Rationale: Acid sensing ion channels (ASICs) are proton-gated ion channels located in the central and peripheral nervous systems. Of particular interest is ASIC1a, which is located in areas associated with fear and anxiety behaviors. Recent reports suggest a role for ASIC1a in preclinical models of fear conditioning and anxiety.
Objectives: The present experiments evaluated various ASIC inhibitors in preclinical models of autonomic and behavioral parameters of anxiety. In addition, neurochemical studies evaluated the effects of an ASIC inhibitor (A-317567) on neurotransmitter levels in the amygdala.
Results: In electrophysiological studies using hippocampal primary neuronal cultures, three ASIC inhibitors (PcTX-1, A-317567, and amiloride) produced concentration-dependent inhibition of acid-evoked currents. In the stress-induced hyperthermia model, acute administration of psalmotoxin 1 (PcTX-1; 10-56 ng, i.c.v.), A-317567 (0.1-1.0 mg/kg, i.p.), and amiloride (10-100 mg/kg, i.p.) prevented stress-induced elevations in core body temperature. In the four-plate test, acute treatment with PcTX-1 (10-56 ng, i.c.v.) and A-317567 (0.01-0.1 mg/kg, i.p.), but not amiloride (3-100 mg/kg, i.p.), produced dose-dependent and significant increases in the number of punished crossings relative to vehicle-treated animals. Additionally, PcTX-1 (56-178 ng, i.c.v.), A-317567 (0.1-10 mg/kg, i.p.), and amiloride (10-100 mg/kg, i.p.) lacked significant anxiolytic-like activity in the elevated zero maze. In neurochemical studies, an infusion of A-317567 (100 microM) into the amygdala significantly elevated the extracellular levels of GABA, but not glutamate, in this brain region.
Conclusions: These findings demonstrate that ASIC inhibition produces anxiolytic-like effects in some behavioral models and indicate a potential role for GABAergic mechanisms to underlie these anxiolytic-like effects.