The role of interaction between orexin receptors and ß2 adrenergic receptors in basolateral amygdala in dentate gyrus synaptic plasticity in male rats.

Orexin receptors expressed in basolateral amygdala (BLA) have been proposed for memory processing and hippocampal plasticity. There are several investigations about the effect of the adrenergic system in BLA on memory enhancement. However, there is no information about the molecular basis of this effect. Adrenergic and orexinergic fibers are found in BLA. In this study, the effects of both adrenergic and orexinergic systems were investigated on the amygdala function. To this end, the selective beta 2 adrenergic agonist (clenbuterol) and orexin receptors' antagonists (OX1R and OX2R, SB-334867-A and TCS-OX2-29, respectively) were administered into the BLA, then the high frequency stimulation (200-Hz) was applied to the perforant pathway and the synaptic plasticity of the dentate granular cells was studied in anaesthetized rats. Clenbuterol injection into the BLA enhanced the population spike (PS) component of LTP in the dentate gyrus (DG), as compared to that observed after dimethyl sulfoxide treatment. In addition, after orexin 1 or 2 receptor antagonists (SB-334867-A and TCS-OX2-29, respectively) injecting into the BLA, the enhancing effect of clenbuterol on PS was reduced. Moreover, the population excitatory post-synaptic potential also decreased in the SB-clenbuterol and TCS- clenbuterol experimental groups. However, the PS amplitude was also decreased in the group treated only by SB or TCS relative to the clenbuterol treated group. The PS amplitude or EPSP slope in the groups treated by both application of orexin receptors' antagonists and clenbuterol was considerably lower relative to the groups treated only by orexin receptors' antagonists. It is concluded that the BLA orexinergic system modulates hippocampal plasticity in relation with the adrenergic system.

Modulation of long-term and short-term plasticity in the dentate gyrus granule cells by activating the ß-adrenergic receptors of the basolateral amygdala.

The beta-adrenergic receptors of the basolateral amygdala (BLA) are involved in modulating emotional memory formation in the hippocampus. The molecular mechanisms of this involvement are still unclear. In this study, we investigate the effects of the beta-adrenergic receptors of the BLA involvements during the major cellular mechanisms that underlie memory formation in hippocampal sub-regions. Wistar rats were injected with the selective beta receptor agonist, clenbuterol (15 ng/0.5 µl) bilaterally into the BLA. Then, the long-term potentiation (LTP) and the paired-pulse responses were recorded. Control rats were injected by saline at the same volume. Our data indicated that the injection of clenbuterol into the BLA area enhanced the amplitude of the population spike (PS) but not the slope of the excitatory postsynaptic potential (EPSP). In addition, short-term plasticity in the dentate gyrus (DG) region was significantly changed at 500 ms inter-pulse interval. These results suggest that the activation of the beta-adrenergic receptors of the BLA can improve LTP induction, which depends on the short-term plasticity with a mechanism related to the GABAergic transmission. Thus, it can be concluded that the adrenergic system of the BLA engages with long-term and short-term plasticity.