Beyond the Paper: A Conversation with Dr. Krishnakanth Kondabolu and Dr. Natalie Doig

Interviewed by Dr. Paige N. McKeon, February 1, 2024

The basal ganglia are a series of subcortical structures that form a feedback loop with the cortex and thalamus to promote or inhibit movement, learning, and emotions. Understanding the anatomy of the basal ganglia and how the structures in it communicate to each other is important for improving treatment outcomes for movement disorders such as Parkinson’s disease or reward-related diseases like addiction, as examples. Most models of basal ganglia organization consider the striatum and subthalamic nucleus (STN) to be the input nuclei of the system, separately innervated by cortex and thalamus with no communication between them. However, in a collaboration between the labs of Tibor Koos and Peter Magill, co-first authors Doig and Kondabolu use whole cell patch-clamp electrophysiology and transsynaptic tracing methods to discover a distinct connection from STN to parvalbumin interneurons in the striatum, thereby revealing that STN can influence internal basal ganglia circuit dynamics.

“I hope the basal ganglia community can extend our findings” -ND

Krishnakanth Kondabolu (left) and Natalie Doig (right)

What drew each of you to pursue this particular line of research?

Krishnakanth: I have always been interested in translational research, and my journey into this particular field began with my fascination for Parkinson's disease (PD) and the intricacies of basal ganglia circuitry.

I was doing research in the laboratories of James Tepper and Tibor Koos at Rutgers University, where the lab utilized electrophysiological and neuroanatomical approaches to unravel basal ganglia circuit connectivity. Our initial research involved conducting retrograde recombinant rabies virus tracing experiments with a focus on striatal interneurons. It was during these experiments that we serendipitously discovered projections from the subthalamic nucleus (STN) to the striatum. Delving into the existing literature, we found previous studies that had described these projections. However, we were determined to leverage whole-cell electrophysiology techniques to gain a more precise understanding of the specific striatal cell types connected to the STN. We discovered that Peter Magill’s lab at Oxford was also doing similar research and had already collected the data for retrograde recombinant rabies virus tracing experiments in striatal interneurons. That sparked a collaboration that resulted in this manuscript.

Natalie: I have always been interested in describing the underlying connectivity of the basal ganglia and associated motor circuits. I believe that a fuller and more detailed understanding of these circuits can provide crucial insight into normal function and the changes underlying diseases.

What are each of your career goals and how have your lab and research experiences shaped these goals? What advice do you have for young research investigators?

Krishnakanth: As I previously stated, my research focus and career goals have always been in translational neuroscience. I am currently pursuing this through my role as a senior research scientist at Harvard University, where I work with a team of scientists to develop novel therapies for central nervous system disorders and to develop a better understanding of the pathophysiology of neurodegenerative disorders. My research experience has been instrumental in shaping my understanding of neural circuits and synapses in health and disease states. I have had the good fortune of having great mentors throughout my academic career and I definitely want to do my part and pay it forward.

My advice to young research investigators is to always pursue their scientific interests and be genuinely curious about their research questions. A deep interest in the field can motivate you to overcome the challenges along the way. And seek out mentors who can guide you in your career.

Natalie: That is a big question. I love doing lab-based scientific research and I very much enjoy my current role as a postdoctoral researcher for the moment. Honestly, I am not sure what the future holds for me. Recently I have moved from doing wet lab work to mainly doing data analysis which has been a surprisingly rewarding change. A benefit is that data analysis is more flexible and that is a big bonus for me as I recently had my second child.

I encourage young researchers to seek out experiences in many different labs, gaining exposure to as many techniques as possible to try and find their passion. Learning as many skills as possible also benefits you by giving you more options in the future.

“I have had the good fortune of having great mentors throughout my academic career and I definitely want to do my part and pay it forward.” -KK  

What was it like collaborating together as co-first authors on this publication?

Krishnakanth: I have been lucky to have this collaboration with Peter Magill and Natalie Doig as they have been instrumental in getting this manuscript across the finish line. The data were collected using two different techniques: whole-cell electrophysiology and monosynaptic circuit tracing using recombinant rabies virus. I was responsible for the electrophysiology experiments and Natalie performed the virus tracing experiments. There were some incongruencies in the results between these two experiments that we needed to address. Natalie’s insight and knowledge about the basal ganglia were pivotal in bridging these incongruencies and making sense of the data.

Natalie: This was a great and serendipitous collaboration – I presented some research using techniques similar to those used in this paper at a conference, and a former colleague of mine who worked in the same institution as Krishnakanth at the time told me about the research that Krishnakanth was carrying out in Tibor Koos’ lab. They had similar findings to us using different techniques including whole-cell electrophysiology. This was very exciting, and we got in touch straight away and fortunately they were keen to collaborate. A lot of the hard work to put this paper together happened during COVID lockdowns - so Krishnakanth and I spent time discussing the data over Zoom which was great!

