D-cycloserine enhances both intrinsic excitability of CA1 hippocampal neurons and expression of activity-regulated cytoskeletal (Arc) protein.

The interaction of NMDA receptor (NMDAR) activation and other mechanisms regulating neuronal excitability have not been thoroughly described. While excess activation of NMDARs results in excitotoxicity, partial activation of NMDARs by d-cycloserine (DCS) is nootropic, enhancing both acquisition and extinction of memories. The mechanism by which DCS treatment enhances memory is unclear. NMDAR activation has been shown to increase expression of the activity-regulated cytoskeletal (Arc) protein associated with neural plasticity and enhanced memory. Enhanced memory is also associated with increases in neuronal intrinsic excitability, i.e. reductions in post-burst afterhyperpolarizations (AHPs) after acquisition of new tasks. Reductions in AHPs can occur when Ca(2+) influx is reduced. This study aimed to determine if either if Arc expression, intrinsic excitability, or both were altered following systemic administration of a memory-enhancing dose of DCS, i.e. what form of plasticity would be exhibited. Both Arc protein expression and intrinsic excitability were enhanced in tissue prepared 1h post-administration of a nootropic dose of DCS. Both mechanisms have been strongly associated with memory enhancement, but have not previously been demonstrated to change across the same time frame in the same preparation in response to DCS treatment.

Fear conditioning alters neuron-specific hippocampal place field stability via the basolateral amygdala.

It is well established that physical changes to an environment result in plasticity of hippocampal place cell activity, while in the absence of changes, place fields are remarkably stable. Manipulations of a rat's perception of the environment without physically changing the environment also result in plasticity of place cell firing. Here, we tested the hypothesis that a rat's perception of an environment could be changed by introducing an auditory fear-conditioned stimulus (CS) to a previously neutral environment, inducing plasticity of hippocampal place fields. First, stable place fields were isolated for rats exploring a radial-arm maze in one environment, and then the rats were fear-conditioned to an auditory CS in a completely separate environment. Later, the CS was specifically paired once with a location in the previously neutral radial-arm maze, either within the given neuron's place field (in-field) or an area outside of the place field (out-of-field). A single, paired presentation of the CS with a location in-field for a specific place cell disrupted the stability of that neuron's place field, whereas pairing the CS with a location out-of-field did not affect place field stability. We further showed that this place field disruption for a CS presented in-field was mediated by inputs from the basolateral amygdala (BLA). Temporarily inactivating the BLA immediately post-CS re-exposure attenuated the CS-induced place field destabilization. Our results show neuron-specific conditional plasticity for actively firing hippocampal place cells, and that the BLA mediates this plasticity when an emotionally arousing or fear-related CS is used.

NF-kappa B inhibition markedly enhances sensitivity of resistant breast cancer tumor cells to tamoxifen.

Studies show that high Akt activity in breast carcinoma is associated with endocrine therapy resistance. Breast cancer cell lines expressing a constitutively active Akt are able to proliferate under reduced estrogen conditions, and are resistant to the growth inhibitory effects of tamoxifen. Understanding the targets of Akt signaling mediating tamoxifen resistance is of clinical significance. One possible target is nuclear factor kappa B (NF-kappa B), a transcription factor that plays a critical role in resistance to apoptosis and the induction of angiogenesis and invasion. In the present study, we found that Akt activity correlated with phosphorylation of I kappa B (the negative regulator of NF-kappa B), NF-kappa B DNA binding and tamoxifen resistance in vivo. Importantly, we found that co-treatment with the NF-kappa B inhibitor, parthenolide, or overexpression of I kappa B superrepressor restored tamoxifen sensitivity to our refractory Akt MCF-7 cells. These data suggest that activation of NF-kappa B via the PI3K/Akt signaling pathway may be a significant mechanism for development of endocrine therapy resistance in breast cancer, and that inhibition of NF-kappa B may be an effective treatment strategy to limit the progression of this disease.