Presynaptic Calcium Channel Inhibition Underlies CB1 Cannabinoid Receptor-Mediated Suppression of GABA Release.

CB1 cannabinoid receptors (CB1) are located at axon terminals and effectively control synaptic communication and thereby circuit operation widespread in the CNS. Although it is partially uncovered how CB1 activation leads to the reduction of synaptic excitation, the mechanisms of the decrease of GABA release upon activation of these cannabinoid receptors remain elusive. To determine the mechanisms underlying the suppression of synaptic transmission by CB1 at GABAergic synapses, we recorded unitary IPSCs (uIPSCs) at cholecystokinin-expressing interneuron-pyramidal cell connections and imaged presynaptic [Ca(2+)] transients in mouse hippocampal slices. Our results reveal a power function with an exponent of 2.2 between the amplitude of uIPSCs and intrabouton [Ca(2+)]. Altering CB1 function by either increasing endocannabinoid production or removing its tonic activity allowed us to demonstrate that CB1 controls GABA release by inhibiting Ca(2+) entry into presynaptic axon terminals via N-type (Cav2.2) Ca(2+) channels. These results provide evidence for modulation of intrabouton Ca(2+) influx into GABAergic axon terminals by CB1, leading to the effective suppression of synaptic inhibition

Strategically Positioned Inhibitory Synapses of Axo-axonic Cells Potently Control Principal Neuron Spiking in the Basolateral Amygdala.

Axo-axonic cells (AACs) in cortical regions selectively innervate the axon initial segments (AISs) of principal cells (PCs), where the action potentials are generated. These GABAergic interneurons can alter the activity of PCs, but how the efficacy of spike control correlates with the number of output synapses remains unclear. Moreover, the relationship between the spatial distribution of GABAergic synapses and the action potential initiation site along the AISs is not well defined. Using paired recordings obtained in the mouse basolateral amygdala, we found that AACs powerfully inhibited or delayed the timing of PC spiking by 30 ms, if AAC output preceded PC spiking with no more than 80 ms. By correlating the number of synapses and the probability of spiking, we revealed that larger numbers of presynaptic AAC boutons giving rise to larger postsynaptic responses provided more effective inhibition of PC spiking. At least 10-12 AAC synapses, which could originate from 2-3 AACs on average, were necessary to veto the PC firing under our recording conditions. Furthermore, we determined that the threshold for the action potential generation along PC axons is the lowest between 20 and 40 mum from soma, which axonal segment received the highest density of GABAergic inputs. Single AACs preferentially innervated this narrow portion of the AIS where action potentials were generated with the highest likelihood, regardless of the number of synapses forming a given connection. Our results uncovered a fine organization of AAC innervation maximizing their inhibitory efficacy by strategically positioning synapses along the AISs

Different output properties of perisomatic region-targeting interneurons in the basal amygdala

Perisomatic region of principal neurons in the cortical regions is innervated by three types of GABAergic interneurons, including parvalbumi n - containing basket cells (PVBCs) and axo - axonic cells (AACs), as well as cholecystokinin and type 1 cannabinoid receptor - expressing basket cells (CCK/CB1BCs). These perisomatic inhibitory cell types can also be found in the basal nucleus of the amygdala, however, their output properties are largely unknown. Here, we performed whole - cell recordings in morphologically identified interneurons in slices prepared from transgenic mice, in which the GABAergic cells could be selectively targeted. By investigating the passive and active membrane properties of interneurons located within the bas al amygdala , w e observed that the three interneuron types had distinct single - cell properties . For instance, the input resistance, spike rate, accommodation in discharge rate , or after - hyperpolarization width at the half maximal amplitude separated the three interneuron types . Furthermore , we performed paired recordings from interneurons and principal neurons to uncover the basic features of unitary inhibitory postsynaptic curr ents (uIPSCs). We found that, although there was no difference in the magnitude of responses measured in the principal neurons , the uIPSCs originated from the distinct interneuron types differed in the rise time, failure rate, latency and short - term dynami cs. Moreover, the asynchronous transmitter release induced by a train of action potentials was typical for the output synapses of CCK/CB1BCs. Our results suggest that , although the three perisomatic inhibitory cell types give rise to uIPSCs with similar ma gnitude, their distinct spiking characteristics may help to accomplish specific function in amygdala operation

