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Topic 3. Ecdysis triggering hormone

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(Name)

I. MATERIALS.

Tape recording of ETH action on Manduca larvae.

Sample of ETH and injection syringe.

II. LEARNING OBJECTIVES.

Each student should observe and distinguish the various behaviors during ecdysis.

How:

Watch a short lecture on ETH by Professor M.E. Adams (on tape).

Observe ecdysis behaviors after injection of ETH.

III. INTRODUCTION.

December of 1995, a paper was published in Science (see reference below) that described a new endocrine gland in insects, the epitracheal gland. This new organ is unique in many ways. First, it is an endocrine tissue as distinct from nervous tissue. Second it produces a peptide hormone. The other two endocrine glands in insects, the corpora allata and prothoracic glands synthesize lipid hormones juvenile hormones and ecdysteroid hormones respectively. Thus the epitracheal gland is unique in two ways. Here-to-fore only nervous tissues were thought to synthesize peptide hormones, called neuropeptides.

To further complicate the picture revealed by the Science article, Eclosion Hormone, synthesized and released by the insect brain, was originally thought act directly on the ventral nerve cord to induce stereotyped motor nervous impulses that produced the typical eclosion movements of the body. As revealed by the new study, the eclosion hormone was shown to activate the epitracheal glands instead and to have no effect on the ventral nerve cord itself.

The new picture of eclosion, then, has the epitracheal gland releasing the Eclosion Triggering Hormone, ETH, which acts immediately on the ventral nerve cord to produce the highly stereotyped motor program that controls movements that next stage to peristaltically shed the old cuticle.

The epitracheal glands in Manduca sexta larvae responsible for this vital function are comprised of single cells resting on the large tracheal trunks near each of the abdominal spiracles. It is difficult to believe that such a simple structure can be responsible for such an important function.

IV. DIRECTIONS.

Watch the video provided describing ETH. Also watch the tape of eclosion induced by ETH.

In the space below divide the eclosion behavior into time periods and describe the characteristic movements of the larvae during each period.

1. Normal behavior, time = 0.

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2. Preliminary eclosion behavior, time = +___ minutes.

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3. Mid eclosion behavior, time = + ___ minutes.

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4. Late eclosion behavior, time = + ___ minutes.

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V. SUMMARY ANALYSIS.

Describe in your own words what you have learned from this exercise.

VI. REFERENCES.

Zitnan, D., t. G. Kingan, J. L. Hermesman and M. E. Adams. 1996. Identification of ecdysis-triggering hormone from an epitracheal endocrine system. Science 271: 88-91.

Truman, J. W. 1995. Ecdysis control sheds another layer. Science 271: 40-41.

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(Name)

Topic 4