Anxiety-Related Neurons In Mouse Amygdala Modulate Pharmacologically Induced Anxiety Responses

Potential threats or stresses cause anxiety-a normal and instinctive emotional response in human beings and animals which becomes anxiety disorder when overreact. It has been proposed that the amygdala, a key brain region for emotional processing, contributes to anxiety. However, the neural mechanisms within amygdala that modulate anxiety still remain unclear. With in vivo multichannel recording techniques, we have found a type of neuron in basal lateral amygdala (BLA) of freely behaving mice which closely responses to anxiety-related behaviors in both open field and elevated plus maze. In order to explore whether this type of neuron also mediates pharmacologically induced anxious state, we artificially induced or suppressed the anxiety level of mice by means of pharmacology to see if the firing activities of the anxiety related neurons changed accordingly.We used two widely accepted behavioral paradigms for anxiety level assay in rodents-elevated plus maze (EPM) and open field test (OFT) to assess the drug efficiency and determine the proper doses. Benzodiazepines (BDZs) have broad clinical applications including anti-anxiety, sedation, and anticonvulsive therapy. At cellular level, BDZ receptor is coupled with GABA(A) receptor and chloride channel, forming a complex. BDZ receptors are allosteric modulators of GABA(A) receptors. When positively activated, the receptor of BDZs can increase the combination of GABA and GABA receptors, leading to hyperpolarization of neural membrane and decreasing the neural excitability. Also small doses of BDZ receptor agonists almost do not affect the locomotion of animals while have good anxiolytic effects, and BDZ reverse agonists promote anxiogenic effects on rodents.We mainly chose BDZ receptor agonist diazepam (DZP,1,1.5,2mg/kg) and the BDZ receptor inverse agonists FG-7142(5,10,20mg/kg) and DMCM (1,1.5,2mg/kg) to induce and suppress the anxiety level in mice, respectively. We found that lmg/kg diazepam administration have significant anxiolytic effect, significantly reducing the anxiety level during30min’s EPM test without affecting the locomotion. However, although1.5mg/kg and2mg/kg diazepam showed more significant anxiolytic effects, these two doses increased the locomotion of mice simultaneously. During open field test, none of the three doses of diazepam administration showed any significant anxiolytic effects. And the expected anxiogenic effect of FG7142and DMCM was not seen during EPM test as well.We have recorded5anxiety related neurons in BLA which significantly increased their spiking activities in open field while maintained the basal level of their spiking activities in enriched environment. Also when the mice were put back to the open field again, the anxiety-related cells increased firing activities as well, which showed adaptive responses to the anxiety level of mice. When we administrated lmg/kg diazepam (i.p.) to the mice with anxiety related neurons recorded30min before putting them to the open field, the firing frequency of anxiety related cells did not increase gradually, which means this type of anxiety related cell has a role in modulating the pharmacologically induced anxiety and thus indicates a potential target for anxiety disorder therapy.