ventrolateral medulla in α-chloralose anesthetized cats. These were classified as cardiovascular(28), respiratory(16), both
cardiovascular
and respiratory(2) and noncardiovascular-nonrespiratory(7).
Among the 28 cardiovascular neurons eleven showed increased activities during arterial hypercapnia, thirteen showed decreased responses, and four showed no change. Nine respiratory neurons showed increased responses to arterial hypercapnia, six
showed
decreased responses and one showed no change. Neither of th ecardiovascular and respiratory neurons showed significant change in its activity during arterial hypercapnia; however, four of the noncardiovascular-nonrespiratory neurcns exhibited
decreased
their activities in response to arterial hypercapnia while two exhibited increased activvities.
Arterial hypercapnia increased the responses of cardiovascular neurons to peripheral nerve stimulation with C-intensity, while not changing the responses to Aδ-stimulation significantly.
From the above results it was concluded that during arterial hypercaqpnia, some cardiovascular neurons and respiratory neurons have increased activities as well as increased reponses to C-fiber stimulation.
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