Inhibitory effect of activation of GABA(A) receptor in the central nucleus of amygdala on the sodium intake in the sodium-depleted rat

Abstract

The present study investigated the effects of a microinjection of GABA(A) receptor agonist (muscimol) and antagonist (bicuculline) into the central nucleus of the amygdala (CeA) in sodium-depleted rats. We measured the sodium intake and identified the neuronal activation in the brainstem induced by activating the GABA(A) receptors in the CeA using Fos immunohistochemistry. Muscimol (0.20, 0.35 or 0.50 nmol, in 0.2μl) that was injected bilaterally into the CeA decreased the 0.3M NaCl and water intake in a dose-dependent manner. Microinjection of 0.02 nmol/0.2μl muscimol also decreased the NaCl intake, but had no effect on the water intake. The inhibitory effect of muscimol (0.20 nmol) on the sodium and water intake could be blocked by pretreatment with bicuculline intra-CeA microinjection (0.4 nmol). However, bilateral injections of bicuculline alone into the CeA did not affect the NaCl or water intake. Furthermore, microinjection of muscimol (0.20 nmol) into the CeA increased the number of Fos-like immunoreactive (FLI) neurons in the caudal and intermediate parts of the nucleus of the tractus solitarius (cNTS and iNTS) and the lateral parabrachial nucleus (LPBN). These results suggest that GABA(A) receptors within the CeA may be involved in mediating the sodium intake in the sodium-depleted rat, and the cNTS, iNTS and LPBN were probably involved in this mechanism.