Research reportAmygdalar orexinergic-GABAergic interactions regulate anxiety behaviors of the Syrian golden hamster

At present neurobiological interests are directing more attention towards the major role of the amygdalar GABAA receptor on orexin-dependent behaviors. This telencephalic region has been widely studied especially in view of its control on various psychiatric disorders such as anxiety and depression. Recently, cross-talking relationships between these two specific neuroreceptor systems of the central-cortical amygdalar complex has been considered an important element for anxiety type of behaviors. In the present study, we investigated the effects of central amygdalar infusions with orexin-A, orexin-B ± GABAA receptor α2 subunit agonist (flunitrazepam) on elevated plus-maze and light-dark explorative behaviors of the facultative hibernating Syrian hamster. In a first case, it seemed that doses of orexin administered directly into the central nucleus were responsible for greater anxiogenic type of effects as shown by more time being spent both in the dark compartment and the closed arm of the elevated plus-maze, whereas, these effects were suppressed in the presence of flunitrazepam. At the cellular level, the effects of orexin accounted for evident argyrophilic reactions (neurodegeneration phenomena) including altered cell membrane and loss of cytoplasmic architecture in most amygdalar and hippocampal neuronal fields, while in the presence of flunitrazepam these reactions resulted to either be unappreciable or absent. Overall the actions of α2-dependent inhibitory signals tend to corroborate, for the first time, a neuroprotective role against the over-excitatory orexinergic neurodegeneration reactions and thus its abnormal anxiety-like indications may prove to be therapeutically useful for orexin-dependent sleeping disorders.

Research highlights▶ Effects of orexin-A/B ± α2 GABAAR agonist on anxiety states of hibernating hamster. ▶ Elevated plus-maze behaviors were caused by central amygdalar orexin-B infusions. ▶ Orexin-B largely induced evident neurodegenerative reactions in some limbic areas. ▶ α2 inhibitory signals protect such areas against orexinergic-related anxiety states.