And I'd like to ask the first speaker to come to the podium. Zi Huang is going to talk to us about GABAergic Basal Ganglia Output Modulates Tonic and Burst Modes of Thalamic Neurons. All right. Hello. Good afternoon. So my name is Zi. I am a third year medical student at VCU School of Medicine. So in this room, I'm probably the least clinically knowledgeable person, almost. But I'm here to talk about the relationship between basal ganglia and thalamus in dystonic models in rodents. All right. So this picture, for me, is a little nostalgic. I took my step one exam about seven weeks ago. So the importance here is that the GPI is known to, according to the classical model, have a relationship with the via thalamus to influence the thalamocortical drive for movement. But what we observed in rodents is that dystonic movement is correlated with the increased GPI neuron activity. So then we took a closer look at their relationship. And to establish the pathway that we're looking at, we're going to be looking at the EP VL M1 pathway. So for those who is not aware, the EP is the GPI in humans. So in rodents, the EP, via thalamus, and the M1 cortex. So if we injected a recombinant VSV into a dystonic hot spine GP, waited two to four days, and then perfused the rodents, and then did immunohistochemical staining on the brain slices, we would see fluorescence in the EP up here at the top, and then also the via thalamus right here, and the M1 cortex as well. And to know where we are in the brain when we do these injections, we basically record neuron activity using micropeptides. And then using correlation with the atlas, we can estimate where we are. And this is confirmed by histological staining. All right, so with the micropeptides, we can then take the recording and then categorize them into different discharge behaviors. So I know it's a little difficult to see. I was sitting in the back earlier. So I've expanded the legend over here. In blue are the percentage of neurons that behave in a tonic firing pattern. In red are the percentage behaving in a bursty firing pattern. And the yellow is non-stationary. It does not quite fit into either categories. And so if you focus over here on normal, N stands for normal, up here are all the neurons that were recorded in EP, which again is GPI. 98% of the neurons are firing in a constant tonic fashion. And we think that as a result of that, the VL thalamus, a majority, is firing in a bursty pattern. The opposite is true in dystonic models. So we have two here. K stands for conicterus. So these are the bilirubin encephalopathy model of dystonia. L stands for lesion, when we inject a neurotoxin into a dystonia hotspot in GP. Behaviorally, they look almost the same. They both have truncal posturing, as well as extended limb. And the neuronal behavior is also very identical. So as I said earlier, so these are almost opposite. A great number of the neurons are now in GPI behaving in a bursty pattern. And as a result, we think that because of that modulation, the VL thalamus, a great majority is now behaving in tonic firing pattern. And so to look at this more closely, we recorded neuronal activity in the EP, while at the same time, in the VL thalamus, I'm sorry, at the same time we injected neurotoxin into the EP. The injection lasts 10 minutes. Five minutes into the injection, you can see that the VL thalamus burstiness is already decreasing, fluctuating between tonic firing and burst firing mode. And then by the time we finish injection, and for the next five minutes of the recording, it reached a plateau and behaves in a tonic firing pattern. And this is what you would see when you record the neurons. On top is what we would categorize as a normal burst mode in the VL thalamus. On the bottom is after the neurotoxin injection. And for the next five minutes recording, we would see sort of a tonic firing behavior. And another way to look at the same relationship is with optogenetic manipulation. So after we injected inhibitory opsins and then waited 10 days for transfection, and then recorded the VL thalamus neuron burstiness, as well as the EP neurons, when we stimulate with optogenetics, you can see that instantaneously, the firing rate in EP drops. And after that, for the next 400 milliseconds, there is a gradual decrease in the burstiness of the VL thalamus neurons until they reach the plateau. Finally, when we do these surgeries, we can also expose the muscles of the leg and implant EMG. If you pinch the tail of the rodents, they will move their legs, and we can take all this data and look at it together. So on screen, it's a bit of a mess, but if you bear with me, the black is when the movement is initiated. The green and red are when the movement ended. And as you would expect, the normal rodent's movement end before dystonic movement. Now, what's important is that even though the VL thalamus is behaving in a different manner, with movement initiation, they do switch back from tonic to a burst firing mode. So that does look normal there. However, if we look at the quality of the burst, it's different. The number of spikes are drastically decreased compared to normal. And so in summary, what we've seen so far is that for normal rodents at rest, the EEP, or GPI, is firing in a tonic fast mode, and as a result, the VL fires in a bursty pattern. In dystonic models, the EEP fires in irregular reduced rate, and as a result of that, the VL thalamus is firing in a tonic pattern. However, with movement, even in dystonic models, the VL thalamus can fire in a burst pattern, but it has a flatter response. So the relationship that we think we see here is that the EEP is sort of a fast tonic pacemaker, which keeps the VL thalamus in a burst-ready state by hyperpolarization, which allows for normal movement. And then in dystonic rodents, the EEP has reduced discharge rate, which results in inadequate hyperpolarization, and then we can see dystonic movement. And that's my presentation. Any questions? Anybody has any? I'll ask a question. What do you think about, you know, kind of translating this to human physiology and what we might, you know, learn from this in terms of, you know, mood disorder treating with DBS, for example? Right. So, from what I've read so far, the classical model does not adequately explain what we see in dystonic patients. A major possibility of that is because of the wide breadth of pathophysiology that could result in dystonia. But we think that maybe looking at modulating the thalamus could be a novel treatment in the future. As far as the mechanism behind dystonia and the relationship between different nuclei, a lot more studies needs to be done. Thank you very much. One more question. Any more questions? We are gonna do that next, so I've done, I did some reading about that in my background reading and we're gonna try to do that next. And I think my lab has tried to make a computer model to sort of see if we can imitate the neural behavior. So data's generated, being generated right now. I didn't show the images on here, but it's very interesting, so thank you.

basal ganglia

thalamus

dystonic models

GPI neuron activity

dystonia treatment