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Drosophila nociceptors mediate larval aversion to dry surface environments utilizing both the painless TRP channel and the DEG/ENaC subunit, PPK1.

Johnson WA, Carder JW - PLoS ONE (2012)

Bottom Line: Transgenic inactivation of mdIV nociceptor neurons resulted in larvae moving inappropriately into regions of low humidity at the top of the vial reflected as an increased overall pupation height and larval desiccation.Transgenic hyperactivation of mdIV nociceptors caused a reciprocal hypersensitivity to dry surfaces resulting in drastically decreased pupation height but did not induce the writhing nocifensive response previously associated with mdIV nociceptor activation by noxious heat or harsh mechanical stimuli.Larvae carrying mutations in either the Drosophila TRP channel, Painless, or the degenerin/epithelial sodium channel subunit Pickpocket1(PPK1), both expressed in mdIV nociceptors, showed the same inappropriate increased pupation height and lethal desiccation observed with mdIV nociceptor inactivation.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Physiology and Biophysics, Roy and Lucille J Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America. wayne-a-johnson@uiowa.edu

ABSTRACT
A subset of sensory neurons embedded within the Drosophila larval body wall have been characterized as high-threshold polymodal nociceptors capable of responding to noxious heat and noxious mechanical stimulation. They are also sensitized by UV-induced tissue damage leading to both thermal hyperalgesia and allodynia very similar to that observed in vertebrate nociceptors. We show that the class IV multiple-dendritic(mdIV) nociceptors are also required for a normal larval aversion to locomotion on to a dry surface environment. Drosophila melanogaster larvae are acutely susceptible to desiccation displaying a strong aversion to locomotion on dry surfaces severely limiting the distance of movement away from a moist food source. Transgenic inactivation of mdIV nociceptor neurons resulted in larvae moving inappropriately into regions of low humidity at the top of the vial reflected as an increased overall pupation height and larval desiccation. This larval lethal desiccation phenotype was not observed in wild-type controls and was completely suppressed by growth in conditions of high humidity. Transgenic hyperactivation of mdIV nociceptors caused a reciprocal hypersensitivity to dry surfaces resulting in drastically decreased pupation height but did not induce the writhing nocifensive response previously associated with mdIV nociceptor activation by noxious heat or harsh mechanical stimuli. Larvae carrying mutations in either the Drosophila TRP channel, Painless, or the degenerin/epithelial sodium channel subunit Pickpocket1(PPK1), both expressed in mdIV nociceptors, showed the same inappropriate increased pupation height and lethal desiccation observed with mdIV nociceptor inactivation. Larval aversion to dry surfaces appears to utilize the same or overlapping sensory transduction pathways activated by noxious heat and harsh mechanical stimulation but with strikingly different sensitivities and disparate physiological responses.

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Control of pupation height behavior by the internal microenvironment of the culture vial.(A) Schematic representation of a Drosophila culture vial and the internal humidity gradient generated within the microenvironment of the plugged vial. Higher humidity at the bottom near the food surface is indicated as darker shading decreasing to low humidity at the top of the vial. Pupae are shown as black ovals within the designated zones indicated as height(cm) above the vial bottom used to calculate the pupation height index(PHI). PHI = ((#pupae>3 cm)-(#pupae<3 cm))/total # pupae. (BC) Pupation height behavior for ppk1-GAL4/+ control larvae represented by the indicated Pupation Height Index; (B) Pupation height is strongly influenced by external humidity. With constant larval density(50 larvae/vial), low external humidity(25%) causes larvae to pupate at sites lower in the vial indicated as a downward deflection. At higher humidity(50% and 75%), larvae choose to predominantly pupate at higher sites within the vial indicated as an upward deflection. (C) Pupation height is influenced by larval density. With vials grown at constant external humidity(50%), low larval density(25 larvae/vial) causes a low pupation height. Higher larval density causes a drastic increase in pupation height resulting from the altered microenvironment as larvae exit the food source. Error bars represent SEM with n≥15 for all values. ***P<.0001, one-way ANOVA with Tukey posttest.
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pone-0032878-g001: Control of pupation height behavior by the internal microenvironment of the culture vial.(A) Schematic representation of a Drosophila culture vial and the internal humidity gradient generated within the microenvironment of the plugged vial. Higher humidity at the bottom near the food surface is indicated as darker shading decreasing to low humidity at the top of the vial. Pupae are shown as black ovals within the designated zones indicated as height(cm) above the vial bottom used to calculate the pupation height index(PHI). PHI = ((#pupae>3 cm)-(#pupae<3 cm))/total # pupae. (BC) Pupation height behavior for ppk1-GAL4/+ control larvae represented by the indicated Pupation Height Index; (B) Pupation height is strongly influenced by external humidity. With constant larval density(50 larvae/vial), low external humidity(25%) causes larvae to pupate at sites lower in the vial indicated as a downward deflection. At higher humidity(50% and 75%), larvae choose to predominantly pupate at higher sites within the vial indicated as an upward deflection. (C) Pupation height is influenced by larval density. With vials grown at constant external humidity(50%), low larval density(25 larvae/vial) causes a low pupation height. Higher larval density causes a drastic increase in pupation height resulting from the altered microenvironment as larvae exit the food source. Error bars represent SEM with n≥15 for all values. ***P<.0001, one-way ANOVA with Tukey posttest.

