Summary: Scientists have completed the first full connectome of the adult fruit fly, including both the brain and ventral nerve cord, revealing how neural signals travel between these two structures. This breakthrough uncovers never-before-seen neurons in the neck that transmit brain commands to the body.
By comparing male and female connectomes, researchers also identified sex-specific neurons and circuits, offering insight into distinct behaviors such as mating and egg-laying. The study provides a neural roadmap for future experiments and marks a major leap in understanding how complex behaviors are hardwired in the insect brain.
Key Facts:
- First Full Connectome: Includes both brain and ventral nerve cord in Drosophila.
- Sex-Specific Neurons: Researchers found neurons present in only one sex.
- Behavioral Insight: Connectome differences explain sex-specific actions like mating and egg-laying.
Source: University of Leipzig
For the first time, researchers at Leipzig University and other institutions have gained comprehensive insights into the entire nervous system of the fruit fly (Drosophila melanogaster).
The findings were recently published in Nature, marking the first study to describe in detail the neurons that span the entire nervous system of the adult fruit fly.
The researchers also, for the first time, compared the complete set of neural connections (the connectome) in a female and a male specimen – and identified differences.
“At present, there are only a few electron microscopy data sets of the fruit fly’s connectome.
“None of them has so far included the entire central nervous system – that is, both the brain and the ventral nerve cord, the functional equivalent of the vertebrate spinal cord. Until now, the data sets have ended at the neck due to technical limitations,” explains lead researcher Dr Katharina Eichler from Leipzig University, describing the current state of research.
However, the neurons that run through the neck connective – the link between brain and nerve cord – are essential for transmitting the decisions made in the insect’s brain. These neural circuits have so far remained unknown.
“We have now identified these neurons in three connectomes and analysed their pathways. We studied one female brain data set as well as a male and a female nerve cord data set,” says Eichler, who previously conducted research on the topic at the University of Cambridge before continuing her work at Leipzig University.
The paper describes all the neurons in the neck of the fruit fly that could be identified using light microscopy data. This allowed the researchers to analyse the circuits formed by these cells in their entirety.
When comparing male and female neurons, the scientists identified sex-specific differences for the first time.
Previously unknown cells were found that exist only in one sex and are absent in the other.
The researchers also discovered that a descending neuron known as aSP22 communicates, in females, with neurons that are present only in females.
This finding provides the first explanation for the behavioural differences observed when this neuron is active.
Female flies extend their abdomen, probably to lay eggs, while males curl theirs forward in order to mate.
“The study provides an overview of the entire fruit fly connectome. It serves, in a sense, as a kind of roadmap that scientists can use for orientation.
“Based on this, experiments can be intelligently designed to investigate the function of individual neurons or entire circuits – saving considerable time and resources,” explains the biologist.
Now that the technical challenges in analysing the fruit fly’s nervous system have been overcome, Katharina Eichler’s research group is working on two new data sets covering the entire central nervous system of both a female and a male specimen.
About this brain mapping research news
Author: Susann Sika
Source: University of Leipzig
Contact: Susann Sika – University of Leipzig
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Comparative connectomic atlas of Drosophila descending and ascending neurons” by Katharina Eichler et al. Nature
Abstract
Comparative connectomic atlas of Drosophila descending and ascending neurons
In most complex nervous systems there is a clear anatomical separation between the nerve cord, which contains most of the final motor outputs necessary for behaviour, and the brain.
In insects, the neck connective is both a physical and an information bottleneck connecting the brain and the ventral nerve cord (an analogue of the spinal cord) and comprises diverse populations of descending neurons (DNs), ascending neurons (ANs) and sensory ascending neurons, which are crucial for sensorimotor signalling and control.
Here, by integrating three separate electron microscopy (EM) datasets, we provide a complete connectomic description of the ANs and DNs of the Drosophila female nervous system and compare them with neurons of the male nerve cord.
Proofread neuronal reconstructions are matched across hemispheres, datasets and sexes.
Crucially, we also match 51% of DN cell types to light-level data defining specific driver lines, as well as classifying all ascending populations. We use these results to reveal the anatomical and circuit logic of neck connective neurons.
We observe connected chains of DNs and ANs spanning the neck, which may subserve motor sequences.
We provide a complete description of sexually dimorphic DN and AN populations, with detailed analyses of selected circuits for reproductive behaviours, including male courtship (DNa12; also known as aSP22) and song production (AN neurons from hemilineage 08B) and female ovipositor extrusion (DNp13).
Our work provides EM-level circuit analyses that span the entire central nervous system of an adult animal.
