Effects of cold, eating, efferent nerve stimulation and angiotensin on heart rate in sheep before and after autonomic blockade

Spinal plasticity in robot-mediated therapy for the lower limbs

Robot-mediated therapy can help improve walking ability in patients following injuries to the central nervous system. However, the efficacy of this treatment varies between patients, and evidence for the mechanisms underlying functional improvements in humans is poor, particularly in terms of neural changes in the spinal cord. Here, we review the recent literature on spinal plasticity induced by robotic-based training in humans and propose recommendations for the measurement of spinal plasticity using robotic devices. Evidence for spinal plasticity in humans following robotic training is limited to the lower limbs. Body weight-supported (BWS) robotic-assisted step training of patients with spinal cord injury (SCI) or stroke patients has been shown to lead to changes in the amplitude and phase modulation of spinal reflex pathways elicited by electrical stimulation or joint rotations. Of particular importance is the finding that, among other changes to the spinal reflex circuitries, BWS robotic-assisted step training in SCI patients resulted in the re-emergence of a physiological phase modulation of the soleus H-reflex during walking. Stretch reflexes elicited by joint rotations constitute a tool of interest to probe spinal circuitry since the technology necessary to produce these perturbations could be integrated as a natural part of robotic devices. Presently, ad-hoc devices with an actuator capable of producing perturbations powerful enough to elicit the reflex are available but are not part of robotic devices used for training purposes. A further development of robotic devices that include the technology to elicit stretch reflexes would allow for the spinal circuitry to be routinely tested as a part of the training and evaluation protocols.

Urocortin 3 inhibits cardiac sympathetic nerve activity in conscious sheep

There is an increasing body of evidence suggesting a role for the urocortin (Ucn) peptides in blood pressure regulation and in the pathophysiology of cardiovascular disease. Both Ucn1 and Ucn2 have recently been shown to inhibit cardiac sympathetic nerve activity (CSNA) in sheep. However, there are few studies reporting the effects of Ucn3 on the sympathetic nervous system. Hence, this study performed in normal conscious sheep examines the effects of Ucn3 on CSNA. Intravenous Ucn3 (administered at doses of 25 and 100 μg) caused transient falls in arterial pressure (P = 0.025), more prolonged rises in heart rate (P < 0.001), and falls in stroke volume (P < 0.001) and peripheral resistance (P = 0.018). CSNA, measured as burst area and burst incidence, fell in a dose-dependent manner after Ucn3 bolus (all P < 0.001). CSNA burst frequency tended to be reduced after high-dose Ucn3. Ucn3 had no significant effect on plasma catecholamine levels. In conclusion, this study reports for the first time that Ucn3 induces potent inhibition of sympathetic traffic directed toward the heart. This provides further support for a role for Ucn3 in pressure and volume homeostasis and suggests that further investigation of potential therapeutic applications for Ucn3 in cardiovascular disease is warranted.

Insulin and glucagon secretion in goats (Capra hircus Linnaeus) exposed to cold

Cold exposure significantly decreased the insulin response to the intravenous injection of arginine, butyrate and tolbutamide, and tended to reduce the response to glucose in goats. The glucagon responses to these test materials were not different between warm and cold environments. Intravenous phentolamine infusion tended to increase, and propranolol infusion decreased insulin secretion more effectively in the cold than in the warm environment. It is concluded that cold exposure decreases insulin secretion in response to a variety of stimuli in goats.

Electrocutaneous reflexes and multimodality evoked potentials in multiple sclerosis

Electrical stimulation of the digital nerves of the index finger produces changes in the EMG signal during steady voluntary contraction of the first dorsal interosseous muscle. This electrocutaneous reflex (ECR) was studied in 90 patients classified into different categories according to diagnostic criteria for multiple sclerosis. In addition, pattern reversal visual evoked responses (VER), brainstem auditory evoked responses (BAER) as well as spinal and scalp recorded somatosensory evoked potentials (SSEP) were investigated by stimulating both the index finger and the posterior tibial nerve. The reflex response was altered uni- or bilaterally in 56 per cent of the patients and the abnormalities of the ECR were related to the categories of diagnostic probability. Pathological results were found in 28 per cent of the hands without clinical evidence of sensorimotor deficit. Although ECR abnormalities were often associated with clinical signs, significant correlation was found only with hyperreflexia and/or increased muscle tone in the corresponding upper limb. Pathological ECR were more common than pathological SSEPs with finger stimulation recorded under identical stimulus conditions. Fewer abnormalities were found by ECR testing than with VER, but the proportion of abnormal ECR was higher than that of BAER. ECR provides a valuable supplement to existing electrophysiological procedures for detecting lesions in the central nervous system.

