Steroid Regulation of Cell Populations in the Insect Central Nervous System

I. Metamorphosis as a Context for Studying Hormonal Regulation of the Nervous System Development ...................... 32 A. Definition of Holometaboly (Complete Metamorphosis)..... 32 B. Neurometamorphosis .............................................................. 32

1. Choice of a Model Insect for the Study of Neurometamorphosis .................................................... 33

II. Hormones and Neurometamorphosis ......................................... 33 A. Hormonal Regulation of Insect Metamorphosis ................... 33 B. Insect Steroids — the Ecdysteroids........................................ 33

1. Chemistry............................................................................ 33 2. Juvenile Hormones............................................................. 34 3. Changes in Ecdysteroid Secretion during

Metamorphosis ................................................................... 34 4. Insect Steroid Receptors .................................................... 35

III. Effects of Ecdysteroids on Insect Neurons ................................. 35 A. Neurons as Ecdysteroid Targets............................................. 35

1. Distribution of Neuronal Ecdysteroid Receptors in the

Manduca

CNS........................................................... 35 2. Lability of Neuronal Ecdysteroid Receptor

Populations ......................................................................... 36 IV. Effects of Steroids on Insect Glia during Metamorphosis......... 36

A. Insect Glial Cells ..................................................................... 36 B. Glial Cell Expression of EcR .................................................. 37

1. Description of Ganglionic Fusion in

Manduca

................. 38

2. Evidence for Steroid Regulation of Ganglionic Fusion .................................................................................. 39

3. Proposed Model of Migration and Fusion Events involving Glial Cells .......................................................... 39

V. Summary........................................................................................ 41 A. Glia are Underestimated as Steroid Targets in the

Insect CNS ............................................................................... 41 VI. Acknowledgments ........................................................................ 41

References ............................................................................................... 41

A. Definition of Holometaboly (Complete Metamorphosis)

Many of the major taxonomic groups of insects have a life history in which a quiescent pupal stage separates the larval and adult stages. This phenomenon is referred to as holometaboly or complete metamorphosis.