Junction Potentials and Action Potentials of the Crayfish Myocardium

Junction and Action Potentials. Introduction : The purpose of this investigation was to study the properties of junction and action potentials elicited by nerve stimulation in the absence of the cardiac ganglion in crayfish myocardium.
Methods and Results : The cardiac ganglion was surgically removed in isolated crayfish hearts. Electrical stimulation of one of the peripheral anterolateral nerves provided isolated junction potentials and action potentials free of the usual postspike bursts of junction potentials. The single junction potentials displayed amplitudes of up to 25 mV and slow exponential decay; the mean time constant was 170 ± 13 msec (xT ± SD). In fully recovered tissue, the junction potentials triggered action potentials free of repetitive subthreshold discharges. Tetrodotoxin did not alter the amplitude or shape of action potentials initiated by direct electrical stimulation of the muscle cells. Calcium channel blocking agents such as Cd²⁺ and Ni²⁺ eliminated the action potentials but not the junction potentials. Tetraethylammonium markedly prolonged the action potential duration.
Conclusions : Our data suggest that: (1) A slow decay of the junction potentials may result from the disappearance of the neurotransmitter; this process also accounts for the late slow repolarization of the final part of the action potentials; (2) The equilibrium potential of the junction potentials is close to 0 mV; (3) The upstroke of the action potentials is carried by calcium currents; (4) The fast repolarization phase of the action potentials is likely caused by the delayed rectifier; and (5) The refractory phase outlasts the duration of the action potential.     

THE IMPORTANCE OF FAMILY CONTEXT IN ALCOHOLISM

In the present study, 56 chronic alcoholics were compared with56 controls with no excessive drinking habits, all of them male.The drinking habits of their parents were studied, as were parentalrearing, dyadic relations with the spouses, attachment to significantpeople, and the education they gave to their own children. Itwas noted that the alcoholics' parents had heavier drinkinghabits and could have acted as learning models. As regards theother characteristics, the dyadic cohesion, the global scoreof the education received from the father and the personal styleof criticism/rejection in the education of their own childrenwere underlined.     

Severe and Early Alteration of Action Potential During Acute Cardiac Rejection in Rats

Alteration of Cardiac Action Potential . Introduction: Alteration of cardiac action potential and its adaptation to heart rate could contribute to cardiac dysfunction and arrhythmias during acute cardiac rejection.
Methods and Results: Heterotopic heart transplantation was performed in allogeneic and syngeneic rats in which the action potentials of right and left ventricles were measured at 1, 2.5, 3.3, and 5.7 Hz successively using standard microelectrode techniques and compared with nontransplanted hearts. For each frequency, we measured action potential amplitude, action potential duration, transmembrane resting potential, and Vmax. In the right ventricle, at 1 Hz in the presence of rejection (n = 40), a significant increase was observed in action potential duration at 20%, 50%, and 70% repolarization (82.5%, 75.6%, and 70.8%, respectively) and in action potential amplitude (+17.9 mV), and the resting potential was decreased (-5.3 mV). A lack of adaptation of action potential duration to the driving frequency was observed in the rejecting heart group in contrast to controls (n = 20) and nourejecting hearts (n = 13). Similar results were observed in the left ventricle and surprisingly in the native hearts (n = 11) of recipients with allografted rejecting hearts in the abdominal position.
Conclusion: Action potential and its adaptation to the driving frequency is considerably altered during acute rejection. A humoral factor could contribute to cardiac dysfunction.     

Neural Monitoring of Vasovagal Syncope

Head-up tilt testing has become a valuable and widely accepted diagnostic tool for evaluation of patients with vasovagal syncope. This test has afforded clinical researchers the opportunity to focus on the hemodynamic, humoral, and neural changes that accompany syncope. We review the animal and clinical studies that provide insight into the possible pathophysiological mechanisms involved in vasovagal syncope. Hemodynamic measurements in patients with vasovagal syncope suggest that a relative decrease in ventricular size and increase in cardiac contractility may be seen in many patients with vasovagal syncope. Patients with vasovagal syncope have also demonstrated numerous "exaggerated" neurohumoral responses to syncope. Differential changes in plasma levels of epinephrine, renin, endothelin, vasopressin, cortisol, prolactin, beta endorphins, and substance P have been reported by some investigators either prior to or during a syncopal episode in patients with vasovagal syncope. The precise pathophysiological significance of these measurements is unknown at the present time. Measurements of autonomic tone may be accomplished indirectly with analysis of heart rate variability or baroreflex slope, or directly by sympathetic neural recordings of the peroneal nerve. We have demonstrated decreased baroreflex slopes in patients with vasovagal syncope. Using microneurography, we and others have demonstrated decreased sympathetic nerve activity occurring 11 ± 3 seconds prior to syncope during bead-up tilt table testing. A variety of other abnormal reflexes, including blunted forearm blood flow responses during exercise, have been demonstrated by others. These observations suggest that pacing instituted after the event may not be as helpful as the use of a hemodynamic sensor that will result in the initiation of pacing prior to sympathetic withdrawal or modify the decrease in sympathetic tone that occurs prior to syncope.     

Alcohol dependence criteria in DSM-III-R: presence of symptoms according to degree of severity

According to DSM-III-R a positive diagnosis of alcohol dependence requires the presence of at least three of nine symptoms of a core dependence syndrome. In this study the presence of the nine symptoms according to degree of the severity of dependence is examined in 99 patients (mild, n=23; moderate, n = 26; and severe, n = 50). It is shown that although the cut-off point far a positive diagnosis of dependence is the presence of “any three” out of nine DSM-III-R criteria, specific symptoms (“excessive drinking”, “desire or efforts to control drinking”, and “drinking despite major problems”) have a high probability of occurrence across the dependence seventy range (mild, moderate or severe). Conversely, other symptoms appear prominently only in the more were cases (“much time devoted to alcohol”, “important activities given up”, and “drinking to relieve withdrawal”). The results suggest that in the DSM-III-R criteria for alcohol dependence name symptoms are mare frequently associated with the diagnosis, white other symptoms are associated with seventy of the alcohol dependence disorder.