PSD95 and nNOS interaction as a novel molecular target to modulate conditioned fear: relevance to PTSD

L.- P. Li,P. L. Johnson,A. I. Molosh,A. R. Abreu,Y. Lai,G. A. Thakur,M. M. Haulcomb,S. D. Fitz,A. Shekhar,E. T. Dustrude

doi:10.1038/s41398-018-0208-5

Abstract

Stimulation of N-methyl-D-aspartic acid receptors (NMDARs) and the resulting increase of nitric oxide (NO) production are critical for fear memory formation. Following NMDAR activation, efficient production of NO requires linking the 95 kDa postsynaptic density protein (PSD95), a scaffolding protein to neuronal nitric oxide synthase (nNOS). A variety of previously studied NMDAR antagonists and NOS inhibitors can disrupt fear conditioning, but they also affect many other CNS functions such as motor activity, anxiety, and learning. We hypothesized that disrupting nNOS and PSD95 interaction in the amygdala, a critical site for fear memory formation, will reduce conditioned fear. Our results show that systemic treatment with ZL006, a compound that disrupts PSD95/nNOS binding, attenuates fear memory compared to its inactive isomer ZL007. Co-immunoprecipitation after fear conditioning showed a robust increase in the amygdala PSD95/nNOS binding, which was blocked by systemic pre-administration of ZL006. Treatment of amygdala slices with ZL006 also impaired long-term potentiation (LTP), a cellular signature of synaptic plasticity. Direct intra-amygdala infusion of ZL006 also attenuated conditioned fear. Finally, unlike NMDAR antagonist MK-801, ZL006 does not affect locomotion, social interaction, object recognition memory, and spatial memory. These findings support the hypothesis that disrupting the PSD95/nNOS interaction downstream of NMDARs selectively reduces fear memory, and highlights PSD95/nNOS interaction as a novel target for fear-related disorders, such as posttraumatic stress disorder.

Highlights

Normal fear learning and memory allow animals to predict and avoid physical dangers and are essential to survival
When given systemically immediately following fear conditioning sessions, we found that vehicle controls showed robust conditioned fear responses during the testing sessions 24 h later, whereas 10 mg/kg ZL006 treated group had significantly reduced conditioned freezing (Fig. 1a, b)
All three groups showed comparable conditioned freezing response during acquisition (Supplementary Fig. S2b). These findings suggest that fear conditioning causes a robust increase in the amygdala PSD95/neuronal nitric oxide synthase (nNOS) binding, Fig. 2 Disruption of PSD95/nNOS with ZL006 does not have the non-specific behavioral effects seen with N-methyl-D-aspartic acid receptors (NMDARs) antagonist MK-801. a Animals received i.p. injections 1 h prior to the OF Test

Summary

Introduction

Normal fear learning and memory allow animals to predict and avoid physical dangers and are essential to survival. Following traumatic experiences, these mechanisms can lead to symptoms of syndromes such as posttraumatic stress disorder (PTSD)[1,2]. PTSD is a severe psychiatric disorder in which fear responses are likely sustained, generalized, and inappropriately triggered out of context[1,2]. Pavlovian fear conditioning is a well-established laboratory model of fear learning that is often used to elucidate mechanism of fear acquisition and extinction. In this paradigm, a neutral event (a conditioned stimulus, (CS)), such as a tone, is paired with an aversive event (an unconditioned stimulus (US)), such as a footshock. The CS acquires the ability to evoke fear responses, such as freezing in anticipation of the US3

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Conclusion