Neuronal Signaling And Chemosensory Circuit For Feeding Behavior In Caenorhabditis Elegans

In this study,Caenorhabditis elegans was used as an experimental subject,and the feeding behavior of nematodes was calculated by the count of the pharyngeal pumping rates.By reverse genetics and behavior screening,it found that the serotonin signal from ADF sensory neurons played an important role.Then through testing serotoninergic receptor,we found MOD-1 receptor,a gated chloride channels,was involved in nematode feeding behavior control.MOD-1 is expressed in the multiple neurons and further results showed that the expression in RIC interneurons can restore the defect of pumping behavior and the calcium signaling level of RIC neurons in MOD-1 mutants.And the calcium signaling increase of RIC interneurons in MOD-1 mutants suggested that the chloride channel MOD-1 strongly inhibited the activity of RIC interneurons.RIC interneurons are only the neurons that synthetize and release octopamine.By reverse genetic screening of octopaminergic receptors in the nematode feeding behavior,we found that the pumping rate in SER-3 mutants increased under well-fed condition,and the pumping rate in SER-6 mutants decreased under fasted condition.And transgene rescue test showed that SER-3 functionally expressed in SIA interneurons,and SER-6 in AWB neurons.In addition,the calcium signaling of AWB neurons declined in SER-6 mutants or RIC::TeTx transgene worms,and the defect of SER-6 mutants was able to be rescued by SER-6 expression in AWB neurons.Then,the calcium signals results demonstrated AWB neurons positively regulated ADF neurons.Thus,we found two neural circuits,the feedforward neural circuit ADF?RIC?SIA,and the feedback neural circuit ADF?RIC?AWB?ADF.In their common pathways,the neurosignals from ADF?RIC are inhibitory.And in the rest of the pathways,the neurosignals from RIC?SIA are inhibitory for feeding behavior,while the neurosignals in RIC?AWB?ADF pathway are excitatory,so they are disinhibition and disexcitation respectively.These two circuits enable nematodes to reply different changes of the environment in vivo and in vitro,for maintaining physiological homeostasis.In the presence of food,ADF sensory neurons synthesize and release serotonin to inhibit RIC neurons,thereby the inhibition of RIC?SIA signaling pathway on pharyngeal pumping eliminates the promotion of the nematode feeding.On the other hand,in starvation,the inhibition of RIC neurons is relieved for less serotonin released,and much octopamine released from RIC neurons act on AWB neurons,which transmits excitatory neural signals to ADF neurons to maintain the basic pharyngeal pumping.So nematodes can quickly resume normal feeding behavior once they re-encounter food again.