Mentions: Traditional larval culture vials with moist food at the bottom and a porous plug at the top create an internal microenvironment in which a humidity gradient is generated with a maximum at sites very close to the food surface decreasing to a minimum level at the top of the vial (Fig. 1A). The range of maximum and minimum points of the internal humidity gradient are determined by external humidity and food moisture content. When larval density is kept constant(50 larvae/vial), pupation height is strongly influenced by external humidity (Fig. 1B). This response was represented by a Pupation Height Index(PHI = ((#pupae>3 cm)-(#pupae<3 cm))/total # pupae) calculated using the final pupation position above or below a designated height in the vial(Fig. 1). In graphs of PHI, an upward deflection represents a tendency for pupation higher in the vial and a downward deflection, a preference for sites lower in the vial.


Drosophila nociceptors mediate larval aversion to dry surface environments utilizing both the painless TRP channel and the DEG/ENaC subunit, PPK1.

Johnson WA, Carder JW - PLoS ONE (2012)

Control of pupation height behavior by the internal microenvironment of the culture vial.(A) Schematic representation of a Drosophila culture vial and the internal humidity gradient generated within the microenvironment of the plugged vial. Higher humidity at the bottom near the food surface is indicated as darker shading decreasing to low humidity at the top of the vial. Pupae are shown as black ovals within the designated zones indicated as height(cm) above the vial bottom used to calculate the pupation height index(PHI). PHI = ((#pupae>3 cm)-(#pupae<3 cm))/total # pupae. (BC) Pupation height behavior for ppk1-GAL4/+ control larvae represented by the indicated Pupation Height Index; (B) Pupation height is strongly influenced by external humidity. With constant larval density(50 larvae/vial), low external humidity(25%) causes larvae to pupate at sites lower in the vial indicated as a downward deflection. At higher humidity(50% and 75%), larvae choose to predominantly pupate at higher sites within the vial indicated as an upward deflection. (C) Pupation height is influenced by larval density. With vials grown at constant external humidity(50%), low larval density(25 larvae/vial) causes a low pupation height. Higher larval density causes a drastic increase in pupation height resulting from the altered microenvironment as larvae exit the food source. Error bars represent SEM with n≥15 for all values. ***P<.0001, one-way ANOVA with Tukey posttest.
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Related In: Results  -  Collection

