Novel methods for analyzing neural circuits for innate behaviors in insects — ScienceDaily

Insects show a variety of specific types of innate behavior (instinct behavior). For example, worker bees who have found nectar exhibit an 8-shaped swing dance when returning to their beehive. Male moths that have detected sex pheromones fly to find female counterparts. There are still many problems with how the function of the neural circuits in the insect brain produces various innate behaviors.

In order to obtain a complete picture of the neural circuit and its functions responsible for innate behavior, it is necessary to reveal the neural circuits that are activated in the event of an innate behavior. There is also a need for a method that can control insect behavior by manually manipulating the activity of the neural circuit.

The current research team at Kanazawa University has been actively involved in the study of neural circuit function, focusing on the expression of genes that occur in a manner dependent on neural activity. Previously, the team identified a transcription factor gene hormone receptor 38 (Hr38) * 1), which is expressed in insect brains in a neurally active manner and found to be useful for neural activity. mark.

In this study, the team used Drosophila ( Drosophila melanogaster ) to mimic insects to produce a transgenic strain that accurately reflects the expression pattern of Hr38 . One method that specifically displays active neurons by labeling them with green fluorescent protein (GFP) 2). Using this method, they revealed a complete picture of the neural circuits of the male fruit fly in the brain and ventral nerve cords* 3) When male flies interact with female flies. It is well known that the sexually determined gene has no results and doublesex determines the neurological gender of the Drosophila brain and the ventral nerve cord, which are responsible for the development of male and female neural circuits. In this study, the team specifically applied their method to the neural circuit that expresses no results or doublesex . This reveals the active neural circuit within the male neural circuit during the courtship behavior. It was found that in addition to the known neural circuits that are important in regulating mating behavior, the group also found that the plexus aSP2, especially when male flies interact with female flies.

In addition to the visualization of neural circuits activated during behavior, it is important to be able to manipulate neural circuit activity in a desired manner to reveal neural circuit function. Thus, this group produced a Drosophila strain that can express CsChrismon, a photoactivated channel rhodopsin* 4), in place of GFP, in an activity-dependent manner. Male flies of the strain were allowed to mate with female flies; the next day, after removal of the female flies, individual male flies were illuminated. Although male flies do not have any female flies, they show typical abdominal curvature of mating behavior. This indicates that the neural circuit activated during the previous day of mating can be reactivated by light after one day.

In addition, the team analyzed the effect of the neural cluster aSP2 on mating behavior. A detailed analysis of the courtship behavior of male flies with suppressed aSP2 neural activity indicates that male fruit flies approach female flies in a normal manner but often interrupt courtship; as a result, the mating success rate is greatly reduced. In the courtship of fruit flies, male fruit flies are close to the female's continuous dynamics and may be reluctant at first, which is important for females to receive mating. The current results indicate that the neural cluster aSP2 plays an important role in the regulation of motivation in courtship behavior.

This study is the first to establish a method for observing neural circuits and manipulating their activities in an insect-dependent manner. These methods should be applied to the elucidation of neural circuits and their role in the innate behavior of insects. Understanding the neural basis of insect congenital behavior is not only important in basic science, but also helps to effectively use beneficial insects such as bees and silkworms, get rid of harmful insects, prevent the spread of diseases such as malaria, and dengue fever, Zika fever and other mosquito-mediated . This study identified the neural cluster aSP2 as an important neural circuit for insect behavioral motivation. Further research into the mechanism of how the aSP2 neural circuit controls motives is expected to allow for the clarification of the basic regulatory mechanisms of innate behavior in the insect brain.


* 1) Hormone receptor 38 ( Hr38 ) One of the nuclear orphan receptors of insects. In 2013, the research team identified this gene expressed in the insect brain in a neural activity-dependent manner and can be used as a marker gene for neural activity.

* 2) Green Fluorescent Protein Green Fluorescent Protein (GFP) was originally discovered in the 2008 Nobel Prize-winning Nobel Prize winner Osamu SHIMOMURA's luminescent jellyfish Aequorea victoria . Light, it emits green fluorescence. For example, GFP is widely used for visualization of nerve cells.

3459004 * 3) The ventral nerve cord is the insect nerve region corresponding to the spinal cord of the vertebrate. It is found in the chest of the fruit fly and consists of nerve cells that are used to transmit sensory information to the brain and the brain's commands to the muscles.

4459004 * 4) Channel rhodopsin rhodopsin is a light-driven ion channel originally found in unicellular green algae, Chlamydomonas reinhardtii . The channel is tuned to turn on/off by light, so when it is expressed in nerve cells, nerve activity can be modulated by light.

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