X-ray kinematic analysis of forelimb movements during target reaching and food taking in the cat.

We have used a three-dimensional X-ray cinematographic approach to investigate the kinematics of the forelimb during target reaching and food taking in five cats. Measurements of the trajectory of the limb during the reaching movement showed that the movement paths of the metacarpophalangeal joint (MCP) and the wrist were sigmoidal with a long nearly linear segment. The elbow followed a bent movement path with maximal inflection in the middle. The path of the humerus had an ascending parabola-like characteristic. The velocity profiles of the MCP and wrist were nearly bell-shaped and skewed to the left, whereas the profiles of the elbow joint were more or less double peaked with the second peak occurring 60-40 ms before object contact. Several different velocity peaks reflecting specific aspects of the task existed when the bell-shaped velocity profiles were divided in their vectorial components. Angular motion of the elbow consisted of a flexion-extension sequence during the reach and a flexion during the subsequent retraction. After an initial flexion during lift-off the wrist was extended. It kept this extended position during orienting towards the food container. During the retraction phase it was further extended. The angle between the wrist axis and the parasagittal plane changed during the movement. It first increased, then decreased during the last 100 ms before the object was reached. During the retraction it increased again to support the object weight against gravity. The position of the wrist was established by radio-ulnar supination and movements of the whole arm around the shoulder joint. We hypothesize that the position of the wrist axis is the controlled variable during protraction and retraction, regardless of whether it is achieved by radio-ulnar supination or by movements around the shoulder.

Prehension movements and motor development in children.

The maturation of manual dexterity and other sensorimotor functions was assessed with various behavioural tests. In healthy children (age 4-5 years) and in adults, the kinematics of reaching and grasping, a bimanual task and fast repetitive tapping movements were analysed. Furthermore a comprehensive motor function score (MOT), probing agility and balance, was evaluated. In the prehension task, the straightness of the reaching trajectories increased with age. Children opened their grip relatively wider than adults, thus grasping with a higher safety margin. The speed of both tapping and bimanual movements increased with age, and higher scores were reached in the MOT. Although the different behavioural tests sensitively indicated maturational changes, their results were generally not correlated, i.e. the outcome of a particular test could not predict the results of other tasks. Hence there is no simple and uniform relationship between different behavioural data describing maturation of sensorimotor functions.

X-ray kinematic analysis of shoulder movements during target reaching and food taking in the cat.

Co-ordinate movements around the shoulder are essential during reaching movements. We performed a quantitative kinematic analysis of movements of the shoulder girdle: three-dimensional X-ray frames (time resolution 20 ms) were recorded during the target-reaching and food-taking paradigm in five cats either sitting (n = 4) or standing (n = 1) in front of a food well. Movements of the scapula consisted of a flexion of the scapula (anteversion of the glenoid) followed by flexion of the gleno-humeral joint (decrease in the angle between the scapular spine and humerus). In the sitting animals, the gleno-humeral flexion reversed to extension some 120 ms before object contact, while in the standing animal flexion continued during the ongoing scapular flexion. In both cases, the scapula was nearly horizontal at the end of target reaching. The fulcrum for scapular movements was located near the vertebral border of the scapula at the medial elongation of the scapular spine. No major translational components of the fulcrum with respect to the trunk were found during reaching. Together with full flexion of the scapula, this reduces the number of degrees of freedom considerably and thereby probably simplifying the specification of the end-point of the limb chain. End-point specification is further supported by rotational movements of the scapula. In the sitting animal, the amplitude of inward rotation along the long axis of the scapula was around 20 degrees, while it was much more variable in the standing animal, reflecting more variable starting positions. We hypothesize that the glenoid is used to 'foveate' the target object.

Development of prehension movements in children: a kinematic study.

