Orexin Depolarizes Central Amygdala Neurons via Orexin Receptor 1, Phospholipase C and Sodium-Calcium Exchanger and Modulates Conditioned Fear

Abstract

Orexins (OX), also known as hypocretins, are excitatory neuropeptides with well-described roles in regulation of wakefulness, arousal, energy homeostasis, and anxiety. An additional and recently recognized role of OX is modulation of fear responses. We studied the OX neurons of the perifornical hypothalamus (PeF) which send projections to the amygdala, a region critical in fear learning and fear expression. Within the amygdala, the highest density of OX-positive fibers was detected in the central nucleus (CeA). The specific mechanisms underlying OX neurotransmission within the CeA were explored utilizing rat brain slice electrophysiology, pharmacology, and chemogenetic stimulation. We show that OX induces postsynaptic depolarization of medial CeA neurons that is mediated by OX receptor 1 (OXR1) but not OX receptor 2 (OXR2). We further characterized the mechanism of CeA depolarization by OX as phospholipase C (PLC)- and sodium-calcium exchanger (NCX)- dependent. Selective chemogenetic stimulation of OX PeF fibers recapitulated OXR1 dependent depolarization of CeA neurons. We also observed that OXR1 activity modified presynaptic release of glutamate within the CeA. Finally, either systemic or intra-CeA perfusion of OXR1 antagonist reduced the expression of conditioned fear. Together, these data suggest the PeF-CeA orexinergic pathway can modulate conditioned fear through a signal transduction mechanism involving PLC and NCX activity and that selective OXR1 antagonism may be a putative treatment for fear-related disorders.

A balancing act: the role of pro‐ and anti‐stress peptides within the central amygdala in anxiety and alcohol use disorders

“…Central administration of orexin A strongly activated CeA neurons (Sakamoto et al, 2004) and CeA neurons were depolarized by orexin A and B (Bisetti et al, 2006;Dustrude et al, 2018).…”

“…Orexins exert their excitatory actions through two types of receptors (OX 1 and OX 2 ,), with orexin A binding both OX 1 and OX 2 and orexin B showing much greater affinity for OX 2 . Orexin fiber and receptor expression is relatively dense within the amygdala (Ch'ng & Lawrence 2015; Marcus et al, 2001;Peyron et al, 1998), with greater innervation observed in the CeA over the adjacent LA and BLA nuclei (Dustrude et al, 2018;Peyron et al, 1998).…”

Activity dynamics of amygdala GABAergic neurons during cataplexy of narcolepsy

“…In this way, serotonin keeps GABAergic neuronal activity in check. Orexin can also excite inhibitory interneurons in the CeA (Dustrude et al, 2018; Hasegawa et al, 2017). GABAergic hyperactivity once triggered, could successively send overwhelming inhibitory inputs into the brainstem and cortex.…”

Orexins alleviate motor deficits via increasing firing activity of pallidal neurons in a mouse model of Parkinson’s disease

“…Orexin-mediated Ca 2ϩ influx and release are also observed in neurons (28,35). Two different mechanisms, Ca 2ϩ influx via Ca 2ϩ channels and PLC-dependent Ca 2ϩ release, are associated with orexininduced elevation of intracellular Ca 2ϩ (13,33,34,39,68). The L-type Ca 2ϩ channel is involved in orexin-induced functional regulation of many neurons (34,39,64).…”