Worm Breeder's Gazette 14(4): 69 (October 1, 1996)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Ligand-gated chloride channel is necessary for correct thermotaxis

Manabi Fujiwara, Takeshi Ishihara, Isao Katsura

Graduate University for Advanced Studies & National Institute of Genetics, Yata 1111, Mishima, Shizuoka 411, Japan

  We are interested in the information processing in neural circuits,
especially the roles of interneurons. To investigate this problem, we
analyzed three of the GABA-A/glycine receptor-like genes found by the
C.elegans genome project, which we named ggr-1, ggr-2, ggr-3 (GABA-A or
glycine receptor-like genes). In vertebrates, both GABA-A and glycine
receptors are ligand-gated chloride channels that generate inhibitory

  We studied the spatial expression patterns, using stable transgenic
strains carrying ggr-GFP fusion genes.  ggr-1 (in cosmid C09G5) is
expressed in neurons including AIB, PVR, PVQ, AVH, SMDV, and some motor
neurons in the ventral cords.  ggr-2 (C45B2) is expressed in neurons
including SMDV, SMDD, SIAV, CAN, HSN, DD, and slightly in egg-laying
muscles.  ggr-3 (F09C12) is expressed in AVA, AVB, SMDD, DVA, SIAD and
some other neurons in the nerve ring.

  To know their roles in behavior, we isolated deletion mutants in those
genes by insertion and imprecise excision of Tc1. Although we performed
assays of many behaviors such as movement, chemotaxis, osmotic
avoidance, mechanosensation, thermotaxis, defecation and male mating
activity, we found no defect in the ggr-3 mutant. However, the mutants
in ggr-1 and ggr-2 showed abnormalities in thermotaxis.
  The ggr-1 mutant usually moves isothermally at a temperature lower
than the growth temperature, i.e., cryophilic(+) as defined by Mori and
Ohshima (Nature 376: 27, 1995). However, although the mutant spends most
of the time in a cold area, it occasionally makes isothermal tracks near
the growth temperature. It looks as if this mutant has two states, and
in a wild-type worm the cryophilic state is repressed by the GGR-1
  Interestingly, ggr-1 is expressed in AIB neuron, which is predicted by
Mori and Ohshima to play a minor role in moving towards a colder
temperature. We think the cryophilic(+) phenotype is caused by abnormal
excitation of AIB due to the lack of the GGR-1 inhibitory receptor.
Consistent with the hypothesis, some of the ggr-1 animals recovered the
correct thermotactic behavior after laser ablation of AIB. However,
since some of the operated animals remained cryophilic, we are now
testing if other cells expressing ggr-1 also affect thermotaxis or if
ablation is incomplete in these animals.
  The ggr-2 mutant shows a slightly cryophilic phenotype without
isothermal tracking: cryophilic(-). We are now investigating which
neuron is responsible for the phenotype.

  We also found that strychnine, an antagonist of the glycine receptors
of vertebrates, makes wild-type worms cryophilic, if it is contained in
the assay plates. Since strychnine in the growth plates  has no effect,
the result may mean that strychnine disrupts the thermoreception or
assessment but not the memory-formation process of thermotaxis. Although
the ligands of GGR-1 and GGR-2 are unknown for the moment, we plan to
examine by cell-ablation whether the target-cells of strychnine for this
effect are those expressing ggr-1 or ggr-2.