To evaluate the normal development of functional hand motor skill, the kinematics of prehension movements were analyzed in 54 healthy children (age 4-12 years). The subjects repeatedly reached out for cylindrical target objects and grasped them with a precision grip of their dominant hand. The trajectory of the reaching hand and the finger aperture were monitored by optoelectronic motion analysis. To obtain comparable conditions for the different age groups, the experimental setup was scaled according to the individual body proportions of each subject. Within the investigated age range, neither the movement duration nor the normalized (according to body proportions) peak spatial velocity of the reaching hand changed significantly. However, the hand trajectory straightened and the coordination between hand transport and grip formation improved, resulting in smooth and stereotyped kinematic profiles at the age of 12 years. The younger children opened their grip relatively wider than the older ones, thus grasping with a higher safety margin. The dependence on visual control of the movement declined during motor development. Only the oldest children were able to scale the grip aperture adequately, according to various sizes of the target objects, when visual control of the movement was lacking. The results suggest that the development of prehensile skills during childhood lasts until the end of the first decade of life. This functional maturation is discussed in relation to the development of neuronal pathways.

Kinematic analysis of prehension movements in children.

The kinematics of the reach-to-grasp movement were analyzed in ten healthy children (age 6-7 years) under different experimental conditions: distance and size of the target objects, and visual feedback during the reach were varied in a within-subjects design. To assess age-related differences, the same experiments were performed in ten healthy adults. The experimental set-up was scaled according to body proportions to obtain equivalent conditions for both age groups. The temporal coupling between the transport and grasp components of prehension was very similar in children and adults. Peak transport velocity increased by the same factor in both age groups when the object distance was doubled. However, the decelerating approach phase was shorter in the children, who opened their hands relatively wider than adults. Unlike the adults, children failed to scale their grip aperture according to object size when visual feedback during the movement was lacking. The grip aperture increased with object distance in adults, but not in the children. The intrasubject variability of kinematic parameters was distinctly higher in the children. The results suggest that grip formation is not yet mature at an age of 6-7 years, depending more on visual feedback than in adult prehension.

Shaping of the cat paw for food taking and object manipulation: an X-ray analysis.

The kinematics of the cat distal forelimb during food-taking were analysed to obtain information on the movement processes within the paw before and during object taking in a species without monosynaptic corticomotoneuronal projections. The behaviour was investigated with two tests: either the table test (TT, food offered on a table located at ground level in a reaching distance of 22 and 28 cm) or the horizontal test (HT, food offered in a small container located at shoulder level, height 18-25 cm, reaching distance 6-12 cm). In five animals, the changes in configuration and the conjoint actions of the wrist, the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints were assessed with three-dimensional X-ray cinematography (time resolution 20 ms, spatial resolution 1 mm) and video analysis. While approaching the target, the digits were first extended and subsequently abducted. This 'preshaping' consisted of combined angular changes in the MCP and PIP joints, thereby attaining an adequate grip aperture. Each cat used a stable strategy, but different cats used different strategies. In the TT, preshaping involved an MCP extension and a PIP flexion. In the HT, predominant extension of the MCP, predominant extension of the PIP, or a combination of both were used, followed by MCP flexion and PIP flexion. The grip aperture started to decrease before object contact, earlier in the TT, later in the HT. Grasping was achieved by flexion of first the PIP and later the MCP. The X-ray analysis gave evidence for individuated digit movements. Correlation analysis of the angular position of the joints between the different phalanges showed that digits 3 and 4 acted in concert, as did digits 2 and 5, but with clear independence between the different pairs. Furthermore, the different phalanges served different purposes during the grasp. Digits 3, 4 established object contact, digits 2, 5 were mainly used to stabilize the paw onto the surface. The cat distal forelimb displays a refined movement repertoire during the preshaping and grasping phase of food-taking. During the preshaping phase, the kinematics resembled in some aspects the situation in humans. The results demonstrate the ability of the polysynaptic projections from the cortico-motoneuronal system to organize differentiated distal limb movements, including individuated movements of the digits.

The target-reaching and food-taking behaviour in the cat: a model for the investigation of recovery of motor functions.

