Factors influencing the twin-pulse facilitation of the release of transmitter at the mouse neuromuscular junction

Maximum-likelihood q-estimator uncovers the role of potassium at neuromuscular junctions

Recently, we demonstrated the existence of nonextensive behavior in neuromuscular transmission (da Silva et al. in Phys Rev E 84:041925, 2011). In this letter, we first obtain a maximum-likelihood q-estimator to calculate the scale factor ([Formula: see text]) and the q-index of q-Gaussian distributions. Next, we use the indexes to analyze spontaneous miniature end plate potentials in electrophysiological recordings from neuromuscular junctions. These calculations were performed assuming both normal and high extracellular potassium concentrations [Formula: see text]. This protocol was used to test the validity of Tsallis statistics under electrophysiological conditions closely resembling physiological stimuli. The analysis shows that q-indexes are distinct depending on the extracellular potassium concentration. Our letter provides a general way to obtain the best estimate of parameters from a q-Gaussian distribution function. It also expands the validity of Tsallis statistics in realistic physiological stimulus conditions. In addition, we discuss the physical and physiological implications of these findings.

Multiple overlapping processes underlying short-term synaptic enhancement

Recently there have been exciting advances in understanding the mechanisms and functional roles of a form of short-term synaptic enhancement (STE) that results from an activity-dependent accumulation of Ca2+ in the presynaptic terminal. This form of STE is composed of at least four processes: fast-decaying facilitation (FI), slow-decaying facilitation (F2), augmentation (AUG) and post-tetanic potentiation (PTP). Recent results suggest that these processes can now be distinguished mechanistically by the site of their induction within the presynaptic terminal: FI and F2 appear to be induced by a rapid, high concentration of Ca2+ at or near the site of exocytosis, whereas AUG and PTP seem to be induced by lower levels of Ca2+ with slower kinetics, possibly within the core of the terminal. STE is highly conserved across diverse species, and appears to serve as a flexible mechanism for temporal information processing in systems ranging from peripheral motor control to higher cortical integration.

Dependence on temperature of the effect of dinitrophenol on the release of transmitter quanta at neuromuscular junctions in the mouse diaphragm

1. The frequencies (F, s-1) of miniature endplate potentials and the quantal content (m) of endplate potentials were measured intracellularly and simultaneously at mouse diaphragm endplates in a bathing solution that contained 0.6 mM Ca2+ ions and 5 mM Mg2+ ions. 2. Twin pulses at 4 ms intervals gave the quantal contents of the first (m1) and second (m2) responses. The ratio of m2/m1 was taken as an indicator of the temporal facilitation of the release of transmitter. 3. Dinitrophenol (DNP, 10 microM) increased the values of F and m at 36 degrees C. This effect did not depend on extracellular Ca2+ ions. 4. The potentiating effect of DNP disappeared at 24 degrees C but the value of m2/m1 remained constant. 5. These results suggest that the effect of DNP is modifiable by temperature which can affect systems that control the intracellular metabolism of Ca2+ ions.

Caffeine enhances sympathetic purinergic and noradrenergic transmission in the guinea-pig isolated vas deferens

Intracellular recording techniques were used to monitor the resting membrane potential of smooth muscle cells and the excitatory junction potentials (EJPs) evoked by stimulation of the hypogastric nerve. Stimulation with trains of 15 pulses at 1 Hz or 0.33 Hz evoked individual EJPs which increased in amplitude from the first pulse and reached a plateau after 6-8 pulses. Stimulation at 1 Hz resulted in EJPs facilitating to a plateau level of approximately 25 mV, whereas with stimulation at 0.33 Hz the EJPs only facilitated to a plateau level of about 12 mV. With stimulation at 1 Hz, caffeine (3 mM and 10 mM), increased the amplitude of the first few EJPs in each train and decreased the extent of facilitation and reduced the amplitude of fully facilitated EJPs. In comparison, the amplitude of all EJPs evoked by stimulation at 0.33 Hz was increased by caffeine (3 mM and 10 mM). With 0.33 Hz stimulation, facilitation of the first few EJPs was observed in the presence of 3 mM caffeine but not in the presence of 10 mM caffeine. In the presence of the alpha 2-adrenoceptor antagonist idazoxan, caffeine (3 mM and 10 mM) still enhanced the amplitude of EJPs early in trains of stimulation but there was no depression of EJPs later in the trains. Similarly, in reserpine-treated vasa deferentia, caffeine (3 mM) enhanced EJPs early in the train of stimulation at 1 Hz and there was no depression of EJPs at the end of the train. In addition to electrophysiological experiments, the effect of caffeine (0.1-30 mM) on the resting and stimulation-induced (S-I) efflux of radioactivity was investigated in guinea-pig isolated vasa deferentia previously incubated with [3H]-noradrenaline. Caffeine (10 mM) did not affect the resting efflux of [3H]-noradrenaline but significantly enhanced the S-I efflux by 150-160%. The present findings suggest that caffeine enhances sympathetic purinergic and noradrenergic transmission at the sympathetic neuroeffector junction in the guinea-pig vas deferens. Moreover, the increased release of transmitter noradrenaline can modulate purinergic transmission by activation of alpha 2-adrenoceptors located at sympathetic neuroeffector sites.