Aerotaxis Assay in Caenorhabditis elegans to Study Behavioral Plasticity.

C. elegans shows robust and reproducible behavioral responses to oxygen. Specifically, worms prefer O 2 levels of 5-10% and avoid too high or too low O 2 . Their O 2 preference is not fixed but shows plasticity depending on experience, context, or genetic background. We recently showed that this experience-dependent plasticity declines with age, providing a useful behavioral readout for studying the mechanisms of age-related decline of neural plasticity. Here, we describe a technique to visualize behavioral O 2 preference and its plasticity in C. elegans , by creating spatial gradients of [O 2 ] in a microfluidic polydimethylsiloxane (PDMS) chamber and recording the resulting spatial distribution of the animals.

The phosphatidylinositol transfer protein PITP-1 facilitates fast recovery of eating behavior after hypoxia in the nematode Caenorhabditis elegans.

Among the fascinating adaptations to limiting oxygen conditions (hypoxia) is the suppression of food intake and weight loss. In humans, this phenomenon is called high-altitude anorexia and is observed in people suffering from acute mountain syndrome. The high-altitude anorexia appears to be conserved in evolution and has been seen in species across the animal kingdom. However, the mechanism underlying the recovery of eating behavior after hypoxia is still not known. Here, we show that the phosphatidylinositol transfer protein PITP-1 is essential for the fast recovery of eating behavior after hypoxia in the nematode Caenorhabditis elegans. Unlike the neuroglobin GLB-5 that accelerates the recovery of eating behavior through its function in the oxygen (O2 )-sensing neurons, PITP-1 appears to act downstream, in neurons that express the mod-1 serotonin receptor. Indeed, pitp-1 mutants display wild-type-like O2 -evoked-calcium responses in the URX O2 -sensing neuron. Intriguingly, loss-of-function of protein kinase C 1 (PKC-1) rescues pitp-1 mutants' recovery after hypoxia. Increased diacylglycerol (DAG), which activates PKC-1, attenuates the recovery of wild-type worms. Together, these data suggest that PITP-1 enables rapid recovery of eating behavior after hypoxia by limiting DAG's availability, thereby limiting PKC activity in mod-1-expressing neurons.

High neural activity accelerates the decline of cognitive plasticity with age in Caenorhabditis elegans.

The ability to learn progressively declines with age. Neural hyperactivity has been implicated in impairing cognitive plasticity with age, but the molecular mechanisms remain elusive. Here, we show that chronic excitation of the Caenorhabditis elegans O2-sensing neurons during ageing causes a rapid decline of experience-dependent plasticity in response to environmental O2 concentration, whereas sustaining lower activity of O2-sensing neurons retains plasticity with age. We demonstrate that neural activity alters the ageing trajectory in the transcriptome of O2-sensing neurons, and our data suggest that high-activity neurons redirect resources from maintaining plasticity to sustaining continuous firing. Sustaining plasticity with age requires the K+-dependent Na+/Ca2+ (NCKX) exchanger, whereas the decline of plasticity with age in high-activity neurons acts through calmodulin and the scaffold protein Kidins220. Our findings demonstrate directly that the activity of neurons alters neuronal homeostasis to govern the age-related decline of neural plasticity and throw light on the mechanisms involved.

Ferritin is regulated by a neuro-intestinal axis in the nematode Caenorhabditis elegans.

Iron is vital for the life of most organisms. However, when dysregulated, iron can catalyze the formation of oxygen (O2) radicals that can destroy any biological molecule and thus lead to oxidative injury and death. Therefore, iron metabolism must be tightly regulated at all times, as well as coordinated with the metabolism of O2. However, how is this achieved at the whole animal level is not well understood. Here, we explore this question using the nematode Caenorhabditis elegans. Exposure of worms to O2 starvation conditions (i.e. hypoxia) induces a major upregulation in levels of the conserved iron-cage protein ferritin 1 (ftn-1) in the intestine, while exposure to 21% O2 decreases ftn-1 level. This O2-dependent inhibition is mediated by O2-sensing neurons that communicate with the intestine through neurotransmitter and neuropeptide signalling, and requires the activity of hydroxylated HIF-1. By contrast, the induction of ftn-1 in hypoxia appears to be HIF-1-independent. This upregulation provides protection against Pseudomonas aeruginosa bacteria and oxidative injury. Taken together, our studies uncover a neuro-intestine axis that coordinates O2 and iron responses at the whole animal level.