The recovery of motor functions after CNS lesions is a complex action with several restitutional processes occurring in parallel. To describe the function-oriented phenomena and to understand the organisational changes within the neuronal systems in question there is the urgent need for investigations relating the impairment of defined neuronal systems with quantitative and qualitative changes of a behavioural motor paradigm. The system of the C3-C4 propriospinal neurones in the cat is one of the models which could serve such a purpose. It relays disynaptic excitation from several supraspinal motor centres to forelimb motoneurones, parallel to the input to the motoneurones from the same centres via the segmental reflex apparatus. Behavioural studies indicate that the motor command for reaching towards a target with the forelimb is to a large extent mediated in the C3-C4 propriospinal system, whereas the command for taking of the object seems to be organised in the interneuronal systems of the forelimb segments, not depending on an integration in the C3-C4 propriospinal relay. The paper reviews different studies which have analysed the effects of lesions of various motor centres and tracts on this behavioural paradigm. It becomes evident that different components of the motor behaviour have different restitutional capacities. The quantitative analysis of the various dimensions of the cat forelimb together with the possibility to perform localised lesions within defined neuronal systems make this experimental approach suited for the investigation of integrative aspects related to the restitution of function within systems organising motor behaviour.

Responses of distinct types of sympathetic neuron to stimulation of the superior laryngeal nerve in the cat.

Stimulation of afferents in the superior laryngeal nerve (SLN) leads to apnea and evokes reflexes in sympathetic neurons. It is not clear whether these reflexes are secondary to changes in the brainstem respiratory network or due directly to the afferent input on neurons belonging to central sympathetic pathways. To clarify this question, single thoracic preganglionic sympathetic neurons projecting into the cervical sympathetic trunk (CST) were classified as described previously and then tested for their responses to electrical stimulation of the superior laryngeal nerve (SLN) in chloralose-anesthetized, paralysed and artificially ventilated cats. SLN stimulation was performed with intensities sufficient to suppress central inspiratory activity detected by phrenic and recurrent laryngeal nerve recordings. Sympathetic neurons were tested under different levels of respiratory drive. Thirteen group I (putative muscle vasoconstrictor) neurons were mostly activated by SLN stimulation when respiratory drive was low, but depressed when it was high; this was due to the change in inspiration-related activity. Ten of eleven group II (putative cutaneous vasoconstrictor) neurons were depressed during SLN stimulation. This inhibition was independent of central respiratory drive. Inhibition also occurred in those neurons which predominantly discharged during postinspiration. Eight group III neurons which showed a discharge confined to inspiration were inhibited but mostly not silenced by SLN stimulation. Group IV (functionally unclassified) neurons either showed no response (n = 5) or were slightly inhibited (n = 2). The responses of group I neurons, but not the responses of group II and group III neurons, showed a significant positive correlation with those of systemic blood pressure. The observed responses corroborate the classification made previously. The results also demonstrate that the responses of sympathetic neurons to SLN stimulation are not merely due to the respiratory modulation of their activity, but rather consist of two components, one occurring independently of and the other secondary to, the changes in respiration.

Gait analysis during treadmill and overground locomotion in children and adults.

Gait analysis on the treadmill and in the overground condition is used both in scientific approaches for investigating the neuronal organisation and ontogenetic development of locomotion and in a variety of clinical applications. We investigated the differences between overground and treadmill locomotion (at identical gait velocity) in 12 adults and 14 children (6-7 years old). During treadmill locomotion the step frequency increased by 7% in adults and 10% in children compared to overground walking, whereas the stride length and the stance phase of the walking cycle decreased. The swing phase, however, increased significantly by 5% in adults and remained unchanged in children. Balance-related gait parameters such as the step width and foot rotation angles increased during treadmill locomotion. The reduction of the step length was found to be stable after 10 min of treadmill walking in most subjects. With regard to the shifted phases of the walking cycle and the changed balance related gait parameters in the treadmill condition, we assume a different modulation of the central pattern generator in treadmill walking, due to a changed afferent input. Regarding the pronounced differences between overground and treadmill walking in children, it is discussed whether the systems generating and integrating different modulations of locomotion into a stable movement pattern have reached full capacity in 6-7 year old children.

Vesico-sympathetic reflexes in cat vasoconstrictor neurones supplying skin and skeletal muscle depend on the integrity of the sacral bladder afferents.