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pone-0032878-g001: Control of pupation height behavior by the internal microenvironment of the culture vial.(A) Schematic representation of a Drosophila culture vial and the internal humidity gradient generated within the microenvironment of the plugged vial. Higher humidity at the bottom near the food surface is indicated as darker shading decreasing to low humidity at the top of the vial. Pupae are shown as black ovals within the designated zones indicated as height(cm) above the vial bottom used to calculate the pupation height index(PHI). PHI = ((#pupae>3 cm)-(#pupae<3 cm))/total # pupae. (BC) Pupation height behavior for ppk1-GAL4/+ control larvae represented by the indicated Pupation Height Index; (B) Pupation height is strongly influenced by external humidity. With constant larval density(50 larvae/vial), low external humidity(25%) causes larvae to pupate at sites lower in the vial indicated as a downward deflection. At higher humidity(50% and 75%), larvae choose to predominantly pupate at higher sites within the vial indicated as an upward deflection. (C) Pupation height is influenced by larval density. With vials grown at constant external humidity(50%), low larval density(25 larvae/vial) causes a low pupation height. Higher larval density causes a drastic increase in pupation height resulting from the altered microenvironment as larvae exit the food source. Error bars represent SEM with n≥15 for all values. ***P<.0001, one-way ANOVA with Tukey posttest.
Mentions: Traditional larval culture vials with moist food at the bottom and a porous plug at the top create an internal microenvironment in which a humidity gradient is generated with a maximum at sites very close to the food surface decreasing to a minimum level at the top of the vial (Fig. 1A). The range of maximum and minimum points of the internal humidity gradient are determined by external humidity and food moisture content. When larval density is kept constant(50 larvae/vial), pupation height is strongly influenced by external humidity (Fig. 1B). This response was represented by a Pupation Height Index(PHI = ((#pupae>3 cm)-(#pupae<3 cm))/total # pupae) calculated using the final pupation position above or below a designated height in the vial(Fig. 1). In graphs of PHI, an upward deflection represents a tendency for pupation higher in the vial and a downward deflection, a preference for sites lower in the vial.

Bottom Line: Transgenic inactivation of mdIV nociceptor neurons resulted in larvae moving inappropriately into regions of low humidity at the top of the vial reflected as an increased overall pupation height and larval desiccation.Transgenic hyperactivation of mdIV nociceptors caused a reciprocal hypersensitivity to dry surfaces resulting in drastically decreased pupation height but did not induce the writhing nocifensive response previously associated with mdIV nociceptor activation by noxious heat or harsh mechanical stimuli.Larvae carrying mutations in either the Drosophila TRP channel, Painless, or the degenerin/epithelial sodium channel subunit Pickpocket1(PPK1), both expressed in mdIV nociceptors, showed the same inappropriate increased pupation height and lethal desiccation observed with mdIV nociceptor inactivation.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Physiology and Biophysics, Roy and Lucille J Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America. wayne-a-johnson@uiowa.edu

ABSTRACT
A subset of sensory neurons embedded within the Drosophila larval body wall have been characterized as high-threshold polymodal nociceptors capable of responding to noxious heat and noxious mechanical stimulation. They are also sensitized by UV-induced tissue damage leading to both thermal hyperalgesia and allodynia very similar to that observed in vertebrate nociceptors. We show that the class IV multiple-dendritic(mdIV) nociceptors are also required for a normal larval aversion to locomotion on to a dry surface environment. Drosophila melanogaster larvae are acutely susceptible to desiccation displaying a strong aversion to locomotion on dry surfaces severely limiting the distance of movement away from a moist food source. Transgenic inactivation of mdIV nociceptor neurons resulted in larvae moving inappropriately into regions of low humidity at the top of the vial reflected as an increased overall pupation height and larval desiccation. This larval lethal desiccation phenotype was not observed in wild-type controls and was completely suppressed by growth in conditions of high humidity. Transgenic hyperactivation of mdIV nociceptors caused a reciprocal hypersensitivity to dry surfaces resulting in drastically decreased pupation height but did not induce the writhing nocifensive response previously associated with mdIV nociceptor activation by noxious heat or harsh mechanical stimuli. Larvae carrying mutations in either the Drosophila TRP channel, Painless, or the degenerin/epithelial sodium channel subunit Pickpocket1(PPK1), both expressed in mdIV nociceptors, showed the same inappropriate increased pupation height and lethal desiccation observed with mdIV nociceptor inactivation. Larval aversion to dry surfaces appears to utilize the same or overlapping sensory transduction pathways activated by noxious heat and harsh mechanical stimulation but with strikingly different sensitivities and disparate physiological responses.

Show MeSH
Related in: MedlinePlus