Amygdalar excitatory/inhibitory circuits interacting with orexinergic neurons influence differentially feeding behaviors in hamsters

Abstract

Recently, environmental stimuli on different neurobiological events, via participation of distinct amygdalar (AMY) ORXergic fibers have aroused wide interests in view of their ability to modify neuronal linked stressful and physiological homeostatic conditions. Results of the present study indicate that ORXergic (ORX-A/B) circuits of the facultative hibernating golden hamster (Mesocricetus auratus) central AMY (CeA) and basolateral AMY (BlA) nuclei constitute major sites of feeding behaviors. Indeed, hamsters after treatment of BlA with ORX-A frequently ingested greater quantities of food as compared to controls, while ORX-B in CeA induced a very (p<0.001) great consumption of water. The same nuclei treated separately with either ORX-A or ORX-B ± the selective α(1) GABA(A) benzodiazepine receptor agonist (zolpidem) dedicated less time to eating and drinking sessions. Conversely, hamsters that received the same neuropeptides but this time with the glutamatergic agonist NMDA displayed greater hyperphagic effects above all for ORX-A. When behavioral changes were compared to the expression of the specific ORXergic receptor (ORX-2R), an up-/down-regulating pattern was detected in some limbic areas (AMY, hippocampus and hypothalamus) following treatment with ORX-A or ORX-B plus NMDA. Overall, indications deriving from this study strongly point to hamster BlA-enriched ORX-A fibers in combination with either inhibitory or excitatory signals as main targets of hyperphagic responses while CeA ORX-B activities in presence of these same neuronal signals predominantly induced drinking motivational behaviors. The distinct behavioral activities of these two neuropeptides may have useful clinical bearings toward psychiatric and sleeping disorders such as bulimia and narcolepsy.