GDNF Increases Inhibitory Synaptic Drive on Principal Neurons in the Hippocampus via Activation of the Ret Pathway

Glial cell line-derived neurotrophic factor (GDNF) has been shown to counteract seizures when overexpressed or delivered into the brain in various animal models of epileptogenesis or chronic epilepsy. The mechanisms underlying this effect have not been investigated. We here demonstrate for the first time that GDNF enhances GABAergic inhibitory drive onto mouse pyramidal neurons by modulating postsynaptic GABAA receptors, particularly in perisomatic inhibitory synapses, by GFRα1 mediated activation of the Ret receptor pathway. Other GDNF receptors, such as NCAM or Syndecan3, are not contributing to this effect. We observed similar alterations by GDNF in human hippocampal slices resected from epilepsy patients. These data indicate that GDNF may exert its seizure-suppressant action by enhancing GABAergic inhibitory transmission in the hippocampal network, thus counteracting the increased excitability of the epileptic brain. This new knowledge can contribute to the development of novel, more precise treatment strategies based on a GDNF gene therapy approach

Acute pressure overload of the right ventricle. Comparison of two models of right-left shunt. Pulmonary artery to left atrium and right atrium to left atrium: experimental study

<p>Abtract</p> <p>Background</p> <p>In right ventricular failure (RVF), an interatrial shunt can relieve symptoms of severe pulmonary hypertension by reducing right ventricular preload and increasing systemic flow. Using a pig model to determine if a pulmonary artery - left atrium shunt (PA-LA) is better than a right atrial - left atrial shunt (RA-LA), we compared the hemodynamic effects and blood gases between the two shunts.</p> <p>Methods</p> <p>Thirty, male Large White pigs weighting in average 21.3 kg ± 0.7 (SEM) were divided into two groups (15 pigs per group): In group 1, banding of the pulmonary artery and a pulmonary artery to left atrium shunt with an 8 mm graft (PA-LA) was performed and in group 2 banding of the pulmonary artery and right atrial to left atrial shunt (RA-LA) with a similar graft was performed. Hemodynamic parameters and blood gases were measured from all cardiac chambers in 10 and 20 minutes, half and one hour interval from the baseline (30 min from the banding). Cardiac output and flow of at the left anterior descending artery was also monitored.</p> <p>Results</p> <p>In both groups, a stable RVF was generated. The PA-LA shunt compared to the RA-LA shunt has better hemodynamic performance concerning the decreased right ventricle afterload, the 4 fold higher mean pressure of the shunt, the better flow in left anterior descending artery and the decreased systemic vascular resistance. Favorable to the PA-LA shunt is also the tendency - although not statistically significant - in relation to central venous pressure, left atrial filling and cardiac output.</p> <p>Conclusion</p> <p>The PA-LA shunt can effectively reverse the catastrophic effects of acute RVF offering better hemodynamic characteristics than an interatrial shunt.</p

Cholinergic analog effects in adult rat hippocampal slices following generalized convulsions induced in vivo during development

