Learning Curve for Flow Diversion of Posterior Circulation Aneurysms: A Long-Term International Multicenter Cohort Study.

BACKGROUND AND PURPOSE: Flow diversion has gradually become a standard treatment for intracranial aneurysms of the anterior circulation. Recently, the off-label use of the flow diverters to treat posterior circulation aneurysms has also increased despite initial concerns of rupture and the suboptimal results. This study aimed to explore the change in complication rates and treatment outcomes across time for posterior circulation aneurysms treated using flow diversion and to further evaluate the mechanisms and variables that could potentially explain the change and outcomes. MATERIALS AND METHODS: A retrospective review using a standardized data set at multiple international academic institutions was performed to identify patients with ruptured and unruptured posterior circulation aneurysms treated with flow diversion during a decade spanning January 2011 to January 2020. This period was then categorized into 4 intervals. RESULTS: A total of 378 procedures were performed during the study period. Across time, there was an increasing tendency to treat more vertebral artery and fewer large vertebrobasilar aneurysms (P = .05). Moreover, interventionalists have been increasingly using fewer overlapping flow diverters per aneurysm (P = .07). There was a trend toward a decrease in the rate of thromboembolic complications from 15.8% in 2011-13 to 8.9% in 2018-19 (P = .34). CONCLUSIONS: This multicenter experience revealed a trend toward treating fewer basilar aneurysms, smaller aneurysms, and increased usage of a single flow diverter, leading to a decrease in the rate of thromboembolic and hemorrhagic complications.

Pentylenetetrazole-induced inhibition of recombinant gamma-aminobutyric acid type A (GABA(A)) receptors: mechanism and site of action.

Pentylenetetrazole (PTZ) is a central nervous system convulsant that is thought, based on binding studies, to act at the picrotoxin (PTX) site of the gamma-aminobutyric acid type A (GABA(A)) receptor. In the present study, we have investigated the mechanism and site of action of PTZ in recombinant GABA(A) receptors. In rat alpha 1 beta 2 gamma 2 receptors, PTZ inhibited GABA-activated Cl(-) current in a concentration-dependent, voltage-independent manner, with an IC(50) of 0.62 +/- 0.13 mM. The mechanism of inhibition appeared competitive with respect to GABA in both rat and human alpha 1 beta 2 gamma 2 receptors. Varying subunit configuration (change or lack of alpha subunit isoform or lack of gamma 2 subunit) had modest effects on PTZ-induced inhibition, as evidenced by comparable IC(50) values (0.6-2.2 mM) in all receptor configurations tested. This contrasts with PTX and other PTX-site ligands, which have greater affinity in receptors lacking an alpha subunit. Using a one-site model for PTZ interaction with alpha 1 beta 2 gamma 2 receptors, the association rate (k(+1)) was found to be 1.14 x 10(3) M(-1) s(-1) and the dissociation rate (k(-1)) was 0.476 s(-1), producing a functional k(d) of 0.418 mM. PTZ could only gain access to its binding site extracellularly. Single-channel recordings demonstrated that PTZ decreased open probability by increasing the duration of closed states but had no effect on single-channel conductance or open state duration. alpha-Isopropyl-alpha-methyl-gamma-butyrolactone, a compound known to antagonize effects of PTX, also diminished the effects of PTZ. Taken together, our results indicate that pentylenetetrazole and picrotoxin interact with overlapping but distinct domains of the GABA(A) receptor.

The central nervous system convulsant pentylenetetrazole stimulates gamma-aminobutyric acid (GABA)-activated current in picrotoxin-resistant GABA(A) receptors in HEK293 cells.

We tested the ability of the central nervous system convulsant pentylenetetrazole (PTZ) to inhibit gamma-aminobutyric acid (GABA)-gated current in receptors expressing a mutation that rendered them resistant to picrotoxin. Consistent with previous reports, receptors expressing beta2(T246F), along with alpha3 and gamma2 subunits, resulted in a greatly diminished sensitivity to picrotoxin. Sensitivity to PTZ was completely abolished in the mutant receptor, confirming the hypothesis that PTZ acts at the picrotoxin site. Quite unexpected, however, was our finding that PTZ elicited marked stimulation (up to 400% of control) in the mutated receptors. This stimulatory effect was not mediated via an interaction with the benzodiazepine site, as preincubation with the benzodiazepine antagonist flumazenil did not block the PTZ-induced stimulation. Our results reveal the existence of a novel stimulatory domain of PTZ in GABA(A) receptors.

Influence of subunit configuration on the interaction of picrotoxin-site ligands with recombinant GABA(A) receptors.

We have assessed the interaction of picrotoxin and a putative picrotoxin-site ligand [4-dimethyl-3-t-butylcarboxyl-4,5-dihydro (1, 5-a) quinoxaline] (U-93631) with varying configurations of recombinant GABA(A) receptors, using the whole-cell patch clamp technique. In alpha2beta2gamma2 GABA(A) receptors, coapplication of picrotoxin with GABA had minimal effects on initial GABA-activated Cl(-) current amplitude, and subsequently enhanced decay of GABA-activated Cl(-) currents. The half-maximal inhibitory concentration (IC(50)) for picrotoxin in alpha2beta2gamma2 receptors was 10.3+/-1.6 microM. The alpha subunit isoform did not affect picrotoxin-induced inhibition, as IC(50) values for alpha3beta2gamma2 (5.1+/-0.7 microM) and alpha6beta2gamma2 receptors (7.2+/-0.4 microM) were comparable to those obtained in alpha2beta2gamma2 receptors. Interestingly, in receptors lacking an alpha subunit (beta2gamma2 configuration), picrotoxin had a markedly lower IC(50) (0.5+/-0.05 microM) compared to alpha-containing receptors. The inhibitory profile was generally similar for the presumed picrotoxin-site ligand U-93631, i.e., IC(50) values were comparable in all alphabetagamma-containing receptors, but the IC(50) in beta2gamma2 receptors was greater than 10-fold lower. In addition, a modest but significant initial stimulation of GABA-activated current by U-93631 was observed in alpha2beta2gamma2 and beta2gamma2 receptors. A mutation in the second transmembrane domain, shown previously to abolish picrotoxin sensitivity, also greatly attenuated sensitivity to U-93631. Moreover, incubation of receptors with excess U-93631 hindered picrotoxin's ability to gain access to its binding site; both results indicate that U-93631 interacts at the picrotoxin site of the receptor. Our results indicate the presence of an alpha subunit hinders the ability of picrotoxin to block the GABA(A) receptor, and thus provides additional insight into the site of action of picrotoxin. In addition, we have shown that domains important for the actions of picrotoxin also affect U-93631. Thus, this compound should prove to be a useful ligand for analysis of the convulsant site of this receptor.