Oxytocin increases inhibitory synaptic transmission and blocks development of long-term potentiation in the lateral amygdala.

Oxytocin (OT) is a neuroactive peptide that influences the processing of fearful stimuli in the amygdala. In the central nucleus of the amygdala, the activation of OT receptors alters neural activity and ultimately suppresses the behavioral response to a fear conditioned stimulus. Receptors for OT are also found in the lateral amygdala (LA), and infusion of OT into the basolateral amygdala complex affects the formation and consolidation of fear memories. Yet, how OT receptor activation alters neurons and neural networks in the LA is unknown. In this study we used whole cell electrophysiological recordings to determine how OT-receptor activation changes synaptic transmission and synaptic plasticity in the LA of Sprague-Dawley rats. Our results demonstrate that OT-receptor activation results in a 200% increase in spontaneous inhibitory transmission in the LA that leads to the activation of presynaptic GABAB receptors. The activation of these receptors inhibits excitatory transmission in the LA, blocking long-term potentiation of cortical inputs onto LA neurons. Hence, this study provides the first demonstration that OT influences synaptic transmission and plasticity in the LA, revealing a mechanism that could explain how OT regulates the formation and consolidation of conditioned fear memories in the amygdala.NEW & NOTEWORTHY This study investigates modulation of synaptic transmission by oxytocin (OT) in the lateral amygdala (LA). We demonstrate that OT induces transient increases in spontaneous GABAergic transmission by activating interneurons in the basolateral amygdala. The resultant increase in GABA release in the LA activates presynaptic GABAB receptors on both inhibitory and excitatory inputs onto LA neurons, reducing release probability at these synapses. We subsequently demonstrate that OT modulates synaptic plasticity at cortical inputs to the LA.

Baclofen acts in the central amygdala to reduce synaptic transmission and impair context fear conditioning.

The two main sub-divisions of the Central amygdala (CeA), the lateral-capsular (CeA-LC) and the medial (CeA-M), contain extensive networks of inhibitory interneurons. We have previously shown that activation of GABAB-receptors reduces excitatory transmission between axons of the pontine parabrachial nucleus and neurons of the CeA-LC by inhibiting glutamate release from presynaptic terminals13. Here we have characterised GABAB-receptor activation on other excitatory and inhibitory projections within the CeA. Using whole-cell, patch-clamp recordings, we found that the GABAB-receptor agonist baclofen significantly reduced excitatory and inhibitory transmission from all tested inputs into the CeA-LC and CeA-M. In all but one of the inputs, reductions in transmission were accompanied by an increase in paired pulse ratio, indicating that presynaptic GABAB-receptors acted to reduce the release probability of synaptic vesicles. To examine the impact of GABAB-receptors in the CeA on contextual fear-conditioning, we infused baclofen into the CeA immediately prior to training. Compared to vehicle-infused rats, baclofen-infused rats displayed significantly less freezing both during the final stages of the training period and at test 24 hours later. The results of this study demonstrate that, by suppressing excitatory and inhibitory transmission, activation of presynaptic GABAB-receptors in the CeA inhibits the development of context conditioned fear.

α2-adrenoceptor-mediated inhibition in the central amygdala blocks fear-conditioning.

The central amygdala is critical for the acquisition and expression of fear memories. This region receives a dense innervation from brainstem noradrenergic cell groups and has a high level of α2-adrenoceptor expression. Using whole-cell electrophysiological recordings from rat brain slices, we characterise the role of pre-synaptic α2-adrenoceptor in modulating discrete inhibitory and excitatory connections within both the lateral and medial division of the central amygdala. The selective α2-adrenoceptor agonist clonidine blocked the excitatory input from the pontine parabrachial neurons onto neurons of the lateral central amygdala. In addition, clonidine blocked inhibitory connections from the medial paracapsular intercalated cell mass onto both lateral and medial central amygdala neurons. To examine the behavioural consequence of α2-adrenoceptor-mediated inhibition of these inputs, we infused clonidine into the central amygdala prior to contextual fear-conditioning. In contrast to vehicle-infused rats, clonidine-infused animals displayed reduced levels of freezing 24 hours after training, despite showing no difference in freezing during the training session. These results reveal a role for α2-adrenoceptors within the central amygdala in the modulation of synaptic transmission and the formation of fear-memories. In addition, they provide further evidence for a role of the central amygdala in fear-memory formation.

