Action potential characteristics of rabbit papillary muscle

The ionic components of the action potential (AP) in rabbit right papillary muscle (RRPM) were determined by simple methods such as changes in external concentrations of sodium and calcium ions and addition of MnCl2 ot the perfusion fluid. Two components (fast and slow) were clearly visible in the upstroke of AP in normal Tyrode solution. MnCl2 (5 mmol/l) eliminated the slow component which forms the overshoot (OS) leaving the fast one unaffected, indicating that the former was related to a slow inward current. Mn also drastically reduced AP duration without changing the slope of phase 3 of repolarization. Reduction of Na concentration to 90 mmol/l did not affect the peak voltage of the OS but shortened AP. This low-Na solution reduced both (Vmax)f and the amplitude of the fast component. Ca-free solution reduced OS and increased AP duration. In high-Ca Tyrode (7.2 mmol/l) OS was increased and AP shortened. The effects of MN were reversed in this solution. The results suggest that the upstroke of the RRPM action potential is determined by two different ionic currents: a fast Na current responsible for the fast component and a slow inward current carried mainly by Ca, this latter being responsible for the slow component in the upstroke and for the plateau phase. The existence of propagated, Ca-dependent slow responses was demonstrated. Emphasis is placed on the fact that the major determination of the repolarization process in this type of AP is probably the inactivation of the slow inward Ca current.     

Allergen immunotherapy inhibits airway eosinophilia and hyperresponsiveness associated with decreased IL-4 production by lymphocytes in a murine model of allergic asthma

Microelectrode recording methods for stereotactic localization of the subthalamic nucleus (STN) and surrounding structures are described. These methods accurately define targets for chronic deep brain stimulation in the treatment of Parkinson's disease. Mean firing rates and a burst index were determined for all recorded neurons, and responses to active and passive limb and orofacial movements were tested. STN neurons had a mean firing rate of 37+/-17 Hz (n = 248) and an irregular firing pattern (median burst index, 3.3). Movement-related activity and tremor cells were identified in the STN. Ventral to the STN, substantia nigra pars reticulata neurons had a mean rate of 71+/-23 Hz (n = 56) and a more regular firing pattern (median burst index, 1.7). Short trains (1-2 seconds) of electrical microstimulation of STN could produce tremor arrest but were not found to be useful for localization. Compared with data from normal monkeys our findings suggest that STN neuronal activity is elevated in Parkinson's disease.     

Two roads to coma: the Scottish hypothesis

Clinical experience seems to indicate two separate types of entry to coma. Some patients follow a pathway characterized by confusion, hallucinations, mumbling delirium, myoclonic jerks, and seizures. The author has called this sequence of symptoms the high road to coma and hypothesized that its basic underlying pathophysiology involves increased neuronal firing rates. Other patients develop somnolence, lethargy, obtundation, and unresponsiveness without seizures or muscle twitches. This low road to coma involves either anatomical compression of the midbrain reticular formation or a metabolic or toxic disorder characterized by membrane stabilization and decreased neuronal excitability.     

The effects of self-induced mood states on behavior and physiological arousal

The effects of reading emotionally loaded statements on behavioral tasks and physiological measures were investigated. Statements were constructed to arouse elation, depression, or neutrality. Ss were both pre- and posttested on Writing Speed, Reaction Time, Decision Time, and Spontaneous Verbalizations. Base rates were obtained for heart rate and galvanic skin response. Elation Ss significantly outperformed both Neutral and Depression Ss on the Reaction Time task. Scores for Neutral Ss fell between those of Elation and Depression Ss on three of the four behavioral measures. No significant differneces were found on the physiological measures.     

Cardiovascular and neuromuscular effects of dimethyl sulfoxide in anesthetized rabbits

In rabbits anesthetized with pentobarbital, the carotid arterial blood pressure and bilateral contractions of the gastrocnemius muscles due to electrical stimulation of the sciatic nerves were recorded. Intravenous administration of up to 1 ml of dimethyl sulfoxide/kg caused profound hypotension and eventually failure of neuromuscular transmission. Caution must be used in considering dimethyl sulfoxide as a solvent for drug administration.     

Influence of environment on passive immunity in calves

Passive immunity in neonatal calves is influenced by environment. Placing newly born Holstein calves (108 head) in three different housing environments (shade, cooled shade, hutch) during hot weather produced differences in body temperature, serum cortocosteroids, immunoglobulin IgG1 concentrations, and mortality. Experimental design permitted examination of effects due to treatments, time, differences in colostrum, and climatic environment in an analysis of variance. Calves exposed to the hotter, less desirable environment responded by having a higher mortality, higher serum corticosteroid concentration, and lower serum immunoglobulin IgG1 at 2 and 10 days after birth. All of these were correlated. Calves that died had serum immunoglobulin IgG1 falling below the mean for all experimental calves.