Tracing of afferent pathways from the femoral-saphenous vein to the dorsal root ganglia using transport of horseradish peroxidase

Lower-limb venous distension reflex and orthostatic tolerance in young healthy humans

Earlier reports suggest that limb venous distension evokes reflex increases in muscle sympathetic nerve activity (MSNA) and blood pressure (BP) (i.e., venous distension reflex). Our recent report also shows that suction of arterially occluded limb evokes venous distension reflex. We postulate that the venous distension reflex contributes to autonomic responses to orthostatic stress. In this study, we hypothesized that orthostatic tolerance would be linked to the MSNA response seen with lower limb suction. Fifteen healthy subjects were tested in the supine position. Negative pressure (-100 mmHg) was applied on an arterially occluded lower limb for 2 min. MSNA from the peroneal nerve in the limb not exposed to suction, ECG, and BP (Finometer) was recorded throughout the study. Limb occlusion without suction was used as a control trial. In a separate visit, the individual's orthostatic tolerance was assessed using a graded lower body negative pressure (LBNP) tolerance test. Mean arterial BP and MSNA (18.6 ± 1.9 to 23.6 ± 2.0 bursts/min) significantly (both P < 0.05) increased during limb suction. Orthostatic tolerance index positively correlated (R = 0.636, P = 0.011) with the MSNA response seen with suction during occlusion. Since the venous distension reflex strength correlates with the level of orthostatic tolerance, we speculate that lower-limb venous distension reflex engagement increases the sympathetic responses during orthostatic challenge and serves to maintain BP with postural stress.

Sympathetic and cardiovascular responses to venous distension in an occluded limb

We recently showed that a fixed volume (i.e., 40 ml) of saline infused into the venous circulation of an arterially occluded vascular bed increases muscle sympathetic nerve activity (MSNA) and blood pressure. In the present report, we hypothesized that the volume and rate of infusion would influence the magnitude of the sympathetic response. Blood pressure, heart rate, and MSNA were assessed in 13 young healthy subjects during forearm saline infusions (arrested circulation). The effects of different volumes of saline (i.e., 2%, 3%, 4%, or 5% forearm volume at 30 ml/min) and different rates of infusion (i.e., 5% forearm volume at 10, 20, or 30 ml/min) were evaluated. MSNA and blood pressure responses were linked with the infusion volume. Infusion of 5% of forearm volume evoked greater MSNA responses than did infusion of 2% of forearm volume (Δ11.6 ± 1.9 vs. Δ3.1 ± 1.8 bursts/min and Δ332 ± 105 vs. Δ38 ± 32 units/min, all P < 0.05). Moreover, greater MSNA responses were evoked by saline infusion at 30 ml/min than 10 ml/min (P < 0.05). Sonographic measurements confirmed that the saline infusions induced forearm venous distension. The results suggest that volume and rate of saline infusion are important factors in evoking sympathetic activation. We postulate that venous distension contributes to cardiovascular autonomic adjustment in humans.

Phrenic nerve afferents elicited cord dorsum potential in the cat cervical spinal cord

BACKGROUND

The diaphragm has sensory innervation from mechanoreceptors with myelinated axons entering the spinal cord via the phrenic nerve that project to the thalamus and somatosensory cortex. It was hypothesized that phrenic nerve afferent (PnA) projection to the central nervous system is via the spinal dorsal column pathway.

RESULTS

A single N1 peak of the CDP was found in the C4 and C7 spinal segments. Three peaks (N1, N2, and N3) were found in the C5 and C6 segments. No CDP was recorded at C8 dorsal spinal cord surface in cats.

CONCLUSION

These results demonstrate PnA activation of neurons in the cervical spinal cord. Three populations of myelinated PnA (Group I, Group II, and Group III) enter the cat's cervical spinal segments that supply the phrenic nerve.

Infants with univentricular heart have reduced heart rate and blood pressure responses to side motion and altered responses to head-up tilt

Cardiovascular control was studied in infants with univentricular heart (UVH). Side motion tests and 45-s 45° head-up tilt tests were performed in 11 control and 9 UVH infants at the age of 13 ± 3.2 wk. In addition, heart rate (HR) reactions to spontaneous arousals and HR variability during slow-wave sleep (SWS) were determined. All UVH infants had been hypoxic for several weeks, and during the sleep study the mean arterial oxyhemoglobin saturation was 82 ± 5%. Tests were done at night during SWS, confirmed by polysomnographic recording. Continuous beat-to-beat blood pressure (BP) was measured. In the side-motion tests, control infants consistently showed a transient increase in HR and BP. This response was markedly reduced in all of the UVH infants ( P < 0.0001). In tilt tests, the UVH infants showed normal BP responses, but, although a sustained 2.0% decrease in HR was observed in the controls, the UVH infants presented with a sustained 2.6% mean HR increase ( P = 0.005). The UVH infants also showed attenuated HR acceleration during spontaneous arousals ( P = 0.01), but HR variability did not differ significantly from the controls. In conclusion, UVH infants with chronic hypoxia exhibit defective vestibulosympathetic pathways, as expressed by an absence of acute HR and BP reactivity to side motion. HR reactions to postural challenge and spontaneous arousal are also altered. Autonomic function abnormalities in these infants are suggested to be secondary to hypoxia.

