부산대학교 도서관

In an earlier study, we examined the pressure–response characteristics of rat aortic baroreceptors with C-fibre (non-medullated) afferents. Compared with aortic baroreceptor fibres with A-fibre (medullated) afferents, the C-fibres were activated at higher pressures and discharged more irregularly when stimulated with a steady level of pressure. Here we examine the relationship between discharge and the aortic diameter in these two types of afferents in rats and rabbits. An in vitro aortic arch/aortic nerve preparation was used to record single-fibre activity simultaneously with aortic arch pressure and diameter. Diameter was measured using a highly sensitive non-contact photoelectric device. Baroreceptor discharge was characterized by stimulating the nerve endings with either slow pressure ramps from subthreshold to 200–250 mmHg, at a rate of rise of 2 mmHg s[sup -1], or pressure steps from subthreshold to suprathreshold levels, at amplitudes of 110–180 mmHg. In response to these inputs, C-fibres in rabbits (conduction velocities= 0.8–2.2 m s[sup -1]) behaved much like those in rats. The C-fibres had significantly higher pressure thresholds (95 ± 3 mmHg vs. 53 ± 2 mmHg; mean ± SEM), lower threshold frequencies (2.4 ± 0.5 vs. 27.7 ± 1.8 spikes s[sup -1]), lower maximum discharge frequencies (22.7 ± 2.3 vs. 65 ± 5.8 spikes s[sup -1]) and more irregular discharge in response to a pressure step when compared with A-fibres (conduction velocities of 8–16 m s[sup -1]). When plotted against diameter, C-fibre ramp-evoked discharge increased gradually at first, and then rose steeply at increasingly higher ramp pressures where aortic diameter became relatively constant. In contrast, A-fibre discharge was linearly related to diameter over a wide range of pressure. These results suggest two interpretations: (1) The relation between stretch and C-fibre discharge is highly non-linear, with a marked inc... [ABSTRACT FROM AUTHOR]