Advancing respiratory-cardiovascular physiology with the working heart-brainstem preparation over 25 years

Twenty‐five years ago, a new physiological preparation called the working heart–brainstem preparation (WHBP) was introduced with the claim it would provide a new platform allowing studies not possible before in cardiovascular, neuroendocrine, autonomic and respiratory research. Herein, we review some of the progress made with the WHBP, some advantages and disadvantages along with potential future applications, and provide photographs and technical drawings of all the customised equipment used for the preparation. Using mice or rats, the WHBP is an in situ experimental model that is perfused via an extracorporeal circuit benefitting from unprecedented surgical access, mechanical stability of the brain for whole cell recording and an uncompromised use of pharmacological agents akin to in vitro approaches. The preparation has revealed novel mechanistic insights into, for example, the generation of distinct respiratory rhythms, the neurogenesis of sympathetic activity, coupling between respiration and the heart and circulation, hypothalamic and spinal control mechanisms, and peripheral and central chemoreceptor mechanisms. Insights have been gleaned into diseases such as hypertension, heart failure and sleep apnoea. Findings from the in situ preparation have been ratified in conscious in vivo animals and when tested have translated to humans. We conclude by discussing potential future applications of the WHBP including two‐photon imaging of peripheral and central nervous systems and adoption of pharmacogenetic tools that will improve our understanding of physiological mechanisms and reveal novel mechanisms that may guide new treatment strategies for cardiorespiratory diseases.

Differential regulation of behavioral tolerance to WIN55,212-2 by GASP1

Cannabinoid agonists have shown some promise clinically as analgesics, in particular for cancer pain, in which they have the additional benefit of decreasing nausea. However, as for most other drugs, the long-term use of cannabinoids is limited by the development of tolerance. Several molecular mechanisms have been proposed to explain drug tolerance, including receptor downregulation. The cannabinoid 1 (CB1) receptors can be downregulated in vitro through an interaction with the G-protein-coupled receptor-associated sorting protein1, GASP1, that targets CB1 receptors for degradation after their agonist-mediated endocytosis. To investigate whether GASP1-mediated postendocytic sorting of the CB1 receptor contributes to tolerance to cannabinoid drugs in vivo, we generated a mouse with a disruption of GASP1. In wild-type mice, repeated administration of the cannabinoid agonist WIN55,212-2 promoted downregulation of CB1 receptor levels and concomitant tolerance to the effects of drug on antinociception, motor incoordination, and locomotor hypoactivity. In contrast, GASP1 knockout mice did not develop tolerance to any of these effects and showed no significant receptor downregulation. Taken together, this study provides evidence that GASP1 regulates CB1 receptor downregulation in vivo, and that postendocytic receptor trafficking has a key role in the development of tolerance to WIN55,212-2.

A stop codon-dependent internal secondary translation initiation region in Escherichia coli rpoS

Sigma S (sigmaS) encoded by rpoS is a stationary phase-specific sigma subunit of the Escherichia coli RNA polymerase holoenzyme. In many E. coli strains, rpoS has an amber stop as codon 33 (rpoSAm), resulting in a 32-amino-acid-long peptide. Nevertheless, suppressor-free rpoSAm strains have functional sigmaS. This led us to hypothesize the presence of an intracistronic secondary translational initiation region (STIR) in the E. coli rpoS gene. Here, we demonstrate that the STIR is functional and is controlled by the upstream amber stop codon 33. Removal of the primary translational initiation region did not abolish translation from STIR, ruling out translational coupling. Importantly, the functional STIR conferred survival advantage. Taken together, our results reveal a hitherto unknown physiologically significant post-transcriptional process in E. coli rpoSAm strains.