An early-life Status Epilepticus occurrence may be linked to enhanced long-term seizure recurrence facilitation and cognitive impairment. In this study an in vivo model of sustained generalized seizures is applied to immature rats and the long-term cholinergic/muscarinic –a neuromodulatory system implicated both in seizure generation and physiological cognitive function- effects are evaluated in in vitro preparations of septal and temporal hippocampus –a structure associated both with the most common form generalized epilepsy, temporal lobe epilepsy, and crucial processes for memory and learning- under interictal-like epileptiform activity induction – since interictal spiking may be facilitating seizure generation and is linked to transient cognitive impairment- toaccount for the increased neuronal excitability or synchronization, resembling similar manifestations in humans.A total of 149 (using no more than 2 slices per animal) transverse septal or temporal hippocampal slices from adult Sprague-Dawley rats, normal (n=58) or pentylenetetrazole (PTZ)-treated (n=41) (where a >20 min generalized convulsion had been provoked at postnatal day 20 by a 60-90mg/kg PTZ i.p. injection) were perfused with aCSF (i) with nominally 0-Mg2+ or (ii) containing 50µM 4-aminopyridine (4-AP). CA3 area interictal like epileptiform discharges (IEDs) were recorded extracellularly and their rates of occurrence were quantified in Hz.In a subset of the temporal slices (n=17) the entorhinal cortex was preserved, and simultaneous recordings were made in the CA3a pyramidal field and the MECV-VI layers, during perfusion with the Mg-free aCSF. The rates of IED occurrence as well as the duration of the MEC discharges were measured. Results are presented as average ± s.d. All datasets were checked for normality compliance before performing statistical hypotheses tests.An initial comparison between slices of male and female rats showed no significant difference and these two subsets were subsequently used as a single pooled set. The septal slices displayed a lower baseline discharge rate in comparison to the temporal slices, in both media and in all subgroups, in accordance to previous literature findings (Gilbert et al., 1985; Papatheodoropoulos et al., 2005). Perfusion with the anticholinesterase eserine (10µM) provoked an increase in discharge rates by 67% to 90% in N (temporal and septal) and PTZ temporalslices and by 199% in PTZ septal slices, in the Mg-free aCSF (N-T: 167±79% n=25, N-S:174±66% n=12, PTZ- T:190±92% n=20, PTZ-S:298±177% n=15), though similar increments in all groups in the 4-AP aCSF (N-T: 237±158 n=15, N-S: 249±140% n=10 ,PTZ-T: 261±198% n=9, PTZ-S: 221±50% n=5). The effect of eserine was reversible by the muscarinic antagonist atropine (1µM).Extrinsic stimulation with 1µM carbachol provoked greater increases but also more variable and with less decipherable between slice groups, possibly because of the smaller sample sizes (in Mg-free, N-T: 302±258% n=7, N-S: 443±356% n=6, PTZ-T: 244±146% n=6, PTZ-S: 221±43% n=4, and in 4-AP, N-T: 257±102% n=8, N-S: 197±122 n=3, PTZ-T: 258±81% n=6, PTZ-S: 254±334 n=6).Muscarinic antagonism by perfusion of 1µM atropine (perfused alone) induced a different pattern of frequency decreases between slice groups (in Mg-free, N-T: 80±26% n=19, N-S: 86±31% n=6, PTZ-T: 92±18% n=7, PTZS: 75±18% n=4, and in 4-A-P, N-T: 35±36% n=5, N-S: 91±5% n=6, PTZ-T: 67±32% n=5, PTZ-S: 49±34% n=5), indicating a shift in baseline muscarinic contribution to the excitability in the 4-AP model in the PTZ group, viewed as an increased effect in the septal slices vs. temporal ones instead of the enhanced response in temporal vs. septal slices from normal rats. A similar tendency may be present in the Mg-free model but is less pronounced, perhaps due to the more limited frequency decrements.The experiment with the combined slices showed a distinct difference in MECV-VI discharge rate between normal (0.29±0.29Hz, n=8) and PTZ rat slices (0.42±0.29Hz, n=6). The difference disappeared after cutting the Schaffer collaterals in CA1 (in PTZ slices a drop