In anesthetized cats, distension of the urinary bladder induces powerful reflexes in postganglionic sympathetic neurones projecting to the hindlimb: muscle vasoconstrictor neurones (MVC) are excited and cutaneous vasoconstrictor neurones (CVC) are inhibited. We investigated these reflexes quantitatively before and after sacral rhizotomy. The reflex responses in MVC and CVC neurones were completely abolished after elimination of the pelvic afferent input demonstrating that these reflexes are generated exclusively by excitation of sacral bladder afferents. The activation of lumbar bladder afferents which are supposed to be able to elicit painful sensations did not contribute to vesico-sympathetic reflexes in MVC and CVC neurones.

Kinematic analysis of the cat shoulder girdle during treadmill locomotion: an X-ray study.

A quantitative kinematic analysis of the movements of the shoulder girdle in the three dimensions of space during treadmill locomotion (velocity range 0.33-1.2 m/s) was performed in two cats. Since the movement patterns of the scapula and the humeroscapular joint can only vaguely be estimated through the overlying skin we used implanted metal spheres placed on the scapula in combination with three-dimensional pulsed X-ray cinematography (time resolution 20 ms) to reconstruct the excursions of the scapula, the humerus and the elbow and to calculate the respective angular amplitudes and velocities. The movements of the scapula relative to the Th4 spinous process consist of four major components:(i) a monophasic flexion (caudocranial movement of glenoid fossa during swing)/extension (craniocaudal movement of the glenoid fossa during stance) sequence, the fulcrum for which sequence is situated near the vertebral border of the scapula at the medial elongation of the scapular spine; (ii) a vertical monophasic up/down sequence of the fulcrum relative to the trunk, the highest vertical position being reached during mid-stance and the lowest vertical position during mid-swing; (iii) a biphasic abduction/adduction sequence during swing and during stance respectively; and (iv) small rotations along the scapular spine. The trajectory recordings of the scapula indicate that the scapula yields relative to the trunk under the body weight after ground contact. The angular excursions of the humeroscapular joint consist of : (i) a flexion/extension sequence during swing, a yield after ground contact and a final extension at the end of stance; (ii) an adduction and outward rotation during the early swing phase flexion; (iii) an abduction and inward rotation during the late swing phase extension; and (iv) an adduction during the yield with only minor rotations during the whole stance phase. The movement patterns are discussed in view of the muscular synergies necessary to guide the scapula and the humerus during stance and swing, and in relation to the implications for the organization of these patterns in spinal neuronal systems.

Recovery of locomotion after spinal cord hemisection: an X-ray study of the cat hindlimb.

Hemisection of the spinal cord in adult cats is a suitable model to st udy the mechanisms underlying recovery of motor functions. The initial paresis of the hindlimb is followed by a considerable improvement of locomotor functions of the affected hindlimb. Kinematic analyses of treadmill locomotion were performed from 10 days to 8 months after complete hemisections (right side) of the spinal cord at the thoracolumbar level, using X-ray cinematography for precise measurements of the hindlimb joint angles. The footfall pattern and the electromyogram were recorded. Motor control of both proximal and distal hindlimb joints improved substantially during the 1st postoperative month. However, persistent locomotor deficits were still present several months after hemisection. They could be divided into three groups of symptoms: (1) The gait pattern was disturbed with regard to interlimb coordination. The stance-phase duration of the right hindlimb was shortened. (2) The flexor capacity of the affected hindlimb was reduced, resulting in a slow insufficient flexion of the hip, knee, and ankle during the swing phase. (3) The timing of the flexion-extension events was impaired. The onset of the E1-extension was delayed and the amplitude was reduced. Electromyographic patterns of muscle activity during locomotion of the lesioned side limb differed from the contralateral hindlimb, which served as a contro. The results indicate that in spite of a good short-term functional improvement there are long-term locomotor deficits present after spinal cord hemisection.

X-ray study of the cat hindlimb during treadmill locomotion.

