Cell︱ New Discovery!

Source︱Taobo Biology Author︱Researcher Taotao Responsible Editor︱Wang Sizhen exercise is very important to all biological individuals, from the basic foraging behavior of animals to the escape behavior of avoiding natural enemies, these are all controlled by the brain’s neural circuits, so is there any Many unsolved mysteries about the brain's regulation of movement? Scientific research has found that neural circuits play a very important role in controlling body movement and coordinating the position of the limbs, and it is also of great significance for the treatment of Parkinson's disease
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 The midbrain motor area (MLR) was previously thought to control only vertebrate walking and other forms of movement
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On August 19, 2021, the Silvia Arber Laboratory of the Friedrich Michel Institute of Biomedicine and Biology Center of the University of Basel in Switzerland published an article titled Functional diversity for body actions in the mesencephalic locomotor region on Cell
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In this study of mice, it was found that the midbrain motor area also regulates postural changes and other movements
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This new study uses the Inscopix free behavior microscopic calcium imaging system to observe the excitability of different groups of midbrain motor region (MLR) neurons and found two spatially mixed glutamatergic groups: one connected to the spinal cord and the other Connect the basal ganglia
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This new study shows that those cells directly connected to the spinal cord are involved in regulating body extension and posture changes, which may be necessary to initiate exercise, and may also have implications for posture and gait problems in patients with Parkinson’s disease who are not responding to medications.
Meaning
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Orthographic movement is vital to the survival of all species and is a method of ground movement for the entire body
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It enables people to have many forms of controlled interaction with the environment, including exploration, such as finding food, and responding to emergency responses, such as escape from danger
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Regardless of the form of exercise chosen, its successful completion requires controlled posture adjustments of the entire body, coordination of the limbs to realize the transfer of the body, and effective suppression of other limb movements that are incompatible with exercise
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These behavioral observations suggest a phenomenon that is the underlying neuronal loop mechanism involved in the selection and regulation of exercise and other forms of body movement
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 The midbrain motor region (MLR) combines various important properties of motor regulation by integrating a lot of input information and projecting it to the downward and upward targets
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The historical definition of MLR is functional.
Electrical stimulation to it can trigger whole-body movement, and the speed and gait increase with the stimulation intensity
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After these observations, some questions related to the function of MLR appeared, namely how to determine the precise location of the MLR and how to determine the type of neuron responsible for the observed effect
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Anatomically, the initial functional definition of MLR includes the midbrain region, including the prefrontal nucleus (PPN), cuneiform nucleus and cuneiform adjacent regions of the cuneiform nucleus (pCnF and CnF), and the adjacent midbrain reticular structure (mRT)
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These areas contain a mixture of glutamate and GABAergic neurons.
PPN also contains cholinergic neurons.
A strategy is needed to dissect and understand the location and neurotransmitter identity of MLR functions
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 The study of PPN has clinical significance
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The application of PPN deep brain stimulation (DBS) to improve the gait and balance symptoms of Parkinson's disease has produced different findings
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A recent review article emphasized that although clinical research has been conducted for many years, the functional diversity of the PPN region may be the key reason for the lack of consensus on the application strategy for improving Parkinson's disease (PD) symptoms [1]
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In short, although CnF-vGlut2 neurons can drive movement in escape environments, the results of functions in adjacent regions (including PPN) cannot be coordinated
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These different observations emphasize that, given that only a small percentage of MLR neurons encode movement, it is necessary to better describe the functional neuronal diversity of this midbrain region, as well as other motor behaviors
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In addition, it is also important to consider other aspects besides speed regulation and limb coordination during exercise.