to 0.18±0.29Hz occurred; no difference in normal rat slices 0.27±0.29Hz). The CA3 discharge rate remained unaffected across cuts (0.65±0.29Hz, n=8 with differences between cuts of a 2µηνών) αρουραίους Sprague-Dawley φυσιολογικούς (n=58) ή που είχαν υποστεί µια παρατεταµένη (>20λεπτά) γενικευµένη κρίση µε 60-90mg/kg pentylenetetrazole (“PTZ”) και διαβράχηκαν είτε µε τΕΝΥ άνευ µαγνησίου είτε µε τΕΝΥ µε 50µM 4-αµινοπυριδίνης. Οι επιληπτοειδείς εκφορτίσεις µεσοκρισικού τύπου της περιοχής CA3 καταγράφηκαν εξωκυττάρια, και ο ρυθµός επανεµφάνισής τους µετρήθηκε ως συχνότητα (Hz). Σε µέρος των τοµών (n=17) διατηρήθηκε και ο µέσος ενδορρινικός φλοιός και πραγµατοποιήθηκαν φυσιολογικούς (n=58) ή που είχαν υποστεί µια παρατεταµένη (>20λεπτά) γενικευµένη κρίση µε 60-90mg/kg pentylenetetrazole (“PTZ”) και διαβράχηκαν είτε µε τΕΝΥ άνευ µαγνησίου είτε µε τΕΝΥ µε50µM 4-αµινοπυριδίνης. Οι επιληπτοειδείς εκφορτίσεις µεσοκρισικού τύπου της περιοχής CA3καταγράφηκαν εξωκυττάρια, και ο ρυθµός επανεµφάνισής τους µετρήθηκε ως συχνότητα (Hz). Σεµέρος των τοµών (n=17) διατηρήθηκε και ο µέσος ενδορρινικός φλοιός και πραγµατοποιήθηκαν στην συνεισφορά των µουσκαρινικών υποδοχέων στην βασική κατάσταση στο µοντέλο τηςαµινοπυριδίνης, στην οµάδα των τοµών PTZ πειραµατοζώων, που εµφανίστηκε ως αυξηµένοαποτέλεσµα στις διαφραγµατικές τοµές έναντι των κροταφικών, αντί της ενισχυµένης απόκρισηςστις κροταφικές έναντι των διαφραγµατικών τοµών φυσιολογικών πειραµατοζώων. Μια παρόµοιατάση ίσως υπάρχει στο µοντέλο µε τΕΝΥ άνευ µαγνησίου αλλά είναι λιγότερο έντονο, πιθανώς λόγωτων λιγότερο εκτεταµένων µειώσεων.Το πείραµα µε τις συνδυασµένες τοµές έδειξε µια ευδιάκριτη διαφορά στον ρυθµό εκφορτίσεων τωνστιβάδων V-VI του µέσου ενδορρινικού φλοιού µεταξύ τοµών φυσιολογικών (0.29±0.29Hz, n=8) και PTZ πειραµατοζώων (0.42±0.29Hz, n=6). Η διαφορά αυτή µειώθηκε µετά την διακοπή τωνπαραπλεύρων ινών Schaffer στην περιοχή CA1 (στις τοµές των PTZ πειραµατοζώων µειώθηκε ησυχνότητα σε 0.18±0.29Hz, χωρίς καµµία µεταβολή της συχνότητας των τοµών φυσιολογικώνπειραµατοζώων). Ο ρυθµός εκφορτίσεων της CA3 παρέµεινε ανεπηρέαστος από τις τοµές(0.65±0.29Hz, n=8 µε εύρος διαφορών µεταξύ τοµών <0.03Hz σε τοµές φυσιολογικών πειραµατοζώων, και 0.47±0.29Hz, n=6 µε εύρος διαφορών µεταξύ τοµών <0.05Hz σε τοµές PTZ πειραµατοζώων).Επιπλέον, η διακοπή των ινών Schaffer προκάλεσε µια ορατή αύξηση της διάρκειας των εκφορτίσεων στον ενδορρινικό φλοιό των PTZ πειραµατοζώων έναντι µικρότερης µεταβολής στις τοµές των φυσιολογικών. Η διάρκεια των εκφορτίσεων είχε µια σύντοµη και µια πιο παρατεταµένη συνιστώσα.Στις τοµές των φυσιολογικών πειραµατοζώων η σύντοµη συνιστώσα διπλασιάστηκε από 446 σε 823msec και η παρατεταµένη αυξήθηκε κατά 20% από 1022 σε 1238msec. Στις τοµές των PTZπειραµατοζώων η σύντοµη συνιστώσα αυξήθηκε κατά 50% από 446 σε 665msec και η παρατεταµένη αυξήθηκε κατά 25% από 918 σε 1152msec.Τα αποτελέσµατα δείχνουν ότι µια παρατεταµένη γενικευµένη κρίση κατά την ανάπτυξη (ωςανάλογο του γενικευµένου SE µε σπασµούς) ενισχύει την απόκριση του ιπποκάµπου σε αυξήσεις της διαθέσιµης ακετυλοχολίνης προς την παραγωγή επιληπτοειδών εκφορτίσεων. Το φαινόµενο είναι πιο αυξηµένο σε πειραµατόζωα επιληπτικού ιστορικού, µε ένα µοντέλο ταυτόχρονης ενεργοποίησης των υποδοχέων NMDA, και σε µεγαλύτερο βαθµό στον διαφραγµατικό ιππόκαµπο. Το εύρηµα αυτό µπορεί να δείχνει µια αυξηµένη πιθανότητα παραγωγής ή εξάπλωσης κρίσεων –σε άτοµα που έχουν υποστεί έστω ένα µοναδικό επεισόδιο SE στην παιδική ηλικία- κάτω από ποικίλες συνθήκες συνδυασµένης χολινεργικής/µουσκαρινικής νευρορρύθµισης και γλουταµατεργικής NMDAR µεσολαβούµενης διαβίβασης, και ενδεχοµένως κάποιες όψεις των µακροπρόθεσµων γνωσιακών δυσλειτουργιών. Η έξοδος του ιπποκάµπου επίσης φαίνεται ενισχυµένη στις ίδιες συνθήκες και µετά από µια επιληπτική κρίση σε νεαρή ηλικία, πιθανώς οδηγώντας σε ισχυρότερο/σταθερότερο συγχρονισµό παρακείµενων φλοιικών περιοχών, συγκλίνοντας έτσι στην διευκόλυνση της εξάπλωσης επιληπτικών κρίσεων και µερικώς αιτιολογώντας το αποτέλεσµα της γνωσιακήςδιαταραχής, τουλάχιστον στην περίπτωση των µεσοκρισικών εκφορτίσεων (Kleen et al., 2010)

