Period Of Continuous Stimulation Research Articles

Intercostal muscle pacing with high frequency spinal cord stimulation in dogs

High frequency spinal cord stimulation (HF-SCS) is a novel and more physiologic method of inspiratory muscle activation which involves stimulation of spinal cord pathways. In the present study, we determined if activation of the inspiratory intercostal muscles alone by this technique could be utilized to maintain artificial ventilation. In 7 anesthetized dogs, following C2 spinal cord section and bilateral phrenicotomy, trains of electrical stimulation (12 times/min) were applied at the T2 level. Eucapnea was maintained during an initial 5.5h period of continuous stimulation. During a subsequent 0.5h period, stimulus parameters were increased to induce hyperventilation resulting in a sustained fall in end-tidal P(CO(2)) to 29.3 + or - 0.4 mmHg. Single motor unit peak firing frequencies of the intercostal muscles during HF-SCS were similar to those occurring during spontaneous breathing. This technique holds promise as a method to restore ventilation in ventilator-dependent tetraplegics who do not have adequate phrenic nerve function for diaphragm pacing.

Physiologic effect of electrical stimulation on reinnervation of the canine larynx

Problem: Paralysis of the recurrent laryngeal nerve (RLN) leads to significant functional morbidity in affected patients. Methods: Six canines underwent RLN sectioning and reanastomosis. In the experimental group, the posterior cricoarytenoid (PCA) muscle was stimulated using an implantable electrical stimulator. Reinnervation through the RLN was documented through electromyography of the the thyroarytenoid (TA) and PCA muscles during physiologic trials. Results: At 110 days of interrupted stimulation, there was a trend toward enhanced native reinnervation and reduced foreign reinnervation. By 140 days of stimulation, this reduction became more significant and even approximated the normal contralateral side. Later, a period of continuous stimulation appeared to inhibit further innervation, both native and foreign, while the control group demonstrated a continued increase in overall innervation. Additionally, all reinnervation of the PCA, both foreign and native, was shown to occur exclusively through the reanastomosed RLN. Conclusion: Electrical stimulation of the dennervated larynx appears to inhibit the formation of foreign and erroneous reinnervation after injury to the RLN. When presented intermittently, in a more physiologic fashion, it appears to stimulate proper native reinnervation. Significance: While laryngeal paralysis poses a difficult problem to correct, electrical stimulation of the paralyzed musculature offers a promising option for future study. By showing that this model produces consistently hopeful results in the canine model, the opportunity exists for significant benefits for patients in the years to come. Support: None reported.

Structural and functional characteristics of primary cell cultures derived from the adrenal gland tissue of neonatal mallard ducklings (Anas platyrhynchos)

Primary cell cultures were prepared from the adrenal glands of one-day-old mallard ducklings (Anas platyrhynchos). The cells attached equally well to uncoated plastic and glass surfaces and on surfaces that had been coated with collagen. The phase of logarithmic growth occurred between the second and the fourth day, and the cells became confluent between the fifth and the sixth day. Staining with Sudan black B and toluidine blue and viewing fixed preparations by transmission electron microscopy indicated that the cultures consisted mostly of steroidogenic cells. A smaller population of chromaffin cells was also present. Scanning electron microscopy showed that most of the cells had long filopodia, and some cells had numerous surface blebs that were interpreted as exocytotic vesicles. When incubated in Krebs-Henseleit buffer containing 1–24 ACTH the cultured cells released three corticosteroids, namely, corticosterone, aldosterone and deoxycorticosterone. These responses occurred within 15 min of exposure to medium containing 1–24 ACTH and continued throughout a 60-min period of continuous stimulation. The minimally effective concentration of 1–24 ACTH was 0.078 ng per ml (0.0234 nM) and, as the concentration was increased up to 10 ng per ml (2.99 nM), the total output of each hormone during the 60-min incubation period increased significantly according to the following semi-logarithmic relationship: Y=a+b log X, where Y=the total output of hormone, X=the concentration of 1–24 ACTH in the medium, and a=the total output of hormone when the medium contained 1.0 ng of 1–24 ACTH per ml. The total outputs of each hormone in the presence of a maximally effective concentration of 1–24 ACTH, however, were low compared to the responses of similarly stimulated tissue slices taken from the neonatal duckling. It is concluded that most of the cells comprising the confluent cultures were derived from steroidogenic cells in the neonatal adrenal. These cells appeared to retain corticotropin receptors during the course of developing into confluent monolayers, but their diminished steroidogenic capacity to respond when stimulated maximally suggests that some generational changes may have occurred.

Influence of membrane polarization and hormonal stimulation on the action of lanthanum on frog skin sodium permeability

The effect of mucosal La3+ on short-circuit current (s.c.c.) has been studied on isolated frog skins with normaly polarized or depolarized apical membrane. With skins in "polarized condition", La3+ stimulates transiently the s.c.c. and after a long-lasting presence on the mucosal side (1 h) attenuates significantly the stimulation promoted by oxytocin. With skins in "depolarized conditions", lanthanum stimulates permanently the s.c.c. and does not modifying the oxytocin effect, even over long period of continuous stimulation. In contrast, an inhibitory action of mucosal La3+ develops, when skins submitted to repetitive hormonal stimulation are forced to oscillate from the stimulated to the normal resting state. The significance of this particular mode of action is discussed in terms of a possible electrical potential variation of apical membrane during oxytocin stimulation.