Work done in the lab of Prof Nitin Gupta in the Department of Biological Sciences and Bio-engineering at the Indian Institute of Technology Kanpur, India.
Dr. Pranjul Singh pursued her Ph.D. at the Indian Institute of Technology, Kanpur, under the guidance of Dr. Nitin Gupta in the Department of Biological Sciences and Bio-engineering. Her research focused on comprehending the encoding of ecologically relevant odors in the mosquito brain. Prior to embarking on her doctoral journey, Dr. Singh obtained a B.Tech degree in Biotechnology from Motilal Nehru National Institute of Technology, Allahabad, India. Following the successful completion of her Ph.D., she joined as a post-doc in Dr. Evan Feinberg’s lab at the University of California, San Francisco. In the future, Dr. Singh aspires to become an independent neuroscientist, conducting impactful research and actively promoting the inclusion of women and underrepresented communities in science.
Author Interview
How would you explain your research outcomes to the non-scientific community?
Mosquitoes kill more humans than any other insect species in the world. Female mosquitoes of several species, including Aedes aegypti, require a blood meal to produce eggs and thus act as a vector for deadly diseases like dengue fever and malaria. Mosquitoes rely majorly on their sense of smell to identify humans for blood feeding. Thus, the mosquito olfactory circuit is an attractive target for interventions to prevent the spread of mosquito-borne diseases. Mosquitoes can detect a wide range of odors that can trigger specific behaviors, such as attraction or aversion. For instance, female mosquitoes are drawn to the scent of human skin while repelled by odors like citronellol present in many herbs. Within the odor sensing part of mosquito brain, antennal lobe, a population of neurons called projection neurons (PNs) receive odor information from the sensory neurons and carry this information to higher brain regions that are involved in generating olfactory behaviors. Interestingly, PNs are not just relaying neurons but can encode odor identity and its behavioral significance. However, the representation of ecologically relevant odors in PN activity varies, as certain odors are encoded by dedicated PN types (labeled line model) while others are represented by a combination of different PN types (combinatorial code). Due to a lack of specific genetic and electrophysiological tools, it has been challenging to investigate how odors are encoded and processed in the mosquito antennal lobe. To overcome the existing technical barrier in the field, I developed the application of a technique called in-vivo patch clamp electrophysiology to record the activity of mosquito antennal lobe neurons. In this experimental setup, adult female Aedes aegypti mosquitoes were immobilized within a custom-made recording chamber. This allowed us to expose the mosquitoes’ olfactory organs to various odors (including human and plant-derived odors and commercially used repellents) while providing access to the brain for recording purposes. Consequently, we were able to target individual neurons in the mosquito antennal lobe, observe their activity in response to a range of odors, and visualize their morphology by injecting dye into the recorded neurons.
From a total of about 1250 mosquito preparations, we successfully obtained recordings and morphological identification from approximately 260 antennal lobe neurons. Using this unprecedented dataset, we characterized the morphological and electrophysiological properties of the mosquito antennal lobe neurons. We observed that a given odor could activate multiple PNs, and multiple odors activated a given PN. Through a detailed analysis of PN activity, we discovered that each odor generates a unique pattern of PN population activity, enabling the distinction of odor identities within a few hundred milliseconds of odor encounters. Using a classification accuracy analysis, we were able to correctly classify odors based on the PN activity. The ability to discriminate different odors increased with the number of PNs analyzed. These results support the idea of a combinatorial code for odor representation in the mosquito brain. To further investigate the relationship between PN population responses and the behavioral preferences of mosquitoes, we developed a customized T-maze behavioral assay. This assay allowed us to assess the attractiveness and aversiveness of odors at the same concentrations used in the electrophysiological recordings. By comparing the neuronal and behavioral responses elicited by odors, we discovered that odors evoking similar behaviors also generated correlated PN activity. This suggests that the behavioral significance of odors is reflected in the patterns of PN activity they generate. These findings lay the groundwork for understanding how behaviorally relevant odorants are processed in the mosquito brain and may fuel efforts to develop new mosquito repellents to prevent disease transmission.