With pulsed X-ray cinematography we have analysed the angular excursions of the distal hindlimb joints (proximal interphalangeal, PIP; metatarsophalangeal, MTP; ankle) in cats walking on a treadmill. These distal joints transmit the body weight and the dynamic forces onto the ground. We have included the knee and hip joints in the analysis to relate the angular excursions of the proximal and distal joints and to verify the data previously obtained with external markers on the kinematics of the proximal joints. At the beginning of the stance phase the PIP joints flexed rapidly, the MTP joints extended slowly and the ankle and knee yielded under body weight. Whereas the PIP joints maintained a rather constant angular position of approximately 75 degrees throughout the stance phase, extension continued in the MTP joints from approximately 230 degrees at touch-down to approximately 270 degrees at the end of the stance phase. Around 50 ms before lift-off the MTP joints flexed rapidly. Early (approximately 30 ms) after lift-off this flexion changed into a slow extension. The PIP joints extended swiftly at the stance-swing transition and moderately at the end of the swing phase. During the middle part of the swing phase they flexed slowly. Small rotatory movements around the long axis of the foot took place in the last 100 ms of the swing phase. The results of this study on the distal joints are discussed in relation to the placing of the paw, to the translation of forward propulsion into a MTP movement and to the lifting of the paw (conventionally described as toe curling). They show a differentiated mechanical interaction between the different distal limb joints during these different phases, which must be known in detail to interpret the corresponding electromyographic data and to understand how the hip is moved forward over the MTP joints which serve as the final pivot during stance.

X-ray kinematography as a tool for investigations of distal limb movements of the cat.

X-ray kinematography was used to investigate the kinematics of cat distal forelimb joints during motor behaviour. These joints are not accessible for instrumentation with external markers normally used in conventional motion analysis systems. To trace the movements in space two X-ray systems positioned rectangularly to each other illuminated the forelimb quasi-simultaneously with pulsed X-ray shots (time resolution: 20 ms). A mathematical model was developed for 3-dimensional reconstruction of the object and includes procedures for correction of image distortions, e.g., pincushion distortions and rotation of the image due to interaction of the earth's magnetic field with the electron optics of the image amplifiers. Accuracy of image correction and object reconstruction is +/- 1 pixel, corresponding to +/- 0.5 mm in space which is sufficient for investigation of the kinematics of cat distal forelimb joints. The approach described is of general relevance and useful in kinematic investigations where the structures under study are not directly accessible to external instrumentation with markers.

Spontaneous activity, conduction velocity and segmental origin of different classes of thoracic preganglionic neurons projecting into the cat cervical sympathetic trunk.

Previously, in the anesthetized cat, thoracic preganglionic neurons projecting to the superior cervical ganglion were divided into four classes (groups I-IV) by way of their reflex pattern. Neurons of each class are probably involved in a distinct function, such as regulation of peripheral vascular resistance, regulation of blood flow through skin, regulation of pupil diameter, etc. Here it was tested whether the functionally different classes of thoracic preganglionic neurons also differ in the distribution of their segmental origin, their spontaneous activity and the conduction velocity of their axons. The segmental distribution of preganglionic neurons was almost identical to that determined previously with tracer methods. Distinct classes of neurons had different, although overlapping segmental distributions. Most group III neurons were located in segments T1 and T2, whereas group I, II and IV neurons showed a broader distribution. The subpopulations of preganglionic neurons did not differ in their rate of spontaneous activity. No significant difference was found in segmental distribution between neurons with spontaneous activity and silent neurons. No correlation was found between conduction velocity and spontaneous activity. The proportion of unmyelinated units was greater among group I (16.3%), group II (24.1%) and group IV (22.2%) neurons than among group III neurons (8%). The distributions of conduction velocity were significantly different between group I and group III and between group II and group III neurons. Axons of preganglionic neurons located in segments T1 and T2 conducted faster than axons of neurons located more caudally. The present study shows that distinct subpopulations of preganglionic neurons, as defined by their reflex patterns, differ in their segmental location within the spinal cord and with respect to the conduction velocity of their axons.

Responses of lumbar vasoconstrictor neurons supplying different vascular beds to graded baroreceptor stimuli in the cat.