Localization of sympathetic postganglionic neurons innervating mesenteric artery and vein in rats

Physiological and histochemical studies have demonstrated the control and innervation of sympathetic nerves to the artery and vein vessels of splanchnic circulation. In our laboratory, we first used the technique of retrograde transport of horseradish peroxidase to identify the origin of sympathetic neurons innervating the mesenteric vein. In this study, double fluorescence staining technique was used for a simultaneous localization of the sympathetic postganglionic neurons supplying the mesenteric artery and vein in rats. First-order branches of mesenteric artery (A) and vein (V) in the vicinity of ileo-cecal junction were isolated for application of fluorescent dyes (Fast Blue, FB and Diamidino Yellow, DY). The application of FB and DY on A and V was alternated in the next animal to minimize the difference in dye uptake. The animal was allowed to recover for 6-7 days assuring a complete uptake of FB and DY into the cytoplasm and nucleus, respectively. The number of FB, DY and double staining neurons in the prevertebral and paravertebral ganglia were counted under a fluorescent microscope after animal fixation and serial frozen section (30 microm) of the sympathetic ganglia. Our study revealed the following findings: (1) Distribution of the fluorescence-staining neurons in the sympathetic ganglia was as follows: right celiac ganglion (39%), superior mesenteric ganglion (30%), left celiac ganglion (26%), inferior mesenteric ganglion (1%) and paravertebral ganglia (4%). (2) Double staining neurons that dually innervate A and V amounted to 54% of total staining neurons. There were 41% neurons singly innervating A and 5% innervating V. (3) The ratio of neurons supplying the A and V ranged from 1.41 to 1.75 (average 1.61). (4) There was no distinct topographical distribution with respect to the neuron location innervating A and V. The distribution of neurons appeared in a scattering pattern.

Vestibular influences on the autonomic nervous system

Considerable evidence exists to suggest that both sympathetic and respiratory outflow from the central nervous system are influenced by the vestibular system. Otolith organs that respond to pitch rotations seem to play a predominant role in producing vestibulo-sympathetic and vestibulo-respiratory responses in cats. Because postural changes involving nose-up pitch challenge the maintenance of stable blood pressure and blood oxygenation in this species, vestibular effects on the sympathetic and respiratory systems are appropriate to participate in maintaining homeostasis during movement. Vestibular influences on respiration and circulation are mediated by a relatively small portion of the vestibular nuclear complex comprising regions in the medial and inferior vestibular nuclei just caudal to Deiters' nucleus. Vestibular signals are transmitted to sympathetic preganglionic neurons in the spinal cord through pathways that typically regulate the cardiovascular system. In contrast, vestibular effects on respiratory motoneurons are mediated in part by neural circuits that are not typically involved in the generation of breathing.

The sympathetic efferent innervation of the cutaneous and muscle veins in cats. A comparative study using retrograde localization with horseradish peroxidase

Previous studies using electrical stimulation, tension recording and fluorescence histochemical methods indicate that variations in the sympathoadrenergic innervation exist in regional veins of the limb. In the present experiment, we used horseradish peroxidase (HRP) as a retrograde tracer to localize and quantitate the sympathetic innervations to the saphenous, femoral and muscle veins in the cat. The animal was anesthetized with pentobarbital. In three groups of cats, a segment of saphenous (n = 8), femoral (n = 8) and muscle (n = 10) vein was isolated. HRP was applied on the outer vein wall for 3-4 h to allow uptake into the nerve endings. The paravertebral sympathetic chain on the same side of HRP application was dissected after the animal was killed and fixed 60 h following the application of tracer. HRP-labeled neurons were counted in each sympathetic ganglion from L1 to S1. The average number of neurons (mean +/- SE) were 913 +/- 99, 732 +/- 70 and 234 +/- 32, respectively, for saphenous, femoral and muscle vein. There was no statistical difference between the saphenous and femoral vein (P > 0.1). The muscle vein was far less innervated (P < 0.001). When the surface area (mm2) of the vein segment for HRP application was taken into account, the neurons per mm2 were 44.1 +/- 4.8 for saphenous vein, 24.6 +/- 1.8 for femoral vein and 10.2 +/- 1.3 for muscle vein. The neuron density was significantly different among the three groups (P < 0.01). In a single ganglion, the distribution of HRP-neurons appeared to be scattering in pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of sympathetic postganglionic neurons innervating the femoral-saphenous vein in cats

