title: Pharmacological assays reveal age-related changes in synaptic transmission at the Caenorhabditis elegans neuromuscular junction that are modified by reduced insulin signalling.
abstract: Frailty is a feature of neuromuscular ageing. Here we provide insight into the relative contribution of pre- and postsynaptic dysfunction to neuromuscular ageing using the nematode Caenorhabditis elegans. Assays of C. elegans motility highlight a precipitous decline during ageing. We describe a novel deployment of pharmacological assays of C. elegans neuromuscular function to resolve pre- and postsynaptic dysfunction that underpin this decreased motility during ageing. The cholinergic agonist levamisole and the cholinesterase inhibitor aldicarb elicited whole worm contraction and allowed a direct comparison of neuromuscular integrity, from 1 to 16 days old: measurements could be made from aged worms that were otherwise almost completely immobile. The rapidity and magnitude of the drug-induced contraction provides a measure of neuromuscular signalling whilst the difference between levamisole and aldicarb highlights presynaptic effects. Presynaptic neuromuscular transmission increased between 1 and 5 days old in wild-type but not in the insulin/IGF1 receptor mutant daf-2 (e1370). Intriguingly, there was no evidence of a role for insulin-dependent effects in older worms. Notably in 16-day-old worms, which were virtually devoid of spontaneous movement, the maximal contraction produced by both drugs was unchanged. Taken together the data support a maturation of presynaptic function and/or upstream elements during early ageing that is lost after genetic reduction of insulin signalling. Furthermore, this experimental approach has demonstrated a counterintuitive phenomenon: in aged worms neuromuscular strength is maintained despite the absence of motility.
authors.affiliation: Centre for Biological Sciences, Life Sciences Building 85, University of Southampton, Southampton SO17 1BJ, UK. bm406@soton.ac.uk
authors.forename: Ben
authors.initials: B
authors.lastname: Mulcahy
authors.forename: Lindy
authors.initials: L
authors.lastname: Holden-Dye
authors.forename: Vincent
authors.initials: V
authors.lastname: O'Connor
mesh_terms: D000375:Aging; D000448:Aldicarb / Q000494:pharmacology; D000818:Animals; D017173:Caenorhabditis elegans / Q000187:drug effects / Q000502:physiology*; D018679:Cholinergic Agonists / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D007978:Levamisole / Q000494:pharmacology; D008297:Male; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
chemical_list: D018679:Cholinergic Agonists; D002800:Cholinesterase Inhibitors; D007328:Insulin; D007978:Levamisole; D000448:Aldicarb