A STUDY OF CHEMORECEPTOR AND BARORECEPTOR A AND C-FIBRES IN CAT CAROTID NERVE

1. 149 A‐fibres and 52 C‐fibres from the cat carotid nerve were studied in vivo with single‐unit recording techniques. These units subserved chemoreceptor and baroreceptor modalities. In addition, half of the C‐fibres were determined to be efferent in origin. The estimated fibre diameter spectrum for chemoreceptor and baroreceptor A‐fibres is described. 2. The discharge pattern of chemoreceptor A and C‐fibres was characteristically irregular both at rest and during activation. However, about 5% of the chemoreceptor A‐fibre population exhibited a very regular discharge pattern, even at low rates of firing. 3. In comparing A and C‐fibres, it was found that chemoreceptor and baroreceptor A‐fibres had lower thresholds, shorter response latencies, more rapid acceleration of discharge and higher discharge frequencies than their C‐fibre counterparts. 4. During strong chemoreceptor or baroreceptor stimulation, interaction of the ‘spontaneous’ whole nerve activity with the evoked A and C‐fibre compound action potentials provided a method of estimating the relative proportions of chemoreceptors and baroreceptors in the A and C‐fibre populations of the carotid nerve. The A‐fibre population was found to be comprised of approximately 2/3 chemoreceptors, 1/3 baroreceptors. The reverse was true for the C‐fibre population, i.e. 2/3 baroreceptors, 1/3 chemoreceptors. 5. A stepwise C‐fibre response is described which may arise from the several C‐fibres within a single Schwann cell. © 1969 The Physiological Society