The mouse cortico-basal ganglia-thalamic network

The cortico–basal ganglia–thalamo–cortical loop is one of the fundamental network motifs in the brain. Revealing its structural and functional organization is critical to understanding cognition, sensorimotor behaviour, and the natural history of many neurological and neuropsychiatric disorders. Classically, this network is conceptualized to contain three information channels: motor, limbic and associative^1–4. Yet this three-channel view cannot explain the myriad functions of the basal ganglia. We previously subdivided the dorsal striatum into 29 functional domains on the basis of the topography of inputs from the entire cortex⁵. Here we map the multi-synaptic output pathways of these striatal domains through the globus pallidus external part (GPe), substantia nigra reticular part (SNr), thalamic nuclei and cortex. Accordingly, we identify 14 SNr and 36 GPe domains and a direct cortico-SNr projection. The striatonigral direct pathway displays a greater convergence of striatal inputs than the more parallel striatopallidal indirect pathway, although direct and indirect pathways originating from the same striatal domain ultimately converge onto the same postsynaptic SNr neurons. Following the SNr outputs, we delineate six domains in the parafascicular and ventromedial thalamic nuclei. Subsequently, we identify six parallel cortico–basal ganglia–thalamic subnetworks that sequentially transduce specific subsets of cortical information through every elemental node of the cortico–basal ganglia–thalamic loop. Thalamic domains relay this output back to the originating corticostriatal neurons of each subnetwork in a bona fide closed loop.

Mesoscale connectomic mapping of the cortico–basal ganglia–thalamic network reveals key architectural and information processing features.

Spatially resolved cell atlas of the mouse primary motor cortex by MERFISH

A mammalian brain is composed of numerous cell types organized in an intricate manner to form functional neural circuits. Single-cell RNA sequencing allows systematic identification of cell types based on their gene expression profiles and has revealed many distinct cell populations in the brain1,2. Single-cell epigenomic profiling3,4 further provides information on gene-regulatory signatures of different cell types. Understanding how different cell types contribute to brain function, however, requires knowledge of their spatial organization and connectivity, which is not preserved in sequencing-based methods that involve cell dissociation. Here we used a single-cell transcriptome-imaging method, multiplexed error-robust fluorescence in situ hybridization (MERFISH)5, to generate a molecularly defined and spatially resolved cell atlas of the mouse primary motor cortex. We profiled approximately 300,000 cells in the mouse primary motor cortex and its adjacent areas, identified 95 neuronal and non-neuronal cell clusters, and revealed a complex spatial map in which not only excitatory but also most inhibitory neuronal clusters adopted laminar organizations. Intratelencephalic neurons formed a largely continuous gradient along the cortical depth axis, in which the gene expression of individual cells correlated with their cortical depths. Furthermore, we integrated MERFISH with retrograde labelling to probe projection targets of neurons of the mouse primary motor cortex and found that their cortical projections formed a complex network in which individual neuronal clusters project to multiple target regions and individual target regions receive inputs from multiple neuronal clusters.

Prospective evaluation of combined high-frequency ventilation in post-traumatic patients with adult respiratory distress syndrome refractory to optimized conventional ventilatory management

This study explores the value of combined high-frequency ventilation (CHFV) in a prospective clinical trial of 35 patients suffering from severe post-traumatic and/or septic adult respiratory distress syndrome (ARDS) who were refractory to conventional controlled mechanical ventilatory (CMV) support. The severity of ARDS was quantified by lung mechanics and gas exchange variables and the patients were classified on clinical grounds as well as on the basis of their respiratory index/pulmonary shunt relationship [RI/(Qsp/Qt)]. During the same time period as the CHFV study, data from these patients were compared to those from 88 ARDS patients who had quantitatively similar degrees of respiratory insufficiency, but who were treated only with controlled mechanical ventilation (CMV). The use of CHFV in the 35 CMV refractory patients resulted in an increase in expired tidal volume (VTE) by reducing the CMV inspired tidal volume (VTI) while increasing the volume component derived from high-frequency ventilation (HFV). This procedure appeared to reveal potentially salvageable ARDS patients who were refractory to CMV. In these patients, CHFV significantly reduced pulmonary mean airway pressure (Paw). The RI also decreased significantly and it was possible to reduce significantly the FIO2. In surviving ARDS patients treated with CHFV, an improvement in blood gases at reduced FIO2, without decreased cardiac output, was produced. The CHFV technique was used for less than or equal to 25 days and resulted in 23% survival of patients who were clinically and physiologically indistinguishable from the patients in the ARDS nonsurvivor group who were treated by CMV only. In surviving CHFV patients the decrease in Paw permitted a sustained, or increased, cardiac output with a rise in the oxygen delivery/oxygen consumption ratio, thus allowing for a higher PaO2 for any given level of pulmonary shunt.

Prediction of arterial blood gases by transcutaneous O2 and CO2 in critically ill hyperdynamic trauma patients

The management of severe adult respiratory distress syndrome in critically injured patients requires the frequent measurement of arterial blood gases for adjustment of cardiovascular and ventilatory support. Since these require blood withdrawal and laboratory determinations, a noninvasive method of assessment of arterial gas tensions would permit more frequent assessment of the patient as well as permitting rapid changes in the patient's ventilatory status to be detected earlier in the clinical course. The role of transcutaneous O2 and CO2 tension in providing these measurements was evaluated in 92 studies in 38 critically ill patients with ARDS due to trauma and/or sepsis. All patients were normodynamic or hyperdynamic at the time of study (cardiac index 2.5 to 7.6 L/min/m2) and were intubated and on increased inspired oxygen fractions (FIO2 = 30 to 100%) delivered by mechanical ventilation, had a range of body temperature from 35.0 to 39.5 degrees C and pH from 7.29 to 7.57 The data from a transcutaneous O2 and CO2 sensor applied to the skin of the anterior thorax were analyzed by multiple regression analysis of variances. Prediction of the arterial oxygen tension (PaO2) from 52 to 253 torr was possible from regression-corrected measurements of the transcutaneous O2 (TcO2): [PaO2 = 1.1 (TcO2) - 0.28 (FIO2) + 45.5]. The arterial carbon dioxide tension (PaCO2) from 26 to 57 torr was predicted from the transcutaneous CO2 (TcCO2):[PaCO2 = 0.76 (TcCO2) + 0.06 (FIO2) + 0.035 (TcO2) + 4.1]. With these corrections, a noninvasive Respiratory Index was computed for assessing ARDS severity, and dynamic changes in arterial gases could be followed in response to postural changes, ventilatory alterations, or cardiovascular perturbations. These data suggest that a reasonable estimate of the arterial blood gases can be obtained from a regression-corrected measurement of the transcutaneous O2 and CO2 tensions in critically injured normodynamic or hyperdynamic ARDS patients.