Abstract
Orexin-B (ORX-B) acts upon orexin 1 (OX1R) and orexin 2 (OX2R) receptors, and is involved in the regulation of feeding, sleep-wakefulness and locomotor activity. Orexin neurons project to the shell of the nucleus accumbens (AccSh), which plays an important role in the regulation of reinforced behaviors including feeding, and may participate in the control of feeding behavior through the modulation of AccSh neuron activity. Therefore, the effects of ORX-B on AccSh neurons were investigated using cytosolic Ca2+ concentration ([Ca2+]i) imaging study in rat brain slice preparations. When ORX-B was applied to AccSh neurons in artificial cerebrospinal fluid (ACSF), it increased [Ca2+]i dose-dependently. The ORX-B-induced increase of [Ca2+]i was also seen in the presence of tetrodotoxin, suggesting that ORX-B directly affects AccSh neurons, but not via synaptic transmissions. Increase of [Ca2+]i induced by ORX-B in normal ACSF disappeared completely when tested in N-methyl-D-glucamine (NMDG)-containing ACSF. [Ca2+]i increase induced by ORX-B in normal ACSF was also attenuated in about 60% of neurons tested in Ni2+-containing ACSF. Results suggest that in many AccSh neurons, orexins increase [Ca2+]i via non-selective cation channels and Ni2+-sensitive voltage-dependent Ca2+ channels, and that orexins may participate in the regulation of feeding behavior through the activation of AccSh neurons. [J Physiol Sci. 2006;56 Suppl:S207]
