Two types of non‐selective cation channel opened by muscarinic stimulation with carbachol in bovine ciliary muscle cells

Orexin neurons (hypocretin neurons) have a critical role in the regulation of sleep/wakefulness, especially in the maintenance of arousal. Here, we revealed that orexin neurons are directly and indirectly activated by orexin via the orexin 2 receptor (OX2R). Orexin B (1 M) induced depolarization in orexin neurons, which was still observed in the presence of TTX (1 M), AP-5 (50 M), and CNQX (20 M). In addition, orexin B induced inward currents in the presence of TTX, suggesting a direct activation of orexin neurons. Although orexin B application induced depolarization in orexin neurons of OX1R knock-out mice at comparable levels to wild-type mice, the observation that orexin B failed to depolarize orexin neurons in the OX2R knock-out mice suggested that OX2R was a primary receptor for this response. Moreover, immunoelectron microscopic analyses revealed direct contacts among orexin neurons, which exhibited structural similarities to the glutamatergic synapses. Together, these results suggest that orexin neurons form a positive-feedback circuit through indirect and direct pathways, which results in the preservation of the orexin neuron network at a high activity level and/or for a longer period. Therefore, the activation of orexin neurons through OX2R might have an important role in the maintenance of arousal.

Section: Activation Of Nonselective Cation Channel Is Involved In Orementioning

confidence: 99%

Orexin Directly Excites Orexin Neurons through Orexin 2 Receptor

Yamanaka¹,

Tabuchi²,

Tsunematsu³

et al. 2010

“…These reversal potentials are consistent with activation of nonselective cation channels in AVP-induced depolarization of orexin neurons. Several recent reports suggest that the transient receptor potential (TRP) channel family plays an important role in the receptor-operated influx of cations (Spassova et al, 2004;Takai et al, 2004). In addition, the current through TRP channels is known to be suppressed by the presence of extracellular calcium ions (Lintschinger et al, 2000;Hill, 2001).…”

Section: Activation Of Nonselective Cation Channels Are Involved In Amentioning

confidence: 99%

Vasopressin Increases Locomotion through a V1a Receptor in Orexin/Hypocretin Neurons: Implications for Water Homeostasis

Tsunematsu¹,

Fu²,

Yamanaka³

et al. 2008

Water homeostasis is a critical challenge to survival for land mammals. Mice display increased locomotor activity when dehydrated, a behavior that improves the likelihood of locating new sources of water and simultaneously places additional demands on compromised hydration levels. The neurophysiology underlying this well known behavior has not been previously elucidated. We report that the anti-diuretic hormone arginine-vasopressin (AVP) is involved in this response. AVP and oxytocin directly induced depolarization and an inward current in orexin/hypocretin neurons. AVP-induced activation of orexin neurons was inhibited by a V1a receptor (V1aR)-selective antagonist and was not observed in V1aR knock-out mice, suggesting an involvement of V1aR. Subsequently activation of phospholipase C␤ triggers an increase in intracellular calcium by both calcium influx through nonselective cation channels and calcium release from calcium stores in orexin neurons. Intracerebroventricular injection of AVP or water deprivation increased locomotor activity in wild-type mice, but not in transgenic mice lacking orexin neurons. V1aR knock-out mice were less active than wild-type mice. These results suggest that the activation of orexin neurons by AVP or oxytocin has an important role in the regulation of spontaneous locomotor activity in mice. This system appears to play a key role in water deprivation-induced hyperlocomotor activity, a response to dehydration that increases the chance of locating water in nature.

“…Several recent reports suggest that the transient receptor potential (TRP) channel family plays an important role in the receptor-operated influx of cations (Spassova et al, 2004;Takai et al, 2004). In addition, the current through TRP channels are known to be suppressed by the presence of extracellular calcium ions (Lintschinger et al, 2000;Hill, 2001).…”

Section: ؉mentioning

confidence: 99%

Cholecystokinin Activates Orexin/Hypocretin Neurons through the Cholecystokinin A Receptor

Tsujino¹,

Yamanaka²,

Ichiki³

et al. 2005

133

Orexin A and B are neuropeptides implicated in the regulation of sleep/wakefulness and energy homeostasis. The regulatory mechanism of the activity of orexin neurons is not precisely understood. Using transgenic mice in which orexin neurons specifically express yellow cameleon 2.1, we screened for factors that affect the activity of orexin neurons (a total of 21 peptides and six other factors were examined) and found that a sulfated octapeptide form of cholecystokinin (CCK-8S), neurotensin, oxytocin, and vasopressin activate orexin neurons. The mechanisms that underlie CCK-8S-induced activation of orexin neurons were studied by both calcium imaging and slice patch-clamp recording. CCK-8S induced inward current in the orexin neurons. The CCK A receptor antagonist lorglumide inhibited CCK-8S-induced activation of orexin neurons, whereas the CCK B receptor agonists CCK-4 (a tetrapeptide form of cholecystokinin) and nonsulfated CCK-8 had little effect. The CCK-8S-induced increase in intracellular calcium concentration was eliminated by removing extracellular calcium but not by an addition of thapsigargin. Nifedipine, -conotoxin, -agatoxin, 4-ethylphenylamino-1,2-dimethyl-6-methylaminopyrimidinium chloride, and SNX-482 had little effect, but La 3ϩ , Gd 3ϩ , and 2-aminoethoxydiphenylborate inhibited CCK-8S-induced calcium influx. Additionally, the CCK-8S-induced inward current was dramatically enhanced in the calcium-free solution and was inhibited by the cation channel blocker SKF96365, suggesting an involvement of extracellular calcium-sensitive cation channels. CCK-8S did not induce an increase in intracellular calcium concentration when membrane potential was clamped at Ϫ60 mV, suggesting that the calcium increase is induced by depolarization. The evidence presented here expands our understanding of the regulation of orexin neurons and the physiological role of CCK in the CNS.