SUMMARY1. Action potentials were recorded in single baroreceptor fibres dissected from the carotid sinus nerves in dogs during increases in blood pressure caused by i.v. injection of angiotensin II, and by i.v. injection of phenylephrine or inflation of an aortic balloon. Action potentials were recorded in single cardiac efferent fibres dissected from the right cervical vagus nerve in other dogs during increases in blood pressure caused by angiotensin II, and by phenylephrine or by inflation of an aortic balloon.2. There was no difference in the discharge frequency of single carotid sinus baroreceptor fibres at any blood pressure when phenylephrine, balloon inflation, or angiotensin II were used to raise the pressure.3. Activity in single cardiac vagal efferent fibres was increased when blood pressure was increased by phenylephrine or by inflation of an aortic balloon. However, when blood pressure rose by a comparable amount in response to angiotensin II, vagal firing decreased (three fibres), was little changed from control levels (four fibres), or increased less than it did in response to phenylephrine (one fibre).4. It is concluded that while angiotensin II has no effect on baroreceptor sensitivity, it does inhibit vagal discharge which is evoked by stimulation of arterial baroreceptors.

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SUMMARY1. This paper extends previous work (Gandevia & McCloskey, 1976) on proprioception in the terminal joint of the middle finger. By positioning the finger in appropriate ways proprioceptive acuity at the joint can be assessed when no muscular afferents could contribute, or when afferents in the flexor but not the extensor could contribute, or when afferents from both muscles could contribute. Digital nerve block anaesthetizes joint and cutaneous receptors and so was used to study the contributions from muscle afferents in isolation.2. Displacements (100) at various angular velocities were better detected when muscle afferents from both flexor and extensor muscles could contribute. This was so whether joint and cutaneous receptors were also available, or after digital anaesthesia. Performance when only muscle afferents are available is, however, inferior to that when all sensory mechanisms are intact. It is concluded that muscle afferents contribute to kinaesthesia, and that a full complement of such receptors from agonist and antagonist muscles gives superior acuity to that achieved when only the receptors of one of the muscle groups is available.3. The angular displacements necessary for 70 % correct detection were determined at angular velocities between 0.25°and 160'/s. Proprioceptive performance was optimal with all proprioceptive mechanisms intact over the range ofangular velocities 10O-80'/s: 70 % correct detection of displacements of0-8°-1-2°occurred in this range.Performance deteriorated slightly at higher velocities of displacement. Performance was significantly poorer when only joint and cutaneous receptors could contribute (in the absence of intramuscular receptors), and when only intramuscular receptors could contribute (in the absence of joint and cutaneous receptors).4. Full proprioceptive acuity depends upon the availability of receptors in muscles and in skin and/or joints.

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