Monosynaptic Ia pathways at the cat shoulder

The study aimed to describe in cat forelimb and shoulder motoneurones the convergence and projection patterns from large muscle spindle afferents (Ia). In 11 chloralose-anaesthetized cats maximum Ia EPSPs evoked by electrical stimulation of ipsilateral forelimb nerves were obtained in 309 intracellularly recorded α-motoneurones.Groups of motor nuclei displayed similar Ia patterns. As in the distal forelimb they were often interconnected by bidirectional pathways, which were used to combine Ia synergistic groups. Three such groups are described at the shoulder.The first group was composed of the main flexors of the scapulo-humeral joint. Regular disto-proximal Ia excitation from elbow extensors (and median afferents) indicates a coupling of flexion in the scapulo-humeral joint to the angular position of the elbow.The second group comprised the outward rotators of the humerus with differentiated Ia convergence onto the different group members. The patterns of Ia excitation received and sent by the group members demonstrate that the outward rotators are incorporated in versatile synergisms and may occupy a central position in steering forelimb movements.The third group was formed by the spinatus muscle and the subscapularis. This arrangement is suggested by the common convergence onto them from the elbow extensors and flexors. The pattern may serve to guide and keep the humeral head in the joint capsule.The Ia synergistic groups receive Ia convergence from muscles acting at distant joints and also project to distant muscles. This is discussed as part of an extended pattern of Ia connections along the forelimb. In this way the shoulder muscles would be incorporated in flexor and extensor oriented synergisms which are needed to co-ordinate the muscular activation along the multijoint forelimb during locomotion. When the shoulder Ia pathways are compared with those in the distal forelimb, organization of the Ia system apparently follows a few basic principles which have adapted to the mechanical situation at the particular joints and their mechanical interaction

Respiratory inputs to central cardiovascular neurons

Precise coordination of respiration and circulation is essential to obtain optimal delivery of oxygen and removal of carbon dioxide and to ensure normal homeostasis. One way that this coordination occurs is through connections between respiratory and sympathetic neurons in the brain stem and spinal cord. We know that these connections exist because sympathetic nerve activity often has a pronounced respiratory modulation. Respiratory modulation of sympathetic nerve activity was first noted by Adrian et a/. 1 in 1932. In the subsequent 60 years, much was discovered about the relationship between central inspiratory activity and sympathetic nerve activity. It is now clear that respiratory modulation of sympathetic nerve activity is a result of connections between central respiratory neurons and central cardiovascular neurons. It is not due simply to phasic changes in baroreceptor activation that might occur because of ventilation-induced changes in hemodynamics. This information has frequently been obtained by comparing the phasic discharges recorded from the phrenic nerve in paralyzed, ventilated, and often vagotomized animals in order to remove sources of external inputs to central autonomic neurons. Experiments of this type have shown, first, that respiratory rhythmicity, as measured by synchronization with phrenic nerve discharge, is present in animals that are ventilated at a rate different from phrenic nerve discharge.2·3 This means that changes in the activity of sensory afferent nerves are not the sole cause of the coupling between respiration and sympathetic nerve activity. Second, not all sympathetic nerves have the same type of respiratory rhythmicity. This means that different central sympathetic pathways must receive inputs from different components of the central respiratory rhythm generating network or at least that the proportion of such inputs received is variable

Skin Potential Recordings During Cystometry in Spinal-cord Injured Patients

In order to investigate autonomic mechanisms associated with bladder filling and bladder contraction, skin potentials from the hands and the feet of 32 spinal cord injured patients were recorded during cystometry. All had a complete clinical loss of motor and sensory function below the lesion, but in 3 patients. the autonomic lesion was electrophysiologically assessed as incomplete. In patients with a complete autonomic lesion, any rise in intravesical pressure associated with bladder hyperreflexia induced SP responses below the level of the lesion. SP responses were never obtained during bladder filling, as the intravesical pressure remained low. These results tend to confirm those of Guttmann and Whitteridge, but differ in so far as SP responses at the foot were a regular finding in all paraplegic and in most tetraplegic patients. Furthermore, bladder contraction failed to elicit SP responses below the level of the lesion in patients with an incomplete autonomic lesion. This study emphasises the importance of assessing the integrity of the autonomic nervous pathways when dealing with autonomic mechanisms in spinal cord injured patients. The possible relation between SP responses and bladder neck dysfunction is further discussed