Did the outcomes of the experiments in this paper surprise you? What challenges or surprises did you run into along the way?

Krishnakanth: The outcomes of this study were definitely a surprise! I had initially thought that we had discovered a novel connection in the basal ganglia. Much to my surprise these connections were previously discovered decades ago! The novelty of our manuscript is parsing out the specificity of these connections as they were not previously described. I had expected more promiscuous connectivity between the STN and the spiny projection neurons that represent about 95% of neurons in the striatum. However, we show a more selective innervation to a specific subtype of striatal interneurons, the parvalbumin (PV) interneurons. This direct connectivity from STN to PV interneurons provides a feedback circuit relaying STN dynamics back to the striatum.

Some of the challenges involved putting the manuscript together, as it was written during the COVID lockdown, which involved many Zoom meetings.

Natalie: Yes, the outcome of this study did surprise me. We found that there is a selective projection from STN to the striatum, using transsynaptic tracing methods (done mainly by myself and other members of the Magill Lab) and electrophysiology (done by Krishnakanth and the Koos Lab). This was surprising for two reasons: 1) the STN à striatum projection has been described previously, but we had to trawl through the literature to find the original studies. It is still largely ignored – you do not see it on any classical diagrams of basal ganglia connectivity. And 2) we found that the STN-striatal projection selectively innervates PV-expressing interneurons, using both anatomical and electrophysiological techniques. As far as I am aware, this is a novel finding. The selectivity of the pathway is very striking, as both the anatomy and physiology illustrate.

One of the biggest challenges along the way was probably putting this together during COVID – although it was good to have something to work on. I then had my first child at the end of 2020, so things have gotten delayed along the way! It is great to have it out there, and I hope the basal ganglia community can extend our findings.

In each of your opinions, what is/are the most valuable contribution(s) of this paper to the field and where do you see the project going?

Krishnakanth: This paper adds to the diversity and complexity of the basal ganglia circuitry. We shed new light on the synaptic connections of the STN on striatal neurons by selectively innervating PV-expressing interneurons.

STN is one of the targets for deep brain stimulation in patients suffering from Parkinson’s disease. These circuit mappings could help in developing a better understanding of the mechanisms through which deep brain stimulation achieves its therapeutic benefit. This STN-striatal circuit could also have implications in the hyperdirect pathway, where cortical activation of the STN neurons could send rapid action potentials that could then interfere with subsequent/ongoing striatal dynamics.

Natalie: The most valuable contribution of this manuscript is the detailed description and demonstration of the selective projection from the STN to PV interneurons of the striatum using multiple complimentary techniques. This provides a mechanism whereby the STN can rapidly alter the ongoing processing of the striatum and thus modulate internal basal ganglia dynamics. To further this work, it would be interesting to see what manipulation of this pathway does in vivo and how it affects behavior. A computational study by Adam et al., (2022; DOI: 10.1073/pnas.2120808119) looked at how this pathway could play a pivotal role in the efficacy of deep brain stimulation, so it would be very exciting to follow up this finding in vivo in an animal model of PD.

If I had the time, I would love to look at the finer details of the synaptic connectivity within the striatum using electron microscopy. I would predict, from the electrophysiology results, that the glutamatergic terminals from the STN might form multiple synapses onto the PV interneurons and/or the synapses are located somewhere where they can have the most effect such as on the soma.

“These circuit mappings could help in developing a better understanding of the mechanisms through which deep brain stimulation achieves its therapeutic benefit.” -KK

How was your experience with the eNeuro review process? How did it compare other publication experiences you each have had?

Krishnakanth: The review process at eNeuro was really transparent and fair with a quick turnaround time. The editor's response summarizing the reviewer comments was especially helpful in consolidating all the feedback and streamlining the response. The open access nature of eNeuro, along with its affiliation to the Society for Neuroscience, makes publishing even more appealing.

Natalie: The experience at eNeuro was very good – it was very efficient and transparent. We greatly appreciated that they extended deadlines for us to get the paper back to them. I also believe that it is important for us as scientists to support our Society owned Journals, as we know how important the work that the Society for Neuroscience is for our community.

Read the full article:

A Selective Projection from the Subthalamic Nucleus to Parvalbumin-Expressing Interneurons of the Striatum
Krishnakanth Kondabolu, Natalie M. Doig, Olaoluwa Ayeko, Bakhtawer Khan, Alexandra Torres, Daniela Calvigioni, Konstantinos Meletis, Tibor Koós, and Peter J. Magill