Pannexin 1 (Panx1) represents a class of vertebrate membrane channels, bearing significant sequence homology with the invertebrate gap junction proteins, the innexins and more distant similarities in the membrane topologies and pharmacological sensitivities with gap junction proteins of the connexin family. In the nervous system, cooperation among pannexin channels, adenosine receptors, and K_ATP channels modulating neuronal excitability via ATP and adenosine has been recognized, but little is known about the significance in vivo. However, the localization of Panx1 at postsynaptic sites in hippocampal neurons and astrocytes in close proximity together with the fundamental role of ATP and adenosine for CNS metabolism and cell signaling underscore the potential relevance of this channel to synaptic plasticity and higher brain functions. Here, we report increased excitability and potently enhanced early and persistent LTP responses in the CA1 region of acute slice preparations from adult Panx1^−/− mice. Adenosine application and N-methyl-D-aspartate receptor (NMDAR)-blocking normalized this phenotype, suggesting that absence of Panx1 causes chronic extracellular ATP/adenosine depletion, thus facilitating postsynaptic NMDAR activation. Compensatory transcriptional up-regulation of metabotropic glutamate receptor 4 (grm4) accompanies these adaptive changes. The physiological modification, promoted by loss of Panx1, led to distinct behavioral alterations, enhancing anxiety and impairing object recognition and spatial learning in Panx1^−/− mice. We conclude that ATP release through Panx1 channels plays a critical role in maintaining synaptic strength and plasticity in CA1 neurons of the adult hippocampus. This result provides the rationale for in-depth analysis of Panx1 function and adenosine based therapies in CNS disorders.

Gap junction communication mediated by connexins is critical for heart function. To gain insight into the causal relationship of molecular mechanisms of disease pathology, it is important to understand which mechanisms contribute to impairment of gap junctional communication. Here, we present an update on the known modulators of connexins, including various interaction partners, kinases and signaling cascades. This gap junction network can serve as a blueprint for data mining approaches exploring the growing number of publicly available data sets from experimental and clinical studies.

In mammals, a single pannexin1 gene (Panx1) is widely expressed in the CNS including the inner and outer retinae, forming large-pore voltage-gated membrane channels, which are involved in calcium and ATP signaling. Previously, we discovered that zebrafish lack Panx1 expression in the inner retina, with drPanx1a exclusively expressed in horizontal cells of the outer retina. Here, we characterize a second drPanx1 protein, drPanx1b, generated by whole-genome duplications during teleost evolution. Homology searches strongly support the presence of pannexin sequences in cartilaginous fish and provide evidence that pannexins evolved when urochordata and chordata evolution split. Further, we confirm Panx1 ohnologs being solely present in teleosts. A hallmark of differential expression of drPanx1a and drPanx1b in various zebrafish brain areas is the non-overlapping protein localization of drPanx1a in the outer and drPanx1b in the inner fish retina. A functional comparison of the evolutionary distant fish and mouse Panx1s revealed both, preserved and unique properties. Preserved functions are the capability to form channels opening at resting potential, which are sensitive to known gap junction and hemichannel blockers, intracellular calcium, extracellular ATP and pH changes. However, drPanx1b is unique due to its highly complex glycosylation pattern and distinct electrophysiological gating kinetics. The existence of two Panx1 proteins in zebrafish displaying distinct tissue distribution, protein modification and electrophysiological properties, suggests that both proteins fulfill different functions in vivo.

The zebrafish larva is an important vertebrate model for sensory–motor integration studies, genetic screening, and drug discovery because of its excellent characteristics such as optical transparency, genetic manipulability, and genetic similarity to humans. Operations such as precise manipulation of zebrafish larvae, controlled exposure to chemicals, and behavioural monitoring are of utmost importance to the abovementioned studies. In this work, a novel microfluidic device is presented to easily stabilize an individual larva's head using a microfluidic trap while leaving the majority of the body and the tail unhindered to move freely in a downstream chamber. The device is equipped with a microvalve to prevent the larva's escape from the trap and a microchannel beside the larva's head to expose it to chemicals at desired concentrations and times, while investigating multiple behaviours such as the tail, eye, and mouth movement frequencies. An in situ air bubble removal module was also incorporated to increase the yield of experiments. The functionality of our device in comparison to a conventional droplet-based technique was tested using L-arginine exposure and viability assays. We found that the larvae in the device and the droplet exhibit similar tail and eye response trends to nM–mM concentrations of L-arginine, and that the survival of the larvae is not affected by the device. However, the tail responses in the device were numerically higher than the droplet-tested larvae at nM–mM L-arginine concentrations. In the future, our device has the potential to be used for conducting simultaneous whole-brain functional imaging, upon optimized immobilization of the brain, and behavioural analysis to uncover differences between diseased and healthy states in zebrafish.