AMPAR receptor inhibitors suppress proliferation of human small cell lung cancer cell lines.

BACKGROUND: Small cell lung cancer (SCLC) is a neuroendocrine tumor with poor prognosis. Neuroendocrine tumors possess characteristics of both nerve cells and hormone-secreting cells; therefore, targeting the neuronal properties of these tumors may lead to the development of new therapeutic options. Among the endogenous signaling pathways in the nervous system, targeting the glutamate pathway may be a useful strategy for glioblastoma treatment. Perampanel, an antagonist of the synaptic glutamate α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR), has been reported to be effective in patients with glioblastoma. In this study, we aimed to investigate the antitumor effects of AMPAR antagonists in human SCLC cell lines. METHODS: We performed to examine the expression of AMPAR using Western blot and immunohistochemical analysis. The antitumor effects of AMPAR antagonists on human SCLC cell lines were investigated in vitro and in vivo. We also analyzed the signaling pathway of AMPAR antagonists in SCLC cell lines. Statistical analysis was performed by the GraphPad Prism 6 software. RESULTS: We first examined the expression of endogenous AMPAR in six human SCLC cell lines, detecting AMPAR proteins in all of them. Next, we tested the anti-proliferative effect of two AMPAR antagonists, talampanel and cyanquixaline, using SCLC cells in vitro and in vivo. Both AMPAR antagonists inhibited cell proliferation and mitogen-activated protein kinase (MAPK) phosphorylation in SCLC cells in vitro. Further, we observed reduced proliferation of implanted cell lines in an in vivo setting, assessed by Ki-67 immunohistochemistry. Additionally, using immunohistochemical analysis we confirmed AMPAR protein expression in human SCLC samples. CONCLUSION: AMPAR may be a potential therapeutic target for SCLC.

Estrous Cycle-Dependent Phasic Changes in the Stoichiometry of Hippocampal Synaptic AMPA Receptors in Rats.

Cognitive function can be affected by the estrous cycle. However, the effect of the estrous cycle on synaptic functions is poorly understood. Here we show that in female rats, inhibitory-avoidance (IA) task (hippocampus-dependent contextual fear-learning task) drives GluA2-lacking Ca2+-permeable AMPA receptors (CP-AMPARs) into the hippocampal CA3-CA1 synapses during all periods of the estrous cycle except the proestrous period, when estrogen levels are high. In addition, IA task failed to drive CP-AMPARs into the CA3-CA1 synapses of ovariectomized rats only when estrogen was present. Thus, changes in the stoichiometry of AMPA receptors during learning depend on estrogen levels. Furthermore, the induction of long-term potentiation (LTP) after IA task was prevented during the proestrous period, while intact LTP is still expressed after IA task during other period of the estrous cycle. Consistent with this finding, rats conditioned by IA training failed to acquire hippocampus-dependent Y-maze task during the proestrous period. On the other hand, during other estrous period, rats were able to learn Y-maze task after IA conditioning. These results suggest that high estrogen levels prevent the IA learning-induced delivery of CP-AMPARs into hippocampal CA3-CA1 synapses and limit synaptic plasticity after IA task, thus preventing the acquisition of additional learning.

Nicotine inhibition of pulsatile GnRH secretion is mediated by GABAA receptor system in the cultured rat embryonic olfactory placode.

In past work, we suggested that nicotine inhibition of in vivo pulsatile LH release is not mediated by opiate receptors known to be involved in the inhibition of LH release. In the present study, we examined whether nicotine inhibits the pulsatile gonadotropin-releasing hormone (GnRH) release, and whether this inhibition of GnRH release by nicotine is mediated by the GABA receptor system, by checking in vitro pulsatile GnRH release from cultured GnRH neurons obtained from olfactory placodes of rat embryos at E13.5. The mean interpulse interval of pulsatile GnRH release into the medium was 34.2+/-2.0 min in the control period and increased to 95.3+/-19.0 min (n=6) in the period of nicotine treatment at a concentration of 500 nM, showing an inhibitory effect of nicotine on pulsatile GnRH release. The GABA(A) receptor antagonist bicuculline used alone at a concentration of 20 microM caused no significant changes in the pulsatile GnRH release, but when used in combination with 500 nM of nicotine, bicuculline blocked the nicotine inhibition of GnRH release. In a separate experiment, nicotine treatment at a concentration of 500 nM significantly increased GABA release. These results suggest that, in the cultured embryonic olfactory placode, nicotine stimulates GABA release, which then inhibits GnRH release through GABA(A) receptor system.

Role of gamma-aminobutyric acid neurons in the release of gonadotropin-releasing hormone in cultured rat embryonic olfactory placodes.

We recently established a primary cell culture system of gonadotropin-releasing hormone (GnRH) neurons originating from olfactory placodes of rat embryos at E13.5 and showed that cultured olfactory placodes released GnRH into the medium in a pulsatile fashion with an interpulse interval of about 30 min. Since the reported presence of gamma-aminobutyric acid (GABA) neurons in the culture of rat olfactory placode raises questions as to the role played by these GABA neurons in the GnRH pulse generation, we immunostained GnRH neurons and GABA neurons in this culture system to examine the interrelationship between both types of neurons, and determined the effects of GABA and the GABA(A) receptor antagonist, bicuculline, on GnRH release. The immunohistochemical study showed that GnRH neurons received fiber terminals from GABA neurons. GnRH neurons in culture released GnRH into the medium at intervals of 30-40 min, confirming our previous study. Treatment with 20 microM GABA prolonged the interpulse interval and decreased the amplitude of GnRH pulses. Bicuculline administered at 20 microM did not affect either parameter, but 50 microM bicuculline elevated the mean GnRH level, although it did not affect either the interpulse interval or the amplitude of GnRH pulses. In addition, 50 microM bicuculline increased the mean trough levels of GnRH pulses, although 20 microM bicuculline did not. In light of the in vivo studies performed previously, we suggest that the GnRH pulse generator, which probably consists of a small population of GnRH neurons in the culture, does not involve GABA neurons to generate the pulsatile GnRH release, although it may be responsive to the inhibitory transmitter GABA. We also found that there may be another population of GnRH neurons in the culture whose activity is strongly suppressed by the tonic inhibition of GABA neurons. Although it is speculative, these latter GnRH neurons may be responsible for the surge of GnRH release.