Assessment of Methods for the Intracellular Blockade of GABAA Receptors.

Selective blockade of inhibitory synaptic transmission onto specific neurons is a useful tool for dissecting the excitatory and inhibitory synaptic components of ongoing network activity. To achieve this, intracellular recording with a patch solution capable of blocking GABAA receptors has advantages over other manipulations, such as pharmacological application of GABAergic antagonists or optogenetic inhibition of populations of interneurones, in that the majority of inhibitory transmission is unaffected and hence the remaining network activity preserved. Here, we assess three previously described methods to block inhibition: intracellular application of the molecules picrotoxin, 4,4'-dinitro-stilbene-2,2'-disulphonic acid (DNDS) and 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS). DNDS and picrotoxin were both found to be ineffective at blocking evoked, monosynaptic inhibitory postsynaptic currents (IPSCs) onto mouse CA1 pyramidal cells. An intracellular solution containing DIDS and caesium fluoride, but lacking nucleotides ATP and GTP, was effective at decreasing the amplitude of IPSCs. However, this effect was found to be independent of DIDS, and the absence of intracellular nucleotides, and was instead due to the presence of fluoride ions in this intracellular solution, which also blocked spontaneously occurring IPSCs during hippocampal sharp waves. Critically, intracellular fluoride ions also caused a decrease in both spontaneous and evoked excitatory synaptic currents and precluded the inclusion of nucleotides in the intracellular solution. Therefore, of the methods tested, only fluoride ions were effective for intracellular blockade of IPSCs but this approach has additional cellular effects reducing its selectivity and utility.

Bifurcation analysis of a two-compartment hippocampal pyramidal cell model.

The Pinsky-Rinzel model is a non-smooth 2-compartmental CA3 pyramidal cell model that has been used widely within the field of neuroscience. Here we propose a modified (smooth) system that captures the qualitative behaviour of the original model, while allowing the use of available, numerical continuation methods to perform full-system bifurcation and fast-slow analysis. We study the bifurcation structure of the full system as a function of the applied current and the maximal calcium conductance. We identify the bifurcations that shape the transitions between resting, bursting and spiking behaviours, and which lead to the disappearance of bursting when the calcium conductance is reduced. Insights gained from this analysis, are then used to firstly illustrate how the irregular spiking activity found between bursting and stable spiking states, can be influenced by phase differences in the calcium and dendritic voltage, which lead to corresponding changes in the calcium-sensitive potassium current. Furthermore, we use fast-slow analysis to investigate the mechanisms of bursting and show that bursting in the model is dependent on the intermediately slow variable, calcium, while the other slow variable, the activation gate of the afterhyperpolarisation current, does not contribute to setting the intraburst dynamics but participates in setting the interburst interval. Finally, we discuss how some of the described bifurcations affect spiking behaviour, during sharp-wave ripples, in a larger network of Pinsky-Rinzel cells.

Memory trace replay: the shaping of memory consolidation by neuromodulation.

The consolidation of memories for places and events is thought to rely, at the network level, on the replay of spatially tuned neuronal firing patterns representing discrete places and spatial trajectories. This occurs in the hippocampal-entorhinal circuit during sharp wave ripple events (SWRs) that occur during sleep or rest. Here, we review theoretical models of lingering place cell excitability and behaviorally induced synaptic plasticity within cell assemblies to explain which sequences or places are replayed. We further provide new insights into how fluctuations in cholinergic tone during different behavioral states might shape the direction of replay and how dopaminergic release in response to novelty or reward can modulate which cell assemblies are replayed.

Incidental oesophageal leiomyoma during laparoscopic Roux-en-Y gastric bypass: finding the unexpected does not affect outcomes.

Most bariatric procedures are now performed laparoscopically. Here, we describe a case of incidental oesophageal leiomyoma found during laparoscopic Roux-en-Y gastric bypass (LRYGB). To our knowledge, this is the first such case reported. Our patient was admitted for an elective LRYGB. She had no upper gastrointestinal symptoms, and therefore did not undergo preoperative oesophagogastroduodenoscopy (OGD). During surgery, a hiatus hernia and an incidental oesophageal leiomyoma were found and treated with hernia repair and enucleation. The end outcome was unaffected. We were able to concomitantly treat the unexpected finding of an oesophageal leiomyoma and a hiatus hernia during the LRYGB. The routine use of OGD prior to bariatric surgery is still controversial. While surgeons should be prepared for unexpected pathologies, when performing laparoscopic bariatric surgery, a routine OGD prior to LRYGB is probably not necessary in asymptomatic patients. Laparoscopic enucleation of oesophageal leiomyoma during LRYGB is feasible and safe.

Long-term depression of synaptic kainate receptors reduces excitability by relieving inhibition of the slow afterhyperpolarization.

Kainate receptors (KARs) are ionotropic glutamate receptors that also activate noncanonical G-protein-coupled signaling pathways to depress the slow afterhyperpolarization (sAHP). Here we show that long-term depression of KAR-mediated synaptic transmission (KAR LTD) at rat hippocampal mossy fiber synapses relieves inhibition of the sAHP by synaptic transmission. KAR LTD is induced by high-frequency mossy fiber stimulation and natural spike patterns and requires activation of adenosine A2A receptors. Natural spike patterns also cause long-term potentiation of NMDA receptor-mediated synaptic transmission that overrides the effects of KAR LTD on the cellular response to low-frequency synaptic input. However, KAR LTD is dominant at higher frequency synaptic stimulation where it decreases the cellular response by relieving inhibition of the sAHP. Thus we describe a form of glutamate receptor plasticity induced by natural spike patterns whose primary physiological function is to regulate cellular excitability.