Findings in fruit flies help to better understand important functions in mammalian brains.
GABAergic neurons are important inhibitory neurons in the central nervous system. In Drosophila brain, a pair of GABAergic neurons form a negative feedback with the learning center neurons, and this recurrent circuit is essential for odour discrimination, which is the base for olfactory learning. Activating these GABAergic neurons negatively regulates olfactory learning, and precise control of the GABAergic activity is vital for learning and memory.
In neural circuits of learning, dopaminergic (DA) neurons usually present the positive or negative values.
In Drosophila aversive olfactory learning, a group of dopaminergic neurons convey the punitive electric shock signal through activating the learning center neurons. In a recent study published in PNAS, scientists from the Institute of Biophysics of Chinese Academy of Sciences reported that the same group of DA neurons form direct synaptic connections with these GABAergic neurons.
Utilising in vivo functional imaging, researchers demonstrated that these DA neurons suppress the latter through inhibitory DA receptor DD2R, thereby restraining the GABAergic inhibition.
The DA-to-GABA regulation releases the restriction on the learning center neurons. More importantly, this regulation is crucial for the eliciting synaptic modification in this circuit. Such modification leads to a change in neural response lasting to post-learning phase, which stands for a memory trace.
Behavioral results showed that defects in DD2R or its downstream molecules lead to impaired learning and memory.
Therefore, this study revealed the neural circuit for precise control of GABAergic neurons and uncovered its important function in synaptic modification during learning and memory formation. It deepened the understanding of neural architecture and circuit mechanism of disinhibition, which may be conserved for associative learning across species.
How the brain achieves efficient learning and memory is one of the most intriguing questions for researchers. It is believed that the neural basis of this function relays on synaptic modification within certain neural circuits. Suppression of inhibitory neurons is known as disinhibition, has also been found to play important functions in mammalian brains. [APBN]