Spinal and supraspinal components of the reflex discharges into lumbar and thoracic white rami

1. In chloralose anaesthetized cats reflex discharges in thoracic and lumbar white rami were elicited by single shock stimulation of intercostal, spinal and hind limb nerves.2. In animals with an intact neuraxis single stimuli of sufficient strength usually elicited a white rami mass discharge having two distinct components. Following spinal transection only the late reflex component disappeared.3. The early (spinal) reflex component had its largest amplitude if the afferent volley entered the spinal cord at the same or an adjacent segment of the white ramus under observation, whereas the size of the late (supraspinal) component was rather independent of the segmental level of the afferent input.4. It was concluded that somatic afferent volleys have a twofold action on the sympathetic nervous system: a more generalized action via the supraspinal sympathetic reflex centres and a more circumscribed action on the preganglionic neurones at the segmental level.

A study of chemoreceptor and baroreceptor A and C-fibres in the 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.