Lumbar sympathetic vasoconstrictor neurons supplying skeletal muscle, hairy skin and pelvic organs were tested for their responses to carotid baroreceptor stimulation in chloralose-anaesthetized cats. Using single- and few-fibre recordings, the responses of the different types of vasoconstrictor neuron to graded steps of non-pulsatile pressure ranging from 110 to 260 mmHg in a vascularly isolated carotid sinus were analyzed quantitatively during the first 10 s of stimulation. The activity in all postganglionic muscle vasoconstrictor (MVC) neurons, preganglionic visceral vasoconstrictor (VVC) neurons and one third of the postganglionic cutaneous vasoconstrictor (CVC1) neurons was strongly depressed by maximal baroreceptor stimulation. Moreover, quantitative analysis revealed no significant differences of the baroreceptor sensitivity of MVC and CVC1 neurons as compared with VVC neurons at all levels of carotid sinus pressure. In contrast, two-thirds of the postganglionic cutaneous vasoconstrictor (CVC2) neurons exhibited a significantly weaker barosensitivity. The functional implications are discussed.

Respiratory-related activity patterns in preganglionic neurones projecting into the cat cervical sympathetic trunk.

1. Activity in 233 single sympathetic preganglionic neurones that project to the superior cervical ganglion was analysed with respect to central components of respiration (phrenic nerve discharge) and to the afferent feedback generated by mechanical events occurring with ventilation in anaesthetized and artificially ventilated cats. 2. The activity in ninety-one neurones was modulated during the respiratory cycle in two ways: directly by the central inspiratory drive, and indirectly by ventilation-related blood pressure changes, acting via the systemic baroreceptors. The direct influence was prominent in vagotomized animals or those with a raised respiratory drive, and consisted of an inspiratory increase in activity and decreases of activity in early inspiration and postinspiration. The indirect influence (excitation due to baroreceptor unloading) usually dominated in normocapnic cats with intact vagus nerves. This population of neurones showed both similar reflex responses and a similar respiratory modulation of activity as postganglionic neurones supplying hindlimb skeletal muscle. 3. Sixty-one neurones discharged exclusively, or almost exclusively, during central inspiration. This discharge pattern neither depended on the integrity of vagal nor baroreceptor afferents. The activity of these neurones was abolished during hyperventilation and enhanced during hypercapnia. In the latter state, a small activation was often seen in stage II expiration. 4. In normocapnia the remainder of neurones (n = 81) exhibited no, or no pronounced, respiratory modulation of activity, except three neurones which showed a prominent expiratory pattern being of central and not of reflex origin. They were not a homogeneous population and included neurones exhibiting reflex responses similar to those of postganglionic neurones supplying hindlimb skin (n = 36), neurones responding to light (n = 4), and others (n = 41). 5. It is concluded that distinct types of thoracic preganglionic neurone differ with respect to respiratory modulation of their activity stemming from both central and reflex sources. Thus, the temporal profile of activity in these neurones in relation to respiration is another functional characteristic which can be used to distinguish between populations of sympathetic neurones.

Respiratory modulation of the activity in sympathetic neurones supplying muscle, skin and pelvic organs in the cat.

1. The respiratory-related modulation of activity in neurones of the lumbar sympathetic outflow to skeletal muscle, skin and pelvic organs was investigated in anaesthetized, paralysed and artificially ventilated cats, using single- and multi-unit recordings. The activity of the neurones was analysed with respect to the phrenic nerve discharge under various experimental conditions. 2. Neurones tentatively classified as muscle vasoconstrictor and visceral vasoconstrictor neurones exhibited two activity peaks, one caused by baroreceptor unloading during the declining phase of the second order blood pressure waves and a respiratory drive-dependent peak in parallel with inspiration. The two peaks were separated by depressions of activity in early inspiration and post-inspiration. After cutting vagus and buffer nerves the activity peak during inspiration remained and was followed and sometimes preceded by a depression of activity. 3. The majority of the neurones tentatively classified as cutaneous vasoconstrictor neurones exhibited no respiratory modulation in their activity. Others exhibited an activity peak in expiration, an activity peak in inspiration, or a respiratory profile similar to that in muscle vasoconstrictor neurones. During increased respiratory drive (induced by hypercapnia) some neurones with unmodulated activity changed to an inspiratory or an expiratory pattern. Neurones discharging predominantly in inspiration projected preferentially to hairless skin. 4. Neurones which were tentatively classified as sudomotor neurones discharged predominantly in early expiration. 5. Some preganglionic neurones which were tentatively classified as motility-regulating neurones discharged during expiration. The majority of these neurones disclosed no respiratory modulation of their activity. 6. The study shows that different types of neurone of the lumbar sympathetic system exhibit distinct patterns of respiratory modulation in their activity. We conclude that the type and degree of central coupling between respiratory system and sympathetic nervous system may vary according to the destination of the sympathetic neurones.

