Showing papers by "David Spanswick published in 2021"

Alkyne-Bridged α-Conotoxin Vc1.1 Potently Reverses Mechanical Allodynia in Neuropathic Pain Models.

Abstract: Several Conus-derived venom peptides are promising lead compounds for the management of neuropathic pain, with α-conotoxins being of particular interest. Modification of the interlocked disulfide framework of α-conotoxin Vc1.1 has been achieved using on-resin alkyne metathesis. Although introduction of a metabolically stable alkyne motif significantly disrupts backbone topography, the structural modification generates a potent and selective GABAB receptor agonist that inhibits Cav2.2 channels and exhibits dose-dependent reversal of mechanical allodynia in a behavioral rat model of neuropathic pain. The findings herein support the hypothesis that analgesia can be achieved via activation of GABABRs expressed in dorsal root ganglion (DRG) sensory neurons.

Glucose-sensing in AgRP neurons integrates homeostatic energy state with dopamine signalling in the striatum.

Abstract: Hunger increases the motivation of an organism to seek out and consume highly palatable energy dense foods by acting on the midbrain dopaminergic system. Here, we identify a novel molecular mechanism through which hunger-sensing AgRP neurons detect low energy availability and modulate dopamine release to increase motivation for food reward. We tested the hypothesis that carnitine acetyltransferase (Crat), a metabolic enzyme regulating glucose and fatty acid oxidation, in AgRP neurons is necessary to sense low energy states and regulate motivation for food rewards by modulating accumbal or striatal dopamine release. In support of this, electrophysiological studies show that AgRP neurons require Crat for appropriate glucose-sensing. Intact glucose-sensing in AgRP neurons controls post-ingestive dopamine accumulation in the dorsal striatum. Fibre photometry experiments, using the dopamine sensor GRABDA, revealed that impaired glucose-sensing, in mice lacking Crat in AgRP neurons, reduces dopamine release in the nucleus accumbens to palatable food consumption and during operant responding, particularly in the fasted state. Finally, the reduced dopamine release in the nucleus accumbens of mice lacking Crat in AgRP neurons affects sucrose preference and motivated operant responding for sucrose rewards. Notably, these effects are potentiated in the hungry state and therefore highlight that glucose-sensing by Crat in AgRP neurons is required for the appropriate integration and transmission of homeostatic hunger-sensing to dopamine signalling in the striatum. These studies offer a novel molecular target to control the overconsumption of palatable foods in a population of hunger-sensing AgRP neurons.

Metabolic-sensing in AgRP neurons integrates homeostatic state with dopamine signalling in the striatum

Abstract: Hunger increases the motivation of an organism to seek out and consume highly palatable energy dense foods. While hunger-sensing Agouti-related peptide (AgRP) neurons influence this process, whether metabolic detection of homeostatic state via metabolic sensing in AgRP neurons potentiates motivation through the midbrain dopamine system is unexplored. Here, we used the AgRP-specific deletion of carnitine acetyltransferase (Crat), a metabolic enzyme regulating glucose and fatty acid oxidation, as a model of impaired metabolic-sensing in AgRP neurons. We then tested the hypothesis that appropriate metabolic-sensing in AgRP neurons is required to increase food reward motivation by modulating accumbal or striatal dopamine release. Electrophysiological studies confirm that Crat deletion in AgRP neurons (KO) impairs normal ex vivo glucose-sensing, and in vivo photometry experiments show that AgRP neurons in KO mice do not exhibit normal responses to repeated palatable food presentation and consumption, highlighting that this model is appropriate to test the hypothesis. Fiber photometry experiments, using the dopamine sensor GRAB-DA, revealed that impaired metabolic-sensing reduces acute dopamine release (seconds) in the nucleus accumbens, but not the dorsal striatum, to palatable food consumption and during operant responding. Positron electron tomography (PET) methods indicated that impaired metabolic-sensing in AgRP neurons suppressed radiolabelled 18F-fDOPA accumulation after ∼30 minutes in the dorsal striatum but not the ventral striatum, suggesting a role for AgRP neurons to restrict a long term post-ingestive dopamine response in the dorsal striatum. Finally, impaired metabolic-sensing in AgRP neurons suppresses motivated operant responding for sucrose rewards. Notably, these behavioural effects are potentiated in the hungry state and therefore highlight that metabolic-sensing in AgRP neurons is required for the appropriate temporal integration and transmission of homeostatic hunger-sensing to dopamine signalling in the striatum.