“The insights gained from this research have the potential to guide the future development of innovative approaches to mosquito control.”
How do these findings contribute to your research area?
This study establishes a viable setup for studying the antennal lobe neurons in mosquitoes and presents the first detailed account of the morphological, physiological, and functional properties of mosquito antennal lobe neurons. It was commonly thought in the field of insect olfaction that behaviorally significant odors are encoded by dedicated pathways in olfactory circuits. In the absence of knowledge of the organization and the activities of antennal lobe neurons in mosquitoes, earlier studies have favored this model. However, the findings of this study change this view and show that odors are represented by the population of projection neurons rather than specific neurons. Moreover, the physiological and morphological characterization of antennal lobe neurons laid out in this study establishes a solid foundation for future investigations. Many researchers in entomology, vector biology, and neuroscience communities will consider these results valuable. The insights gained from this research have the potential to guide the future development of innovative approaches to mosquito control.
What was the exciting moment during your research?
Performing in-vivo patch clamp electrophysiology for small neurons (such as mosquito olfactory neurons) poses a notable challenge as it requires a highly delicate sample preparation, and even the slightest vibrations can derail the experiment. So, I will never forget the day when I successfully recorded the first antennal lobe neuron. I called every lab member to my workbench to show what I recorded. Nitin gave me a high-five and said that I might be the first person in the world to do this. What an exciting moment it was! Another particularly thrilling moment was when I was recording from two different neurons at the same time and observed that the activity in one cell influenced the activity in the other. It was like witnessing two neurons’ talking.’ As discussed in the paper, the simultaneous recordings obtained from these two neurons indicated the presence of excitatory lateral connections within the mosquito antennal lobe.
What do you hope to do next?
As an aspiring neuroscientist, my interest lies in the field of systems neuroscience, which focuses on understanding the complex workings of the brain. My doctoral work has significantly advanced my knowledge of how sensory information is processed in neural circuits and intensified my curiosity about the ability of the brain to transform sensory inputs into behavioral outputs. I am currently working as a post-doc in Dr. Evan Feinberg’s lab at the University of California, San Francisco. During my post-doctoral training, I will use the genetically tractable mice model to study the complex neural circuits that generate goal-directed behaviors such as gaze shifts.
Where do you seek scientific inspiration from?
Every day, I find inspiration in the things I see around me. It’s fascinating to observe various organisms, from small insects to larger animals, engaging in different behaviors. Some behaviors seem straightforward, like fruit flies getting attracted to a fruit odor, while others seem more intricate, like dogs learning a trick. These observations ignite my curiosity and make me wonder: how does our brain control and coordinate our behaviors? What processes occur inside our minds that enable us to move, think, and interact with the world? Exploring these questions motivates me to delve deeper into the study of neuroscience, seeking to understand the mysteries of the brain.
How do you intend to help Indian science improve?
It is very inspiring to see that the scientific landscape in India is undergoing a remarkable transformation with a surge of cutting-edge research emerging from Indian laboratories. My aspiration is to become a principal investigator, leading an independent research lab in India. In pursuit of this career goal, I am driven to contribute to the Indian scientific community in various impactful ways. Creating an inclusive and diverse scientific community within my lab that values different perspectives and fosters critical thinking is one of my top priorities. Furthermore, I am deeply passionate about science collaborations and outreach. By actively collaborating with fellow researchers, both within India and internationally, we can leverage collective expertise, exchange ideas, and share resources to accelerate the progress of Indian science.
Reference:
Singh P, Goyal S, Gupta S, Garg S, Tiwari A, Rajput V, Bates AS, Gupta AK, Gupta N. 2023; Combinatorial encoding of odors in the mosquito antennal lobe. Nature Communications. https://doi.org/10.1038/s41467-023-39303-w
Edited by: Pragya Gupta