Genetically-coded brain circuits switch feeding and drinking behaviours on and off in mice.
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 which promote and suppress appetite behaviours, and also drive responses to fear-inducing stimuli. The team states that their findings build on evidence that the amygdala regulates behaviours 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 which promote and inhibit movement. The current study shows that the primary function of the central amygdala is for reward-related behaviours, rather than for fear-related behaviour, as was believed in many previous studies.
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 which promote or extinguish reward-seeking behaviour in mice. Results show that the previously reported negative and positive neurons of the basolateral amygdala were found to feed into three central amygdala zones. Data findings show that 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.
Results show that the negative and positive neurons, identified by their expression of the genes Rpso2 and Ppp1r1b, mediate pathways which suppress or promote appetite behaviours. Data findings show that the neurons expressing the gene Prkcd emerged as essential for regulating defensive behaviours; 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. The lab state that another subtype of neurons expressing the gene Drd1, were shown to be critical for feeding and drinking behaviour in the central amygdala.
The team surmise that their study identifies genetically defined neural circuits in the amygdala which promote and suppress appetite behaviours in mice. They go on to add that the pathway from the basolateral to central amygdala which regulates appetite behaviour has cellular-level similarities with a connection from cortex to the sub-cortical striatum. For the future, the researchers state that their findings are a further indication that different parts of the brain may be organized along common developmental principles.