It is necessary to know that its successful execution also requires posture adjustment and inhibition of other exercise procedures
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 Here, the author identified and functionally dissected glutamatergic MLR subgroups based on the premise that target connection may be related to function
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The authors found that spatially adjacent MLR-vGlut2 neurons separate different groups of neurons based on their role in axon targets, transgenic marker expression, neuronal activity, and behavior
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The spine projection population (MLR>SC) is different from the ascending population that targets the output structure of the basal ganglia specifically marked by the Rbp4Cre transgene (MLR-Rbp4)
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Although MLR>SC neurons are positively regulated during erection, MLR-Rbp4 neurons mainly exhibit excitability during the process of grasping and grooming forelimb behavior
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Optogenetic experiments proved the role of MLR>SC neurons in body stretching, and pointed out the role of MLR-Rbp4 neurons in regulating various behaviors
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The authors concluded that the proximity of functionally different MLR subgroups may explain the different results of glutamatergic MLR neurons and provide important information for designing new strategies to improve PD symptoms involving PPN areas
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 Results MLR-vGlut2 neurons were divided into independent descending and ascending groups.
The author first determined the precise location of glutamatergic MLR neurons through descending and/or ascending projections
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The author injected adeno-associated viruses (AAVs) with Cre-dependent conditional expression and retrograde neuron targeting potential (rAAV) [2] into selected descending and ascending MLR projection targets
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The author provides RAAV expressing different marker proteins that target the nucleus (nTag) to detect the location of the cell body
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The authors restricted the analysis to glutamatergic MLR neurons by injecting the rAAV-flex-nTag variant into vGlut2Cre mice (Figure 1A)
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In order to target MLR-vGlut2 neurons with descending projection, the authors injected rAAV-flex-nTag1 and -Tag2 into the medulla oblongata (Med) and SC respectively
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As the main ascending target of MLR-vGlut2 neurons, the author injected rAAV-flex-nTag3 into rodent’s main basal ganglia output structure-substantia nigra reticulum (SNr) [3,4] (Figure 1A)
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Figure 1 Isolation of glutamatergic MLR neurons of MLR by projection target (picture quoted from: Ferreira-Pinto MJ, et al.
, Cell 2021; 184: 4564-4578) Rbp4Cre transgenic marker for glutamatergic MLR with SN projection The cluster of glutamatergic SN projection neurons in close proximity to the cholinergic PPN neurons prompted the authors to determine whether they could find a genetic pathway to enter these neurons
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The author injected the AAV-PHP.
eB-flex-nTag virus (a variant of AAV that effectively transduces the central nervous system) systemically into an existing mouse line expressing Cre recombinase [5]
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The authors found that the transgenic mouse line Rbp4Cre [6], which is widely used to target neurons in the fifth layer of the pyramidal tract (PT) of the cerebral cortex, also showed selective expression in the neuronal population next to the cholinergic PPN neurons ( Figure 2A)
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The quantification of MLR-Rbp4 neurons showed that the distribution of mRT and PPN subregions was more obvious than that of pCnF and CnF, and the rostral distribution was consistent with the distribution of glutamatergic MLR>SN neurons (Figure 2A)
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Figure 2 Glutamatergic MLR neurons projected by the Rbp4 transgenic marker to the basal ganglia (picture quoted from: Ferreira-Pinto MJ, et al.
, Cell 2021; 184: 4564-4578) Differences in glutamatergic MLR subgroups The effect adjustment is aimed at the possibility of descending and ascending excitatory MLR neuron groups.
Their activity is monitored by the Inscopix free behavior microscopic calcium imaging system, and the nerve firing during the free activity behavior of the animal is recorded in the open field test (Figure 3A)
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Previous studies have shown that the activity of some MLR-vGlut2 neurons can track motor status.
The authors first assessed whether neurons that are preferentially active during motor episodes are detected
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In order to determine the changes in neuron activity during the behavior, the authors calculated the average fluorescence during the study behavior and subtracted the average fluorescence during the frame during which the behavior was not detected, thereby deriving the behavior assigned to each neuron compared to the resting event Modulation index
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The author found that during exercise, only a small part of neurons are positively modulated during exercise.
