Stress eating is something many people are familiar with, however, just how the brain links food to emotional states such as fear or anxiety is still not well-understood. Now, a study from researchers at RIKEN-MIT identifies two opposing pathways within the amygdala shown to promote and suppress appetite behaviors, whilst also driving responses to fear-inducing stimuli. The team states their findings build on evidence the amygdala regulates behaviors tied to negative and positive stimuli in a push-pull manner. The study is published in the journal Neuron.
Earlier studies from the lab identified neurons in the amygdala tied to positive and negative memories. Therefore, the group expanded mapping of this circuitry between the basolateral and central regions of the amygdala, to reveal how these limbic system projections are highly similar to cortico-striatal ones promoting and inhibiting movement. The current study shows the primary function of the central amygdala is for reward-related behaviors, rather than for fear-related behavior, as was believed for many years.
The current study uses optogenetics, a method for manipulating genetically tagged cells with light, to identify complex interactions between the seven genetically distinct types of neurons in the central amygdala known to promote or extinguish reward-seeking behavior in mice. Results show the previously reported negative and positive neurons of the basolateral amygdala were found to feed into three central amygdala zones. Data findings show the seven neuron types also had different patterns of activation in response to opposite appetite and threatening stimuli, such as unlimited food versus food deprivation, or foot shocks versus no shocks.
The goup explains the negative and positive neurons, identified by their expression of the genes Rpso2 and Ppp1r1b, mediate pathways that suppress or promote appetite behaviors. They go on to add the neurons expressing the gene Prkcd emerged as essential for regulating defensive behaviors, and that separate groups of these neurons in the capsular and lateral nuclei of the central amygdala act in opposition to inhibit or promote freezing in response to foot shocks. It was also observed another subtype of neurons expressing the gene Drd1 was shown to be critical for feeding and drinking behavior in the central amygdala.
The team surmises their study identifies genetically defined neural circuits in the amygdala promoting and suppressing appetite behaviors in mice. For the future, the researchers state their findings are a further indication different parts of the brain may be organized along with common developmental principles.
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