Physiological and histochemical studies have suggested that the limb veins are innervated by sympathetic adrenergic fibers. In the present experiment, horseradish peroxidase (HRP) was used as a retrograde tracer to identify and localize the sympathetic postganglionic neurons that innervate the femoral-saphenous vein in cats. In anesthetized cats, HRP was applied perivascularly on a femoral and a saphenous vein segment (4-8 mm in length for each segment) to allow uptake into the nerve endings. The sympathetic chains on both sides were dissected after the animal was sacrificed and fixed 60 h following the HRP application. Histological examination on serial section was done to count the HRP-labeled neurons in each sympathetic ganglion from L1 to S1. In 10 cats, the total number of HRP neurons amounted to 8569. Most neurons arose from L3 (47%) and then L4 (31%). The number of neurons became progressively decreasing towards both ends of the sympathetic chain. Few neurons (less than 2% of the total) were discovered in the contralateral sympathetic ganglia. In each ganglion, the distribution of HRP neurons appeared to be scattering. Our findings provide anatomical evidence to support that the femoral-saphenous vein of the cat was innervated by the sympathetic efferent fibers. The main origins of these neurons are the third and fourth lumbar sympathetic ganglia.

Pain evoked by polymodal stimulation of hand veins in humans

1. To explore the function of the sensory innervation of veins in humans we used a psychophysical approach to study painful and non-painful sensations by applying polymodal stimuli (electrical, stretch, cold/heat and osmotic) inside vascularly isolated hand vein segments before and after blockade of either venous or cutaneous afferents. 2. All modes of stimulation elicited pain, which showed only slight adaptation during 10 min of maintained stimulation. Pain increased monotonically with stimulus intensity between threshold and the maximally tolerable pain. 3. The exponents of the power functions of the pain magnitude-stimulus strength relations for five stimulus modes ranged between 2.5 and 3.3 but did not significantly differ from one another (P = 0.3). 4. Pain evoked by all stimuli was reported to be of similar quality, i.e. sharp, aching and unpleasant; it was accompanied by non-painful sensations (skin movements on stretching, warm and cold sensation with intravenous thermal stimulation) unless the skin above the stimulated vein segment was numbed with benzocaine ointment. 5. Pain could no longer be evoked in the presence of 0.4-0.8% procaine within the stimulated vein segment. 6. These observations are consistent with the view that veins are invested with polymodal nociceptors only, which in all likelihood are connected with thinly myelinated afferents of the A delta group. 7. The vascularly isolated vein segment may open a new avenue for pain research in humans.

Responses of spinal cord neurons following stimulation of A beta femoral-saphenous venous afferent fibers

A population of large (A beta) afferents is known to have endings in the wall of the femoral-saphenous vein. These afferents project to the lower lumbar spinal cord. The purpose of the present study was to identify, localize, and characterize spinal neurons that receive inputs from such afferents. Responses of 50 neurons in the L6 spinal cord segment of decerebrate-spinal cats or intact cats anesthetized using alpha-chloralose were recorded following electrical stimulation of these afferents. Observations were also made on the convergence of muscle and cutaneous afferent inputs onto neurons driven by stimulation of afferents terminating in the femoral-saphenous vein. All recording sites were marked either by intracellularly staining the element characterized with HRP or by extracellularly iontophoresing a small quantity of this tracer. The cells were driven for long durations (mean of 51.5 ms, S.E.M. of 10.0) by single-shock stimulation of femoral-saphenous venous afferents. The recording sites were located in Rexed's laminae IV-VIII and X. Eight of the 50 neurons were activated by venous afferent stimulation at latencies equal to or shorter than that of the first negative wave of the cord dorsum potential; these units were driven at a mean latency of 1.4 ms (S.E.M. of 0.25) following the arrival of the afferent volley at the cord and were assumed to receive monosynaptic, or at least relatively direct, inputs from the primary afferents. Most of these cells (6 of 8) were located in lamina V. The majority of the neurons studied (37 of 50) were activated at latencies longer than 3 ms following the arrival of the afferent volley at the cord; about half (19 of 37) of those activated at longer latencies were located in lamina VII, and the rest were scattered among the other laminae. Twenty-eight of 40 venous afferent-driven cells tested could also be activated by electrical stimulation of either the posterior tibial or sural nerve. In general, the stimulation intensities necessary to activate the neurons were only sufficient to excite large (A alpha or A beta) muscle and cutaneous afferents. Neurons receiving the shortest latency inputs from the femoral-saphenous vein were less likely to receive convergent inputs from muscle or skin than were neurons activated by venous afferents at longer latency.