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Optogenetic Insights Mapping functional neural circuits for many behaviors has been almost impossible, so Vogelstein et al. (p. 386 , published online 27 March; see the Perspective by O'Leary and Marder ) developed a broadly applicable optogenetic method for neuron-behavior mapping and used it to phenotype larval Drosophila and thus developed a reference atlas. As optogenetic experiments become routine in certain fields of neuroscience research, creating even more specialized tools is imperative (see the Perspective by Hayashi ). By engineering channelrhodopsin, Wietek et al. (p. 409 , published online 27 March) and Berndt et al. (p. 420 ) created two different light-gated anion channels to block action potential generation during synaptic stimulation or depolarizing current injections. These new tools not only improve understanding of channelrhodopsins but also provide a way to silence cells.

Adult emergence at the end of metamorphosis in the moth Manduca sexta is followed by the death of abdominal interneurons and motoneurons. Abdominal ganglia removed from insects before this period of naturally occurring cell death and maintained in vitro showed neuronal death confined to the same cells that normally die in vivo. Addition of physiological levels of the steroid 20-hydroxyecdysone to the culture system prevented the selective death of these motoneurons.

In the tobacco hornworm, many larval motoneurons become respecified and supply new muscles in the adult. Changes in the morphology of one such neuron were examined through metamorphosis. The dendritic pattern of the adult comes about both by outgrowth from the primary and secondary branches of the larval neuron and by the development of new branches that are unique to the adult.

An adult moth sheds its pupal skin only during a specific period of the day. The brain is necessary for the synchronization of this behavior with the environmental photoperiod. This function is fully preserved when all the brain's nervous connections are severed or when a "loose" brain is transplanted into the tip of the abdomen. By appropriate experiments it was possible to show that the entire mechanism is brain-centered. The components include a photoreceptor mechanism, a clock, and a neuroendocrine output. The clock-controlled release of the hormone acts on the central nervous system to trigger a species-specific behavior pattern which culminates in ecdysis.

The emergence of the adult cecropia silk moth from the pupal skin involves a stereotyped series of abdominal movements-the pre-eclosion behavior. This behavior, triggered by a neurosecretory hormone, consists of three phases that are characterized by the relative frequency and pattern of movements. Electrical recordings from a nerve cord with severed peripheral nerves demonstrate that the pre-eclosion behavior is prepatterned in the abdominal ganglia. In response to the hormone, the entire 1.25-hour behavioral program can be activated and "read off" in the absence of sensory feedback.

When males of the silkmoth Antheraea pernyi were exposed to 12 degrees C diuring adult development and then tested for flight activity at 25 degrees C, the time of the onset of the activity was advanced to the early part of the night. This change in the time of activity was stable and persisted through the life of the moth. Females showed a corresponding shift in the time of sex pheromone release when they were treated in the same fashion.

Two types of cell death occur in the intersegmental muscles of the giant silkmoth Antheraea polyphemus. The first results from a slow atrophy of the fibers, and the second is a rapid, programmed dissolution of the muscle. Both types appear to be mediated by endocrine factors. The slow atrophy is brought about by the decline in the steroid molting hormone 20-hydroxyecdysone and can be prevented with exogenous steroid. The rapid degeneration is triggered by the peptide eclosion hormone, but the sensitivity of the muscle to the peptide depends on the history of exposure of the muscle to 20-hydroxyecdysone.