This characteristic is more significantly correlated with MLR>SC than MLR-Rbp4 neurons (MLR>SC: 39.
3%; MLR-Rbp4: 19.
9%)
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 These findings raise the question of whether MLR>SC and MLR-Rbp4 neurons exhibit excitability in other behaviors
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Therefore, the author tracked the occurrence of other frequent spontaneous behaviors-standing upright in the open, grooming, and grabbing food (Figure 3B)
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Recognize behavioral events through a supervised learning algorithm using high-speed video and acceleration sensor data (Figure 3C)
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By analyzing the response of MLR>SC neurons (Figure 3D-3H), the authors found that the fluorescence signal associated with the onset of erection increased significantly (Figure 3E)
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In contrast, the beginning of exercise or the grasping and grooming of forelimb behavior did not lead to an increase in the distribution of the overall MLR>SC group (Figure 3E)
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 Next, the author determined the modulation index of a single MLR>SC neuron and its distribution in the four analytical behaviors
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The author found that during the erection process, the firing of MLR>SC neurons was the most significant, while in the other three behaviors, only a few neurons were strongly positively regulated (Figure 3F, 3G)
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Therefore, also at the single neuron level, the positive regulation during erection is the most significant influence, while the regulation influence in other behaviors can be detected in some neurons, but is much smaller (Figure 3E-3G)
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The author also studied the relationship between neuronal activity and the upright phase through single neuron and single trial analysis (Figure 3D)
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A single MLR>SC neuron exhibits different dynamics in time and size, which can be particularly clearly seen when analyzing multiple MLR>SC neurons imaged in a mouse on the same behavioral time frame ( Figure 3D)
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In summary, these findings indicate that MLR>SC neurons tend to be upright
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 Figure 3 Excitability of different subgroups of MLR during animal free behavior (picture quoted from: Ferreira-Pinto MJ, et al.
, Cell 2021; 184: 4564-4578) Decoding of behavioral differences in MLR neuron populations in order to further explore neuronal activity The author takes the opposite approach to the relationship between characteristics and different behaviors
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The author extracted the highest peak of neuronal activity of all analyzed neurons, and calculated the probability of each behavior occurring during the peak time (Figure 4A) or a specific time-the time window of a single neuron is 2.
5s to +5s ( Figure 4B)
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The authors found that MLR>SC neurons have the highest probability of strong response during the animal's upright period, followed by walking, but the highest peak is rarely found during grasping and grooming (Figure 4A and 4B)
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In contrast, the highest activity peaks of MLR-Rbp4 neurons were most significantly related to grasping, followed by grooming, while walking and standing were weak (Figures 4A and 4B)
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In summary, these findings support the observation that most MLR>SC neurons respond during systemic behavior, while MLR-Rbp4 neurons show the most significant response during forelimb grasping and grooming behavior
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Figure 4 Decoding the differential behavior of MLR>SC and MLR-Rbp4 neuron activity (picture quoted from: Ferreira-Pinto MJ, et al.
, Cell 2021; 184: 4564-4578) MLR>SC neuron regulates body stretching Next, The author studied the role of MLR>SC and MLR-Rbp4 neurons in behavior through functional complementarity loss and enhancement experiments
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Considering the observation that both the MLR>SC and MLR-Rbp4 populations exhibit complex regulatory characteristics related to multiple behaviors, predict the optogenetic perturbation of each overall population to test the joint down-regulation or up-regulation of neuronal activity on behavioral output Impact
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Figure 5 MLR neurons with spinal cord projection regulate body extension (picture quoted from: Ferreira-Pinto MJ, et al.
, Cell 2021; 184: 4564-4578) MLR-Rbp4 neurons regulate behavior by affecting the basal ganglia.
