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.

Alpha-1 adrenoreceptors modulate GABA release onto ventral tegmental area dopamine neurons.

The ventral tegmental area (VTA) plays an important role in reward and motivational processes involved in drug addiction. Previous studies have shown that alpha1-adrenoreceptors (α1-AR) are primarily found pre-synaptically at this area. We hypothesized that GABA released onto VTA-dopamine (DA) cells is modulated by pre-synaptic α1-AR. Recordings were obtained from putative VTA-DA cells of male Sprague-Dawley rats (28-50 days postnatal) using whole-cell voltage clamp technique. Phenylephrine (10 µM; α1-AR agonist) decreased the amplitude of GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) evoked by electrical stimulation of afferent fibers (n = 7; p < 0.05). Prazosin (1 µM, α1-AR antagonist), blocked this effect. Paired-pulse ratios were increased by phenylephrine application (n = 13; p < 0.05) indicating a presynaptic site of action. Spontaneous IPSCs frequency but not amplitude, were decreased in the presence of phenylephrine (n = 7; p < 0.05). However, frequency or amplitude of miniature IPSCs were not changed (n = 9; p > 0.05). Phenylephrine in low Ca(2+) (1 mM) medium decreased IPSC amplitude (n = 7; p < 0.05). Chelerythrine (a protein kinase C inhibitor) blocked the α1-AR action on IPSC amplitude (n = 6; p < 0.05). Phenylephrine failed to decrease IPSCs amplitude in the presence of paxilline, a BK channel blocker (n = 7; p < 0.05). Taken together, these results demonstrate that α1-ARs at presynaptic terminals can modulate GABA release onto VTA-DA cells. Drug-induced changes in α1-AR could contribute to the modifications occurring in the VTA during the addiction process.

Membrane cholesterol regulates different modes of synaptic vesicle release and retrieval at the frog neuromuscular junction.

We investigated the effects of cholesterol removal on spontaneous and KCl-evoked synaptic vesicle recycling at the frog neuromuscular junction. Cholesterol removal by methyl-ß-cyclodextrin (MßCD) induced an increase in the frequency of miniature end-plate potentials (MEPPs) and spontaneous destaining of synaptic vesicles labeled with the styryl dye FM1-43. Treatment with MßCD also increased the size of MEPPs without causing significant changes in nicotinic receptor clustering. At the ultrastructural level, synaptic vesicles from nerve terminals treated with MßCD were larger than those from control. In addition, treatment with MßCD reduced the fusion of synaptic vesicles that are mobilized during KCl-evoked stimulation, but induced recycling of those vesicles that fuse spontaneously. We therefore suggest that MßCD might favor the release of vesicles that belong to a pool that is different from that involved in the KCl-evoked release. These results reveal fundamental differences in the synaptic vesicle cycle for spontaneous and evoked release, and suggest that deregulation of cholesterol affects synaptic vesicle biogenesis and increases transmitter packing.

Nonextensivity and self-affinity in the mammalian neuromuscular junction.

We study time series and the spontaneous miniature end-plate potentials (MEPPs) of mammals recorded at neuromuscular junctions using two different approaches: generalized thermostatistics and detrended fluctuation analysis (DFA). Classical concepts establish that the magnitude of these potentials is characterized by Gaussian statistics and that their intervals are randomly displayed. First we show that MEPP distributions adequately satisfy the q-Gaussian distributions that maximize the Tsallis entropy, indicating their nonextensive and nonequilibrium behavior. We then examine the intervals between the miniature potentials via DFA, where the profile of the intervals between events configures a deviation from the expected random behavior. Some possible physiological substrates for these findings are discussed.

Wnt-5a modulates recycling of functional GABAA receptors on hippocampal neurons.

GABA(A) receptors (GABA(A)-Rs) play a significant role in mediating fast synaptic inhibition and it is the main inhibitory receptor in the CNS. The role of Wnt signaling in coordinating synapse structure and function in the mature CNS is poorly understood. In previous studies we found that Wnt ligands can modulate excitatory synapses through remodeling both presynaptic and postsynaptic regions. In this current study we provide evidence for the effect of Wnt-5a on postsynaptic GABA(A)-Rs. We observed that Wnt-5a induces surface expression and maintenance of this receptor in the neuronal membrane. The evoked IPSC recordings in rat hippocampal slice indicate that Wnt-5a can regulates postsynaptically the hippocampal inhibitory synapses. We found also that Wnt-5a: (a) induces the insertion and clustering of GABA(A)-Rs in the membrane; (b) increases the amplitude of GABA-currents due exclusively to postsynaptic mechanisms; (c) does not affect the endocytic process, but increases the receptor recycling. Finally, all these effects on the GABA(A)-Rs are mediated by the activation of calcium/calmodulin-dependent kinase II (CaMKII). Therefore, we postulate that Wnt-5a, by activation of CaMKII, induces the recycling of functional GABA(A)-Rs on the mature hippocampal neurons.