Gustatory behavior and electrophysiological responses to sucrose in fifth instar larvae of Spodoptera litura and activity-dependent labeling of sucrose-sensitive neurons in lateral styloconic sensilla
[Objective]To investigate the gustatory behavior and electrophysiological responses of fifth instar larvae of Spodoptera litura to sucrose,and to label the sucrose-sensitive neurons in the lateral styloconic sensilla using agmatine activity-dependent neuron labeling,which could provide reference for the study of function and activity pattern of gusta-tory neurons in larva of Lepidoptera.[Method]The behavioral responses of fifth instar larvae to sucrose at different con-centrations(10,25,50 and 100 mmol/L)were studied by double selection method.The electrophysiological responses to agmatine(20 mmol/L)and sucrose at different concentrations(1,10,50 and 100 mmol/L)of fifth instar larvae of Spodoptera litura lateral styloconic sensilla were studied by electrophysiological apical recording technique,and 2 mmol/L KCl solution was as control.The distribution of sucrose-sensitive neurons in lateral styloconic sensilla was marked by agmatine activity-dependent labeling technique.[Result]Sucrose at concentrations of 10 and 25 mmol/L had no significant stimulatory effect on larval feeding behavior(P>0.05,the same below).However,sucrose at concentrations of 50 and 100 mmol/L extremely significantly stimulated larval feeding behavior(P<0.001,the same below).Lateral styloconic sensilla of Spodoptera litura contained sucrose-sensitive neurons,and the electrophysiological responses to 50 mmol/L sucrose were extremely significantly stronger than the control.The response intensity of sucrose-sensitive neurons in la-teral styloconic sensilla of larvae was extremely significantly stronger than that in the medial styloconic sensilla.The lateral styloconic sensilla of larvae exhibited strong responses to 1,10,50 and 100 mmol/L sucrose,with extremely sig-nificant differences among these concentrations compared with control,peaking at 50 mmol/L sucrose.There was no significant difference in the response of medial styloconic sensilla to 50 mmol/L sucrose.There was no significant dif-ference in the electrophysiological response of lateral styloconic sensilla of the lateral Spodoptera litura to agmatine solu-tion.Agmatine activity-dependent labeling technique could be used to label sucrose-sensitive neurons in lateral stylo-conic sensilla.[Conclusion]Sucrose exhibits significant feeding-stimulatory effect on Spodoptera litura larvae.However,no sucrose-sensitive neurons have been identified in the medial sensilla styloconica of Spodoptera litura larvae,whereas a single sucrose-sensitive neuron is present in the lateral styloconic sensilla.Using agmatine activity-dependent labeling,the sucrose-sensitive neurons in the lateral sensilla styloconica of Lepidopteran larvae can be effectively labeled,enabling clear visualization under a microscope.
Spodoptera liturasucrose-sensitive neuronsagmatine activity-dependent labelingelectrophysiologi-cal tip recording
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