To be sure The role of MLR-Rbp4 neurons in behavior, the authors performed loss-of-function experiments by expressing stGtACR2 in Rbp4 neurons (Figure 6A)
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The authors infer that acute reduction of the neuronal activity of MLR-Rbp4 neurons may lead to general disinhibition of behavior because of the reduction of excitatory drive that promotes behavioral inhibition of the basal ganglia output structure (Figure 2)
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Bilateral optogenetic suppression of MLR-Rbp4 neurons does lead to uncoordinated body movements (Figure 6B)
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Optogenetic-induced movement included all body parts with highly variable movement sequences throughout the experiment (Figure 6B), independent of the specific movement of the mouse during stimulation (data not shown)
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The authors found that when the light stimulation was still in progress, the abnormal light-induced motion stopped, and no additional excessive motion was observed during or after the laser shift (Figure 6C)
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The light of the mice in the control group did not cause changes in the speed of tracking body parts
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In summary, these findings indicate that optogenetic inhibition of MLR-Rbp4 neurons leads to rapid dysregulation of motor output in various parts of the body, which may be due to the interference of physiological modulation signals between MLR-Rbp4 neurons and the output structure of the basal ganglia
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Figure 6 MLR-Rbp4 neurons are mainly involved in the coordination of animal movements (picture quoted from: Ferreira-Pinto MJ, et al.
, Cell 2021; 184: 4564-4578) Article pattern picture: The function of the body movement in the midbrain motor area is diverse Sex (picture quoted from: Ferreira-Pinto MJ, et al.
, Cell 2021; 184: 4564-4578) The conclusion and discussion of the article, enlightenment and prospect movement is a common animal behavior involving distributed neuronal circuits
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Cumulative studies of MLR have sparked discussions about understanding its function in natural motor behavior, but the application of DBS in the treatment of refractory PD symptoms is unclear
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Here, the author shows that specialized neuron groups respond to different forms of body movement
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The author believes that these findings provide clues to the ongoing debate and call for a fundamental update of the view of neuronal function in the midbrain region
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The author will use the inscopix system to continue to study the influence of midbrain neurons on motor system function and DBS intervention design.
Original link: https://doi.
org/10.
1016/j.
cell.
2021.
07.
002 Selected previous articles [1] Cereb Cortex︱MET tyrosine kinase signal transduction timing abnormality is a key mechanism that affects the development and behavior of normal cortical neural circuits in mice [2] Nat Biomed Eng︱Ye Yuru’s team developed a whole brain gene editing-mediated treatment of Alzheimer’s disease New strategy [3] Luo Liqun Science heavy review System interpretation ︱ Neural circuit structure-the system that makes the brain "computer" run at high speed [4] Sci Adv︱ important discovery! The calcium homeostasis regulatory protein Calhm2 regulates the activation of microglia and participates in the process of Alzheimer's disease [5] EMBO J︱ new discovery! AGHGAP11B promotes the expansion of the neocortex into adulthood and improves cognitive ability [6] Cell Death Differ︱ Qi Yitao/Wu Hongmei and others cooperate to reveal the molecular mechanism of SUMO modification regulating neurogenesis in adult mice [7] Cereb Cortex︱A2A receptor antagonist can Reversing sequence learning impairment induced by abnormal aggregation of α-Syn [8] Neuron︱Nicotine promotes anxious mood new discovery-the important role of inhibiting the ventral tegmental area-amygdala dopamine pathway [9] Int J Mol Sci︱ Frontier review Interpretation: Pathophysiological response and role of astrocytes in traumatic brain injury [10] Cereb Cortex | Wang Lang's research group reveals that astrocytes have experience-dependent steady-state plasticity [11] New discovery in Nature︱! References on social communication of oxytocin neurons causing maternal behavior (slide up and down to view) [1] Garcia-Rill, E.
, Saper, CB, Rye, DB, Kofler, M.
, Nonnekes, J.
, Lozano, A.
, Valls-Sole´, J.
, and Hallett, M.
(2019).
Focus on the pedunculopontine nucleus.
Consensus review from the May 2018 brainstem society meeting in Washington,
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