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PubMed1984

[Relation between intracardiac reflex effects on the rate of atrioventricular conduction and parameters of neural pathway stimulation].

Intracardiac nerves of the frog isolated heart were cut and the central or the peripheral end was stimulated. The atrioventricular (a-v) conduction was measured. The data showed that the intracardiac parasympathetic nervous system could induce both acceleration and deceleration of the a-v conduction, depending on the parameters of stimulation. Atropine blocked both the positive and the negative dromotropic effects whereas beta-adrenoblocking agent inderal was ineffective. The possible mechanism of the dromotropic effects observed are discussed.

Animals↗
PubMed2005

Fabrication and biocompatibility of polypyrrole implants suitable for neural prosthetics.

Finding a conductive substrate that promotes neural interactions is an essential step for advancing neural interfaces. The biocompatibility and conductive properties of polypyrrole (PPy) make it an attractive substrate for neural scaffolds, electrodes, and devices. Stand-alone polymer implants also provide the additional advantages of flexibility and biodegradability. To examine PPy biocompatibility, dissociated primary cerebral cortical cells were cultured on PPy samples that had been doped with polystyrene-sulfonate (PSS) or sodium dodecylbenzenesulfonate (NaDBS). Various conditions were used for electrodeposition to produce different surface properties. Neural networks grew on all of the PPy surfaces. PPy implants, consisting of the same dopants and conditions, were surgically implanted in the cerebral cortex of the rat. The results were compared to stab wounds and Teflon implants of the same size. Quantification of the intensity and extent of gliosis at 3- and 6-week time points demonstrated that all versions of PPy were at least as biocompatible as Teflon and in fact performed better in most cases. In all of the PPy implant cases, neurons and glial cells enveloped the implant. In several cases, neural tissue was present in the lumen of the implants, allowing contact of the brain parenchyma through the implants.

Animals↗
PubMed1983

Inhibitory conductance changes at synapses in the lamprey brainstem.

Although the conductance and kinetic behavior of inhibitory synaptic channels have been studied in a number of nerve and muscle cells, there has been little if any detailed study of such channels at synapses in the vertebrate central nervous system or of the relation of such channels to natural synaptic events. In the experiments reported here, current noise measurements were used to obtain such information at synapses on Müller cells in the lamprey brainstem. Application of glycine to the cells activated synaptic channels with large conductances and relaxation time constants (70 picosiemens and 33 milliseconds, respectively, at 3 degrees to 10 degrees C). Spontaneous inhibitory synaptic currents had a mean conductance of 107 nanosiemens and decayed with the same time constant. In addition, the glycine responses and the spontaneous currents had the same reversal potential and both were abolished by strychnine. These results support the idea that glycine is the natural inhibitory transmitter at these synapses and suggest that one quantum of transmitter activates about 1500 elementary conductance channels.

Animals↗
PubMed1979

After hyperpolarization conductance time-course and repetitive firing in a motoneurone model with early inactivation of the slow potassium conductance system.

Early inactivation of the slow potassium conductance system (GK), responsible for the spike afterhyperpolarization (AHP) in spinal alpha motoneurones, has been introduced in a motoneurone model whose GK kinetics give rise to an exponentially decaying AHP conductance. After this modification, the model displays a plateau shaped time-course of the AHP conductance and a faster shortening of the first interval during repetitive firing induced by current steps of increasing intensities. Both features increase the resemblance between the model and the motoneurone behaviour. Comparison with real motoneurones also suggests that GK inactivation may be more developed in "slow" than in "fast" motoneurones.

Electric Conductivity↗