Are BVS suitable for ACS patients? Support from a large single center real live registry.

OBJECTIVES: To investigate one-year outcomes after implantation of a bioresorbable vascular scaffold (BVS) in patients presenting with acute coronary syndrome (ACS) compared to stable angina patients. BACKGROUND: Robust data on the outcome of BVS in the setting of ACS is still scarce. METHODS: Two investigator initiated, single-center, single-arm BVS registries have been pooled for the purpose of this study, namely the BVS Expand and BVS STEMI registries. RESULTS: From September 2012-October 2014, 351 patients with a total of 428 lesions were enrolled. 255 (72.6%) were ACS patients and 99 (27.4%) presented with stable angina/silent ischemia. Mean number of scaffold/patient was 1.55±0.91 in ACS group versus 1.91±1.11 in non-ACS group (P=0.11). Pre- and post-dilatation were performed less frequent in ACS patients, 75.7% and 41.3% versus 89.0% and 62.0% respectively (P=0.05 and P=0.001). Interestingly, post-procedural acute lumen gain and percentage diameter stenosis were superior in ACS patients, 1.62±0.65mm (versus 1.22±0.49mm, P<0.001) and 15.51±8.47% (versus 18.46±9.54%, P=0.04). Major adverse cardiac events (MACE) rate at 12months was 5.5% in the ACS group (versus 5.3% in stable group, P=0.90). One-year definite scaffold thrombosis rate was comparable: 2.0% for ACS population versus 2.1% for stable population (P=0.94), however, early scaffold thromboses occurred only in ACS patients. CONCLUSIONS: One-year clinical outcomes in ACS patients treated with BVS were similar to non-ACS patients. Acute angiographic outcomes were better in ACS than in non-ACS, yet the early thrombotic events require attention and further research.

Ketamine and suicidal ideation in depression: Jumping the gun?

Depression and suicide are known to be intricately entwined but the neurobiological basis underlying this association is yet to be understood. Ketamine is an N-methyl d-aspartate (NMDA) receptor antagonist used for induction and maintenance of general anaesthesia but paradoxically its euphoric effects lead to its classification under drugs of abuse. The serendipitous finding of rapid-onset antidepressant action of subanaesthetic dosing with ketamine by intravenous infusion has sparked many preclinical and clinical investigations. A remarkable suppression of suicidal ideation was also reported in depressed patients. This review focuses on the clinical trials on ketamine that reported remedial effects in suicidal ideation in depression and addresses also the molecular mechanisms underlying the antidepressant and psychotomimetic actions of ketamine. The neuropsychiatric profile of subanaesthetic doses of ketamine encourages its use in the management of suicidal ideation that could avert emergent self-harm or suicide. Finally, the need for neuroimaging studies in suicidal patients to identify the brain region specific and temporal effects of ketamine, and the possibility of employing ketamine as an experimental tool in rodent-based studies to study the mechanisms underlying suicidal behaviour are highlighted.

The rapid identification of Clostridium perfringens as the possible aetiology of a diarrhoeal outbreak using PCR.

A gastroenteritis outbreak occurred in a military camp where a laboratory and epidemiological investigation was carried out. The early onset of symptoms indicated probable food contamination with Clostridium perfringens. Stool samples collected from affected patients were tested within 4 h via real-time polymerase chain reaction (PCR) for the presence of the C. perfringens plc gene. Ten out of the 12 stool samples were positive. Confirmation of the molecular test results was carried out by enumeration of C. perfringens in stool by culture and shown to be in excess of 106 spores/g stool. The isolates obtained from culture were further analysed by PCR for the presence of the chromosomal enterotoxin (cpe) gene. Based on the clinical symptoms, epidemiological and laboratory investigations, C. perfringens was implicated as the aetiological agent. The ability to conduct real-time PCR analysis greatly shortens the time to diagnosis and allows for preventive and control measures to be effected quickly.