Global variation in the long-term outcomes of ypT0 rectal cancers

Background Colorectal cancer mortality presents world-wide variation. In rectal cancers presenting a complete/nearly-complete tumor response (ypT0/ypTis) following neoadjuvant treatment, the features correlated to nodal metastases and relapses still need to be defined. Methods An international cohort study enrolling ypT0/ypTis rectal cancers surgically treated from 2012 to 2017 was conducted. A propensity matching was used to balance nodal-positive and nodal-negative patients and statistical analyses were performed to investigate survivals, using a bootstrap model for internal validation. The features correlated with nodal metastasis were studied. Countries with participating centers were ranked using the World Bank (WBI), Human Development (HDI) and Global Gender Gap (GGG) indexes to compare survivals. Results 680 ypT0/ypTis from 52 European, Australian, Indian and American Institutions were analyzed. Mean follow-up was of 30.4 months. 96.5% were treated with total mesorectal excision, 7.2% were nodal-positive and 8.8% relapsed. Distal cancers (HR 0.71 95%CI: 0.56-0.91) and nodal metastasis and nodal metastasis (HR 3.85 95%CI:1.12–13.19) correlated with worse DFS, whereas a younger age was of borderline significance (HR 0.95 95%CI:0.91–0.99). The bootstrap analysis validated the model on 5000 repetitions. A short-course radiotherapy (OR 0.18 95%CI:0.09–0.37) correlated with the occurrence of nodal metastasis. Those countries classified in the low/medium-WBI, medium-HDI and lower-GGG ranks documented worse DFS curves (respectively p < 0.0001, p < 0.0001 and p 0.0002). However, the clinical stages were similar and patients from medium-HDI countries received more adjuvant chemotherapy than the others (p < 0.0001). Conclusion Sub-groups at risk for relapses and nodal metastasis were identified. A global variation exists also when benchmarking a rectal cancer complete regression

Excitation of Diverse Classes of Cholecystokinin Interneurons in the Basal Amygdala Facilitates Fear Extinction

There is growing evidence that interneurons (INs) orchestrate neural activity and plasticity in corticoamygdala circuits to regulate fear behaviors. However, defining the precise role of cholecystokinin-expressing INs (CCK INs) remains elusive due to the technical challenge of parsing this population from CCK-expressing principal neurons (CCK PNs). Here, we used an intersectional genetic strategy in CCK-Cre;Dlx5/6-Flpe double-transgenic mice to study the anatomical, molecular and electrophysiological properties of CCK INs in the basal amygdala (BA) and optogenetically manipulate these cells during fear extinction. Electrophysiological recordings confirmed that this strategy targeted GABAergic cells and that a significant proportion expressed functional cannabinoid CB1 receptors; a defining characteristic of CCK-expressing basket cells. However, immunostaining showed that subsets of the genetically-targeted cells expressed either neuropeptide Y (NPY; 29%) or parvalbumin (PV; 17%), but not somatostatin (SOM) or Ca2+/calmodulin-dependent protein kinase II (CaMKII)-α. Further morphological and electrophysiological analyses showed that four IN types could be identified among the EYFP-expressing cells: CCK/cannabinoid receptor type 1 (CB1R)-expressing basket cells, neurogliaform cells, PV+ basket cells, and PV+ axo-axonic cells. At the behavioral level, in vivo optogenetic photostimulation of the targeted population during extinction acquisition led to reduced freezing on a light-free extinction retrieval test, indicating extinction memory facilitation; whereas photosilencing was without effect. Conversely, non-selective (i.e., inclusive of INs and PNs) photostimulation or photosilencing of CCK-targeted cells, using CCK-Cre single-transgenic mice, impaired extinction. These data reveal an unexpectedly high degree of phenotypic complexity in a unique population of extinction-modulating BA INs

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