Frequency Of Burst Activity Research Articles

Distal small bowel motility and lipid absorption in patients following abdominal aortic aneurysm repair surgery

To investigate distal small bowel motility and lipid absorption in patients following elective abdominal aortic aneurysm (AAA) repair surgery. Nine patients (aged 35-78 years; body mass index (BMI) range: 23-36 kg/m(2)) post-surgery for AAA repair, and seven healthy control subjects (20-50 years; BMI range: 21-29 kg/m(2)) were studied. Continuous distal small bowel manometry was performed for up to 72 h, during periods of fasting and enteral feeding (Nutrison). Recordings were analyzed for the frequency, origin, length of migration, and direction of small intestinal burst activity. Lipid absorption was assessed on the first day and the third day post surgery in a subset of patients using the (13)C-triolein-breath test, and compared with healthy controls. Subjects received a 20-min intraduodenal infusion of 50 mL liquid feed mixed with 200 microL (13)C-triolein. End-expiratory breath samples were collected for 6 h and analyzed for (13)CO(2) concentration. The frequency of burst activity in the proximal and distal small intestine was higher in patients than in healthy subjects, under both fasting and fed conditions (P<0.005). In patients there was a higher proportion of abnormally propagated bursts (71% abnormal), which began to normalize by d 3 (25% abnormal) post-surgery. Lipid absorption data was available for seven patients on d 1 and four patients on d 3 post surgery. In patients, absorption on d 1 post-surgery was half that of healthy control subjects (AUC (13)CO(2) 1323+/-244 vs 2646+/-365; P<0.05, respectively), and was reduced to the one-fifth that of healthy controls by d 3 (AUC (13)CO(2) 470+/-832 vs 2646+/-365; P<0.05, respectively). Both proximal and distal small intestinal motor activity are transiently disrupted in critically ill patients immediately after major surgery, with abnormal motility patterns extending as far as the ileum. These motor disturbances may contribute to impaired absorption of enteral nutrition, especially when intraluminal processing is necessary for efficient digestion.

Neurohormonal Modulation of the Limulus Heart: Amine Actions on Cardiac Ganglion Neurones

ABSTRACT Octopamine (OCT), dopamine (DA), epinephrine (EPI) and norepine-phrine (NE) are endogenous excitors of the Limulus heart. The cellular sites of action of these amines were investigated by recording responses of neurones in the cardiac ganglion. There was an increase in spike frequency in pacemaker neurones, accompanied by a depolarization and an increase in the rate of repolarization of the ‘pacemaker potential’. DA also produced a transient decrease in pacemaker spike frequency which preceded its excitatory effect. All four amines produced slow, dose-dependent increases in the frequency of bursting activity in cardiac ganglion follower neurones. These increases were blocked by the antagonist phentolamine. DA and NE also produced transient decreases in burst rate which were blocked by the antagonist metergoline. Local application of DA on to pacemaker cells increased follower cell burst frequency, while similar applications on to follower cells did not affect burst frequency. This indicates that DA acts directly upon pacemaker neurones to increase cardiac ganglion burst activity. In addition to their pacemaker-mediated effects, the amines also had direct effects upon follower cells. These effects were examined after eliminating follower cell bursting activity with cobalt ions. OCT and, to a smaller extent, EPI, depolarized follower cells. DA and, occasionally, NE hyperpolarized follower cells. The hyperpolarizing DA response was due to a conductance increase and was blocked by metergoline and ergonovine.

On the membrane potential independent mechanism of the sodium pump-induced inhibition of spontaneous electrical activity of japanese land snail neurons

1. 1. The dependence of excitability on pump activity of bursting pacemaker of Japanese land snail neurons was studied. 2. 2. The incubation of neurons in potassium-free solution, in spite of the fact that the membrane was hyperpolarized, the frequency of bursting activity was increased and sometimes the interburst hyperpolarization fully disappeared. 3. 3. The 4 mM potassium or rubidium pump activation after preincubation of the neurons in potassiumfree solution leads to transient inhibition of bursting activity independent of the membrane potential level. 4. 4. Adrenaline has a potentiation effect on the potassium-induced inhibition of electrical activity after preincubation of the neurons in the potassium free solutions. This effect of adrenaline was absent in ouabain containing medium. 5. 5. Increasing the external medium tonicity has an inhibitory effect on electrical activity of neurons. 6. 6. It was suggested that the pump-induced cell volume changes could be one of the membrane potential independent mechanisms by which Na-K pump could modulate the membrane excitability.

Electrical and mechanical activity of rat uterus in vivo during the estrous cycle

Electromyograms were obtained from three different locations on the uterus of conscious, unrestrained rats during the 4 days estrous cycle. Intrauterine pressure changes were monitored simultaneously by means of indwelling intraluminal balloons (vol. 0.02 to 0.05 ml.). Electrical activity consisted of bursts of action potentials that were usually initiated at either end of the uterus. Propagated burst activity gave rise to cyclic intrauterine pressure changes, whereas bursts appearing at one electrode only did not elicit any measurable contractions. The rate of intrauterine pressure development depended on the propagation velocity, whereas the tension achieved was related to the duration of burst activity. All three parameters of electrical activity studied, namely, the duration and frequency of spike bursts, as well as their rate of propagation, varied significantly during the cycle. Regional differences were also subject to cyclic variations; thus, in proestrus the bursts originated predominantly at the cervical end, whereas in diestrus they were usually initiated at the ovarian end. Oxytocin stimulated the frequency and duration of bursts along the whole uterus and elicited corresponding changes in intrauterine pressure. Response to oxytocin was dose dependent and modified by cycle stage. Norepinephrine caused a transient prolongation of burst activity that was not dose dependent; epinephrine had a marked dose-dependent inhibitory action. The response to catecholamines did not vary significantly during the cycle. The variations in electrical and mechanical activity were characteristic for each stage of the ovarian cycle and could be correlated with the well-known hormonal changes. High circulating estrogen levels in proestrus are associated with infrequent but rapidly propagated spike bursts, whereas low levels in estrus are associated with frequent and sometimes nonpropaged bursts. The rise in plasma estrogen in diestrus coincides with a decrease in the frequency of burst activity, and the elevated progesterone levels are probably causally related to the significant drop in propagation velocity and the increase in duration of bursts observed in diestrus. These findings are consistent with the concept that estrogen withdrawal activates the estrogen-primed, quiescent myometrium, and that progesterone has an effect similar to that of estrogen withdrawal—at least in the rat.