Administration of the glutamate-modulating drug riluzole after stress reverses its delayed effects on the amygdala

Abstract

Extracellular glutamate levels are elevated across brain regions immediately after stress. Despite sharing common features in their genesis, the patterns of stress-induced plasticity that eventually take shape are strikingly different between these brain areas. While stress impairs structure and function in the hippocampus, it has the opposite effect on the amygdala. Riluzole, an FDA-approved drug known to modulate glutamate release and facilitate glutamate clearance, prevents stress-induced deficits in the hippocampus. But, whether the same drug is also effective in countering the opposite effects of stress in the amygdala remains unexplored. We addressed this question by using a rat model wherein even a single 2-hour acute immobilization stress causes a delayed build-up, 10 days later, in anxiety-like behavior, alongside stronger excitatory synaptic connectivity in the basolateral amygdala (BLA). This temporal profile - several days separating the acute stressor and its delayed impact - allowed us to test if these effects can be reversed by administering riluzole in the drinking water after acute stress. Post-stress riluzole not only prevented the delayed increase in anxiety-like behavior on the elevated plus-maze, but also reversed the increase in spine-density on BLA neurons 10 days later. Further, stress-induced increase in the frequency of miniature excitatory postsynaptic currents recorded in BLA slices, 10 days later, was reversed by the same post-stress riluzole administration. Together, these findings underscore the importance of therapeutic strategies, aimed at glutamate uptake and modulation, in correcting the delayed behavioral, physiological, and morphological effects of stress on the amygdala. Significance statementStress disorders are characterized by impaired cognitive function alongside enhanced emotionality. Consistent with this, the same stress elicits contrasting effects in the rodent hippocampus versus amygdala. This poses a therapeutic challenge - the same pharmacological intervention against stress has to counter these opposite effects. Yet, the immediate consequence of stress - enhanced extracellular glutamate - is similar across these two areas. To target this common feature, we treated rats with riluzole, a drug that prevents stress-induced glutamate surge. Although the drug was administered after the end of stress, it reversed its delayed impact on amygdalar structure and function. Since riluzole also enhances glutamate-uptake through glial-transporters and is approved for human use, these results highlight the importance of therapeutic strategies focused on neuron-astrocyte interactions.