Influence of plantar cutaneous afferents on early compensatory reactions to forward fall

The influence of cutaneous afferents in the compensatory reactions to a forward fall was investigated. Modification of cutaneous afferent activity was obtained in two different ways: first, by varying the initial pedal support conditions, secondly by anesthetizing the plantar foot sole. The initial pedal support conditions were: 1) bipedal posture, 2) unipedal posture, with contact and 3) unipedal posture, without contact. Nine healthy subjects participated in the control (without anesthesia) experimental session, of which three subjects participated in a session where the plantar sole was anesthetized. The compensatory reactions to a perturbation of balance of a subject initially with a bipedal stance, showed synchronized EMG activity in both Soleus muscles, starting on average at 59 ms, and a burst of EMG activity in the Tibialis Anterior of the starting foot after 200 ms. When the subject was in unipedal posture, the EMG responses on the side which was without support, showed several modifications: the EMG burst in Soleus was strikingly depressed, the response in Tibialis Anterior appeared earlier (mean latency 90 ms) and its magnitude was enhanced. When this foot was in contact with a rigid support, the Soleus showed a short burst of activity and the activity in Tibialis Anterior started at a mean latency of 150 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin secretion in sheep exposed to cold

1. Cold exposure caused a marked decrease in insulin response to intravenous injection of glucose, with a sharply declining response over the first 4 days of cold exposure followed by a constant low response up to 13 days of the experimental cold period. 2. The glucose-induced insulin response was unaffected by concomitant infusion of phentolamine in the warm environment. In contrast, the low response of insulin secretion to glucose during cold exposure was so augmented by concomitant infusion of phentolamine as to exceed the response observed in the warm environment. 3. Intravenous infusion of phentolamine caused an increase in the concentration of plasma insulin in the cold but not in the warm environment. 4. Adrenaline completely abolished the insulin response to glucose in the warm environment. 5. Exposure to cold environment brought about an increase in urinary excretion of adrenaline and noradrenaline and in heart rate, but rectal temperature was unchanged. 6. It is concluded that cold exposure insufficient to cause hypothermia produces a marked decrease in insulin secretion by the pancreas of sheep, mediated through adrenergic alpha-receptors stimulated by augmented sympatho-adrenomedullary activity.

Oscillatory electromyographic responses to limb displacement in Parkinsonism

Forty Parkinsonian patients and 26 normal subjects were instructed not to resist movements of a handle which they maintained in a specified position (1) during tonic activation of muscles against the force produced by a torque motor and (2) while no force was produced by the motor. Electromyographic responses to handle displacements were recorded in biceps muscle (pronating or supinating displacements) or in wrist extensor and flexor muscles (displacements which extended or flexed the wrist). Displacements involving changes of muscle length elicited (1) excitation and inhibition occurring at monosynaptic latency in muscles which were stretched and shortened, respectively; (2) a "silent period" following the initial excitation in the stretched muscle and excitation following the initial inhibition in the shortened muscle (shortening reaction); and (3) (in Parkinsonian patients) sustained oscillations at about 4 to 5 Hz (at rest) or about 6 to 8 Hz (during maintained posture). It was also observed that the initial muscle responses in both the stretched and shortened muscle could be reciprocal and biphasic, with the two peaks of excitation in the agonist occurring during reduced activity of antagonist muscles, and vice versa.

Alp and valley cattle: exercise in cold, hot and high environments

Two groups of cattle, one kept on an alpine pasture (1700--2600 m altitude) for 5 summer months and the kept in a barn at 400 m, were subjected to treadmill exercise for 15 min at a speed of 2 km/h in environments of 15 degrees C, -10 degrees C, 35 degrees C (all at 400 m) and at simulated altitude of 3500 m (at 15 degrees C). In the resting conditions, the alpine cattle had higher respiration rates and body temperatures at an air temperature of 35 degrees C than the valley cattle which was attributed to a greater hair insulation and possibly a low responsiveness of the sweat glands. At 3500 m, the alpine animals had higher resting heart rates than the valley animals, which was attributed to a greater blood volume. After exercise, heart rates in the alpine cattle were from 10--19 beats/min lower than in the valley cattle, due to exercise conditioning in the former animals. This training effect on heart rates in the alpine animals was paralleled by reduction in intrinsic heart rates (using atropine and propranolol as blocking agents). Atropine blockade also indicated that exercise-trained cattle have a lower vagus tone compared to non-exercise-trained cattle.

Changes during eating in oxygen consumption, cardiac function and body fluids of sheep

1. A study was made of the changes taking place in O(2) consumption, cardiac function and the volume and composition of the body fluids of sheep while they consumed a meal of hay.2. During eating P(a, CO2) and P(v, CO2) both increased, pH decreased and free plasma [HCO(3) (-)] increased. Venous haematocrit increased sharply at the beginning of the meal, and declined slowly after feed was removed.3. Arterial P(O2) did not change significantly during eating. However P(v, O2) fell slightly but significantly. The O(2) saturation of venous blood fell due to the decline in pH. Estimated CO(2) in arterial blood increased as a consequence of increased haemoglobin content. The net effect was to increase arteriovenous difference in O(2) content from 4.4 ml./100 ml. before eating to 6.0 ml./100 ml. at the end of the meal.4. O(2) consumption increased about 60% during eating and fell rapidly thereafter. Heart rate followed a similar pattern. Cardiac output however increased only about 17%, from 6 to 7 l./min. Consequently stroke volume declined throughout the meal from 76 to 52 ml./beat.5. Plasma volume, estimated from measurements of T-1824, declined sharply by about 300 ml. at the beginning of the meal and recovered slowly after feed was removed. Blood volume declined less because of a rise in circulating erythrocytes.6. Extracellular fluid volume was estimated from measurements of thiocyanate and thiosulphate spaces. Thiocyanate space measurements were abandoned after thiocyanate was found to be concentrated in saliva. Considerable random variation occurred in measurements of changes in extracellular fluid from thiosulphate disappearance but the results did reveal a significant fall of 1000-1500 ml. in extracellular fluid volume during eating.7. The significance of these interrelated changes is discussed in relation to the maintenance of homoeostasis during eating in the sheep.