Classification of preganglionic neurones projecting into the cat cervical sympathetic trunk.

1. The spontaneous and reflex activity patterns of 167 single preganglionic axons dissected from the cervical sympathetic trunk were examined in chloralose-anaesthetized cats. Each neurone was classified into one of four major groups, on the basis of three principal criteria: the presence or absence of significant cardiac rhythmicity of the activity, the response to noxious stimulation of the skin, and the coupling of its activity to central inspiratory drive (phrenic nerve activity). Most neurones were also subjected to additional tests, which included carotid chemoreceptor stimulation, nasopharyngeal probing, systemic hypercapnia (ventilation with 8% CO2), hyperventilation, adrenaline-induced blood pressure rises and retinal illumination. 2. Group I neurones (n = 69; 41%) showed significant cardiac rhythmicity, indicating strong baroreceptor control. Most (54/69) were excited by noxious stimuli, the rest being unaffected. Their activity showed variable degrees of excitatory coupling to the central inspiratory drive, and was enhanced by hypercapnia (35/39). Their responses to stimulation of arterial chemoreceptors (12/15) and nasopharyngeal receptors (24/35) were excitatory. 3. Group II neurones (n = 39; 23%) were inhibited by noxious stimulation of skin. With nine exceptions, they showed no significant cardiac rhythmicity, although they were weakly inhibited by an adrenaline-induced blood pressure rise. Their coupling to central inspiratory drive was weak or absent, and their responses to hypercapnia and hyperventilation were variable. By contrast to other groups, they were inhibited by both chemoreceptor stimulation (9/10) and nasopharyngeal stimulation (17/18). 4. Group III neurones (n = 33; 20%) showed no significant cardiac rhythmicity, but their activity was closely coupled to central inspiratory drive. They were inhibited by hyperventilation (9/9) and excited by hypercapnia (20/21), but only fired during the central inspiratory phase and sometimes during late expiration. Their responses to noxious stimulation (28/33), chemoreceptor stimulation (8/11) and nasopharyngeal probing (24/24) were excitatory, but the induced activity was 'gated' by the respiratory cycle, occurring primarily during inspiration and avoiding the postinspiratory phase. 5. Group IV neurones (n = 26; 16%) showed no significant cardiac or respiratory related activity and were either excited (n = 22) or unaffected (n = 4) by noxious stimuli. One of the latter and three group II neurones were inhibited by retinal illumination; thirty-one other neurones of all classes were unaffected. 6. Approximately 45% of thoracic sympathetic neurones were silent under the experimental conditions. About 25% of these could be recruited by systemic hypercapnia leaving 34% without spontaneous and reflex activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid phasic baroreceptor inhibition of the activity in sympathetic preganglionic neurones does not change throughout the respiratory cycle.

We tested the hypothesis that the inhibitory influence of rapid phasic arterial baroreceptor stimulation on activity in sympathetic preganglionic neurones is weaker in inspiration than in expiration. Using neurophysiological techniques, 59 single preganglionic neurones with typical reflex pattern of muscle vasoconstrictor neurones that projected in the cervical sympathetic trunk were analysed. The inhibitory modulation of the ongoing activity in these neurones by the pulsatile activation of the arterial baroreceptors was determined by constructing post-R-wave histograms separately for both respiratory phases (as indicated by the discharge in the phrenic nerve). Quantitative measurements showed that the inhibition of the activity in the preganglionic neurones following phasic stimulation of arterial baroreceptors by the pulse pressure wave was not statistically different in both respiratory phases, even with increased respiratory drive.