Aortic Arch. The Final Frontier in Cardiac Surgery

Aortic arch pathologies such as acute aortic dissection and aneurysmal disease represent surgical challenges. Various emerging techniques and surgical prostheses have expanded the therapeutic armamentarium over the last years with one principal objective; to simplify the operation and reduce the surgical time. Besides the classic elephant trunk which has been regarded as an evolutionary leap in the treatment of extensive thoracic disease, other novel surgical approaches such as the frozen elephant trunk, the thoracic endovascular aortic repair (TEVAR) and the hybrid open branched stent grafts have been introduced. This brief review aims to evaluate the surgical alternatives used in the management of complex aortic arch and proximal descending aorta pathologies with particular consideration given to the contemporary approaches which endorse single stage operation

Human stem cell‐derived gabaergic interneurons establish efferent synapses onto host neurons in rat epileptic hippocampus and inhibit spontaneous recurrent seizures

Epilepsy is a complex disorder affecting the central nervous system and is characterised by spontaneously recurring seizures (SRSs). Epileptic patients undergo symptomatic pharmacolog-ical treatments, however, in 30% of cases, they are ineffective, mostly in patients with temporal lobe epilepsy. Therefore, there is a need for developing novel treatment strategies. Transplantation of cells releasing γ‐aminobutyric acid (GABA) could be used to counteract the imbalance between ex-citation and inhibition within epileptic neuronal networks. We generated GABAergic interneuron precursors from human embryonic stem cells (hESCs) and grafted them in the hippocampi of rats developing chronic SRSs after kainic acid‐induced status epilepticus. Using whole‐cell patch‐clamp recordings, we characterised the maturation of the grafted cells into functional GABAergic inter-neurons in the host brain, and we confirmed the presence of functional inhibitory synaptic connections from grafted cells onto the host neurons. Moreover, optogenetic stimulation of grafted hESC-derived interneurons reduced the rate of epileptiform discharges in vitro. We also observed decreased SRS frequency and total time spent in SRSs in these animals in vivo as compared to non-grafted controls. These data represent a proof‐of‐concept that hESC‐derived GABAergic neurons can exert a therapeutic effect on epileptic animals presumably through establishing inhibitory synapses with host neurons

Human stem cell-derived GABAergic neurons functionally integrate into human neuronal networks

Gamma-aminobutyric acid (GABA)-releasing interneurons modulate neuronal network activity in the brain by inhibiting other neurons. The alteration or absence of these cells disrupts the balance between excitatory and inhibitory processes, leading to neurological disorders such as epilepsy. In this regard, cell-based therapy may be an alternative therapeutic approach. We generated light-sensitive human embryonic stem cell (hESC)-derived GABAergic interneurons (hdIN) and tested their functionality. After 35 days in vitro (DIV), hdINs showed electrophysiological properties and spontaneous synaptic currents comparable to mature neurons. In co-culture with human cortical neurons and after transplantation (AT) into human brain tissue resected from patients with drug-resistant epilepsy, light-activated channelrhodopsin-2 (ChR2) expressing hdINs induced postsynaptic currents in human neurons, strongly suggesting functional efferent synapse formation. These results provide a proof-of-concept that hESC-derived neurons can integrate and modulate the activity of a human host neuronal network. Therefore, this study supports the possibility of precise temporal control of network excitability by transplantation of light-sensitive interneurons