Relationship between general anesthesia and memory in Drosophila involving the cAMP/PKA pathways and adhesion-related molecules.

On undergoing an operation under general anesthesia, we tend to lose consciousness, and on recovering from the anesthetic effect, we realize a memory loss during the operation, but do remember the happenings before the operation. It implies that the anesthesia deprivers us of short-term memory without affecting long-term memory. Drosophila melanogaster is known to be an excellent model for genetic studies related to general anesthesia and memory. The various mutants in the genes related to general anesthesia and memory have been found to influence these mechanisms at the molecular level. In Drosophila, learning and memory are classified into four distinct phases: (1) short-term memory (STM), (2) middle-term memory (MTM), (3) longer-lasting anesthesia-resistant memory (ARM), and (4) long-term memory (LTM). On the other hand, based on the genetic studies of the putative target molecules of general anesthetics in model animals, the anesthetic action is classified into five pathways: (1) presynaptic pathway including action potential production, its transmission, and neurotransmitter release; (2) postsynaptic pathway including inhibitory receptors for sleep and pain; (3) memory pathway coupled with cAMP/PKA signaling; (4) adhesion pathway in neuron; and (5) energy production pathway. Memory and adhesion pathways of the anesthetic action are developed in the Drosophila melanogaster model. Many mutants of general anesthesia and those of memory are overlapped suggesting that common molecules and signal pathways are involved in both phenomena. In this review, we will describe the relation between anesthesia and memory, especially highlighting the interaction between the general anesthetics and STM and MTM processes in Drosophila, especially concentrating on the cAMP/PKA signaling and molecular adhesion pathways.

Patterning cultured cells by visible light illumination with photosensitizers.

We showed that PC12 cells and 3T3 cells cultured in dishes were killed by illumination with visible white light from a halogen lamp at 7 x 10(4) lx for 5 min in the presence of either 10 microM hematoporphyrin or 2 microM methylene blue as a photosensitizer. This simple technique, based on the photodynamic reaction via generation of reactive oxygen species can be applicable for patterning cultured cells.

Studies on target genes of general anesthetics.

Generally speaking, we cannot fully understand the mechanisms of general anesthesia until the molecular mechanisms of consciousness are fully elucidated. Loss of consciousness induced by general anesthetics might involve sensation, motor activity, behavior, memory and self-consciousness. The effects of many anesthetics are not limited to humans but also extend to the animals. Similar levels of minimum anesthetic concentrations are required to induce anesthesia in animals and human, i.e., the minimum alveolar concentration (MAC). Such similarity probably reflects identical anesthetic target molecules and functional conservation based on gene conservation. Thus, to study the mechanisms of anesthetic action, various animal models that are accessible to genetic manipulation, such as nematodes (Caenorhabditis elegans), fruit flies (Drosophila) and mice can be used. Genetic techniques allow for the rapid identification and characterization of genes involved in the actions of general anesthetics. In this review, I will describe the genetic mutations and putative target genes of general anesthetics.

Calreticulin mediates anesthetic sensitivity in Drosophila melanogaster.

BACKGROUND: Various species, e.g., Caenorhabditis elegans, Drosophila melanogaster, and mice, have been used to explore the mechanisms of action of general anesthetics in vivo. The authors isolated a Drosophila mutant, ethas311, that was hypersensitive to diethylether and characterized the calreticulin (crc) gene as a candidate of altered anesthetic sensitivity. METHODS: Molecular analysis of crc included cloning and sequencing of the cDNA, Northern blotting, and in situ hybridization to accomplish the function of the gene and its mutation. For anesthetic phenotype assay, the 50% anesthetizing concentrations were determined for ethas311, revertants, and double-mutant strains (wild-type crc transgene plus ethas311). RESULTS: Expression of the crc 1.4-kb transcript was lower in the mutant ethas311 than in the wild type at all developmental stages. The highest expression at 19 h after pupation was observed in the brain of the wild type but was still low in the mutant at that stage. The mutant showed resistance to isoflurane as well as hypersensitivity to diethylether, whereas it showed the wild phenotype to halothane. Both mutant phenotypes were restored to the wild type in the revertants and double-mutant strains. CONCLUSION: ethas311 is a mutation of low expression of the Drosophila calreticulin gene. The authors demonstrated that hypersensitivity to diethylether and resistance to isoflurane are associated with low expression of the gene. In Drosophila, calreticulin seems to mediate these anesthetic sensitivities, and it is a possible target for diethylether and isoflurane, although the predicted anesthetic targets based on many studies in vitro and in vivo are the membrane proteins, such as ion channels and receptors.