Husna, Amity University Kolkata
A balance of energy is very much essential for survival. Many factors influence the intake of food in our body, not only the caloric need or “hunger” factor. Only some neurons that govern the feeding in mice are known as “hunger neurons,” whereas others are not. There are different neural circuits present in the hypothalamus region of the brain. They can control the stimulus or the interoceptive hunger.
A fundamental challenge of neuroscience is to understand whether behaviour reflects the internal state of an animal. It is a well-understood fact that many behaviours rely on internal feelings. For instance, reflexive withdrawal due to pain or eating when hungry. However, these behaviours are not always unique to the internal state. One might withdraw a hand due to surprise and not only due to pain or one might eat even when not feeling hungry. But again, the lack of a behavioural response does not essentially mean the absence of the internal state. For instance, despite extreme hunger, a boxer might not eat when trying to make a weight class. Also, he might continue a match despite being injured and in physical pain. As specific neural circuits are involved in the control of behaviour, an understanding of them will be required to draw accurate conclusions regarding behaviour.
Recent study:
A recent study by Justin N. Siemian in July 2021 published in Current Biology, introspects the role of specific hypothalamic circuits in controlling the stimulus or interoceptive hunger. In the study, mice were trained in both the fasting period and the satiation period. When the mice were performing the task, three hypothalamic neuronal populations with well-known effects on feeding were manipulated.
Results of the study:
The introspective study on three hypothalamic neuronal populations characterized their specific effects on food intake and their ability to modulate both interoceptive hunger and satiety-like states. It had been found that, within the Sated mice, activation of agouti-related peptide-expressing (ARCAGRP) neurons reported them to be food-restricted, but LHVGAT neuron activation or LH glutamatergic (LHVGLUT2) neuron inhibition didn’t have much effect. However, inhibition of the LHVGAT neuron or activation of the LHVGLUT2 neuron in fasted mice weakened their natural hunger, but inhibition of the ARCAGRP neuron did not affect it here. This shows each neuronal population evoked some distinguishable effects on food consumption and reward. Moreover, manipulations of lateral hypothalamus (LH) circuits had no hunger-like effects in the sated mice; this suggests that their feeding is governed more based on reward, compulsion, or generalized consumption rather than energy balance. It also shows that these LH circuits can be powerful modulators for a negative appetite in the fasted mice. ARCAGRP neurons also had a role in driving calorie-specific food intake. This strongly suggests a role for ARCAGRP neurons in mediating homeostatic feeding and hunger. Hence, this study has highlighted the complexity of hypothalamic feeding regulation which can be used as a framework to characterize how other neuronal circuits affect hunger and it recognizes some potential therapeutic targets that cause eating disorders.
Significance and Conclusion of the study:
The pathway from ARCAGRP neurons to the insular cortex passes through the paraventricular nucleus of the hypothalamus and the basolateral amygdala which indicates that several layers and types of information are integrated together in this system. A characterization of ARCAGRP neurons and LH neuronal subpopulations has revealed how they can affect cortical processing as well as hunger stimuli or interoception. In summary, this was the first study that has used an operant discriminating task for determining the role of specific neuronal circuits for modulating both the interoceptive hunger and the satiety states.
Also read: Role of lysosomes and α-synuclein fibrils in protein misfolding
Source: Siemian, J. N., Arenivar, M. A., Sarsfield, S., & Aponte, Y. (2021). Hypothalamic control of interoceptive hunger. Current Biology, S0960982221008770. https://doi.org/10.1016/j.cub.2021.06.048
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About the Author: Husna is an undergraduate student of BTech Biotechnology at Amity University Kolkata. She is a research enthusiast in Immunology and Immunotherapy but she has a keen interest in various other Bioscience subjects as well. She is constantly focused on improving her knowledge and laboratory skills through various internships. She is a Scientific content writer who has knowledge in diverse backgrounds of Biotechnology.
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