Saakshi Bangera, DY Patil School of Biotechnology and Bioinformatics
Animals are constantly required to make crucial behavioural choices to survive in the ever-changing environment. A significant amount of these decisions is binary. For instance, on discovering a food source, the organism can choose to pursue it or ignore it. However, environmental conditions and internal drives often stimulate incompatible behaviour. For instance, the organism may make incompatible choices if faced with the option of choosing one between hunger and threat avoidance. It is crucial to understand how specific actions are prioritized in the brain.
Findings of the studies conducted so far
According to invertebrate studies, behavioural selections are achieved by reciprocal inhibition between neurons that control mismatched behaviour. For example, neurons of the feeding network in sea slugs suppress withdrawal command neurons. This promotes feeding instead of escape responses. Multifunctional neurons are known to be able to mediate behavioural decisions. For instance, in leeches, swimming and crawling behaviours are partly controlled by overlapping central pattern generator interneurons.
In Drosophila, neurons mediate the choice between competing behaviours. Coordination between feeding and walking behaviours depends on a single pair of interneurons present in the ventral nerve cord. The activation of these neurons suppresses feeding while the fly is walking. On the contrary, inhibition of these neurons induces feeding behaviour at the expense of locomotion. Food-deprived flies give up sleep to favour feeding. This behaviour is mediated by the activation of allatostatin-A that promotes sleep and inhibits feeding. Neuronal modulation under the state of deprivation involves different subsets of dopaminergic neurons. A significant behavioural conflict arises when an animal lacks both food and sex. Under such circumstances, the organism must decide its priority. However, it is unclear if reproduction can override hunger under certain situations.
Male fruit flies exchange a variety of sensory cues during a courtship ritual and evaluate the suitability of a potential mate. They find sex rewarding and are highly motivated towards the act. Neurons expressing the sex determination genes receive, process, and transfer information that mediates male courtship. Approximately 20 male-specific P1 neurons control the initiation of courtship in response to sensory signals.
Drosophila feeding behaviour consists of several cycles of food-seeking and consumption. Detection of food and subsequent feeding is commenced by the activation of gustatory neurons on the fly’s proboscis and legs. Dopamine, neuropeptide F, and insulin-like peptides play an important role in developing the feeding response for the nutritional status of the fly. Satiety signals dismiss feeding.
Findings and conclusion of the study
In this study, an assay was established to understand the neuronal mechanisms that allowed Drosophila to choose between feeding and courtship. The flies were observed to prioritize feeding over courtship. Tyramine signalling was found to be an important mediator of Drosophila’s choice. Tyramine antagonistically modulated feeding-promoting tyramine receptor (TyrR) neurons and courtship-promoting P1 neurons. This modulation matches the fly’s behaviour with starvation state and food availability. In C. elegans, tyramine signalling plays a significant role in hunger-dependent decision making. This suggests that several components of decision-making circuits are conserved across animal species. A functional analogue of tyramine, norepinephrine has been found to mediate food intake and some control of reproductive behavioural choices. Biogenic amines may control neuronal pathways as such to facilitate behaviour in mammals.
Also read: DNA methylation and early pregnancy: An epigenetic study
Reference
Cheriyamkunnel, S. J., Rose, S., Jacob, P. F., Blackburn, L. A., Glasgow, S., Moorse, J., Winstanley, M., Moynihan, P. J., Waddell, S., & Rezaval, C. (2021). A neuronal mechanism controlling the choice between feeding and sexual behaviors in Drosophila. Current Biology, S0960982221009842. https://doi.org/10.1016/j.cub.2021.07.029
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About the author: Saakshi is currently pursuing MSc in Biotechnology from DY Patil School of Biotechnology and Bioinformatics. She believes that she doesn’t have a specific area of interest yet. She wishes to explore toxicology and food biotechnology. She’s quite passionate about Biotechnology and aims to grab every opportunity she comes across.
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